QGIS Desktop 3.16 User Guide
QGIS Project
02.04.2022
Obsah
1 Úvod 1
1.1 What is new in QGIS 3.16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Předmluva 3
3 Konvence 5
3.1 GUI konvence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2 Textové nebo klávesové konvence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.3 Platformy – pokyny . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4 Funkce 7
4.1 Prohlížení dat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.2 Prozkoumávání dat a vytváření map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.3 Tvorba, editace, správa a export dat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.4 Analýza dat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.5 Publikování map na internetu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.6 Rozšíření QGIS funkcí prostřednictvím pluginů (zásuvných modulů) . . . . . . . . . . . . . . . . 9
4.6.1 Základní Pluginy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.6.2 Externí Python zásuvné moduly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.7 Konzole Python . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.8 Známé problémy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.8.1 Omezení počtu otevřených souborů . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5 Začínáme 11
5.1 Installing QGIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1.1 Installing from binaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1.2 Installing from source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1.3 Installing on external media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.1.4 Downloading sample data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.2 Starting and stopping QGIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.3 Sample Session: Loading raster and vector layers . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6 Working with Project Files 19
6.1 Introducing QGIS projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
6.2 Handling broken file paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
6.3 Generating output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7 QGIS GUI 23
7.1 Menu lišta . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
7.1.1 Projekt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
7.1.2 Editovat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
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7.1.3 Zobrazit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
7.1.4 Vrstva . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
7.1.5 Nastavení . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
7.1.6 Zásuvné moduly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
7.1.7 Vektor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
7.1.8 Rastr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
7.1.9 Databáze . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
7.1.10 Web . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
7.1.11 Mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
7.1.12 Zpracování . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
7.1.13 Nápověda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
7.1.14 QGIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
7.2 Panely a nástrojové lišty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
7.2.1 Nástrojové lišty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
7.2.2 Panely . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
7.3 Zobrazení mapy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
7.3.1 Exploring the map view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
7.3.2 Setting additional map views . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
7.3.3 Exporting the map view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
7.4 3D Map View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
7.4.1 Navigation options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
7.4.2 Creating an animation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
7.4.3 Scene Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
7.4.4 3D vector layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
7.5 Stavová lišta . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
7.5.1 Locator bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
7.5.2 Reporting actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
7.5.3 Control the map canvas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
7.5.4 Messaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
8 The Browser panel 55
8.1 Resources that can be opened / run from the Browser . . . . . . . . . . . . . . . . . . . . . . . . 57
8.2 Browser panel top-level entries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
8.2.1 Favorites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
8.2.2 Prostorové záložky . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
8.2.3 Home . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
8.2.4 / . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
8.2.5 Geopackage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
8.2.6 SpatiaLite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
8.2.7 PostGIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
8.2.8 MSSQL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
8.2.9 DB2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
8.2.10 WMS/WMTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
8.2.11 Vector Tiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
8.2.12 XYZ Tiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
8.2.13 WCS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
8.2.14 WFS / OGC API - Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
8.2.15 OWS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
8.2.16 ArcGIS Map Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
8.2.17 ArcGIS Features Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
8.2.18 GeoNode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
8.3 Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
9 QGIS Konfigurace 63
9.1 Možnosti . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
9.1.1 General Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
9.1.2 System Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
9.1.3 CRS Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
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9.1.4 Transformations Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
9.1.5 Data Sources Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
9.1.6 Rendering Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
9.1.7 Canvas and Legend Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
9.1.8 Map tools Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
9.1.9 Colors Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
9.1.10 Digitizing Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
9.1.11 Layouts Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
9.1.12 GDAL Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
9.1.13 Variables Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
9.1.14 Authentication Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
9.1.15 Network Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
9.1.16 Locator Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
9.1.17 Advanced Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
9.1.18 Acceleration Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
9.1.19 Processing Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
9.1.20 Python Console Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
9.1.21 Code Editor Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
9.2 Working with User Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
9.3 Vlastnosti projektu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
9.3.1 General Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
9.3.2 Metadata Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
9.3.3 CRS Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
9.3.4 Transformations Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
9.3.5 Default Styles Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
9.3.6 Data Sources Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
9.3.7 Relations Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
9.3.8 Variables Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
9.3.9 Macros Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
9.3.10 QGIS Server Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
9.3.11 Temporal Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
9.4 Přizpůsobení . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
9.5 Keyboard shortcuts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
9.6 Running QGIS with advanced settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
9.6.1 Command line and environment variables . . . . . . . . . . . . . . . . . . . . . . . . . . 104
9.6.2 Deploying QGIS within an organization . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
10 Práce s projekcemi 111
10.1 Přehled projekční podpory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
10.2 Layer Coordinate Reference Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
10.3 Project Coordinate Reference Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
10.4 Coordinate Reference System Selector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
10.5 Vlastní souřadnicový referenční systém . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
10.5.1 Integrate an NTv2-transformation in QGIS . . . . . . . . . . . . . . . . . . . . . . . . . 116
10.6 Datum Transformations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
11 Obecné nástroje 119
11.1 Kontextová nápověda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
11.2 Panely . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
11.2.1 Layers Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
11.2.2 Layer Styling Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
11.2.3 Layer Order Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
11.2.4 Overview Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
11.2.5 Log Messages Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
11.2.6 Undo/Redo Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
11.2.7 Statistical Summary Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
11.3 Vnořování projektů . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
11.4 Working with the map canvas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
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11.4.1 Vykreslování . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
11.4.2 Zooming and Panning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
11.4.3 Prostorové záložky . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
11.4.4 Dekorace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
11.4.5 Anotační nástroje . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
11.4.6 Měření . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
11.5 Interacting with features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
11.5.1 Selecting features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
11.5.2 Identifying Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
11.6 Save and Share Layer Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
11.6.1 Managing Custom Styles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
11.6.2 Storing Styles in a File or a Database . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
11.6.3 Layer definition file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
11.7 Storing values in Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
11.8 Authentication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
11.9 Common widgets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
11.9.1 Výběr barvy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
11.9.2 Symbol Widget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
11.9.3 Font Selector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
11.9.4 Unit Selector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
11.9.5 Number Formatting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
11.9.6 Režim míchání . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
11.9.7 Data defined override setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
12 The Style Library 169
12.1 The Style Manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
12.1.1 The Style Manager dialog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
12.1.2 Setting a Color Ramp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
12.2 The Symbol Selector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
12.2.1 The symbol layer tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
12.2.2 Configuring a symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
12.3 Setting a label . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
12.3.1 Formatting the label text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
12.3.2 Configuring interaction with labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
12.4 Creating 3D Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
12.4.1 Point Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
12.4.2 Line layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
12.4.3 Polygon Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
12.4.4 Application example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
13 Managing Data Source 207
13.1 Opening Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
13.1.1 The Browser Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
13.1.2 The DB Manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
13.1.3 Provider-based loading tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
13.1.4 QGIS Custom formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
13.1.5 QLR - QGIS Layer Definition File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
13.1.6 Connecting to web services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
13.2 Creating Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
13.2.1 Creating new vector layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
13.2.2 Creating new layers from an existing layer . . . . . . . . . . . . . . . . . . . . . . . . . 238
13.2.3 Creating new DXF files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
13.2.4 Creating new layers from the clipboard . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
13.2.5 Creating virtual layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
13.3 Exploring Data Formats and Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246
13.3.1 Raster data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246
13.3.2 Vektorová data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
iv
14 Working with Vector Data 255
14.1 The Vector Properties Dialog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
14.1.1 Information Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
14.1.2 Source Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
14.1.3 Symbology Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
14.1.4 Labels Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
14.1.5 Diagrams Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
14.1.6 Masks Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296
14.1.7 3D View Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296
14.1.8 Fields Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
14.1.9 Attributes Form Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
14.1.10 Joins Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306
14.1.11 Auxiliary Storage Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308
14.1.12 Actions Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317
14.1.13 Display Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322
14.1.14 Rendering Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324
14.1.15 Variables Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
14.1.16 Metadata Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
14.1.17 Dependencies Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
14.1.18 Legend Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326
14.1.19 QGIS Server Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326
14.1.20 Digitizing Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
14.2 Výrazy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330
14.2.1 The Expression string builder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330
14.2.2 Function Editor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
14.3 List of functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337
14.3.1 Aggregates Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337
14.3.2 Array Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
14.3.3 Funkce barev . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356
14.3.4 Conditional Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362
14.3.5 Conversions Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365
14.3.6 Custom Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
14.3.7 Funkce dat a časů . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
14.3.8 Pole a hodnoty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381
14.3.9 Files and Paths Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381
14.3.10 Form Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384
14.3.11 Fuzzy Matching Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384
14.3.12 General Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386
14.3.13 Funkce geometrie . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389
14.3.14 Layout Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437
14.3.15 Map Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437
14.3.16 Maps Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438
14.3.17 Matematické funkce . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
14.3.18 Operátory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
14.3.19 Processing Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
14.3.20 Rasters Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
14.3.21 Record and Attributes Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453
14.3.22 Relations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
14.3.23 Funkce řetězců . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
14.3.24 User Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469
14.3.25 Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469
14.3.26 Recent Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473
14.4 Working with the Attribute Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473
14.4.1 Foreword: Spatial and non-spatial tables . . . . . . . . . . . . . . . . . . . . . . . . . . . 473
14.4.2 Introducing the attribute table interface . . . . . . . . . . . . . . . . . . . . . . . . . . . 473
14.4.3 Interacting with features in an attribute table . . . . . . . . . . . . . . . . . . . . . . . . 478
14.4.4 Using action on features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480
14.4.5 Editing attribute values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482
v
14.4.6 Creating one or many to many relations . . . . . . . . . . . . . . . . . . . . . . . . . . . 485
14.5 Editování . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494
14.5.1 Nastavení přichytávací tolerance a vyhledání poloměru . . . . . . . . . . . . . . . . . . . 494
14.5.2 Topologická editace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496
14.5.3 Digitizing an existing layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498
14.5.4 Advanced digitizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505
14.5.5 Shape digitizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513
14.5.6 The Advanced Digitizing panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516
14.5.7 The Processing in-place layer modifier . . . . . . . . . . . . . . . . . . . . . . . . . . . 522
15 Working with Raster Data 525
15.1 Raster Properties Dialog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525
15.1.1 Information Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 526
15.1.2 Source Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 526
15.1.3 Symbology Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 527
15.1.4 Transparency Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534
15.1.5 Histogram Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536
15.1.6 Rendering Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537
15.1.7 Pyramids Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537
15.1.8 Metadata Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 538
15.1.9 Legend Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 539
15.1.10 QGIS Server Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 540
15.2 Raster Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 541
15.2.1 Raster Calculator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 541
15.2.2 Raster Alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543
15.3 Georeferencer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545
15.3.1 Usual procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 546
16 Working with Mesh Data 551
16.1 What’s a mesh? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551
16.2 Supported formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553
16.3 Mesh Dataset Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
16.3.1 Information Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
16.3.2 Source Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
16.3.3 Symbology Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
17 Working with Vector Tiles 561
17.1 What are Vector Tiles? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
17.2 Supported Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 562
18 Laying out the maps 563
18.1 Overview of the Print Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563
18.1.1 Sample Session for beginners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563
18.1.2 The Layout Manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
18.1.3 Menus, tools and panels of the print layout . . . . . . . . . . . . . . . . . . . . . . . . . 565
18.2 Layout Items . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 579
18.2.1 Layout Items Common Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 579
18.2.2 The Map Item . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584
18.2.3 The 3D Map Item . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593
18.2.4 The Label Item . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 594
18.2.5 The Legend Item . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597
18.2.6 The Scale Bar Item . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604
18.2.7 Položky tabulky . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 607
18.2.8 The Picture and the North Arrow Items . . . . . . . . . . . . . . . . . . . . . . . . . . . 616
18.2.9 The HTML Frame Item . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 618
18.2.10 The Shape Items . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 621
18.3 Creating an Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 624
18.3.1 Export settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 624
18.3.2 Export as Image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625
vi
18.3.3 Export as SVG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 626
18.3.4 Export as PDF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627
18.3.5 Generate an Atlas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 628
18.4 Creating a Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634
18.4.1 What is it? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634
18.4.2 Get started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634
18.4.3 Layout Report Workspace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 635
18.4.4 Export settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 650
19 Working with OGC / ISO protocols 651
19.1 WMS/WMTS Client . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 652
19.1.1 Overview of WMS Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 652
19.1.2 Overview of WMTS Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 652
19.1.3 Selecting WMS/WMTS Servers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653
19.1.4 Loading WMS/WMTS Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 655
19.1.5 Sady dlaždic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 657
19.1.6 Using the Identify Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 657
19.1.7 Show WMS legend graphic in table of contents and layout . . . . . . . . . . . . . . . . . 659
19.1.8 WMS Client Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 659
19.2 WCS Client . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 659
19.3 WFS and WFS-T Client . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 660
20 Working with GPS Data 663
20.1 GPS Plugin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 663
20.1.1 What is GPS? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 663
20.1.2 Loading GPS data from a file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 663
20.1.3 GPSBabel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 664
20.1.4 Importing GPS data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 664
20.1.5 Downloading GPS data from a device . . . . . . . . . . . . . . . . . . . . . . . . . . . . 665
20.1.6 Uploading GPS data to a device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 665
20.1.7 Defining new device types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 665
20.1.8 Download of points/tracks from GPS units . . . . . . . . . . . . . . . . . . . . . . . . . 666
20.2 Live GPS tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 667
20.2.1 Position and additional attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 668
20.2.2 GPS signal strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 669
20.2.3 GPS options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 669
20.2.4 Connect to a Bluetooth GPS for live tracking . . . . . . . . . . . . . . . . . . . . . . . . 671
20.2.5 Using GPSMAP 60cs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671
20.2.6 Using BTGP-38KM datalogger (only Bluetooth) . . . . . . . . . . . . . . . . . . . . . . 672
20.2.7 Using BlueMax GPS-4044 datalogger (both BT and USB) . . . . . . . . . . . . . . . . . 672
21 Ověřovací systém 673
21.1 Authentication System Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 673
21.1.1 Authentication database . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 673
21.1.2 Master password . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 674
21.1.3 Authentication Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 675
21.1.4 Authentication Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 677
21.1.5 Master Password and Auth Config Utilities . . . . . . . . . . . . . . . . . . . . . . . . . 681
21.1.6 Using authentication configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 682
21.1.7 Python bindings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 682
21.2 User Authentication Workflows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 683
21.2.1 HTTP(S) authentication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 683
21.2.2 Database authentication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 684
21.2.3 PKI authentication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 685
21.2.4 Handling bad layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 692
21.2.5 Changing authentication config ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 693
21.2.6 QGIS Server support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 694
21.2.7 SSL server exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 694
21.3 Security Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 697
vii
21.3.1 Restrictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 698
22 GRASS GIS Integration 699
22.1 Demo dataset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 699
22.2 Loading GRASS raster and vector layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 699
22.3 Importing data into a GRASS LOCATION via drag and drop . . . . . . . . . . . . . . . . . . . . 700
22.4 Managing GRASS data in QGIS Browser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 700
22.5 GRASS Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 700
22.6 Starting the GRASS plugin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 700
22.7 Opening GRASS mapset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 701
22.8 GRASS LOCATION and MAPSET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 701
22.9 Importing data into a GRASS LOCATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 701
22.9.1 Creating a new GRASS LOCATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702
22.9.2 Adding a new MAPSET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703
22.10 The GRASS vector data model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 704
22.11 Creating a new GRASS vector layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 704
22.12 Digitizing and editing a GRASS vector layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 705
22.13 The GRASS region tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 707
22.14 The GRASS Toolbox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 707
22.14.1 Working with GRASS modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 708
22.14.2 GRASS module examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 711
22.14.3 Customizing the GRASS Toolbox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 714
23 QGIS processing framework 717
23.1 Úvod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 717
23.2 Configuring the Processing Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 719
23.3 The Toolbox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 721
23.3.1 The algorithm dialog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 722
23.3.2 Data objects generated by algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 727
23.4 The history manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 728
23.4.1 The processing history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 728
23.4.2 The processing log . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 729
23.5 The graphical modeler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 729
23.5.1 Definition of inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 730
23.5.2 Definition of the workflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 733
23.5.3 Interacting with the canvas and elements . . . . . . . . . . . . . . . . . . . . . . . . . . 736
23.5.4 Saving and loading models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 738
23.5.5 Editing a model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 739
23.5.6 Editing model help files and meta-information . . . . . . . . . . . . . . . . . . . . . . . 740
23.5.7 Exporting a model as a Python script . . . . . . . . . . . . . . . . . . . . . . . . . . . . 742
23.5.8 About available algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 742
23.6 The batch processing interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 742
23.6.1 Úvod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 742
23.6.2 The parameters table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 743
23.6.3 Filling the parameters table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 744
23.6.4 Executing the batch process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 745
23.7 Using processing algorithms from the console . . . . . . . . . . . . . . . . . . . . . . . . . . . . 745
23.7.1 Calling algorithms from the Python console . . . . . . . . . . . . . . . . . . . . . . . . . 745
23.7.2 Creating scripts and running them from the toolbox . . . . . . . . . . . . . . . . . . . . 750
23.7.3 Pre- and post-execution script hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 753
23.8 Using processing from the command line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 753
23.9 Writing new Processing algorithms as Python scripts . . . . . . . . . . . . . . . . . . . . . . . . . 754
23.9.1 Extending QgsProcessingAlgorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 755
23.9.2 The @alg decorator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 759
23.9.3 Input and output types for Processing Algorithms . . . . . . . . . . . . . . . . . . . . . . 760
23.9.4 Handing algorithm output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 762
23.9.5 Communicating with the user . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 762
23.9.6 Documenting your scripts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 763
viii
23.9.7 Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 763
23.9.8 Best practices for writing script algorithms . . . . . . . . . . . . . . . . . . . . . . . . . 763
23.10 Configuring external applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 763
23.10.1 A note for Windows users . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 764
23.10.2 A note on file formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 764
23.10.3 A note on vector layer selections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 764
23.10.4 SAGA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 764
23.10.5 R scripts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 765
23.10.6 R libraries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 773
23.10.7 GRASS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 773
23.10.8 LAStools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 774
23.10.9 OTB Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 774
24 Processing providers and algorithms 777
24.1 QGIS algorithm provider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 777
24.1.1 Cartography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 777
24.1.2 Databáze . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 792
24.1.3 File tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 798
24.1.4 Interpolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 799
24.1.5 Layer tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 809
24.1.6 Modeler tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 810
24.1.7 Network analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815
24.1.8 Plots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 826
24.1.9 Rastrová analýza . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 832
24.1.10 Raster Creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 870
24.1.11 Raster terrain analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 883
24.1.12 Raster tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 894
24.1.13 Vector analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 899
24.1.14 Vector creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 917
24.1.15 Vector general . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 940
24.1.16 Vector geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 970
24.1.17 Vector overlay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1082
24.1.18 Vector selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1095
24.1.19 Vector table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1108
24.1.20 Vector Tiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1121
24.2 GDAL algorithm provider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1124
24.2.1 Rastrová analýza . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1124
24.2.2 Raster conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1147
24.2.3 Raster extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1153
24.2.4 Raster miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1159
24.2.5 Raster projections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1176
24.2.6 Vector conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1180
24.2.7 Vector geoprocessing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1185
24.2.8 Vector miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1191
24.3 LAStools algorithm provider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1200
24.3.1 blast2dem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1200
24.3.2 blast2iso . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1202
24.3.3 las2dem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1203
24.3.4 las2iso . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1205
24.3.5 las2las_filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1207
24.3.6 las2las_project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1211
24.3.7 las2las_transform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1217
24.3.8 las2txt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1220
24.3.9 lasindex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1221
24.3.10 lasgrid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1222
24.3.11 lasinfo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1224
24.3.12 lasmerge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1227
24.3.13 lasprecision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1228
ix
24.3.14 lasquery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1229
24.3.15 lasvalidate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1230
24.3.16 laszip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1230
24.3.17 txt2las . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1231
24.4 TauDEM algorithm provider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1235
24.4.1 Basic Grid Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1236
24.4.2 Specialized Grid Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1248
24.4.3 Stream Network Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1273
24.5 OTB applications provider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1291
25 Zásuvné moduly 1293
25.1 QGIS Plugins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1293
25.1.1 Core and External plugins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1293
25.1.2 The Plugins Dialog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1294
25.2 Using QGIS Core Plugins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1299
25.2.1 DB Manager Plugin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1299
25.2.2 Geometry Checker Plugin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1302
25.2.3 MetaSearch Catalog Client . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1306
25.2.4 Offline Editing Plugin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1313
25.2.5 Topology Checker Plugin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1315
25.3 QGIS Python console . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1317
25.3.1 The Interactive Console . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1317
25.3.2 The Code Editor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1318
26 Pomoc a podpora 1321
26.1 Mailing list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1321
26.1.1 Uživatelé QGIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1321
26.1.2 Vývojáři QGIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1321
26.1.3 Komunitní tým QGIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1321
26.1.4 Překlady QGIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1322
26.1.5 Řídící výbor projektu QGIS (PSC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1322
26.1.6 Uživatelské skupiny QGIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1322
26.2 IRC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1322
26.3 Commercial support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1322
26.4 BugTracker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1322
26.5 Blog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1323
26.6 Zásuvné moduly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1323
26.7 Wiki . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1323
27 Contributors 1325
27.1 Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1325
27.2 Translators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1326
27.3 Statistics of translation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1327
28 Dodatky 1329
28.1 Appendix A: GNU General Public License . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1329
28.2 Appendix B: GNU Free Documentation License . . . . . . . . . . . . . . . . . . . . . . . . . . . 1332
28.3 Appendix C: QGIS File Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1337
28.3.1 QGS/QGZ - The QGIS Project File Format . . . . . . . . . . . . . . . . . . . . . . . . 1337
28.3.2 QLR - The QGIS Layer Definition file . . . . . . . . . . . . . . . . . . . . . . . . . . . 1339
28.3.3 QML - The QGIS Style File Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1340
28.4 Appendix D: QGIS R script syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1341
28.4.1 Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1342
28.4.2 Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1342
28.4.3 Syntax Summary for QGIS R scripts . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1342
28.4.4 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1344
29 Literature and Web References 1347
x
KAPITOLA 1
Úvod
This is the user guide for the geographical information system (GIS) software QGIS. QGIS is subject to the GNU
General Public License. More information is available on the QGIS homepage, https://www.qgis.org.
The contents of this document have been written and verified to the best of the knowledge of the authors and editors.
Nevertheless, mistakes are possible.
Therefore, the authors, editors and publishers do not take any responsibility or liability for errors in this document
and their possible consequences. We encourage you to report possible mistakes.
This document has been typeset with reStructuredText. It is available as reST source code on github, and online
as HTML and PDF via https://www.qgis.org/en/docs/. Translated versions of this document can be browsed and
downloaded via the documentation area of the QGIS project as well.
For more information about contributing to this document and about translation, please visit https://qgis.org/en/site/
getinvolved/index.html.
Odkazy v tomto dokumentu
This document contains internal and external links. Clicking on an internal link moves within the document, while
clicking on an external link opens an internet address.
Documentation Authors and Editors
The list of the persons who have contributed with writing, reviewing and translating the following documentation
is available at Contributors.
Copyright (c) 2004 - 2020 QGIS Development Team
Internet: https://www.qgis.org
Licence tohoto dokumentu
Je povoleno kopírovat, šířit a/nebo upravovat tento dokument za podmínek GNU Free Documentation License, verze
1.3 nebo jakýchkoliv pozdějších verzí publikovaných nadací Free Software Foundation; bez Invariant Sections, bez
úvodních a závěrečných textů. Kopie této licence je zahrnuta v dodatku Appendix B: GNU Free Documentation License.
1
QGIS Desktop 3.16 User Guide
1.1 What is new in QGIS 3.16
This release of QGIS includes hundreds of bug fixes and many new features and enhancements, compared to QGIS
3.10. We recommend that you use this version over previous releases. For a list of new features, visit the visual
changelogs at https://qgis.org/en/site/forusers/visualchangelogs.html.
2 Kapitola 1. Úvod
KAPITOLA 2
Předmluva
Vítejte v báječném světě geografických informačních systémů (GIS)!
QGIS is an Open Source Geographic Information System. The project was born in May 2002 and was established
as a project on SourceForge in June the same year. We have worked hard to make GIS software (which is traditionally
expensive proprietary software) available to anyone with access to a personal computer. QGIS currently runs on most
Unix platforms, Windows, and macOS. QGIS is developed using the Qt toolkit (https://www.qt.io) and C++. This
means that QGIS feels snappy and has a pleasing, easy-to-use graphical user interface (GUI).
QGIS aims to be a user-friendly GIS, providing common functions and features. The initial goal of the project was
to provide a GIS data viewer. QGIS has reached the point in its evolution where it is being used for daily GIS data-viewing
needs, for data capture, for advanced GIS analysis, and for presentations in the form of sophisticated maps,
atlases and reports. QGIS supports a wealth of raster and vector data formats, with new format support easily added
using the plugin architecture.
QGIS is released under the GNU General Public License (GPL). Developing QGIS under this license means that you
can inspect and modify the source code, and guarantees that you, our happy user, will always have access to a GIS
program that is free of cost and can be freely modified. You should have received a full copy of the license with your
copy of QGIS, and you can also find it in Appendix Appendix A: GNU General Public License.
Tip: Aktuální dokumentace
The latest version of this document can always be found in the documentation area of the QGIS website at https:
//www.qgis.org/en/docs/.
3
QGIS Desktop 3.16 User Guide
4 Kapitola 2. Předmluva
KAPITOLA 3
Konvence
Tato část popisuje jednotné styly, které budou použity v této příručce.
3.1 GUI konvence
GUI konvenční styly jsou určeny k napodobení vzhledu grafického uživatelského rozhraní. Obecně platí, že styl bude
odrážet non-hover vzhled, takže uživateli stačí zběžně prohlédnout uživatelské rozhraní, aby našel něco, co vypadá
jako instruktáž v návodu.
• Menu Možnosti: Vrstva ► Přidat vektorovou vrstvu or Nastavení ► Nástrojové lišty ► Digitalizace
• Nástroj: Přidat rastrovou vrstvu
• Button : Save as Default
• Dialogové okno Název: Vlastnosti vrstvy
• Záložka: Obecné
• Zaškrtávací pole: Render
• Přepínač: Postgis SRID EPSG ID
• Zvolit číslo:
• Zvolit řetězec:
• Browse for a file: …
• Zvolit barvu:
• Posuvník:
• Vložit text:
Stín označuje klikací GUI komponenty.
5
QGIS Desktop 3.16 User Guide
3.2 Textové nebo klávesové konvence
Příručka též obsahuje styly vztahující se k textu, klávesovým zkratkám a kódování k označení různých subjektů, jako
jsou třídy nebo metody. Tyto styly neodpovídají skutečnému vzhledu jakéhokoli textu či kódování v QGIS.
• Hyperlinks: https://qgis.org
• Kombinace kláves: Stisknout Ctrl+B, myšleno stisknout a držet klávesu Ctrl a poté stisknout klávesu B
• Název souboru: jezera.shp
• Název třídy: Nová Vrstva
• Metoda: classFactory
• Server: myhost.de
• Návod: qgis --Nápověda
Řádky kódu jsou označeny pevnou šířkou písma:
PROJCS["NAD_1927_Albers",
GEOGCS["GCS_North_American_1927",
3.3 Platformy – pokyny
GUI sekvence a malá množství textu mohou být formátovány v řadě za sebou: klikněte na File QGIS ►
Quit to close QGIS. To znamená, že v operačních systémech Linux, Unix a Windows, byste měli nejprve kliknout na
nabídku Soubor a poté Zavřít, zatímco u macOS systému, byste měli nejprve kliknout na nabídku QGIS, pak Zavřít.
Větší množství textu může být formátováno jako seznam:
• Udělej tohle
• Udělej tamto
• Iosxl Nebo udělej tamto
nebo jako odstavce:
Udělej tohle a tohle a tohle. Pak udělej tohle a tohle a tohle, a tohle a tohle a tohle, a tohle a tohle a tohle.
Udělej tamto. Pak udělej tamto a tamto a tamto, a tamto a tamto a tamto, tamto a tamto a tamto, a tamto a tamto.
Screenshots that appear throughout the user guide have been created on different platforms.
6 Kapitola 3. Konvence
KAPITOLA 4
Funkce
QGIS offers a wealth of GIS functions, provided by core features and plugins. The locator bar makes it easy to search
for functions, datasets and more.
A short summary of six general categories of features and plugins is presented below, followed by first insights into
the integrated Python console.
4.1 Prohlížení dat
You can view combinations of vector and raster data (in 2D or 3D) in different formats and projections without
conversion to an internal or common format. Supported formats include:
• Spatially-enabled tables and views using PostGIS, SpatiaLite and MS SQL Spatial, Oracle Spatial, vector
formats supported by the installed OGR library, including GeoPackage, ESRI Shapefile, MapInfo, SDTS, GML
and many more. See section Working with Vector Data.
• Rastrové a obrazové formáty podporované nainstalovanou knihovnou GDAL (Geospatial Data Abstraction
Library), jako je GeoTIFF, Erdas IMG, ArcInfo ASCII GRID, JPEG, PNG a mnoho dalších. Viz část Working
with Raster Data.
• Mesh data (TINs and regular grids are supported). See Working with Mesh Data.
• Vector tiles
• GRASS rastrová a vektorová data z GRASS databází (location/mapset). Viz část GRASS GIS Integration.
• Online spatial data served as OGC Web Services, including WMS, WMTS, WCS, WFS, and WFS-T. See
section Working with OGC / ISO protocols.
The QGIS authentication infrastructure helps you manage user/password, certificates and keys for web services
and other resources.
• Spreadsheets (ODS / XLSX)
Temporal data are supported.
7
QGIS Desktop 3.16 User Guide
4.2 Prozkoumávání dat a vytváření map
Můžete vytvářet mapy a interaktivně prozkoumávat prostorová data s přátelským grafickým uživatelským rozhraním.
Mezi mnohé užitečné nástroje, které jsou k dispozici v GUI, patří:
• QGIS prohlížeč
• Reprojekce
• Správce databází
• Print layout
• Report
• Přehled panelů
• Prostorové záložky
• Vysvětlivky k nástrojům
• Identifikace/výběr prvků
• Editace/zobrazení/vyhledávání vlastností
• Data-defined feature labeling
• Symbolika vektorových a rastrových nástrojů
• Mapové kompozice s vrstvami souřadnicových sítí
• North arrow, scale bar and copyright label for maps
• Podpora pro ukládání a obnovování projektů
4.3 Tvorba, editace, správa a export dat
Můžete vytvářet, upravovat, spravovat a exportovat vektorové a rastrové vrstvy v několika formátech. QGIS nabízí
následující:
• Vector digitizing tools
• Ability to create and edit multiple file formats and GRASS vector layers
• Georeferenční zásuvný modul pro geokódování obrázků
• GPS tools to import and export GPX format, and convert other GPS formats to GPX or down/upload directly
to a GPS unit (on Linux, usb: has been added to list of GPS devices)
• Podpora pro vizualizaci a editaci dat OpenStreetMap
• Ability to create spatial database tables from files with the DB Manager plugin
• Vylepšená manipulace s tabulkami geodatabáze
• Nástroje pro správu vektorových atributových tabulek
• Možnost uložení screenshotů jako georeferencované obrázky
• Nástroj DXF-Export s rozšířenými možnostmi pro export stylů a zásuvných modulů pro provádění
CADovských funkcí
8 Kapitola 4. Funkce
QGIS Desktop 3.16 User Guide
4.4 Analýza dat
You can perform spatial data analysis on spatial databases and other OGR-supported formats. QGIS currently offers
vector analysis, raster analysis, sampling, geoprocessing, geometry and database management tools. You can also
use the integrated GRASS tools, which include the complete GRASS functionality of more than 400 modules (see
section GRASS GIS Integration). Or, you can work with the Processing plugin, which provides a powerful geospatial
analysis framework to call native and third-party algorithms from QGIS, such as GDAL, SAGA, GRASS, R, and
more (see section Úvod). All analysis functions are run in the background, allowing you to continue your work before
the processing has finished.
The graphical modeller allows you to combine / chain functions into a complete workflow in an intuitive graphical
environment.
4.5 Publikování map na internetu
QGIS can be used as a WMS, WMTS, WMS-C or WFS and WFS-T client (see section Working with OGC /
ISO protocols), and QGIS Server (see the QGIS-Server-manual) allows you to publish your data through the WMS,
WCS and WFS protocols on the Internet using a webserver.
4.6 Rozšíření QGIS funkcí prostřednictvím pluginů (zásuvných
modulů)
QGIS lze přizpůsobit vašim speciálním potřebám díky rozšiřitelné plugin struktuře a knihovnám, které mohou být
použity k vytvoření pluginů. Můžete dokonce vytvářet nové aplikace pomocí C ++ nebo Python!
4.6.1 Základní Pluginy
Základní pluginy zahrnují:
1. DB Manager (exchange, edit and view layers and tables from/to databases; execute SQL queries)
2. Geometry Checker (check geometries for errors)
3. Georeferencer GDAL (add projection information to rasters using GDAL)
4. GPS Tools (load and import GPS data)
5. GRASS 7 (integrate GRASS GIS)
6. MetaSearch Catalogue Client (interacting with metadata catalog services supporting the OGC Catalog Service
for the Web (CSW) standard)
7. Offline Editing (allow offline editing and synchronizing with databases)
8. Processing (the spatial data processing framework for QGIS)
9. Topology Checker (find topological errors in vector layers)
4.4. Analýza dat 9
QGIS Desktop 3.16 User Guide
4.6.2 Externí Python zásuvné moduly
QGIS nabízí rostoucí počet externích Pythonu pluginů, které jsou poskytovány komunitou. Tyto zásuvné moduly jsou
umístěny v oficiálním archivu zásuvných modulů a mohou být snadno nainstalovány pomocí Python Plugin Installeru.
Viz oddíl The Plugins Dialog.
4.7 Konzole Python
For scripting, it is possible to take advantage of an integrated Python console, which can be opened with: Plugins ►
Python Console. The console opens as a non-modal utility window. For interaction with the QGIS environment, there
is the qgis.utils.iface variable, which is an instance of QgisInterface. This interface provides access
to the map canvas, menus, toolbars and other parts of the QGIS application. You can create a script, then drag and
drop it into the QGIS window and it will be executed automatically.
For further information about working with the Python console and programming QGIS plugins and applications,
please refer to QGIS Python console and PyQGIS-Developer-Cookbook.
4.8 Známé problémy
4.8.1 Omezení počtu otevřených souborů
Pokud otevíráte rozsáhlý QGIS projekt, a jste si jisti, že všechny vrstvy jsou validní, ale některé vrstvy jsou označeny
jako špatné, pravděpodobně se potýkáte s tímto problémem. Linux (a jiné OS rovněž) má limit otevřených souborů
během procesu. Zdrojové limity jsou od výrobce a dědičné. Příkaz ulimit, který je vestavěný, mění limity pouze
pro aktuální proces. Nový limit bude zděděn každým odvozeným procesem.
Můžete vidět všechny aktuální informace o ulimit zadáním :
$ ulimit -aS
Můžete vidět aktuální povolený počet otevřených souborů od výrobce pomocí následujícího příkazu v konzoli :
$ ulimit -Sn
Chcete-li změnit limity pro existující relaci, budete moci použít něco jako :
$ ulimit -Sn #number_of_allowed_open_files
$ ulimit -Sn
$ qgis
Chcete-li je zafixovat navždy
Ve většině linuxových systémů, jsou zdrojové limity nastaveny na přihlášení modulem pam_limits podle nastavení
obsažených v /etc/security/limits.conf nebo /etc/security/limits.d/*.conf. Pokud máte
kořenové oprávnění (root privilege, též via sudo), měli byste být schopni upravit tyto soubory, ale, aby změny vstoupily
v platnost, budete se muset znovu přihlásit.
Více informací:
https://www.cyberciti.biz/faq/linux-increase-the-maximum-number-of-open-files/ https://linuxaria.com/article/
open-files-in-linux
10 Kapitola 4. Funkce
KAPITOLA 5
Začínáme
This chapter provides a quick overview of installing QGIS, downloading QGIS sample data, and running a first simple
session visualizing raster and vector data.
5.1 Installing QGIS
QGIS project provides different ways to install QGIS depending on your platform.
5.1.1 Installing from binaries
Standard installers are available for MS Windows and macOS. Binary packages (rpm and deb) or software
repositories are provided for many flavors of GNU/Linux .
For more information and instructions for your operating system check https://download.qgis.org.
5.1.2 Installing from source
If you need to build QGIS from source, please refer to the installation instructions. They are distributed with the
QGIS source code in a file called INSTALL. You can also find them online at https://github.com/qgis/QGIS/blob/
master/INSTALL.md.
If you want to build a particular release and not the version in development, you should replace master with the
release branch (commonly in the release-X_Y form) in the above-mentioned link (installation instructions may
differ).
11
QGIS Desktop 3.16 User Guide
5.1.3 Installing on external media
It is possible to install QGIS (with all plugins and settings) on a flash drive. This is achieved by defining a –profiles-path
option that overrides the default user profile path and forces QSettings to use this directory, too. See section
System Settings for additional information.
5.1.4 Downloading sample data
This user guide contains examples based on the QGIS sample dataset (also called the Alaska dataset).
Download the sample data from https://github.com/qgis/QGIS-Sample-Data/archive/master.zip and unzip the
archive on any convenient location on your system.
The Alaska dataset includes all GIS data that are used for the examples and screenshots in this user guide; it also
includes a small GRASS database. The projection for the QGIS sample datasets is Alaska Albers Equal Area with
units feet. The EPSG code is 2964.
PROJCS["Albers Equal Area",
GEOGCS["NAD27",
DATUM["North_American_Datum_1927",
SPHEROID["Clarke 1866",6378206.4,294.978698213898,
AUTHORITY["EPSG","7008"]],
TOWGS84[-3,142,183,0,0,0,0],
AUTHORITY["EPSG","6267"]],
PRIMEM["Greenwich",0,
AUTHORITY["EPSG","8901"]],
UNIT["degree",0.0174532925199433,
AUTHORITY["EPSG","9108"]],
AUTHORITY["EPSG","4267"]],
PROJECTION["Albers_Conic_Equal_Area"],
PARAMETER["standard_parallel_1",55],
PARAMETER["standard_parallel_2",65],
PARAMETER["latitude_of_center",50],
PARAMETER["longitude_of_center",-154],
PARAMETER["false_easting",0],
PARAMETER["false_northing",0],
UNIT["us_survey_feet",0.3048006096012192]]
If you intend to use QGIS as a graphical front end for GRASS, you can find a selection of sample locations (e.g.,
Spearfish or South Dakota) at the official GRASS GIS website, https://grass.osgeo.org/download/sample-data/.
5.2 Starting and stopping QGIS
QGIS can be started like any other application on your computer. This means that you can launch QGIS by:
• using the Applications menu, the Start menu, or the Dock
• Dvakrát klikněte na ikonu ve složce „Aplikace“ nebo plocha zástupce.
• double clicking an existing QGIS project file (with .qgz or .qgs extension). Note that this will also open the
project.
• typing qgis in a command prompt (assuming that QGIS is added to your PATH or you are in its installation
folder)
To stop QGIS, use:
• volba menu Project ► Exit QGIS nebo použijte klávesovou zkratku Ctrl+Q
• :menuselection: QGIS –> Quit QGIS nebo použijte klávesovou zkratku Ctrl+Q
• or use the red cross at the top-right corner of the main interface of the application.
12 Kapitola 5. Začínáme
QGIS Desktop 3.16 User Guide
5.3 Sample Session: Loading raster and vector layers
Now that you have QGIS installed and a sample dataset available, we will demonstrate a first sample session. In this
example, we will visualize a raster and a vector layer. We will use:
• the landcover raster layer (qgis_sample_data/raster/landcover.img)
• and the lakes vector layer (qgis_sample_data/gml/lakes.gml)
Where qgis_sample_data represents the path to the unzipped dataset.
1. Start QGIS as seen in Starting and stopping QGIS.
2. To load the files in QGIS:
1. Click on the Open Data Source Manager
icon. The Data Source Manager should open in Browser mode.
2. Browse to the folder qgis_sample_data/raster/
3. Select the ERDAS IMG file landcover.img and double-click it. The landcover layer is added in the
background while the Data Source Manager window remains open.
Obr. 5.1: Adding data to a new project in QGIS
4. To load the lakes data, browse to the folder qgis_sample_data/gml/, and double-click the
lakes.gml file to open it.
5. A Coordinate Reference System Selector dialog opens. In the Filter menu, type 2964, filtering the list of
Coordinate Reference Systems below.
5.3. Sample Session: Loading raster and vector layers 13
QGIS Desktop 3.16 User Guide
Obr. 5.2: Select the Coordinate Reference System of data
6. Select the NAD27 / Alaska Albers entry
7. Click OK
8. Close the Data Source Manager window
You now have the two layers available in your project in some random colours. Let’s do some customization on the
lakes layer.
1. Select the Zoom In
tool on the Navigation toolbar
2. Zoom to an area with some lakes
3. Double-click the lakes layer in the map legend to open the Properties dialog
4. To change the lakes color:
1. Click on the Symbology tab
2. Select blue as fill color.
14 Kapitola 5. Začínáme
QGIS Desktop 3.16 User Guide
Obr. 5.3: Selecting Lakes color
3. Press OK. Lakes are now displayed in blue in the map canvas.
5. To display the name of the lakes:
1. Reopen the lakes layer Properties dialog
2. Click on the Labels tab
3. Select Single labels in the drop-down menu to enable labeling.
4. From the Label with list, choose the NAMES field.
5.3. Sample Session: Loading raster and vector layers 15
QGIS Desktop 3.16 User Guide
Obr. 5.4: Showing Lakes names
5. Press Apply. Names will now load over the boundaries.
6. You can improve readability of the labels by adding a white buffer around them:
1. Click the Buffer tab in the list on the left
2. Check Draw text buffer
3. Choose 3 as buffer size
4. Click Apply
5. Check if the result looks good, and update the value if needed.
6. Finally click OK to close the Layer Properties dialog and apply the changes.
Let’s now add some decorations in order to shape the map and export it out of QGIS:
1. Select View ► Decorations ► Scale Bar menu
2. In the dialog that opens, check Enable Scale Bar option
3. Customize the options of the dialog as you want
4. Press Apply
5. Likewise, from the decorations menu, add more items (north arrow, copyright…) to the map canvas with
custom properties.
6. Click Project ► Import/Export ► Export Map to Image…
7. Press Save in the opened dialog
8. Select a file location, a format and confirm by pressing Save again.
16 Kapitola 5. Začínáme
QGIS Desktop 3.16 User Guide
9. Press Project ► Save… to store your changes as a .qgz project file.
That’s it! You can see how easy it is to visualize raster and vector layers in QGIS, configure them and generate your
map in an image format you can use in other softwares. Let’s move on to learn more about the available functionality,
features and settings, and how to use them.
Poznámka: To continue learning QGIS through step-by-step exercises, follow the Training manual.
5.3. Sample Session: Loading raster and vector layers 17
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18 Kapitola 5. Začínáme
KAPITOLA 6
Working with Project Files
6.1 Introducing QGIS projects
The state of your QGIS session is called a project. QGIS works on one project at a time. A settings can be project-specific
or an application-wide default for new projects (see section Možnosti). QGIS can save the state of your
workspace into a QGIS project file using the menu options Project ► Save or Project ► Save As….
Poznámka: If the project has been modified the * symbol will appear in the title bar and QGIS will, by default,
ask you if you would like to save the changes. This behavior is controlled by the Prompt to save project and data
source changes when required setting under Settings ► Options ► General.
You can load existing projects into QGIS from the Browser panel or by through Project ► Open…, Project ►
New from template or Project ► Open Recent ►.
At startup, a list of Project Templates and Recent Projects are displayed, including screenshots, names and file paths
(for up to ten projects). The Recent Projects list is handy to access recently used projects. Double-click an entry to
open the project or project template. You can also add a layer to create a new project automatically. The lists will
then disappear, giving way to the map canvas.
If you want to clear your session and start fresh, go to Project ► New. This will prompt you to save the existing
project if changes have been made since it was opened or last saved.
When you open a fresh project, the title bar will show Untitled Project until you save it.
19
QGIS Desktop 3.16 User Guide
Obr. 6.1: Starting a new project in QGIS
The information saved in a project file includes:
• Layers added
• Which layers can be queried
• Layer properties, including symbolization and styles
• Projection for the map view
• Last viewed extent
• Print layouts
• Print layout elements with settings
• Print layout atlas settings
• Digitizing settings
• Table Relations
• Project Macros
• Project default styles
• Plugins settings
• QGIS Server settings from the OWS settings tab in the Project properties
• Queries stored in the DB Manager
The project file is saved in XML format (see QGS/QGZ - The QGIS Project File Format). This means that it is possible
to edit the file outside of QGIS if you know what you are doing. The project file format has been updated several
times. Project files from older QGIS versions may not work properly any more.
20 Kapitola 6. Working with Project Files
QGIS Desktop 3.16 User Guide
Poznámka: By default, QGIS will warn you of version differences. This behavior is controlled in the General tab of
Settings ► Options ( Warn when opening a project file saved with an older version of QGIS).
Whenever you save a .qgs project file in QGIS, a backup of the file is created in the same directory as the project
file, with the extension .qgs~.
The extension for QGIS projects is .qgs but when saving from QGIS, the default is to save using a compressed format
with the .qgz extension. The .qgs file is embedded in the .qgz file (a zip archive), together with its associated
sqlite database (.qgd) for auxiliary data. You can get to these files by unzipping the .qgz file.
Poznámka: The Auxiliary Storage Properties mechanism makes a zipped project particularly useful, since it embeds
auxiliary data.
Projects can also be saved/loaded to/from a PostgreSQL database using the following Project menu items:
• Project ► Open from
• Project ► Save to
Both menu items have a sub-menu with a list of extra project storage implementations (PostgreSQL and GeoPackage).
Clicking the action will open a dialog to pick a GeoPackage connection and project or a PostgreSQL connection,
schema and project.
Projects stored in Geopackage or PostgreSQL can also be loaded through the QGIS browser panel, either by double-clicking
them or by dragging them to the map canvas.
6.2 Handling broken file paths
When opening a project, QGIS may fail to reach some data sources due to unavailable service/database, or to
a renamed or moved file. QGIS then opens the Handle Unavailable Layers dialog, referencing the unfound layers.
You can:
• Double-click in the Datasource field, adjust the path of each layer and click Apply changes;
• Select a row, press Browse to indicate the correct location and click Apply changes;
• Press Auto-Find to browse the folders and try to automatically fix all or selected broken path(s). Be aware that
the browsing may take some time.
• Ignore the message and open your project with the broken path(s) by clicking Keep Unavailable Layers. Your
layer is then displayed in the Layers panel, but without any data until you fix the path using the Unavailable layer!
icon next to it in the Layers panel, or Repair Data Source… in the layer contextual menu.
With the Repair Data Source… tool, once a layer path has been fixed, QGIS scans through all other broken
paths and tries to auto-fix those that have the same broken file path.
• Remove Unavailable Layers from the project.
6.2. Handling broken file paths 21
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6.3 Generating output
There are several ways to generate output from your QGIS session. We have already discussed saving as a project file
in Introducing QGIS projects. Other ways to produce output files are:
• Creating images: Project ► Import/Export ► Export Map to Image… outputs the map canvas rendering to an
image format (PNG, JPG, TIFF…) at custom scale, resolution, size, … Georeferencing the image is possible.
See Exporting the map view for more details.
• Exporting to PDF files: Project ► Import/Export ► Export Map to PDF… outputs the map canvas rendering
to PDF at custom scale, resolution, and with some advanced settings (simplification, georeferencing, …). See
Exporting the map view for more details.
• Exporting to DXF files: Project ► Import/Export ► Export Project to DXF… opens a dialog where you can
define the ‚Symbology mode‘, the ‚Symbology scale‘ and vector layers you want to export to DXF. Through the
‚Symbology mode‘, symbols from the original QGIS Symbology can be exported with high fidelity (see section
Creating new DXF files).
• Designing maps: Project ► New Print Layout… opens a dialog where you can layout and print the current
map canvas (see section Laying out the maps).
22 Kapitola 6. Working with Project Files
KAPITOLA 7
QGIS GUI
The QGIS graphical user interface (GUI) is shown in the figure below (the numbers 1 through 5 in yellow circles
indicate important elements of the QGIS GUI, and are discussed below).
Obr. 7.1: QGIS uživatelské rozhraní se vzorovými daty Alaska
Poznámka: Vzhled Vašeho okna (záhlaví atd.) se může lišit v závislosti na Vašem operačním systému a správci
okna.
The main QGIS GUI (Obr. 7.1) consists of five components / component types:
1. Menu Bar
2. Toolbars
3. Panels
4. Map View
23
QGIS Desktop 3.16 User Guide
5. Status Bar
Scroll down for detailed explanations of these.
7.1 Menu lišta
The Menu bar provides access to QGIS functions using standard hierarchical menus. The Menus, their options,
associated icons and keyboard shortcuts are described below. The keyboard shortcuts can be reconfigured (Settings ►
Keyboard Shortcuts).
Most menu options have a corresponding tool and vice-versa. However, the Menus are not organized exactly like the
toolbars. The locations of menu options in the toolbars are indicated below in the table. Plugins may add new options
to Menus. For more information about tools and toolbars, see Nástrojové lišty.
Poznámka: QGIS is a cross-platform application. Tools are generally available on all platforms, but they may be
placed in different menus, depending on the operating systems. The lists below show the most common locations,
including known variations.
7.1.1 Projekt
The Project menu provides access and exit points for project files. It provides tools to:
• Create a New project file from scratch or use another project file as a template (see Project files options for
template configuration)
• Open… a project from a file, a GeoPackage or a PostgreSQL database
• Close a project or revert it to its last saved state
• Save a project in .qgs or .qgz file format, either as a file or within a GeoPackage or PostgreSQL database
• Export the map canvas to different formats or use a print layout for more complex output
• Set project properties and snapping options for geometry editing.
24 Kapitola 7. QGIS GUI
QGIS Desktop 3.16 User Guide
Menu Možnosti Zkratka Panel
nástrojů
Reference
Nové Ctrl+N Projekt Introducing QGIS projects
Nový ze šablony ► Introducing QGIS projects
Open… Ctrl+O Projekt Introducing QGIS projects
Open from ►
► GeoPackage… Introducing QGIS projects
► PostgreSQL… Introducing QGIS projects
Otevřít nedávné ► Alt+J + R Introducing QGIS projects
Close Introducing QGIS projects
Uložit Ctrl+S Projekt Introducing QGIS projects
Uložit jako… Ctrl+Shift+S Projekt Introducing QGIS projects
Save to ►
► Templates… Introducing QGIS projects
► GeoPackage… Introducing QGIS projects
► PostgreSQL… Introducing QGIS projects
Revert…
Vlastnosti… Ctrl+Shift+P Vlastnosti projektu
Možnosti přichytávání… Nastavení přichytávací
tolerance a vyhledání poloměru
Import/Export ►
► Export Map to Image… Exporting the map view
► Export Map to PDF… Exporting the map view
► Export Project to DXF… Creating new DXF files
► Import Layers from DWG/DXF… Importing a DXF or DWG file
New Print Layout… Ctrl+P Projekt Laying out the maps
New Report… Creating a Report
Layout Manager… Projekt Laying out the maps
Layouts ► Laying out the maps
Ukončit QGIS Ctrl+Q
Pod macOS, Ukončit QGIS příkaz odpovídá QGIS ► Ukončit QGIS (Cmd+Q).
7.1.2 Editovat
The Edit menu provides most of the native tools needed to edit layer attributes or geometry (see Editování for details).
Menu Možnosti Zkratka Panel
nástrojů
Reference
Zpět Ctrl+Z Digitalizace Zpět a znovu
Znovu Ctrl+Shift+Z Digitalizace Zpět a znovu
Vyjmout prvky Ctrl+X Digitalizace Cutting, Copying and
Pasting Features
Kopírovat prvky Ctrl+C Digitalizace Cutting, Copying and
Pasting Features
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QGIS Desktop 3.16 User Guide
Tabulka 7.1 – pokračujte na předchozí stránce
Menu Možnosti Zkratka Panel
nástrojů
Reference
Vložit prvky Ctrl+V Digitalizace Cutting, Copying and
Pasting Features
Paste Features as ► Working with the
Attribute Table
► New Vector Layer… Working with the
Attribute Table
► Temporary Scratch Layer… Ctrl+Alt+V Working with the
Attribute Table
Vybrat ► Selecting features
► Select Feature(s) Selection Selecting features
► Select Features by Polygon Selection Selecting features
► Select Features by Freehand Selection Selecting features
► Select Features by Radius Selection Selecting features
► Select Features by Value… F3 Selection Selecting features
► Select Features by Expression… Ctrl+F3 Selection Selecting features
► Deselect Features from All Layers Ctrl+Alt+A Selection Selecting features
► Deselect Features from the Current Active
Layer
Ctrl+Shift+A Selection Selecting features
► Reselect Features Selecting features
► Select All Features Ctrl+A Selection Selecting features
► Invert Feature Selection Selection Selecting features
Add Record Ctrl+. Digitalizace
Add Point Feature Ctrl+. Digitalizace Adding Features
Add Line Feature Ctrl+. Digitalizace Adding Features
Add Polygon Feature Ctrl+. Digitalizace Adding Features
Přidat kruhový řetězec Shape
Digitizing
Add Circular string
Přidat kruhový řeězec podle poloměru Shape
Digitizing
Add Circular string
Add Circle ► Shape
Digitizing
Draw Circles
► Add Circle from 2 Points Shape
Digitizing
Draw Circles
► Add Circle from 3 Points Shape
Digitizing
Draw Circles
► Add Circle from 3 Tangents Shape
Digitizing
Draw Circles
► Add Circle from 2 Tangents and a Point Shape
Digitizing
Draw Circles
► Add Circle by a Center Point and Another
Point
Shape
Digitizing
Draw Circles
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26 Kapitola 7. QGIS GUI
QGIS Desktop 3.16 User Guide
Tabulka 7.1 – pokračujte na předchozí stránce
Menu Možnosti Zkratka Panel
nástrojů
Reference
Add Rectangle ► Shape
Digitizing
Draw Rectangles
► Add Rectangle from Extent Shape
Digitizing
Draw Rectangles
► Add Rectangle from Center and a Point Shape
Digitizing
Draw Rectangles
► Add Rectangle from 3 Points (Distance
from 2nd and 3rd point)
Shape
Digitizing
Draw Rectangles
► Add Rectangle from 3 Points (Distance
from projected point on segment p1 and p2)
Shape
Digitizing
Draw Rectangles
Add Regular Polygon ► Shape
Digitizing
Draw Regular Polygons
► Add Regular Polygon from Center and
a Point
Shape
Digitizing
Draw Regular Polygons
► Add Regular Polygon from Center and
a Corner
Shape
Digitizing
Draw Regular Polygons
► Add Regular Polygon from 2 Points Shape
Digitizing
Draw Regular Polygons
Add Ellipse ► Shape
Digitizing
Draw Ellipses
► Add Ellipse from Center and 2 Points Shape
Digitizing
Draw Ellipses
► Add Ellipse from Center and a Point Shape
Digitizing
Draw Ellipses
► Add Ellipse from Extent Shape
Digitizing
Draw Ellipses
► Add Ellipse from Foci Shape
Digitizing
Draw Ellipses
Add Annotation ► Anotační nástroje
► Text Annotation Atributy Anotační nástroje
► Form Annotation Atributy Anotační nástroje
► HTML Annotation Atributy Anotační nástroje
► SVG Annotation Atributy Anotační nástroje
Přesunout prvek/(prvky) Advanced
Digitizing
Move Feature(s)
Copy and Move Feature(s) Advanced
Digitizing
Move Feature(s)
Delete Selected Digitalizace Deleting Selected
Features
Upravit atributy vybraných prvků Digitalizace Editing attribute values
Rotovat prvek/(prvky) Advanced
Digitizing
Rotovat prvek(prvky)
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QGIS Desktop 3.16 User Guide
Tabulka 7.1 – pokračujte na předchozí stránce
Menu Možnosti Zkratka Panel
nástrojů
Reference
Zjednodušit prvek Advanced
Digitizing
Zjednodušit prvek
Přidat prstenec Advanced
Digitizing
Přidat prstenec
Přidat část Advanced
Digitizing
Přidat část
Vyplnit prstenec Advanced
Digitizing
Fill Ring
Smazat prstenec Advanced
Digitizing
Smazat prstenec
Smazat část Advanced
Digitizing
Smazat část
Změnit tvar prvků Advanced
Digitizing
Změnit tvar prvků
Odsazení křivky Advanced
Digitizing
Odsazení křivek
Rozdělit objekt Advanced
Digitizing
Rozdělit objekt
Rozdělit části Advanced
Digitizing
Split parts
Sloučit vybrané prvky Advanced
Digitizing
Sloučit vybrané prvky
Merge Attributes of Selected Features Advanced
Digitizing
Sloučit atributy
vybraných prvků
Vertex Tool (All Layers) Digitalizace Vertex tool
Vertex Tool (Current Layer) Digitalizace Vertex tool
Rotovat symboly bodů Advanced
Digitizing
Rotovat symboly bodů
Odsazení bodových symbolů Advanced
Digitizing
Offset Point Symbols
Reverse Line Advanced
Digitizing
Reverse Line
Trim/extend Feature Advanced
Digitizing
Trim/Extend Feature
Tools that depend on the selected layer geometry type i.e. point, polyline or polygon, are activated accordingly:
Menu Možnosti Bod Polyline Polygon
Move Feature(s)
Copy and Move Feature(s)
28 Kapitola 7. QGIS GUI
QGIS Desktop 3.16 User Guide
7.1.3 Zobrazit
The map is rendered in map views. You can interact with these views using the View tools (see Working with the map
canvas for more information). For example, you can:
• Create new 2D or 3D map views next to the main map canvas
• Zoom or pan to any place
• Query displayed features‘ attributes or geometry
• Enhance the map view with preview modes, annotations or decorations
• Access any panel or toolbar
The menu also allows you to reorganize the QGIS interface itself using actions like:
• Toggle Full Screen Mode: covers the whole screen while hiding the title bar
• Toggle Panel Visibility: shows or hides enabled panels - useful when digitizing features (for maximum canvas
visibility) as well as for (projected/recorded) presentations using QGIS‘ main canvas
• Toggle Map Only: hides panels, toolbars, menus and status bar and only shows the map canvas. Combined with
the full screen option, it makes your screen display only the map
Menu Možnosti Zkratka Panel
nástrojů
Reference
New Map View Ctrl+M Zobrazení mapy
New 3D Map View Ctrl+Alt+M 3D Map View
Posunout mapu Map
Navigation
Zooming and Panning
Posunout mapu na výběr Map
Navigation
Přiblížit Ctrl+Alt++ Map
Navigation
Zooming and Panning
Oddálit Ctrl+Alt+- Map
Navigation
Zooming and Panning
Identifikovat prvky Ctrl+Shift+I Atributy Identifying Features
Měřit ► Atributy Měření
► Measure Line Ctrl+Shift+M Atributy Měření
► Measure Area Ctrl+Shift+J Atributy Měření
► Measure Angle Atributy Měření
Statistický souhrn Atributy Statistical Summary
Panel
Přiblížit na rozměry okna Ctrl+Shift+F Map
Navigation
Zooming and Panning
Přiblížit na výběr Ctrl+J Map
Navigation
Zooming and Panning
Přiblížit na vsrtvu Map
Navigation
Zooming and Panning
Zoom To Native Resolution (100%) Map
Navigation
Zooming and Panning
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7.1. Menu lišta 29
QGIS Desktop 3.16 User Guide
Tabulka 7.2 – pokračujte na předchozí stránce
Menu Možnosti Zkratka Panel
nástrojů
Reference
Zvětšit podle posledního výřezu Map
Navigation
Zooming and Panning
Přiblížit na další Map
Navigation
Zooming and Panning
Dekorace ► Alt+V + D Dekorace
► Grid… Mřížka
► Scale Bar… Měřítko
► Image… Image Decoration
► North Arrow… Směrová růžice
► Title Label… Title Label
► Copyright Label… Copyright Label
► Layout Extents… Layout Extents
Režim náhledu ►
► Normal
► Simulate Photocopy (Grayscale)
► Simulate Fax (Mono)
► Simulate Color Blindness (Protanope)
► Simulate Color Blindness (Deuteronope)
Show Map Tips Atributy Display Properties
New Spatial Bookmark… Ctrl+B Map
Navigation
Prostorové záložky
Show Spatial Bookmarks Ctrl+Shift+B Map
Navigation
Prostorové záložky
Show Spatial Bookmark Manager Prostorové záložky
Refresh F5 Map
Navigation
Zobrazit všechny vrstvy Ctrl+Shift+U Layers Panel
Skrýt všechny vrstvy Ctrl+Shift+H Layers Panel
Show Selected Layers Layers Panel
Hide Selected Layers Layers Panel
Toggle Selected Layers Layers Panel
Toogle Selected Layers Independently Layers Panel
Hide Deselected Layers Layers Panel
Panely ► Panely a nástrojové lišty
► Advanced Digitizing The Advanced Digitizing
panel
► Browser The Browser Panel
► Browser (2) The Browser Panel
► GPS Information Live GPS tracking
► GRASS Tools GRASS GIS Integration
► Layer Order Layer Order Panel
► Layer Styling Layer Styling Panel
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Tabulka 7.2 – pokračujte na předchozí stránce
Menu Možnosti Zkratka Panel
nástrojů
Reference
► Layers Layers Panel
► Log Messages Log Messages Panel
► Overview Overview Panel
► Processing Toolbox The Toolbox
► Results Viewer The Toolbox
► Snapping and Digitizing Options Nastavení přichytávací
tolerance a vyhledání
poloměru
► Spatial Bookmark Manager Prostorové záložky
► Statistics Statistical Summary
Panel
► Tile Scale Sady dlaždic
► Undo/Redo Undo/Redo Panel
Nástrojové lišty ► Panely a nástrojové lišty
► Advanced Digitizing Toolbar Advanced digitizing
► Attributes Toolbar
► Data Source Manager Toolbar Managing Data Source
► Database Toolbar
► Digitizing Toolbar Digitizing an existing
layer
► Help Toolbar
► Label Toolbar The Label Toolbar
► Manage Layers Toolbar Managing Data Source
► Map Navigation Toolbar
► Plugins Toolbar Zásuvné moduly
► Project Toolbar
► Raster Toolbar
► Selection Toolbar Selecting features
► Shape Digitizing Toolbar Shape digitizing
► Snapping Toolbar Nastavení přichytávací
tolerance a vyhledání
poloměru
► Vector Toolbar
► Web Toolbar
► GRASS GRASS GIS Integration
Přepnout režim celé obrazovky F11
Toggle Panel Visibility Ctrl+Tab
Toggle Map Only Ctrl+Shift+Tab
Under Linux KDE, Panels ►, Toolbars ► and Toggle Full Screen Mode are in the Settings menu.
7.1.4 Vrstva
The Layer menu provides a large set of tools to create new data sources, add them to a project or save modifications
to them. Using the same data sources, you can also:
• Duplicate a layer to generate a copy where you can modify the name, style (symbology, labels, …), joins, …
The copy uses the same data source as the original.
• Copy and Paste layers or groups from one project to another as a new instance whose properties can be modified
independently. As for Duplicate, the layers are still based on the same data source.
• or Embed Layers and Groups… from another project, as read-only copies which you cannot modify (see
Vnořování projektů)
7.1. Menu lišta 31
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The Layer menu also contains tools to configure, copy or paste layer properties (style, scale, CRS…).
Menu Možnosti Zkratka Panel nástrojů Reference
Data Source Manager Ctrl+L Data Source
Manager
Opening Data
Vytvořit vrstvu ► Creating new vector layers
► New GeoPackage Layer… Ctrl+Shift+N Data Source
Manager
Creating a new GeoPackage
layer
► New Shapefile Layer… Data Source
Manager
Creating a new Shapefile
layer
► New SpatiaLite Layer… Data Source
Manager
Creating a new SpatiaLite
layer
► New Temporary Scratch Layer… Data Source
Manager
Creating a new Temporary
Scratch Layer
► New Virtual Layer… Data Source
Manager
Creating virtual layers
Přidat vrstvu ► Opening Data
► Add Vector Layer…… Ctrl+Shift+V Manage Layers Loading a layer from a file
► Add Raster Layer… Ctrl+Shift+R Manage Layers Loading a layer from a file
► Add Mesh Layer… Manage Layers Loading a mesh layer
► Add Delimited Text Layer… Ctrl+Shift+T Manage Layers Importing a delimited text
file
► Add PostGIS Layer… Ctrl+Shift+D Manage Layers Database related tools
► Add SpatiaLite Layer… Ctrl+Shift+L Manage Layers SpatiaLite Layers
► Add MSSQL Spatial Layer… Manage Layers Database related tools
► Add Oracle Spatial Layer… Manage Layers Database related tools
► Add DB2 Spatial Layer… Ctrl+Shift+2 Manage Layers Database related tools
► Add/Edit Virtual Layer… Manage Layers Creating virtual layers
► Add WMS/WMTS Layer… Ctrl+Shift+W Manage Layers Loading WMS/WMTS
Layers
► Add XYZ Layer… Using XYZ Tile services
► Add ArcGIS Map Service Layer… Manage Layers
► Add WCS Layer… Manage Layers WCS Client
► Add WFS Layer… Manage Layers WFS and WFS-T Client
► Add ArcGIS Feature Service
Layer…
Manage Layers
► Add Vector Tile Layer…
Přiložit vrstvy a skupiny… Vnořování projektů
Přidat ze souboru definice vrstvy… Layer definition file
Copy Style Save and Share Layer
Properties
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Tabulka 7.3 – pokračujte na předchozí stránce
Menu Možnosti Zkratka Panel nástrojů Reference
Paste Style Save and Share Layer
Properties
Copy Layer
Paste Layer/Group
Otevřít atributovou tabulku F6 Atributy Working with the Attribute
Table
Přepnout editaci Digitalizace Digitizing an existing layer
Uložit změny vrstvy Digitalizace Saving Edited Layers
Aktuální změny ► Digitalizace Saving Edited Layers
► Save for Selected Layer(s) Digitalizace Saving Edited Layers
► Rollback for Selected Layer(s) Digitalizace Saving Edited Layers
► Cancel for Selected Layer(s) Digitalizace Saving Edited Layers
► Save for all Layers Digitalizace Saving Edited Layers
► Rollback for all Layers Digitalizace Saving Edited Layers
► Cancel for all Layers Digitalizace Saving Edited Layers
Save As… Creating new layers from an
existing layer
Save As Layer Definition File… Layer definition file
Odstranit vrstvu/skupinu Ctrl+D
Duplikovat vrstvu(vrstvy)
Nastavit měřítko viditelnosti
vrstvy(vrstev)
Nastavit SRS vrstvy/(vrstev) Ctrl+Shift+C Layer Coordinate Reference
Systems
Nastavit projekt CRS z vrstvy Project Coordinate
Reference Systems
Layer Properties… The Vector Properties
Dialog, Raster Properties
Dialog, Mesh Dataset
Properties
Filtrovat… Ctrl+F Query Builder
Tvorba popisků Labels Properties
Show in Overview Overview Panel
Show All in Overview Overview Panel
Hide All from Overview Overview Panel
7.1. Menu lišta 33
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7.1.5 Nastavení
Menu Možnosti Reference
User Profiles ► Working with User Profiles
► default Working with User Profiles
► Open Active Profile Folder Working with User Profiles
► New Profile… Working with User Profiles
Style Manager… The Style Manager
Custom Projections… Vlastní souřadnicový referenční systém
Keyboard Shortcuts… Keyboard shortcuts
Interface Customization… Přizpůsobení
Možnosti… Možnosti
Under Linux KDE, you’ll find more tools in the Settings menu such as Panels ►, Toolbars ► and Toggle Full
Screen Mode.
7.1.6 Zásuvné moduly
Menu Možnosti Zkratka Panel nástrojů Reference
Spravovat a instalovat zásuvné
moduly…
The Plugins Dialog
„ Python Console Ctrl+Alt+P Plugins QGIS Python console
Při prvním spuštění QGIS nejsou načteny všechny základní zásuvný moduly.
7.1.7 Vektor
This is what the Vector menu looks like if all core plugins are enabled.
Menu Možnosti Zkratka Panel
nástrojů
Reference
Check Geometries… Geometry Checker Plugin
GPS Tools Alt+O + G Vector GPS Plugin
Topology Checker Vector Topology Checker Plugin
Geoprocessing Tools ► Alt+O + G
► Buffer… Buffer
► Clip… Clip
► Convex Hull… Convex hull
► Difference… Difference
► Dissolve… Dissolve
► Intersection… Intersection
► Symmetrical Difference… Symmetrical difference
► Union… Union
► Eliminate Selected Polygons… Eliminate selected polygons
Geometry Tools ► Alt+O + E
► Centroids… Centroids
► Collect Geometries… Collect geometries
continues on next page
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Tabulka 7.4 – pokračujte na předchozí stránce
Menu Možnosti Zkratka Panel
nástrojů
Reference
► Extract Vertices… Extract vertices
► Multipart to Singleparts… Multipart to singleparts
► Polygons to Lines… Polygons to lines
► Simplify… Simplify
► Check Validity… Check validity
► Delaunay Triangulation… Delaunay triangulation
► Densify by Count… Densify by count
► Add Geometry Attributes… Add geometry attributes
► Lines to Polygons… Lines to polygons
► Voronoi Polygons… Voronoi polygons
Analysis Tools ► Alt+O + A
► Line Intersection… Line intersections
► Mean Coordinate(s)… Mean coordinate(s)
► Basic Statistics for Fields… Basic statistics for fields
► Count Points in Polygon… Count points in polygon
► Distance Matrix… Distance matrix
► List Unique Values… List unique values
► Nearest Neighbour Analysis… Nearest neighbour analysis
► Sum Line Lengths… Sum line lengths
Data Management Tools ► Alt+O + D
► Merge Vector Layers… Merge vector layers
► Reproject Layer… Reproject layer
► Create Spatial Index… Create spatial index
► Join Attributes by Location… Join attributes by location
► Split Vector Layer… Split vector layer
Research Tools ► Alt+O + R
► Select by Location… Select by location
► Extract Layer Extent… Extract layer extent
► Random Points in Extent… Random points in extent
► Random Points in Layer Bounds… Random points in layer bounds
► Random Points Inside Polygons… Random points inside polygons
► Random Selection… Random selection
► Random Selection Within Subsets… Random selection within subsets
► Regular Points… Regular points
By default, QGIS adds Processing algorithms to the Vector menu, grouped by sub-menus. This provides shortcuts for
many common vector-based GIS tasks from different providers. If not all these sub-menus are available, enable the
Processing plugin in Plugins ► Manage and Install Plugins….
Note that the list of the Vector menu tools can be extended with any Processing algorithms or some external plugins.
7.1.8 Rastr
This is what the Raster menu looks like if all core plugins are enabled.
Menu Možnosti Zkratka Panel
nástrojů
Reference
Raster calculator… Raster Calculator
Zarovnat rastry… Raster Alignment
Georeferencer Alt+R + G Raster Georeferencer
Analysis ►
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QGIS Desktop 3.16 User Guide
Tabulka 7.5 – pokračujte na předchozí stránce
Menu Možnosti Zkratka Panel
nástrojů
Reference
► Aspect… Aspect
► Fill nodata… Fill nodata
► Grid (Moving Average)… Grid (Moving average)
► Grid (Data Metrics)… Grid (Data metrics)
► Grid (Inverse Distance to a Power)… Grid (Inverse distance to a power)
► Grid (Nearest Neighbor)… Grid (IDW with nearest neighbor
searching)
► Hillshade… Hillshade
► Proximity (Raster Distance)… Proximity (raster distance)
► Roughness… Roughness
► Sieve… Sieve
► Slope… Slope
► Topographic Position Index (TPI)… Topographic Position Index (TPI)
► Terrain Ruggedness Index (TRI)… Terrain Ruggedness Index (TRI)
Projections ►
► Assign Projection… Assign projection
► Extract Projection… Extract projection
► Warp (Reproject)… Warp (reproject)
Miscellaneous ►
► Build Virtual Raster… Build virtual raster
► Raster Information… Raster information
► Merge… Merge
► Build Overviews (Pyramids)… Build overviews (pyramids)
► Tile Index… Tile index
Extraction ►
► Clip Raster by Extent… Clip raster by extent
► Clip Raster by Mask Layer… Clip raster by mask layer
► Contour… Contour
Conversion ►
► PCT to RGB… PCT to RGB
► Polygonize (Raster to Vector)… Polygonize (raster to vector)
► Rasterize (Vector to Raster)… Rasterize (vector to raster)
► RGB to PCT… RGB to PCT
► Translate (Convert Format)… Translate (convert format)
By default, QGIS adds Processing algorithms to the Raster menu, grouped by sub-menus. This provides a shortcut for
many common raster-based GIS tasks from different providers. If not all these sub-menus are available, enable the
Processing plugin in Plugins ► Manage and Install Plugins….
Note that the list of the Raster menu tools can be extended with any Processing algorithms or some external plugins.
7.1.9 Databáze
This is what the Database menu looks like if all the core plugins are enabled. If no database plugins are enabled, there
will be no Database menu.
Menu Možnosti Zkratka Panel
nástrojů
Reference
Offline editing… Alt+D + O Offline Editing Plugin
► Convert to Offline Project… Databáze Offline Editing Plugin
► Synchronize Databáze Offline Editing Plugin
DB Manager… Databáze DB Manager Plugin
36 Kapitola 7. QGIS GUI
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Při prvním spuštění QGIS nejsou načteny všechny základní zásuvný moduly.
7.1.10 Web
This is what the Web menu looks like if all the core plugins are enabled. If no web plugins are enabled, there will be
no Web menu.
Menu Možnosti Zkratka Panel
nástrojů
Reference
MetaSearch ► Alt+W + M MetaSearch Catalog Client
► Metasearch Web MetaSearch Catalog Client
► Help MetaSearch Catalog Client
Při prvním spuštění QGIS nejsou načteny všechny základní zásuvný moduly.
7.1.11 Mesh
The Mesh menu provides tools needed to manipulate mesh layers.
Menu Možnosti Zkratka Panel
nástrojů
Reference
Mesh Calculator…
7.1.12 Zpracování
Menu Možnosti Zkratka Panel
nástrojů
Reference
Toolbox Ctrl+Alt+T The Toolbox
Grafický modelář… Ctrl+Alt+G The graphical modeler
History… Ctrl+Alt+H The history manager
Results Viewer Ctrl+Alt+R Configuring external applications
Edit Features In-Place The Processing in-place layer modifier
Při prvním spuštění QGIS nejsou načteny všechny základní zásuvný moduly.
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QGIS Desktop 3.16 User Guide
7.1.13 Nápověda
Menu Možnosti Zkratka Panel
nástrojů
Reference
Obsah nápovědy F1 Nápověda
API dokumentace
Plugins ►
Nahlásit problém
Potřebujete komerční podporu?
QGIS domovská stránka Ctrl+H
Check QGIS Version
About
QGIS Sustaining Members
7.1.14 QGIS
Toto menu je přístupné pod macOS a obsahuje některé OS spojené příkazy.
Menu Možnosti Zkratka
Preference
O QGIS
Skrýt QGIS
Ukázat vše
Skrýt ostatní
Ukončit QGIS Cmd+Q
Preferences correspond to Settings ► Options, About QGIS corresponds to Help ► About and Quit QGIS corresponds
to Project ► Exit QGIS for other platforms.
7.2 Panely a nástrojové lišty
From the View menu (or Settings), you can switch QGIS widgets (Panels ►) and toolbars (Toolbars ►) on and off.
To (de)activate any of them, right-click the menu bar or toolbar and choose the item you want. Panels and toolbars can
be moved and placed wherever you like within the QGIS interface. The list can also be extended with the activation
of Core or external plugins.
7.2.1 Nástrojové lišty
The toolbars provide access to most of the functions in the menus, plus additional tools for interacting with the map.
Each toolbar item has pop-up help available. Hover your mouse over the item and a short description of the tool’s
purpose will be displayed.
Každou nástrojovou lištou lze pohyboval podle vašich potřeb. Navíc každou lištu lze vypnout pomocí pravého tlačítka
myši kontextového menu nebo podržením myši nad nástrojovou lištou.
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Obr. 7.2: Nástrojové lišty menu
Tip: Obnovení panelu nástrojů
If you have accidentally hidden a toolbar, you can get it back using View ► Toolbars ► (or Settings ► Toolbars
►). If, for some reason, a toolbar (or any other widget) totally disappears from the interface, you’ll find tips to get it
back at restoring initial GUI.
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7.2.2 Panely
QGIS provides many panels. Panels are special widgets that you can interact with (selecting options, checking boxes,
filling values…) to perform more complex tasks.
Obr. 7.3: Panelové menu
Below is a list of the default panels provided by QGIS:
• Výhodná digitalizace
• the Browser Panel
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• the GPS informační panel
• the Identifikační panel
• Panel pořadí vrstev
• the Layer Styling Panel
• the Layers Panel
• the Log Messages Panel
• the Overview Panel
• the Toolbox zpracování
• the Result Viewer Panel
• the Spatial Bookmark Manager Panel
• the Statistics Panel
• the Měřítkový panel
• the Undo/Redo Panel
7.3 Zobrazení mapy
7.3.1 Exploring the map view
The map view (also called Map canvas) is the „business end“ of QGIS — maps are displayed in this area, in 2D.
The map displayed in this window will reflect the rendering (symbology, labeling, visibilities…) you applied to the
layers you have loaded. It also depends on the layers and the project’s Coordinate Reference System (CRS).
When you add a layer (see e.g. Opening Data), QGIS automatically looks for its CRS. If a different CRS is set by
default for the project (see Project Coordinate Reference Systems) then the layer extent is „on-the-fly“ translated to that
CRS, and the map view is zoomed to that extent if you start with a blank QGIS project. If there are already layers in
the project, no map canvas resize is performed, so only features falling within the current map canvas extent will be
visible.
Click on the map view and you should be able to interact with it:
• it can be panned, shifting the display to another region of the map: this is performed using the Pan Map
tool,
the arrow keys, moving the mouse while any of the Space key, the middle mouse button or the mouse wheel
is held down.
• it can be zoomed in and out, with the dedicated Zoom In
and Zoom Out
tools. Hold the Alt key to switch
from one tool to the other. Zooming is also performed by rolling the wheel forward to zoom in and backwards
to zoom out. The zoom is centered on the mouse cursor position.
You can customize the Zoom factor under the Settings ► Options ► Map tools menu.
• it can be zoomed to the full extent of all loaded layers ( Zoom Full
), to a layer extent ( Zoom to Layer
) or to
the extent of selected features ( Zoom to Selection
)
• you can navigate back/forward through the canvas view history with the Zoom Last
and Zoom Next
buttons
or using the back/forward mouse buttons.
Right-click over the map and you should be able to Copy coordinates of the clicked point in the map CRS, in
WGS84 or in a custom CRS. The copied information can then be pasted in an expression, a script, text editor or
spreadsheet…
By default, QGIS opens a single map view (called „main map“), which is tightly bound to the Layers panel; the main
map automatically reflects the changes you do in the Layers panel area. But it is also possible to open additional map
7.3. Zobrazení mapy 41
QGIS Desktop 3.16 User Guide
views whose content could diverge from the Layers panel current state. They can be of 2D or 3D type, show different
scale or extent, or display a different set of the loaded layers thanks to map themes.
7.3.2 Setting additional map views
To add a new map view, go to View ► New Map View. A new floating widget, mimicking the main map view’s
rendering, is added to QGIS. You can add as many map views as you need. They can be kept floating, placed side by
side or stacked on top of each other.
Obr. 7.4: Multiple map views with different settings
At the top of an additional map canvas, there’s a toolbar with the following capabilities:
• Zoom Full
, Zoom to Selection
and Zoom to Layer
to navigate within the view
• Set View Theme
to select the map theme to display in the map view. If set to (none), the view will follow the
Layers panel changes.
• View settings
to configure the map view:
– Synchronize view center with main map: syncs the center of the map views without changing the scale.
This allows you to have an overview style or magnified map which follows the main canvas center.
– Synchronize view to selection: same as zoom to selection
– Scale
– Rotation
– Magnification
– Synchronize scale with the main map scale. A Scale factor can then be applied, allowing you to have
a view which is e.g. always 2x the scale of the main canvas.
– Show annotations
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– Show cursor position
– Show main canvas extent
– Show labels: allows to hide labels regardless they are set in the displayed layers‘ properties
– Change map CRS…
– Rename view…
7.3.3 Exporting the map view
Maps you make can be layout and exported to various formats using the advanced capabilities of the print layout or
report. It’s also possible to directly export the current rendering, without a layout. This quick „screenshot“ of the map
view has some convenient features.
To export the map canvas with the current rendering:
1. Go to Project ► Import/Export
2. Depending on your output format, select either
• Export Map to Image…
• or Export Map to PDF…
The two tools provide you with a common set of options. In the dialog that opens:
Obr. 7.5: The Save Map as Image dialog
1. Choose the Extent to export: it can be the current view extent (the default), the extent of a layer or a custom
extent drawn over the map canvas. Coordinates of the selected area are displayed and manually editable.
2. Enter the Scale of the map or select it from the predefined scales: changing the scale will resize the extent to
export (from the center).
3. Set the Resolution of the output
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QGIS Desktop 3.16 User Guide
4. Control the Output width and Output height in pixels of the image: based by default on the current resolution and
extent, they can be customized and will resize the map extent (from the center). The size ratio can be locked,
which may be particularly convenient when drawing the extent on the canvas.
5. Draw active decorations: in use decorations (scale bar, title, grid, north arrow…) are exported with the map
6. Draw annotations to export any annotation
7. Append georeference information (embedded or via world file): depending on the output format, a world
file of the same name (with extension PNGW for PNG images, JPGW for JPG, …) is saved in the same folder
as your image. The PDF format embeds the information in the PDF file.
8. When exporting to PDF, more options are available in the Save map as PDF… dialog:
Obr. 7.6: The Save Map as PDF dialog
• Export RDF metadata of the document such as the title, author, date, description…
• Create Geospatial PDF (GeoPDF): Generate a georeferenced PDF file (requires GDAL version 3 or
later). You can:
– Choose the GeoPDF Format
– Include vector feature information in the GeoPDF file: will include all the geometry and attribute
information from features visible within the map in the output GeoPDF file.
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Poznámka: Since QGIS 3.10, with GDAL 3 a GeoPDF file can also be used as a data source. For more
on GeoPDF support in QGIS, see https://north-road.com/2019/09/03/qgis-3-10-loves-geopdf/.
• Rasterize map
• Simplify geometries to reduce output file size: Geometries will be simplified while exporting the map by
removing vertices that are not discernably different at the export resolution (e.g. if the export resolution
is 300 dpi, vertices that are less than 1/600 inch apart will be removed). This can reduce the size
and complexity of the export file (very large files can fail to load in other applications).
• Set the Text export: controls whether text labels are exported as proper text objects (Always export texts
as text objects) or as paths only (Always export texts as paths). If they are exported as text objects then
they can be edited in external applications (e.g. Inkscape) as normal text. BUT the side effect is that the
rendering quality is decreased, AND there are issues with rendering when certain text settings like buffers
are in place. That’s why exporting as paths is recommended.
9. Click Save to select file location, name and format.
When exporting to image, it’s also possible to Copy to clipboard the expected result of the above settings and
paste the map in another application such as LibreOffice, GIMP…
7.4 3D Map View
3D visualization support is offered through the 3D map view. You create and open a 3D map view via View ►
New 3D Map View. A floating QGIS panel will appear. The panel can be docked.
To begin with, the 3D map view has the same extent and view as the 2D main map canvas. A set of navigation tools
are available to turn the view into 3D.
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QGIS Desktop 3.16 User Guide
Obr. 7.7: The 3D Map View dialog
The following tools are provided at the top of the 3D map view panel:
• Camera control
: moves the view, keeping the same angle and direction of the camera
• Zoom Full
: resizes the view to the whole layers‘ extent
• Toggle on-screen notification
: shows/hides the navigation widget (that is meant to ease controlling of the map view)
• Identify
: returns information on the clicked point of the terrain or the clicked 3D feature(s) – More details
at Identifying Features
• Measurement line
: measures the horizontal distance between points
• Animations
: shows/hides the animation player widget
• Save as image…
: exports the current view to an image file format
• Export 3D Scene…
: exports the current view as a 3D scene (.obj file), allowing post-processing in applications
like Blender… The terrain and vector features are exported as 3D objects. The export settings, overriding the
layers properties or map view configuration, include:
– Scene name and destination Folder
– Terrain resolution
– Terrain texture resolution
– Model scale
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– Smooth edges
– Export normals
– Export textures
• Set View Theme
: Allows you to select the set of layers to display in the map view from predefined map themes.
• Configure
the map view settings
7.4.1 Navigation options
To explore the map view in 3D:
• Tilt the terrain (rotating it around a horizontal axis that goes through the center of the window)
– Press the Tilt up
and Tilt down
tools
– Press Shift and use the up/down keys
– Drag the mouse forward/backward with the middle mouse button pressed
– Press Shift and drag the mouse forward/backward with the left mouse button pressed
• Rotate the terrain (around a vertical axis that goes through the center of the window)
– Turn the compass of the navigation widget to the watching direction
– Press Shift and use the left/right keys
– Drag the mouse right/left with the middle mouse button pressed
– Press Shift and drag the mouse right/left with the left mouse button pressed
• Change the camera position (and the view center), moving it around in a horizontal plan
– Drag the mouse with the left mouse button pressed, and the Camera control
button enabled
– Press the directional arrows of the navigation widget
– Use the up/down/left/right keys to move the camera forward, backward, right and left, respectively
• Change the camera altitude: press the Page Up/Page Down keys
• Change the camera orientation (the camera is kept at its position but the view center point moves)
– Press Ctrl and use the arrow keys to turn the camera up, down, left and right
– Press Ctrl and drag the mouse with the left mouse button pressed
• Zoom in and out
– Press the corresponding Zoom In
and Zoom Out
tools of the navigation widget
– Scroll the mouse wheel (keep Ctrl pressed results in finer zooms)
– Drag the mouse with the right mouse button pressed to zoom in (drag down) and out (drag up)
To reset the camera view, click the Zoom Full
button on the top of the 3D canvas panel.
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7.4.2 Creating an animation
An animation is based on a set of keyframes - camera positions at particular times. To create an animation:
1. Toggle on the Animations
tool, displaying the animation player widget
2. Click the Add keyframe
button and enter a Keyframe time in seconds. The Keyframe combo box now displays
the time set.
3. Using the navigation tools, move the camera to the position to associate with the current keyframe time.
4. Repeat the previous steps to add as many keyframes (with time and position) as necessary.
5. Click the button to preview the animation. QGIS will generate scenes using the camera positions/rotations
at set times, and interpolating them in between these keyframes. Various Interpolation modes for animations
are available (eg, linear, inQuad, outQuad, inCirc… – more details at https://doc.qt.io/qt-5/qeasingcurve.html#
EasingFunction-typedef).
The animation can also be previewed by moving the time slider. Keeping the Repeat
button pressed will
repeatedly run the animation while clicking stops a running animation.
It is possible to browse the different views of the camera, using the Keyframe list. Whenever a time is active, changing
the map view will automatically update the associated position. You can also Edit keyframe
(time only) or
Remove keyframe
.
Click Export animation frames
to generate a series of images representing the scene. Other than the filename Template
and the Output directory, you can set the number of Frames per second, the Output width and Output height.
7.4.3 Scene Configuration
The 3D map view opens with some default settings you can customize. To do so, click the Configure…
button at the
top of the 3D canvas panel to open the 3D configuration window.
Obr. 7.8: The 3D Map Configuration dialog
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In the 3D Configuration window there are various options to fine-tune the 3D scene:
Terrain
• Terrain: Before diving into the details, it is worth noting that the terrain in a 3D view is represented by
a hierarchy of terrain tiles and as the camera moves closer to the terrain, existing tiles that do not have sufficient
details are replaced by smaller tiles with more details. Each tile has mesh geometry derived from the elevation
raster layer and texture from 2D map layers.
– The elevation terrain Type can be:
∗ a Flat terrain
∗ a loaded DEM (Raster Layer)
∗ an Online service, loading elevation tiles produced by Mapzen tools – more details at https://registry.
opendata.aws/terrain-tiles/
∗ a loaded Mesh dataset
– Elevation: Raster or mesh layer to be used for generation of the terrain. The raster layer must contain
a band that represents elevation. For a mesh layer, the Z values of the vertices are used.
– Vertical scale: Scale factor for vertical axis. Increasing the scale will exaggerate the height of the
landforms.
– Tile resolution: How many samples from the terrain raster layer to use for each tile. A value of 16px
means that the geometry of each tile will consist of 16x16 elevation samples. Higher numbers create
more detailed terrain tiles at the expense of increased rendering complexity.
– Skirt height: Sometimes it is possible to see small cracks between tiles of the terrain. Raising this value
will add vertical walls („skirts“) around terrain tiles to hide the cracks.
• When a mesh layer is used as terrain, you can configure the Triangles settings (wireframe display, smooth
triangles) and the Rendering colors settings (as uniform or depending on terrain level). More details in the Mesh
layer properties section.
• Terrain shading: Allows you to choose how the terrain should be rendered:
– Shading disabled - terrain color is determined only from map texture
– Shading enabled - terrain color is determined using Phong’s shading model, taking into account map
texture, the terrain normal vector, scene light(s) and the terrain material’s Ambient and Specular colors
and Shininess
Lights
From the Lights tab, press the menu to add
• up to eight Point lights: emits light in all directions, like a sphere of light filling an area. Objects closer to the
light will be brighter, and objects further away will be darker. A point light has a set position (X, Y and Z),
a Color, an Intensity and an Attenuation
• up to four Directional lights: mimics the lighting that you would get from a giant flash light very far away
from your objects, always centered and that never dies off (e.g. the sun). It emits parallel light rays in a single
direction but the light reaches out into infinity. A directional light can be rotated given an Azimuth, have an
Altitude, a Color and an Intensity.
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QGIS Desktop 3.16 User Guide
Obr. 7.9: The 3D Map Lights Configuration dialog
Shadow
Check Show shadow to display shadow within your scene, given:
• a Directional light
• a Shadow rendering maximum distance: to avoid rendering shadow of too distant objects, particularly when the
camera looks up along the horizon
• a Shadow bias: to avoid self-shadowing effects that could make some areas darker than others, due to differences
between map sizes. The lower the better
• a Shadow map resolution: to make shadows look sharper. It may result in less performance if the resolution
parameter is too high.
Camera & Skybox
• Camera’s Field of view: allowing to create panoramic scenes. Default value is 45°.
• Check Show skybox to enable skybox rendering in the scene. The skybox type can be:
– Panoramic texture, with a single file providing sight on 360°
– Distinct faces, with a texture file for each of the six sides of a box containing the scene
Texture files can be files on the disk, remote URLs or embedded in the project (more details).
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Advanced
• Map tile resolution: Width and height of the 2D map images used as textures for the terrain tiles. 256px means
that each tile will be rendered into an image of 256x256 pixels. Higher numbers create more detailed terrain
tiles at the expense of increased rendering complexity.
• Max. screen error: Determines the threshold for swapping terrain tiles with more detailed ones (and vice versa)
- i.e. how soon the 3D view will use higher quality tiles. Lower numbers mean more details in the scene at the
expense of increased rendering complexity.
• Max. ground error: The resolution of the terrain tiles at which dividing tiles into more detailed ones will stop
(splitting them would not introduce any extra detail anyway). This value limits the depth of the hierarchy of
tiles: lower values make the hierarchy deep, increasing rendering complexity.
• Zoom levels: Shows the number of zoom levels (depends on the map tile resolution and max. ground error).
• Show labels: Toggles map labels on/off
• Show map tile info: Include border and tile numbers for the terrain tiles (useful for troubleshooting terrain
issues)
• Show bounding boxes: Show 3D bounding boxes of the terrain tiles (useful for troubleshooting terrain
issues)
• Show camera’s view center
• Show light sources: shows a sphere at light source origins, allowing easier repositioning and placement of
light sources relative to the scene contents
7.4.4 3D vector layers
A vector layer with elevation values can be shown in the 3D map view by checking Enable 3D Renderer in the 3D
View section of the vector layer properties. A number of options are available for controlling the rendering of the 3D
vector layer.
7.5 Stavová lišta
The status bar provides you with general information about the map view and processed or available actions, and
offers you tools to manage the map view.
7.5.1 Locator bar
On the left side of the status bar, the locator bar, a quick search widget, helps you find and run any feature or options
in QGIS:
1. Click in the text widget to activate the locator search bar or press Ctrl+K.
2. Type a text associated with the item you are looking for (name, tag, keyword, …). By default, results are
returned for the enabled locator filters, but you can limit the search to a certain scope by prefixing your text
with the locator filters prefix, ie. typing l cad will return only the layers whose name contains cad.
The filter can also be selected with a double-click in the menu that shows when accessing the locator widget.
3. Click on a result to execute the corresponding action, depending on the type of item.
Tip: Limit the lookup to one field of the active layer
By default, a search with the „active layer features“ filter (f) runs through the whole attribute table of the layer. You
can limit the search to a particular field using the @ prefix. E.g., f @name sal or @name sal returns only the
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features whose „name“ attribute contains ‚sal‘. Text autocompletion is active when writing and the suggestion can be
applied using Tab key.
Searching is handled using threads, so that results always become available as quickly as possible, even if slow search
filters are installed. They also appear as soon as they are encountered by a filter, which means that e.g. a file search
filter will show results one by one as the file tree is scanned. This ensures that the UI is always responsive, even if
a very slow search filter is present (e.g. one which uses an online service).
Tip: Quick access to the locator’s configurations
Click on the icon inside the locator widget on the status bar to display the list of filters you can use and a Configure
entry that opens the Locator tab of the Settings ► Options… menu.
7.5.2 Reporting actions
In the area next to the locator bar, a summary of actions you’ve carried out will be shown when needed (such
as selecting features in a layer, removing layer) or a long description of the tool you are hovering over (not available
for all tools).
In case of lengthy operations, such as gathering of statistics in raster layers, executing Processing algorithms or
rendering several layers in the map view, a progress bar is displayed in the status bar.
7.5.3 Control the map canvas
The Coordinate option shows the current position of the mouse, following it while moving across the map view.
You can set the units (and precision) in the Project ► Properties… ► General tab. Click on the small button at the
left of the textbox to toggle between the Coordinate option and the Extents option that displays the coordinates
of the current bottom-left and top-right corners of the map view in map units.
Next to the coordinate display you will find the Scale display. It shows the scale of the map view. There is a scale
selector, which allows you to choose between predefined and custom scales.
On the right side of the scale display, press the button to lock the scale to use the magnifier to zoom in or out.
The magnifier allows you to zoom in to a map without altering the map scale, making it easier to tweak the positions
of labels and symbols accurately. The magnification level is expressed as a percentage. If the Magnifier has a level
of 100%, then the current map is not magnified. Additionally, a default magnification value can be defined within
Settings ► Options ► Rendering ► Rendering behavior, which is very useful for high-resolution screens to enlarge
small symbols.
To the right of the magnifier tool you can define a current clockwise rotation for your map view in degrees.
On the right side of the status bar, there is a small checkbox which can be used temporarily to prevent layers being
rendered to the map view (see section Vykreslování).
To the right of the render functions, you find the EPSG:code button showing the current project CRS. Clicking
on this opens the Project Properties dialog and lets you apply another CRS to the map view.
Tip: Výpočet správného měřítka vašeho mapového plátna
When you start QGIS, the default CRS is WGS 84 (EPSG 4326) and units are degrees. This means that QGIS
will interpret any coordinate in your layer as specified in degrees. To get correct scale values, you can either manually
change this setting in the General tab under Project ► Properties… (e.g. to meters), or you can use the EPSG:code
icon seen above. In the latter case, the units are set to what the project projection specifies (e.g., +units=us-ft).
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Všimněte si, že volba CRS při spuštění může být nastavena v :menuselection: „Nastavení -> Volba -> CRS“.
7.5.4 Messaging
The Messages
button next to it opens the Log Messages Panel which has information on underlying processes (QGIS
startup, plugins loading, processing tools…)
Depending on the Plugin Manager settings, the status bar can sometimes show icons to the right to inform you about
the availability of new ( ) or upgradeable ( ) plugins. Click the icon to open the Plugin Manager dialog.
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54 Kapitola 7. QGIS GUI
KAPITOLA 8
The Browser panel
The QGIS Browser panel is a great tool for browsing, searching, inspecting, copying and loading QGIS resources.
Only resources that QGIS knows how to handle are shown in the browser.
Using the Browser panel you can locate, inspect and add data, as described in The Browser Panel. In addition, the
Browser panel supports drag and drop of many QGIS resources, such as project files, Python scripts, Processing
scripts and Processing models.
Python scripts, Processing scripts and Processing models can also be opened for editing in an external editor and the
graphical modeller.
You can drag and drop layers from the Layers panel to the Browser panel, for instance into a GeoPackage or a PostGIS
database.
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Obr. 8.1: The Browser panel
The browser panel (Obr. 8.1) is organised as an expandable hierarchy with some fixed top-level entries that organise
the resources handled by the browser. Node entries are expanded by clicking on to the left of the entry name.
A branch is collapsed by clicking on . The Collapse All
button collapses all top-level entries.
In Settings ► Interface Customization it is possible to disable resources. If you, for instance, would not like to show
Python scripts in the browser, you can uncheck the Browser ► py entry, and if you want to get rid of your home
folder in the browser, you can uncheck the Browser ► special:Home entry.
A filter ( Filter Browser
) can be used for searching based on entry names (both leaf entries and node entries in the
hierarchy). Using the Options
pull-down menu next to the filter text field, you can
• toggle Case Sensitive search
• set the Filter pattern syntax to one of
– Normal
– Wildcard(s)
– Regular Expressions
The Properties widget, showing useful information about some entries / resources, can be enabled / disabled using the
Enable/disable properties widget
button. When enabled, it opens at the bottom of the browser panel, as shown in Obr. 8.2.
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Obr. 8.2: The properties widget
A second browser panel can be opened by activating the Browser (2) panel in View ► Panels. Having two browser
panels can be useful when copying layers between resources that are locationed deep down in different branches of
the browser hierarchy.
8.1 Resources that can be opened / run from the Browser
A lot can be accomplished in the Browser panel
• Add vector, raster and mesh layers to your map by double-clicking, dragging onto the map canvas or clicking
the Add Selected Layers
button (after selecting layers)
• Run Python scripts (including Processing algorithms) by double-clicking or dragging onto the map canvas
• Run models by double-clicking or dragging onto the map canvas
• Extract Symbols… from QGIS Project files using the context menu
• Open files with their default applications (Open <file type> Externally… in the context menu). Examples: HTML
files, spreadsheets, images, PDFs, text files, …
• Copy entries
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Resource specific actions are listed for the different resource groups sorted under the top-level entries listed below.
8.2 Browser panel top-level entries
8.2.1 Favorites
Often used file system locations can be tagged as favorites. The ones you have tagged will appear here.
In addition to the operations described under Home, the context menu allows you to Rename Favorite… and Remove
Favorite.
8.2.2 Prostorové záložky
This is where you will find your spatial bookmarks, organised into Project Bookmarks and User Bookmarks.
From the top level context menu, you can create a bookmark (New Spatial Bookmark…), Show the Spatial Bookmark
Manager, Import Spatial Bookmarks… and Export Spatial Bookmarks….
For bookmark entries you can Zoom to Bookmark, Edit Spatial Bookmark… and Delete Spatial Bookmark
8.2.3 Home
Your file system home directory / folder. By right-clicking on an entry, and choosing Add as a Favorite, the location
will be added to Favorites. From the context menu, you can also
• add a directory, Geopackage or ESRI Shapefile format dataset (Add)
• hide the directory (Hide from Browser)
• toggle Fast Scan this Directory
• open the directory in your file manager (Open Directory)
• open the directory in a terminal window (Open in Terminal)
• inspect properties (Properties…, Directory Properties…)
8.2.4 /
Your file system root directory / folder.
8.2.5 Geopackage
Geopackage files / databases. From the top level context menu, you can create a Geopackage file / database (Create
Database…) or add an existing Geopackage file / database (New Connection…).
The context menu of each Geopackage lets you remove it from the list (Remove connection…), add a new layer or
table to the Geopackage (Create new Layer or Table…), delete the Geopackage (Delete <name of geopackage>) and
Compact Database (VACUUM).
For layer/table entries you can
• rename it (Rename Layer <layer name>…)
• export it (Export Layer ► To file)
• add it to the project Add Layer to Project
• delete it (Delete Layer)
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• inspect properties (Layer Properties…, File Properties…)
8.2.6 SpatiaLite
SpatiaLite database connections.
From the top level context menu, you can create a SpatiaLite file / database (Create Database…) or add an existing
SpatiaLite file / database (New Connection…).
The context menu of each SpatiaLite file lets you delete it (Delete).
For layer/table entries you can
• export it (Export Layer ► To file)
• add it to the project Add Layer to Project
• delete it (Delete Layer)
• inspect properties (Layer Properties…)
8.2.7 PostGIS
PostGIS database connections.
From the top level context menu, you can add a new connection (New Connection…).
The context menu of each connection lets you Refresh it, edit it Edit connection…, delete it (Delete connection) or
Create Schema….
The context menu of each schema lets you Refresh, Rename Schema… or Delete Schema.
For layers/tables you can
• rename it (Rename Table…)
• remove its contents (Truncate Table…)
• export it (Export Layer ► To file)
• add it to the project (Add Layer to Project)
• delete it (Delete Layer)
• inspect its properties (Layer Properties…)
8.2.8 MSSQL
Microsoft SQL Server connections.
From the top level context menu, you can add a new connection (New Connection…).
The context menu of each connection lets you Refresh it, edit it Edit connection…, delete it (Delete connection) or
Create Schema….
The context menu of each schema lets you Refresh, Rename Schema… or Delete Schema.
For layers/tables you can
• rename it (Rename Table…)
• remove its contents (Truncate Table…)
• export it (Export Layer ► To file)
• add it to the project (Add Layer to Project)
• delete it (Delete Layer)
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• inspect its properties (Layer Properties…)
8.2.9 DB2
IBM DB2 database connections.
From the top level context menu, you can add a new connection (New Connection…).
The context menu of each connection lets you Refresh it, edit it Edit connection…, delete it (Delete connection) or
Create Schema….
The context menu of each schema lets you Refresh, Rename Schema… or Delete Schema.
For layers/tables you can
• rename it (Rename Table…)
• remove its contents (Truncate Table…)
• export it (Export Layer ► To file)
• add it to the project (Add Layer to Project)
• delete it (Delete Layer)
• inspect its properties (Layer Properties…)
8.2.10 WMS/WMTS
Web Map Services (WMS) and Web Map Tile Services (WMTS)
From the top level context menu, you can add a new connection (New Connection…).
The context menu of each WSM/WMTS service lets you Refresh it, Edit… it and delete it (Delete).
Group layers can be added by dragging them onto the map canvas.
For WMS/WMTS layer entries you can
• export it (Export Layer ► To file)
• add it to the project (Add Layer to Project)
• inspect properties (Layer Properties…)
8.2.11 Vector Tiles
Vector tile services
From the top level context menu, you add an existing service (New Connection…), and you can Save Connections…
or Load Connections… to / from XML files.
8.2.12 XYZ Tiles
XYZ tile services
From the top level context menu, you add an existing service (New Connection…), and you can Save Connections…
or Load Connections… to / from XML files.
For the XYZ tile service entries you can
• edit it (Edit…)
• delete it (Delete)
• export it (Export Layer ► To file)
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• add it to the project Add Layer to Project
• inspect properties (Layer Properties…)
8.2.13 WCS
Web Coverage Services
From the top level context menu, you can add a new connection (New Connection…).
The context menu of each WCS lets you Refresh it, Edit… it and delete it (Delete).
For WCS layer entries you can
• export it (Export Layer ► To file)
• add it to the project (Add Layer to Project)
• inspect properties (Layer Properties…)
8.2.14 WFS / OGC API - Features
Web Feature Services (WFS) and OGC API - Features services (aka WFS3)
From the top level context menu, you can add a new connection (New Connection…).
The context menu of each WFS lets you Refresh it, Edit… it and delete it (Delete).
For WFS layer entries you can
• export it (Export Layer ► To file)
• add it to the project (Add Layer to Project)
• inspect properties (Layer Properties…)
8.2.15 OWS
Here you will find a read-only list of all your Open Web Services (OWS) - WMS / WCS / WFS / …
8.2.16 ArcGIS Map Service
8.2.17 ArcGIS Features Service
8.2.18 GeoNode
From the top level context menu, you can add a new connection (New Connection…).
The context menu of each service lets you Refresh it, Edit… it and delete it (Delete).
For the service layer entries you can
• export it (Export Layer ► To file)
• add it to the project (Add Layer to Project)
• inspect properties (Layer Properties…)
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8.3 Resources
• Project files. The context menu for QGIS project files allows you to:
– open it (Open Project)
– extract symbols (Extract Symbols…) - opens the style manager that allows you to export symbols to an
XML file, add symbols to the default style or export as PNG or SVG.
– inspect properties (File Properties…)
You can expand the project file to see its layers. The context menu of a layer offers the same actions as elsewhere
in the browser.
• QGIS Layer Definition files (QLR). The following actions are available from the context menu:
– export it (Export Layer ► To file)
– add it to the project (Add Layer to Project)
– inspect properties (Layer Properties…)
• Processing models (.model3). The following actions are available from the context menu:
– Run Model…)
– Edit Model…)
• QGIS print composer templates (QPT). The following action is available from the context menu:
– (New Layout from Template)
• Python scripts (.py). The following actions are available from the context menu:
– (Run script…)
– (Open in External Editor)
• Recognized raster formats. The following actions are available from the context menu:
– delete it (Delete File <dataset name>)
– export it (Export Layer ► To file)
– add it to the project (Add Layer to Project)
– inspect properties (Layer Properties…, File Properties…)
For some formats you can also Open <file type> Externally…
• Recognized vector formats. The following actions are available from the context menu:
– delete it (Delete File <dataset name>)
– export it (Export Layer ► To file)
– add it to the project (Add Layer to Project)
– inspect properties (Layer Properties…, File Properties…)
For some formats you can also Open <file type> Externally…
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KAPITOLA 9
QGIS Konfigurace
QGIS is highly configurable. Through the Settings menu, it provides different tools to:
• Style Manager…: create and manage symbols, styles and color ramps.
• Custom Projections…: create your own coordinate reference systems.
• Keyboard Shortcuts…: define your own set of keyboard shortcuts. Also, they can be overridden during each
QGIS session by the project properties (accessible under Project menu).
• Interface Customization…: configure the application interface, hiding dialogs or tools you may not need.
• Options…: set global options to apply in different areas of the software. These preferences are saved in the
active User profile settings and applied by default whenever you open a new project with this profile.
9.1 Možnosti
Some basic options for QGIS can be selected using the Options dialog. Select the menu option Settings ►
Options. You can modify the options according to your needs. Some of the changes may require a restart of QGIS
before they will be effective.
The tabs where you can customize your options are described below.
Poznámka: Plugins can embed their settings within the Options dialog
While only Core settings are presented below, note that this list can be extended by installed plugins implementing
their own options into the standard Options dialog. This avoids each plugin having their own config dialog with extra
menu items just for them…
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9.1.1 General Settings
Override System Locale
By default, QGIS relies on your Operating System configuration to set language and manipulate numerical values.
Enabling this group allows you to customize the behavior.
• Select from User interface translation the language to apply to the GUI
• Select in Locale (number, date and currency formats) the system on which date and numeric values should be
input and rendered
• Show group (thousand) separator
A summary of the selected settings and how they would be interpreted is displayed at the bottom of the frame.
Aplikace
• Select the Style (QGIS restart required) ie, the widgets look and placement in dialogs. Possible values depend
on your Operating System.
• Define the UI theme (QGIS restart required) . It can be ‚default‘, ‚Night Mapping‘, or ‚Blend of Gray‘
• Define the Icon size
• Define the Font and its Size. The font can be Qt default or a user-defined one
• Change the Timeout for timed messages or dialogs
• Hide splash screen at startup
• Show QGIS news feed on welcome page: displays a curated QGIS news feed on the welcome page, giving
you a direct way to be aware of project news (user/developer meetings date and summary, community surveys,
releases announcements, various tips…)
• Check QGIS version at startup to keep you informed if a newer version is released
• Use native color chooser dialogs (see Výběr barvy)
• Modeless data source manager dialog to keep the data source manager dialog opened and allow interaction
with QGIS interface while adding layers to project
Soubory projektu
• Open project on launch
– ‚Welcome Page‘ (default): can display the „News“ feed, the project template(s) and the most recent
projects (with thumbnails) of the user profile. No project is opened by default.
– ‚New‘: opens a new project, based on the default template
– ‚Most recent‘: reopens the last saved project
– and ‚Specific‘: opens a particular project. Use the … button to define the project to use by default.
• Vytvořit nový projekt z výchozího projektu. Máte možnost vybrat Nastavit aktuální projekt jako výchozí nebo
Obnovit výchozí. Můžete procházet soubory a definovat adresář, kde najdete své uživatelsky definované šablony
projektů. Ty budou přidávány z Projekt ► Nový ze šablony. V případě, že nejprve aktivujete Vytvořit nový
projekt z výchozího projektu a poté uložíte projekt do složky šablon projektů.
• Prompt to save project and data source changes when required to avoid losing changes you made.
• Žádat o upozornění při odstraňování vrstvy
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• Warn when opening a project file saved with an older version of QGIS. You can always open projects created
with older version of QGIS but once the project is saved, trying to open with older release may fail because of
features not available in that version.
• Enable macros . This option was created to handle macros that are written to perform an action on project
events. You can choose between ‚Never‘, ‚Ask‘, ‚For this session only‘ and ‚Always (not recommended)‘.
• Default project file format
– QGZ Archive file format, embeds auxiliary data (see auxiliary data)
– QGS Project saved in a clear text, does not embed auxiliary data: the auxiliary data is stored in
a separate .qgd file along with the project file.
9.1.2 System Settings
SVG paths
Add or Remove Path(s) to search for Scalable Vector Graphic (SVG) symbols. These SVG files are then available to
symbolize or label the features or decorate your map composition.
When using an SVG file in a symbol or a label, QGIS allows you to:
• load the file from the file system: the file is identified through the file path and QGIS needs to resolve the path
in order to display the corresponding image
• load the file from a remote URL: as above, the image will only be loaded on successful retrieval of the remote
resource
• embed the SVG file into the item: the file is embedded inside the current project, style database, or print
layout template. The SVG file is then always rendered as part of the item. This is a convenient way to create
self-contained projects with custom SVG symbols which can be easily shared amongst different users and
installations of QGIS.
It is also possible to extract the embedded SVG file from a symbol or label and save it on disk.
Poznámka: The above mentioned options for loading and storing an SVG file in a project are also applicable to
raster images you may want to use for customizing symbols, labels or decorations.
Cesty k zásuvným modulům
Add or Remove Path(s) to search for additional C++ plugin libraries.
Documentation paths
Add or Remove Documentation Path(s) to use for QGIS help. By default, a link to the official online User Manual
corresponding to the version being used is added. You can however add other links and prioritize them from top to
bottom: each time you click on a Help button in a dialog, the topmost link is checked and if no corresponding page
is found, the next one is tried, and so on.
Poznámka: Documentation is versioned and translated only for QGIS Long Term Releases (LTR), meaning that
if you are running a regular release (eg, QGIS 3.0), the help button will by default open the next LTR manual page
(ie. 3.4 LTR), which may contain description of features in newer releases (3.2 and 3.4). If no LTR documentation
is available then the testing doc, with features from newer and development versions, is used.
Settings
It helps you Reset user interface to default settings (restart required) if you made any customization.
Prostředí
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Obr. 9.1: System environment variables in QGIS
System environment variables can be viewed, and many configured, in the Environment group. This is useful for
platforms, such as Mac, where a GUI application does not necessarily inherit the user’s shell environment. It’s also
useful for setting and viewing environment variables for the external tool sets controlled by the Processing toolbox
(e.g., SAGA, GRASS), and for turning on debugging output for specific sections of the source code.
Use custom variables (restart required - include separators). You can Add and Remove variables. Already defined
environment variables are displayed in Current environment variables, and it’s possible to filter them by activating
Show only QGIS-specific variables.
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9.1.3 CRS Settings
Poznámka: For more information on how QGIS handles layer projection, please read the dedicated section at Práce
s projekcemi.
Obr. 9.2: CRS Settings in QGIS
CRS for projects
There is an option to automatically set new project’s CRS:
• Use CRS from first layer added: the CRS of the project will be set to the CRS of the first layer loaded into
it
• Use a default CRS: a preselected CRS is applied by default to any new project and is left unchanged when
adding layers to the project.
The choice will be saved for use in subsequent QGIS sessions. The Coordinate Reference System of the project can
still be overridden from the Project ► Properties… ► CRS tab.
CRS for layers
Default CRS for layers: select a default CRS to use when you create a layer
You can also define the action to take when a new layer is created, or when a layer without a CRS is loaded.
• Leave as unknown CRS (take no action)
• Prompt for CRS
• Použít CRS projektu
• Use a default CRS
Planimetric measurements: sets the default for the „planimetric measurements“ property for newly created projects.
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9.1.4 Transformations Settings
The Transformations tab helps you set coordinate transformations and operations to apply when loading a layer
to a project or reprojecting a layer.
Obr. 9.3: Transformations Settings
Výchozí transformace souřadnic
In this group, you can control whether reprojecting layers to another CRS should be:
• automatically processed using QGIS default transformations settings;
• and/or more controlled by you with custom preferences such as:
– Ask for datum transformation if several are available
– a predefined list of datum transformations to apply by default. See Datum Transformations for more
details.
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9.1.5 Data Sources Settings
Obr. 9.4: Data Sources Settings in QGIS
Atributy prvku a tabulka
• Open new attribute tables as docked windows
• Copy features as ‚Plain text, no geometry‘, ‚Plain text, WKT geometry‘, or ‚GeoJSON‘ when pasting features in
other applications.
• Attribute table behavior : set filter on the attribute table at the opening. There are three possibilities:
‚Show all features‘, ‚Show selected features‘ and ‚Show features visible on map‘.
• Default view: define the view mode of the attribute table at every opening. It can be ‚Remember last view‘,
‚Table view‘ or ‚Form view‘.
• Attribute table row cache . This row cache makes it possible to save the last loaded N attribute rows
so that working with the attribute table will be quicker. The cache will be deleted when closing the attribute
table.
• Reprezentace pro NULL hodnoty. Zde můžete definovat hodnotu datových polí, které obsahují NULL hodnotu.
Tip: Improve opening of big data attribute table
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When working with layers with big amount of records, opening the attribute table may be slow as the dialog request
all the rows in the layer. Setting the Attribute table behavior to Show features visible on map will make QGIS request
only the features in the current map canvas when opening the table, allowing a quick data loading.
Note that data in this attribute table instance will be always tied to the canvas extent it was opened with, meaning
that selecting Show All Features within such a table will not display new features. You can however update the set
of displayed features by changing the canvas extent and selecting Show Features Visible On Map option in the
attribute table.
Zacházení s datovými zdroji
• Scan for valid items in the browser dock . You can choose between ‚Check extension‘ and ‚Check file
contents‘.
• Scan for contents of compressed files (.zip) in browser dock defines how detailed is the widget information
at the bottom of the Browser panel when querying such files. ‚No‘, ‚Basic scan‘ and ‚Full scan‘ are possible
options.
• Výzva pro rastrové subvrstvy při otevírání. Některé podpůrné rastrové subvrstvy — jsou v GDAL nazývány jako
podřízené datové sady. Například v netCDF souborech — pokud obsahují mnho netCDF proměnných, GDAL
vidí každou proměnnou jako podřízenou datovou sadu. ‚Možnosti‘ umožňují kontrolovat, jak se vypořádat
s podvrstvami při otevření souboru se subvrstvami. Máte následující možnosti:
– ‘Vždy’: Vždy se dotázat (pokud existují nějaké subvrstvy)
– ‘Pokud je potřeba’: Dotázat se, jestli nemá vrstva žádná pásma, ale má podvrstvy
– ‘Nikdy’: Nikdy nevyzve a nenačte nic
– ‘Načíst vše’: Nikdy nevyzve, ale načte všechny subvrstvy
• Ignore shapefile encoding declaration. If a shapefile has encoding information, this will be ignored by QGIS.
• Execute expressions on server-side if possible: When requesting features from a datasource, QGIS will try
to optimize requests by sending filter criteria directly to the server and only download the features which match
the criteria. For example, if for a list on the user interface only the farmers which live in Bern should be listed,
QGIS will send a WHERE "hometown" = 'Bern' to the database. In some cases, filter criteria are
too complex to be translated from QGIS Expressions to database compatible SQL. In those cases, QGIS will
download the whole data and filter locally to be on the safe side, which is much less performant.
By disabling this option, QGIS can be forced to always download the whole data and filter locally, at the expense
of a performance penalty. This option is meant as a safety break and should only be deactivated if you identify
a misbehavior of the QGIS expression translation engine.
Hidden Browser Path
This widget lists all the folders you chose to hide from the Browser panel. Removing a folder from the list will make
it available in the Browser panel.
Localized paths
It is possible to use localized paths for any kind of file based data source. They are a list of paths which
are used to abstract the data source location. For instance, if C:\my_maps is listed in the localized paths,
a layer having C:\my_maps\my_country\ortho.tif as data source will be saved in the project using
localized:my_country\ortho.tif.
The paths are listed by order of preference, in other words QGIS will first look for the file in the first path, then in
the second one, etc.
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9.1.6 Rendering Settings
Obr. 9.5: Rendering tab of Project Properties dialog
Rendering behavior
• By default new layers added to the map should be displayed: unchecking this option can be handy when
loading multiple layers to avoid each new layer being rendered in the canvas and slow down the process
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• Pokud to jde, používat vyrovnávací paměť pro zrychlení překreslování
• Vykreslovat vrstvy paralelně pomocí více jader CPU
• Maximální počet jader k dispozici
• Interval aktualizace mapy (výchozí hodnota 250 ms)
• Enable feature simplification by default for newly added layers
• Simplification threshold
• Simplification algorithm: This option performs a local „on-the-fly“ simplification on feature’s and speeds up
geometry rendering. It doesn’t change the geometry fetched from the data providers. This is important when
you have expressions that use the feature geometry (e.g. calculation of area) - it ensures that these calculations
are done on the original geometry, not on the simplified one. For this purpose, QGIS provides three algorithms:
‚Distance‘ (default), ‚SnapToGrid‘ and ‚Visvalingam‘.
• Simplify on provider side if possible: the geometries are simplified by the provider (PostGIS, Oracle…) and
unlike the local-side simplification, geometry-based calculations may be affected
• Maximum scale at which the layer should be simplified
• Magnification level (see the magnifier)
Poznámka: Besides the global setting, feature simplification can be set for any specific layer from its Layer properties
► Rendering menu.
Kvalita vykreslování
• Linie bude vykreslena jako méně roztřepená, nicméně na úkor rychlosti vykreslování
Curve segmentation
• Segmentation tolerance: this setting controls the way circular arcs are rendered. The smaller maximum angle
(between the two consecutive vertices and the curve center, in degrees) or maximum difference (distance
between the segment of the two vertices and the curve line, in map units), the more straight line segments
will be used during rendering.
• Tolerance type: it can be Maximum angle or Maximum difference between approximation and curve.
Rastry
• S Výběr RGB pásma můžete definovat hodnotu pro červené, zelené a modré pásmo.
• The Zoomed in resampling and the Zoomed out resampling methods can be defined. For Zoomed in resampling
you can choose between three resampling methods: ‚Nearest Neighbour‘, ‚Bilinear‘ and ‚Cubic‘. For Zoomed
out resampling you can choose between ‚Nearest Neighbour‘ and ‚Average‘. You can also set the Oversampling
value (between 0.0 and 99.99 - a large value means more work for QGIS - the default value is 2.0).
Vylepšení kontrastu
Contrast enhancement options can be applied to Single band gray, Multi band color (byte/band) or Multi band color
(>byte/band). For each, you can set:
• the Algorithm to use, whose values can be ‚No stretch‘, ‚Stretch to MinMax‘, ‚Stretch and Clip to MinMax‘ or
‚Clip to MinMax‘
• the Limits (minimum/maximum) to apply, with values such as ‚Cumulative pixel count cut‘,
‚Minimum/Maximum‘, ‚Mean +/- standard deviation‘.
For rasters rendering, you can also define the following options:
• Limity ořezu dle kumulativního počtu pixelů
• Multiplikátor směrodatné odchylky
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Ladění
• Map canvas refresh to debug rendering duration in the Log Messages panel.
9.1.7 Canvas and Legend Settings
Obr. 9.6: Canvas and Legend Settings
These properties let you set:
• the Default map appearance (overridden by project properties): the Selection color and Background color.
• Layer legend interaction:
– Double click action in legend . You can either ‚Open layer properties‘, ‚Open attribute table‘ or ‚Open
layer styling dock‘ with the double click.
– Display classification attribute names in the Layers panel, e.g. when applying a categorized or rule-based
renderer (see Symbology Properties for more information).
– the WMS getLegendGraphic Resolution
– Minimum and Maximum legend symbol size to control symbol size display in the Layers panel
• the Delay in milliseconds of layers map tips display
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9.1.8 Map tools Settings
Obr. 9.7: Map tools Settings in QGIS
This tab offers some options regarding the behavior of the Identify tool.
• Search radius for identifying features and displaying map tips is a tolerance distance within which the identify
tool will depict results as long as you click within this tolerance.
• Highlight color allows you to choose with which color features being identified should be highlighted.
• Buffer determines a buffer distance to be rendered from the outline of the identify highlight.
• Minimum width determines how thick should the outline of a highlighted object be.
Nástroj pro měření
• Definujte Barva pravítka pro měřící nástroje
• Definujte Desetinná místa
• Keep base unit to not automatically convert large numbers (e.g., meters to kilometers)
• Preferred distance units: options are ‚Meters‘, ‚Kilometers‘, ‚Feet‘, ‚Yards‘, ‚Miles‘, ‚Nautical Miles‘,
‚Centimeters‘, ‚Millimeters‘, ‚Degrees‘ or ‚Map Units‘
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• Preferred area units: options are ‚Square meters‘, ‚Square kilometers‘, ‚Square feet‘, ‚Square yards‘, ‚Square
miles‘, ‚Hectares‘, ‚Acres‘, ‚Square nautical miles‘, ‚Square centimeters‘, ‚Square millimeters‘, ‚Square degrees‘
or ‚Map Units‘
• Preferred angle units: options are ‚Degrees‘, ‚Radians‘, ‚Gon/gradians‘, ‚Minutes of arc‘, ‚Seconds of arc‘,
‚Turns/revolutions‘, milliradians (SI definition) or mil (NATO/military definition)
Coordinate and Bearing Display
• Define Default bearing format for new projects: used to display the mouse coordinate in the status bar when
panning the map canvas. It can be overridden in the project properties dialog.
Posouvat a zvětšovat
• Define a Zoom factor for zoom tools or wheel mouse
Předdefinovaná měřítka
Here, you find a list of predefined scales. With the and buttons you can add or remove your personal scales.
You can also import or export scales from/to a .XML file. Note that you still have the possibility to remove your
changes and reset to the predefined list.
9.1.9 Colors Settings
Obr. 9.8: Colors Settings
This menu allows you to create or update palettes of colors used throughout the application in the color selector widget.
You can choose from:
• Recent colors showing recently used colors
• Standard colors, the default palette of colors
• Project colors, a set of colors specific to the current project (see Default Styles Properties for more details)
• New layer colors, a set of colors to use by default when new layers are added to QGIS
• or custom palette(s) you can create or import using the … button next to the palette combobox.
By default, Recent colors, Standard colors and Project colors palettes can not be removed and are set to appear in the
color button drop-down. Custom palettes can also be added to this widget thanks to the Show in Color Buttons option.
For any of the palettes, you can manage the list of colors using the set of tools next to the frame, ie:
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• Add or Remove color
• Copy or Paste color
• Import or Export the set of colors from/to .gpl file.
Double-click a color in the list to tweak or replace it in the Color Selector dialog. You can also rename it by double-clicking
in the Label column.
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9.1.10 Digitizing Settings
Obr. 9.9: Digitizing Settings in QGIS
This tab helps you configure general settings when editing vector layer (attributes and geometry).
Vytváření prvku
• Suppress attribute form pop-up after feature creation: this choice can be overridden in each layer properties
dialog.
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• Reuse last entered attribute values: remember the last used value of every attribute and use it as default for
the next feature being digitized. Works per layer.
• Validate geometries. Editing complex lines and polygons with many nodes can result in very slow rendering.
This is because the default validation procedures in QGIS can take a lot of time. To speed up rendering, it
is possible to select GEOS geometry validation (starting from GEOS 3.3) or to switch it off. GEOS geometry
validation is much faster, but the disadvantage is that only the first geometry problem will be reported.
Note that depending on the selection, reports of geometry errors may differ (see Types of error messages and
their meanings)
• Default Z value to use when creating new 3D features.
Gumička
• Define Rubberband Line width, Line color and Fill color.
• Don’t update rubberband during vertex editing.
Uchycení
• Enable snapping by default activates snapping when a project is opened
• Define Default snap mode (‚Vertex‘, ‚Vertex and segment‘, ‚Segment‘)
• Definujte Výchozí přichytávací tolerance v mapových jednotkách nebo pixelech
• Definujte Vyhledávající poloměr pro editaci lomových bodů v mapových jednotkách nebo pixelech
• Display main dialog as (restart required): set whether the Advanced Snapping dialog should be shown as ‚Dialog‘
or ‚Dock‘.
• Snapping marker color
• Show snapping tooltips such as name of the layer whose feature you are about to snap. Helpful when multiple
features overlap.
• Enable snapping on invisible features (not shown on the map canvas)
Symboly lomových bodů
• Zobrazit symboly pouze u vybraných prvků
• Define vertex Marker style (‚Cross‘ (default), ‚Semi transparent circle‘ or ‚None‘)
• Define vertex Marker size (in millimeter)
Nástroj odsazení křivky
The next 3 options refer to the Offset Curve
tool in Advanced digitizing. Through the various settings, it is possible
to influence the shape of the line offset. These options are possible starting from GEOS 3.3.
• Join style: ‚Round‘, ‚Mitre‘ or ‚Bevel‘
• Segmenty kvadrantu
• Miter limit
Tracing
By activating the Convert tracing to curve you can create curve segments while digitizing. Keep in mind that your
data provider must support this feature.
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9.1.11 Layouts Settings
Obr. 9.10: Layouts Settings in QGIS
Výchozí nastavení kompozice
You can define the Default font used within the print layout.
Vzhled mřížky
• Define the Grid style (‚Solid‘, ‚Dots‘, ‚Crosses‘)
• Definujte Barva mřížky
Výchozí mřížka a vodítka
• Define the Grid spacing
• Define the Grid offset for X and Y
• Define the Snap tolerance
Layout Paths
• Define Path(s) to search for extra print templates: a list of folders with custom layout templates to use while
creating new one.
9.1.12 GDAL Settings
GDAL is a data exchange library for geospatial data that supports a large number of vector and raster formats. It
provides drivers to read and (often) write data in these formats. The GDAL tab exposes the drivers for raster and
vector formats with their capabilities.
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Raster driver options
This frame provides ways to customize the behavior of raster drivers that support read and write access:
• Edit create options: allows you to edit or add different profiles of file transformation, i.e. a set of predefined
combinations of parameters (type and level of compression, blocks size, overview, colorimetry, alpha…) to
use when outputting raster files. The parameters depend on the driver.
Obr. 9.11: Sample of create options profile (for GeoTiff)
The upper part of the dialog lists the current profile(s) and allows you to add new ones or remove any of them.
You can also reset the profile to its default parameters if you have changed them. Some drivers (eg, GeoTiff)
have some sample of profiles you can work with.
At the bottom of the dialog:
– The button lets you add rows to fill with the parameter name and value
– The button deletes the selected parameter
– Click the Validate button to check that the creation options entered for the given format are valid
– Use the Help button to find the parameters to use, or refer to the GDAL raster drivers documentation.
• Edit Pyramids Options
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Obr. 9.12: Sample of Pyramids profile
GDAL raster and vector drivers
The Raster Drivers and Vector Drivers (in a separated tab) allow you to define which GDAL driver is enabled to read
and/or write files, as in some cases more than one GDAL driver is available.
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Obr. 9.13: GDAL Settings in QGIS - Raster drivers
Tip: Double-click a raster driver that allows read and write access (rw+(v)) opens the Edit Create options dialog
for customization.
9.1.13 Variables Settings
The Variables tab lists all the variables available at the global-level.
It also allows the user to manage global-level variables. Click the button to add a new custom global-level variable.
Likewise, select a custom global-level variable from the list and click the button to remove it.
More information about variables in the Storing values in Variables section.
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Obr. 9.14: Variables Settings in QGIS
9.1.14 Authentication Settings
In the Authentication tab you can set authentication configurations and manage PKI certificates. See Ověřovací systém
for more details.
Obr. 9.15: Authentication Settings in QGIS
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9.1.15 Network Settings
Obecné
• Definujte Časový limit pro síťové požadavky (ms) - výchozí je 60000
• Define Default expiration period for WMS Capabilities (hours) - default is 24
• Define Default expiration period for WMS-C/WMTS tiles (hours) - default is 24
• Define Max retry in case of tile or feature request errors
• Definujte User-Agent
Obr. 9.16: Proxy-settings in QGIS
Nastavení vyrovnávací paměti
Defines the Directory and a Size for the cache. Also offers tools to automatically clear the connection authentication
cache on SSL errors (recommended).
Proxy for web access
• Use proxy for web access
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• Set the Proxy type according to your needs and define ‚Host‘ and ‚Port‘. Available proxy types are:
– Default Proxy: Proxy is determined based on system’s proxy
– Socks5Proxy: Druhový proxy server pro jakýkoliv druh připojení. Podporuje TCP, UDP, vazbu na port
(příchozí spojení) a ověřování.
– HttpProxy: Implementace pomocí příkazu „CONNECT“, podporuje pouze odchozí TCP spojení;
podporuje ověřování.
– HttpCachingProxy: Implementace pomocí běžných příkazů HTTP, je užitečná pouze v kontextu HTTP
požadavků.
– FtpCachingProxy: Implementace pomocí FTP proxy, je užitečná pouze v souvislosti s požadavky FTP.
Credentials of proxy are set using the authentication widget.
Excluding some URLs can be added to the text box below the proxy settings (see Obr. 9.16). No proxy will be used
if the target url starts with one of the string listed in this text box.
If you need more detailed information about the different proxy settings, please refer to the manual of the underlying
QT library documentation at https://doc.qt.io/qt-5.9/qnetworkproxy.html#ProxyType-enum
Tip: Použití proxy
Using proxies can sometimes be tricky. It is useful to proceed by ‚trial and error‘ with the above proxy types, to check
if they succeed in your case.
9.1.16 Locator Settings
The Locator tab lets you configure the Locator bar, a quick search widget available on the status bar to help you
perform searches in the application. It provides some default filters (with prefix) to use:
Obr. 9.17: Locator Settings in QGIS
• Project layers (l): finds and selects a layer in the Layers panel.
• Project layouts (pl): finds and opens a print layout.
• Actions (.): finds and executes a QGIS action; actions can be any tool or menu in QGIS, opening a panel…
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• Active layer features (f): searches for matching attributes in any field from the current active layer and zooms
to the selected feature. Press to configure the maximum number of results.
• Features in all layers (af): searches for matching attributes in the display name of each searchable layers and
zooms to the selected feature. Press to configure the maximum number of results and the maximum number
of results per layer.
• Calculator (=): allows evaluation of any QGIS expression and, if valid, gives an option to copy the result to the
clipboard.
• Spatial bookmarks (b): finds and zooms to the bookmark extent.
• Settings (set): browses and opens project and application-wide properties dialogs.
• Go to coordinate (go): pans the map canvas to a location defined by a comma or space separated pair of x and y
coordinates or a formatted URL (e.g., OpenStreetMap, Leaflet, OpenLayer, Google Maps, …). The coordinate
is expected in WGS 84 (epsg:4326) and/or map canvas CRS.
• Processing algorithms (a): searches and opens a Processing algorithm dialog.
• Edit selected features (ef): gives quick access and runs a compatible modify-in-place Processing algorithm on
the active layer.
In the dialog, you can:
• customize the filter Prefix, i.e. the keyword to use to trigger the filter
• set whether the filter is Enabled: the filter can be used in the searches and a shortcut is available in the locator
bar menu
• set whether the filter is Default: a search not using a filter returns results from only the default filters categories.
• Some filters provide a way to configure the number of results in a search.
The set of default locator filters can be extended by plugins, eg for OSM nominatim searches, direct database
searching, layer catalog searches, …
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9.1.17 Advanced Settings
Obr. 9.18: Advanced Settings tab in QGIS
All the settings related to QGIS (UI, tools, data providers, Processing configurations, default values and paths,
plugins options, expressions, geometry checks…) are saved in a QGIS/QGIS3.ini file under the active user profile
directory. Configurations can be shared by copying this file to other installations.
From within QGIS, the Advanced tab offers a way to manage these settings through the Advanced Settings Editor.
After you promise to be careful, the widget is populated with a tree of all the existing settings, and you can edit
their value. Right-click over a setting or a group and you can delete it (to add a setting or group, you have to edit the
QGIS3.ini file). Changes are automatically saved in the QGIS3.ini file.
Varování: Avoid using the Advanced tab settings blindly
Be careful while modifying items in this dialog given that changes are automatically applied. Doing changes
without knowledge can break your QGIS installation in various ways.
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9.1.18 Acceleration Settings
OpenCL acceleration settings.
Obr. 9.19: Acceleration tab
Depending on your hardware and software, you may have to install additional libraries to enable OpenCL acceleration.
9.1.19 Processing Settings
The Processing tab provides you with general settings of tools and data providers that are used in the QGIS
Processing framework. More information at QGIS processing framework.
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Obr. 9.20: Processing Settings tab in QGIS
9.1.20 Python Console Settings
The Python Console settings help you manage and control the behavior of the Python editors (interactive console,
code editor, project macros, custom expressions, …). It can also be accessed using the Options…
button from:
• the Python console toolbar
• the contextual menu of the Python console widget
• and the contextual menu of the code editor.
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Obr. 9.21: Python Console Settings tab
You can specify:
• Autocompletion: Enables code completion. You can get autocompletion from the current document, the
installed API files or both.
– Autocompletion threshold: Sets the threshold for displaying the autocompletion list (in characters)
• under Typing
– Automatic parentheses insertion: Enables autoclosing for parentheses
– Automatic insertion of the ‚import‘ string on ‚from xxx‘: Enables insertion of ‚import‘ when specifying
imports
• under Run and Debug
– Enable Object Inspector (switching between tabs may be slow): Enable the object inspector.
– Auto-save script before running: Saves the script automatically when executed. This action will store
a temporary file (in the temporary system directory) that will be deleted automatically after running.
For APIs you can specify:
• Using preloaded APIs file: You can choose if you would like to use the preloaded API files. If this is not
checked you can add API files and you can also choose if you would like to use prepared API files (see next
option).
• Using prepared APIs file: If checked, the chosen *.pap file will be used for code completion. To generate
a prepared API file you have to load at least one *.api file and then compile it by clicking the Compile APIs…
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button.
• Under GitHub access token, you can generate a personal token allowing you to share code snippets from within
the Python code editor. More details on GitHub authentication
9.1.21 Code Editor Settings
In the Code Editor tab, you can control the appearance and behaviour of code editor widgets (Python interactive
console and editor, expression widget and function editor, …).
Obr. 9.22: Code Editor Settings tab
At the top of the dialog, a widget provides a live preview of the current settings, in various coding languages (Python,
QGIS expression, HTML, SQL, JavaScript). A convenient way to adjust settings.
• Check Override code editor font to modify the default Font family and Size.
• Under the Colors group, you can:
– select a Color scheme: predefined settings are Default, Solarized Dark and Solarized
Light. A Custom scheme is triggered as soon as you modify a color and can be reset with selecting
a predefined scheme.
– change the color of each element in code writing, such as the colors to use for comments, quotes, functions,
background, …
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9.2 Working with User Profiles
The Settings ► User Profiles menu provides functions to set and access user profiles. A user profile is a unified
application configuration that allows to store in a single folder:
• all the global settings, including locale, projections, authentication settings, color palettes, shortcuts…
• GUI configurations and customization
• grid files and other proj helper files installed for datum transformation
• installed plugins and their configurations
• project templates and history of saved project with their image preview
• processing settings, logs, scripts, models.
By default, a QGIS installation contains a single user profile named default. But you can create as many user
profiles as you want:
1. Click the New profile… entry.
2. You’ll be prompted to provide a profile name, creating a folder of the same name under ~/
<UserProfiles>/ where:
• ~ represents the HOME directory, which on Windows is usually something like C:\Users\
(user).
• and <UserProfiles> represents the main profiles folder, i.e.:
– .local/share/QGIS/QGIS3/profiles/
– AppData\Roaming\QGIS\QGIS3\profiles\
– Library/Application Support/QGIS/QGIS3/profiles/
The user profile folder can be opened from within QGIS using the Open Active Profile Folder.
3. A new instance of QGIS is started, using a clean configuration. You can then set your custom configurations.
If you have more than one profile in your QGIS installation, the name of the active profile is shown in the application
title bar between square brackets.
As each user profile contains isolated settings, plugins and history they can be great for different workflows, demos,
users of the same machine, or testing settings, etc. And you can switch from one to the other by selecting them in the
Settings ► User Profiles menu. You can also run QGIS with a specific user profile from the command line.
Unless changed, the profile of the last closed QGIS session will be used in the following QGIS sessions.
Tip: Run QGIS under a new user profile to check for bug persistence
When you encounter weird behavior with some functions in QGIS, create a new user profile and run the commands
again. Sometimes, bugs are related to some leftovers in the current user profile and creating a new one may fix them
as it restarts QGIS with the new (clean) profile.
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9.3 Vlastnosti projektu
In the properties window for the project under Project ► Project Properties, you can set project-specific options. The
project-specific options overwrite their equivalent in the Options dialog described above.
9.3.1 General Properties
In the General tab, the General settings let you:
• see the location of the project file
• set the folder for the project home (available in the Project Home item in the browser). The path can be
relative to the folder of the project file (type it in) or absolute. The project home can be used for storing data
and other content that is useful for the project.
• Uveďte název projektu spolu s cestou k souboru projektu
• Zvolte barvu, kterou chcete použít pro vrstvy, když jsou vybrány.
• Zvolte barvu pozadí: barvu, kterou chcete použít pro mapový podklad.
• Nastavte, zda má být cesta k vrstvám v projektu uložena jako absolutní (úplná) nebo jako relativní k umístění
souboru projektu. Můžete upřednostnit relativní cestu, pokud lze přesunout nebo sdílet vrstvy i soubory
projektu, nebo pokud je projekt přístupný z počítačů na různých platformách.
• Můžete zvolit vyhýbání se artefaktům, je-li projekt vykreslen jako mapová dlaždice. Všimněte si, že změna
této možnosti může vést k degradaci provedení.
Calculating areas and distances is a common need in GIS. However, these values are really tied to the underlying
projection settings. The Measurements frame lets you control these parameters. You can indeed choose:
• the Ellipsoid, on which distance and area calculations are entirely based; it can be:
– None/Planimetric: returned values are in this case cartesian measurements.
– a Custom one: you’ll need to set values of the semi-major and semi-minor axes.
– or an existing one from a predefined list (Clarke 1866, Clarke 1880 IGN, New International 1967, WGS
84…).
• the units for distance measurements for length and perimeter and the units for area measurements. These settings,
which default to the units set in QGIS options but then overrides it for the current project, are used in:
– Panel pro aktualizaci pole atributové tabulky
– Kalkulace kalkulátoru pole
– Určení nástroje odvození délky, obvodu a plochy
– Výchozí jednotky zobrazované v dialogovém okně měření
The Coordinate and Bearing display allows you to choose and customize the bearing format and the format of units
to use to display the mouse coordinate in the status bar and the derived coordinates shown via the identify tool.
Finally, you can set a Project predefined scales list, which overrides the global predefined scales.
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Obr. 9.23: General tab of the Project Properties dialog
9.3.2 Metadata Properties
The Metadata tab allows detailed metadata to be defined, including (among the others): author, creation date,
language, abstracts, categories, keywords, contact details, links, history. There is also a validation functionality that
checks if specific fields were filled, anyway this is not enforced. See vector layer metadata properties for some details.
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9.3.3 CRS Properties
Poznámka: For more information on how QGIS handles project projection, please read the dedicated section at
Práce s projekcemi.
The CRS tab helps you set the coordinate reference system to use in this project. It can be:
• No CRS (or unknown/non-Earth projection): layers are drawn based on their raw coordinates
• or an existing coordinate reference system that can be geographic, projected or user-defined. Layers added to
the project are translated on-the-fly to this CRS in order to overlay them regardless their original CRS.
9.3.4 Transformations Properties
The Transformations tab helps you control the layers reprojection settings by configuring the datum
transformation preferences to apply in the current project. As usual, these override any corresponding global settings.
See Datum Transformations for more details.
9.3.5 Default Styles Properties
The Default Styles tab lets you control how new layers will be drawn in the project when they do not have an existing
.qml style defined. You can:
• Set default symbols (Marker, Line, Fill) to apply depending on the layer geometry type as well as a default Color
Ramp
• Apply a default Opacity to new layers
• Assign random colors to symbols, modifying the symbols fill colors, hence avoiding same rendering for all
layers.
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Obr. 9.24: Default Styles tab
Using the Style Manager button, you can also quickly access the Style Manager dialog and configure symbols and
color ramps.
There is also an additional section where you can define specific colors for the running project. Like the global colors,
you can:
• Add or Remove color
• Copy or Paste color
• Import or Export the set of colors from/to .gpl file.
Double-click a color in the list to tweak or replace it in the Color Selector dialog. You can also rename it by double-clicking
in the Label column.
These colors are identified as Project colors and listed as part of color widgets.
Tip: Use project colors to quickly assign and update color widgets
Project colors can be refered to using their label and the color widgets they are used in are bound to them. This means
that instead of repeatedly setting the same color for many properties and, to avoid a cumbersome update you can:
1. Define the color as a project color
2. Click the data defined override widget next to the color property you want to set
3. Hover over the Color menu and select the project color. The property is then assigned the expression
project_color('color_label') and the color widget reflects that color.
4. Repeat steps 2 and 3 as much as needed
5. Update the project color once and the change is reflected EVERYWHERE it’s in use.
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9.3.6 Data Sources Properties
In the Data Sources tab, you can:
• Automatically create transaction groups where possible: When this mode is turned on, all layers from the
same database are synchronised in their edit state, i.e. when one layer is put into edit state, all are, when one
layer is committed or one layer is rolled back, so are the others. Also, instead of buffering edit changes locally,
they are directly sent to a transaction in the database which gets committed when the user clicks save layer.
Note that you can (de)activate this option only if no layer is being edited in the project.
• Evaluate default values on provider side: When adding new features in a PostgreSQL table, fields with
default value constraint are evaluated and populated at the form opening, and not at the commit moment.
This means that instead of an expression like nextval('serial'), the field in the Add Feature form will
display expected value (e.g., 25).
• Trust project when data source has no metadata: To speed up project loading by skipping data checks.
Useful in QGIS Server context or in projects with huge database views/materialized views. The extent of layers
will be read from the QGIS project file (instead of data sources) and when using the PostgreSQL provider the
primary key unicity will not be checked for views and materialized views.
• Configure the Layers Capabilities, i.e.:
– Set (or disable) which layers are identifiable, i.e. will respond to the identify tool. By default, layers
are set queryable.
– Set whether a layer should appear as read-only, meaning that it can not be edited by the user,
regardless of the data provider’s capabilities. Although this is a weak protection, it remains a quick and
handy configuration to avoid end-users modifying data when working with file-based layers.
– Define which layers are searchable, i.e. could be queried using the locator widget. By default, layers
are set searchable.
– Define which layers are defined as required. Checked layers in this list are protected from inadvertent
removal from the project.
The Layers Capabilities table provides some convenient tools to:
– Select multiple cells and press Toggle Selection to have them change their checkbox state;
– Show spatial layers only, filtering out non-spatial layers from the layers list;
– Filter layers… and quickly find a particular layer to configure.
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Obr. 9.25: Data Sources tab
9.3.7 Relations Properties
The Relations tab is used to define 1:n relations. The relations are defined in the project properties dialog. Once
relations exist for a layer, a new user interface element in the form view (e.g. when identifying a feature and opening
its form) will list the related entities. This provides a powerful way to express e.g. the inspection history on a length
of pipeline or road segment. You can find out more about 1:n relations support in Section Creating one or many to
many relations.
Obr. 9.26: Relations tab
9.3.8 Variables Properties
The Variables tab lists all the variables available at the project’s level (which includes all global variables). Besides, it
also allows the user to manage project-level variables. Click the button to add a new custom project-level variable.
Likewise, select a custom project-level variable from the list and click the button to remove it. More information
on variables usage in the General Tools Storing values in Variables section.
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9.3.9 Macros Properties
The Macros tab is used to edit Python macros for projects. Currently, only three macros are available:
openProject(), saveProject() and closeProject().
Obr. 9.27: Makro nastavení v QGIS
9.3.10 QGIS Server Properties
The tab QGIS Server allows you to configure your project in order to publish it online. Here you can define information
about the QGIS Server WMS and WFS capabilities, extent and CRS restrictions. More information available in section
Creatingwmsfromproject and subsequent.
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Obr. 9.28: QGIS Server settings tab
9.3.11 Temporal Properties
The tab Temporal is used to set the temporal range of your project, either by using manual input or by calculating it
from the current project temporal layers.
Obr. 9.29: QGIS Temporal tab
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9.4 Přizpůsobení
The customization dialog lets you (de)activate almost every element in the QGIS user interface. This can be very
useful if you want to provide your end-users with a ‚light‘ version of QGIS, containing only the icons, menus or panels
they need.
Poznámka: Before your changes are applied, you need to restart QGIS.
Obr. 9.30: The Customization dialog
Ticking the Enable customization checkbox is the first step on the way to QGIS customization. This enables the
toolbar and the widget panel from which you can uncheck and thus disable some GUI items.
The configurable item can be:
• a Menu or some of its sub-menus from the Menu lišta
• a whole Panel (see Panely a nástrojové lišty)
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• the Status bar described in Stavová lišta or some of its items
• a Toolbar: the whole bar or some of its icons
• or any widget from any dialog in QGIS: label, button, combobox…
With Switch to catching widgets in main application
, you can click on an item in QGIS interface that you want to be hidden
and QGIS automatically unchecks the corresponding entry in the Customization dialog. You can also use the Search
box to find items by their name or label.
Once you setup your configuration, click Apply or OK to validate your changes. This configuration becomes the one
used by default by QGIS at the next startup.
The modifications can also be saved in a .ini file using Save To File
button. This is a handy way to share a common
QGIS interface among multiple users. Just click on Load from File
from the destination computer in order to import
the .ini file. You can also run command line tools and save various setups for different use cases as well.
Tip: Easily restore predefined QGIS
The initial QGIS GUI configuration can be restored by one of the methods below:
• unchecking Enable customization option in the Customization dialog or click the Check All
button
• pressing the Reset button in the Settings frame under Settings ► Options menu, System tab
• launching QGIS at a command prompt with the following command line qgis --nocustomization
• setting to false the value of UI ► Customization ► Enabled variable under Settings ► Options menu, Advanced
tab (see the warning).
In most cases, you need to restart QGIS in order to have the change applied.
9.5 Keyboard shortcuts
QGIS provides default keyboard shortcuts for many features. You can find them in section Menu lišta. Additionally,
the menu option Settings ► Keyboard Shortcuts… allows you to change the default keyboard shortcuts and add
new ones to QGIS features.
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Obr. 9.31: Define shortcut options
Configuration is very simple. Use the search box at the top of the dialog to find a particular action, select it from the
list and click on :
• Change and press the new combination you want to assign as new shortcut
• Set None to clear any assigned shortcut
• or Set Default to backup the shortcut to its original and default value.
Proceed as above for any other tools you wish to customize. Once you have finished your configuration, simply Close
the dialog to have your changes applied. You can also Save the changes as an .XML file and Load them into another
QGIS installation.
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9.6 Running QGIS with advanced settings
9.6.1 Command line and environment variables
We’ve seen that launching QGIS is done as for any application on your OS. QGIS provides command line options for
more advanced use cases (in some cases you can use an environment variable instead of the command line option).
To get a list of the options, enter qgis --help on the command line, which returns:
QGIS is a user friendly Open Source Geographic Information System.
Usage: /usr/bin/qgis.bin [OPTION] [FILE]
OPTION:
[--version] display version information and exit
[--snapshot filename] emit snapshot of loaded datasets to given file
[--width width] width of snapshot to emit
[--height height] height of snapshot to emit
[--lang language] use language for interface text (changes existing␣
→override)
[--project projectfile] load the given QGIS project
[--extent xmin,ymin,xmax,ymax] set initial map extent
[--nologo] hide splash screen
[--noversioncheck] don't check for new version of QGIS at startup
[--noplugins] don't restore plugins on startup
[--nocustomization] don't apply GUI customization
[--customizationfile path] use the given ini file as GUI customization
[--globalsettingsfile path] use the given ini file as Global Settings␣
→(defaults)
[--authdbdirectory path] use the given directory for authentication␣
→database
[--code path] run the given python file on load
[--defaultui] start by resetting user ui settings to default
[--hide-browser] hide the browser widget
[--dxf-export filename.dxf] emit dxf output of loaded datasets to␣
→given file
[--dxf-extent xmin,ymin,xmax,ymax] set extent to export to dxf
[--dxf-symbology-mode none|symbollayer|feature] symbology mode for dxf␣
→output
[--dxf-scale-denom scale] scale for dxf output
[--dxf-encoding encoding] encoding to use for dxf output
[--dxf-map-theme maptheme] map theme to use for dxf output
[--take-screenshots output_path] take screen shots for the user␣
→documentation
[--screenshots-categories categories] specify the categories of␣
→screenshot to be used (see QgsAppScreenShots::Categories).
[--profile name] load a named profile from the user's profiles␣
→folder.
[--profiles-path path] path to store user profile folders. Will create␣
→profiles inside a {path}\profiles folder
[--version-migration] force the settings migration from older version if␣
→found
[--openclprogramfolder] path to the folder containing the sources␣
→for OpenCL programs.
[--help] this text
[--] treat all following arguments as FILEs
FILE:
Files specified on the command line can include rasters,
vectors, and QGIS project files (.qgs and .qgz):
1. Rasters - supported formats include GeoTiff, DEM
and others supported by GDAL
2. Vectors - supported formats include ESRI Shapefiles
and others supported by OGR and PostgreSQL layers using
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(pokračujte na předchozí stránce)
the PostGIS extension
Tip: Example Using command line arguments
You can start QGIS by specifying one or more data files on the command line. For example, assuming you are in the
qgis_sample_data directory, you could start QGIS with a vector layer and a raster file set to load on startup
using the following command: qgis ./raster/landcover.img ./gml/lakes.gml
--version
This option returns QGIS version information.
--snapshot
This option allows you to create a snapshot in PNG format from the current view. This comes in handy when you
have many projects and want to generate snapshots from your data, or when you need to create snapshots of the same
project with updated data.
Currently, it generates a PNG file with 800x600 pixels. The size can be adjusted using the --width and --height
arguments. The filename can be added after --snapshot. For example:
qgis --snapshot my_image.png --width 1000 --height 600 --project my_project.qgs
--width
This option returns the width of the snapshot to be emitted (used with --snapshot).
--height
This option returns the height of the snapshot to be emitted (used with --snapshot).
--lang
Based on your locale, QGIS selects the correct localization. If you would like to change your language, you can specify
a language code. For example, qgis --lang it starts QGIS in Italian localization.
--project
Starting QGIS with an existing project file is also possible. Just add the command line option --project followed
by your project name and QGIS will open with all layers in the given file loaded.
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--extent
To start with a specific map extent use this option. You need to add the bounding box of your extent in the following
order separated by a comma:
--extent xmin,ymin,xmax,ymax
This option probably makes more sense when paired with the --project option to open a specific project at the
desired extent.
--nologo
This option hides the splash screen when you start QGIS.
--noversioncheck
Skip searching for a new version of QGIS at startup.
--noplugins
If you have trouble at start-up with plugins, you can avoid loading them at start-up with this option. They will still be
available from the Plugins Manager afterwards.
--nocustomization
Using this option, any existing GUI customization will not be applied at startup. This means that any hidden buttons,
menu items, toolbars, and so on, will show up on QGIS start up. This is not a permanent change. The customization
will be applied again if QGIS is launched without this option.
This option is useful for temporarily allowing access to tools that have been removed by customization.
--customizationfile
Using this option, you can define a UI customization file, that will be used at startup.
--globalsettingsfile
Using this option, you can specify the path for a Global Settings file (.ini), also known as the Default
Settings. The settings in the specified file replace the original inline default ones, but the user profiles‘ settings
will be set on top of those. The default global settings is located in your_QGIS_PKG_path/resources/
qgis_global_settings.ini.
Presently, there’s no way to specify a file to write settings to; therefore, you can create a copy of an original settings
file, rename, and adapt it.
Setting the qgis_global_setting.ini file path to a network shared folder, allows a system administrator to
change global settings and defaults in several machines by only editing one file.
The equivalent environment variable is QGIS_GLOBAL_SETTINGS_FILE.
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--authdbdirectory
This option is similar to --globalsettingsfile, but defines the path to the directory where the authentication
database will be stored and loaded.
--code
This option can be used to run a given python file directly after QGIS has started.
For example, when you have a python file named load_alaska.py with following content:
from qgis.utils import iface
raster_file = "/home/gisadmin/Documents/qgis_sample_data/raster/landcover.img"
layer_name = "Alaska"
iface.addRasterLayer(raster_file, layer_name)
Assuming you are in the directory where the file load_alaska.py is located, you can start QGIS, load the raster
file landcover.img and give the layer the name ‚Alaska‘ using the following command:
qgis --code load_alaska.py
--defaultui
On load, permanently resets the user interface (UI) to the default settings. This option will restore the panels and
toolbars visibility, position, and size. Unless it’s changed again, the default UI settings will be used in the following
sessions.
Notice that this option doesn’t have any effect on GUI customization. Items hidden by GUI customization (e.g. the
status bar) will remain hidden even using the --defaultui option. See also the --nocustomization option.
--hide-browser
On load, hides the Browser panel from the user interface. The panel can be enabled by right-clicking a space in the
toolbars or using the View ► Panels (Settings ► Panels in Linux KDE).
Unless it’s enabled again, the Browser panel will remain hidden in the following sessions.
--dxf-*
These options can be used to export a QGIS project into a DXF file. Several options are available:
• –dxf-export: the DXF filename into which to export the layers;
• –dxf-extent: the extent of the final DXF file;
• –dxf-symbology-mode: several values can be used here: none (no symbology), symbollayer (Symbol layer
symbology), feature (feature symbology);
• –dxf-scale-denom: the scale denominator of the symbology;
• –dxf-encoding: the file encoding;
• –dxf-map-theme: choose a map theme from the layer tree configuration.
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--take-screenshots
Takes screenshots for the user documentation. Can be used together with --screenshots-categories to filter
which categories/sections of the documentation screenshots should be created (see QgsAppScreenShots::Categories).
--profile
Loads QGIS using a specific profile from the user’s profile folder. Unless changed, the selected profile will be used in
the following QGIS sessions.
--profiles-path
With this option, you can choose a path to load and save the profiles (user settings). It creates profiles inside
a {path}\profiles folder, which includes settings, installed plugins, processing models and scripts, and so on.
This option allows you to, for instance, carry all your plugins and settings in a flash drive, or, for example, share the
settings between different computers using a file sharing service.
The equivalent environment variable is QGIS_CUSTOM_CONFIG_PATH.
--version-migration
If settings from an older version are found (e.g., the .qgis2 folder from QGIS 2.18), this option will import them
into the default QGIS profile.
--openclprogramfolder
Using this option, you can specify an alternative path for your OpenCL programs. This is useful for developers while
testing new versions of the programs without needing to replace the existing ones.
The equivalent environment variable is QGIS_OPENCL_PROGRAM_FOLDER.
9.6.2 Deploying QGIS within an organization
If you need to deploy QGIS within an organization with a custom configuration file, first you need
to copy/paste the content of the default settings file located in your_QGIS_PKG_path/resources/
qgis_global_settings.ini. This file already contains some default sections identified by a block starting
with []. We recommend that you keep these defaults values and add your own sections at the bottom of the file. If
a section is duplicated in the file, QGIS will take the last one from top to bottom.
You can change allowVersionCheck=false to disable the QGIS version check.
If you do not want to display the migration window after a fresh install, you need the following section:
[migration]
fileVersion=2
settings=true
If you want to add a custom variable in the global scope:
[variables]
organisation="Your organization"
To discover the possibilities of the settings INI file, we suggest that you set the config you would like in QGIS Desktop
and then search for it in your INI file located in your profile using a text editor. A lot of settings can be set using the
INI file such as WMS/WMTS, PostGIS connections, proxy settings, maptips…
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Finally, you need to set the environment variable QGIS_GLOBAL_SETTINGS_FILE to the path of your
customized file.
In addition, you can also deploy files such as Python macros, color palettes, layout templates, project templates…
either in the QGIS system directory or in the QGIS user profile.
• Layout templates must be deployed in the composer_templates directory.
• Project templates must be deployed in the project_templates directory.
• Custom Python macros must be deployed in the python directory.
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KAPITOLA 10
Práce s projekcemi
A Coordinate Reference System, or CRS, is a method of associating numerical coordinates with a position on the
surface of the Earth. QGIS has support for approximately 7,000 standard CRSs, each with different use cases, pros
and cons! Choosing an appropriate reference system for your QGIS projects and data can be a complex task, but
fortunately QGIS helps guide you through this choice, and makes working with different CRSs as transparent and
accurate as possible.
10.1 Přehled projekční podpory
QGIS has support for approximately 7,000 known CRSs. These standard CRSs are based on those defined by the
European Petroleum Search Group (EPSG) and the Institut Geographique National de France (IGNF), and are
made available in QGIS through the underlying „Proj“ projection library. Commonly, these standard projections are
identified through use of an authority:code combination, where the authority is an organisation name such as „EPSG“
or „IGNF“, and the code is a unique number associated with a specific CRS. For instance, the common WGS 84
latitude/longitude CRS is known by the identifier EPSG:4326, and the web mapping standard CRS is EPSG:3857.
Custom, user-created CRSs are stored in a user CRS database. See section Vlastní souřadnicový referenční systém for
information on managing your custom coordinate reference systems.
10.2 Layer Coordinate Reference Systems
In order to correctly project data into a specific target CRS, either your data must contain information about its
coordinate reference system or you will need to manually assign the correct CRS to the layer. For PostGIS layers,
QGIS uses the spatial reference identifier that was specified when that PostGIS layer was created. For data supported
by OGR or GDAL, QGIS relies on the presence of a recognized means of specifying the CRS. For instance, for the
Shapefile format this is a file containing an ESRI Well-Known Text (WKT) representation of the layer’s CRS. This
projection file has the same base name as the .shp file and a .prj extension. For example, alaska.shp would
have a corresponding projection file named alaska.prj.
Whenever a layer is loaded into QGIS, QGIS attempts to automatically determine the correct CRS for that layer.
In some cases this is not possible, e.g. when a layer has been provided without retaining this information. You can
configure QGIS behavior whenever it cannot automatically determine the correct CRS for a layer:
1. Open Settings ► Options… ► CRS
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Obr. 10.1: The CRS tab in the QGIS Options Dialog
2. Under the CRS for layers group, set the action to do when a new layer is created, or when a layer is loaded that
has no CRS. One of:
• Leave as unknown CRS (take no action): there will be no prompt to select a CRS when a layer without
CRS is loaded, defering CRS choice to a later time. Convenient when loading a lot of layers at once. Such
layers will be identifiable in the Layers panel by the icon next to them. They’ll also be un-referenced,
with coordinates from the layer treated as purely numerical, non-earth values, i.e. the same behavior as all
layers get when a project is set to have no CRS.
• Prompt for CRS: it will prompt you to manually select the CRS. Selecting the correct choice
is crucial, as a wrong choice will place your layer in the wrong position on the Earth’s surface! Sometimes,
accompanying metadata will describe the correct CRS for a layer, in other cases you will need to contact
the original author of the data to determine the correct CRS to use.
• Použít CRS projektu
• Use default layer CRS, as set in the Default CRS for layers combobox above.
Tip: To assign the same CRS to multiple layers that have no crs or have a wrong one in one operation:
1. Select the layers in the Layers panel
2. Press Ctrl+Shift+C. You could also right-click over one of the selected layers or go to Layer ► Set CRS
of layer(s)
3. Find and select the right CRS to use
4. And press OK. You can confirm that it has been set correctly in the Source tab of the layers‘ properties dialog.
Note that changing the CRS in this setting does not alter the underlying data source in any way, rather it just changes
how QGIS interprets the raw coordinates from the layer in the current QGIS project.
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10.3 Project Coordinate Reference Systems
Every project in QGIS also has an associated Coordinate Reference System. The project CRS determines how data
is projected from its underlying raw coordinates to the flat map rendered within your QGIS map canvas.
QGIS supports „on the fly“ CRS transformation for both raster and vector data. This means that regardless of the
underlying CRS of particular map layers in your project, they will always be automatically transformed into the
common CRS defined for your project. Behind the scenes, QGIS transparently reprojects all layers contained within
your project into the project’s CRS, so that they will all be rendered in the correct position with respect to each other!
It is important to make an appropriate choice of CRS for your QGIS projects. Choosing an inappropriate CRS can
cause your maps to look distorted, and poorly reflect the real-world relative sizes and positions of features. Usually,
while working in smaller geographic areas, there will be a number of standard CRSs used within a particular country
or administrative area. It’s important to research which CRSs are appropriate or standard choices for the area you are
mapping, and ensure that your QGIS project follows these standards.
By default, QGIS starts each new project using a global default projection. This default CRS is EPSG:4326 (also
known as „WGS 84“), and it is a global latitude/longitude based reference system. This default CRS can be changed
via the CRS for New Projects setting in the CRS tab under Settings ► Options… (see Obr. 10.1). There is an option
to automatically set the project’s CRS to match the CRS of the first layer loaded into a new project, or alternatively you
can select a different default CRS to use for all newly created projects. This choice will be saved for use in subsequent
QGIS sessions.
The project CRS can also be set through the CRS tab of the Project ► Properties… dialog. It will also be shown in the
lower-right of the QGIS status bar.
Obr. 10.2: Dialog vlastností projektu
Available options are:
• No CRS (or unknown/non-Earth projection): Checking this setting will disable ALL projection handling
within the QGIS project, causing all layers and map coordinates to be treated as simple 2D Cartesian
coordinates, with no relation to positions on the Earth’s surface. It can be used to guess a layer CRS (based on
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its raw coordinates or when using QGIS for non earth uses like role-playing game maps, building mapping or
microscopic stuff. In this case:
– No reprojection is done while rendering the layers: features are just drawn using their raw coordinates.
– The ellipsoid is locked out and forced to None/Planimetric.
– The distance and area units, and the coordinate display are locked out and forced to „unknown units“; all
measurements are done in unknown map units, and no conversion is possible.
• or an existing coordinate reference system that can be geographic, projected or user-defined. A preview of the
CRS extent on earth is displayed to help you select the appropriate one. Layers added to the project are translated
on-the-fly to this CRS in order to overlay them regardless their original CRS. Use of units and ellipsoid setting
are available and make sense and you can perform calculations accordingly.
Whenever you select a new CRS for your QGIS project, the measurement units will automatically be changed in the
General tab of the Project properties dialog (Project ► Properties…) to match the selected CRS. For instance, some
CRSs define their coordinates in feet instead of meters, so setting your QGIS project to one of these CRSs will also
set your project to measure using feet by default.
Tip: Setting the project CRS from a layer
You can assign a CRS to the project using a layer CRS:
1. In the Layers panel, right-click on the layer you want to pick the CRS
2. Select Set project CRS from Layer.
The project’s CRS is redefined using the layer’s CRS. Map canvas extent, coordinates display are updated accordingly
and all the layers in the project are on-the-fly translated to the new project CRS.
10.4 Coordinate Reference System Selector
This dialog helps you assign a Coordinate Reference System to a project or a layer, provided a set of projection
databases. Items in the dialog are:
• Filter: If you know the EPSG code, the identifier, or the name for a Coordinate Reference System, you can
use the search feature to find it. Enter the EPSG code, the identifier or the name.
• Recently used coordinate reference systems: If you have certain CRSs that you frequently use in your
everyday GIS work, these will be displayed in this list. Click on one of these items to select the associated
CRS.
• Coordinate reference systems of the world: This is a list of all CRSs supported by QGIS, including
Geographic, Projected and Custom coordinate reference systems. To define a CRS, select it from the list by
expanding the appropriate node and selecting the CRS. The active CRS is preselected.
• PROJ text: This is the CRS string used by the PROJ projection engine. This text is read-only and provided
for informational purposes.
The CRS selector also shows a rough preview of the geographic area for which a selected CRS is valid for use. Many
CRSs are designed only for use in small geographic areas, and you should not use these outside of the area they
were designed for. The preview map shades an approximate area of use whenever a CRS is selected from the list. In
addition, this preview map also shows an indicator of the current main canvas map extent.
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10.5 Vlastní souřadnicový referenční systém
Pokud QGIS neposkytuje souřadnicový referenční systém, který potřebujete, můžete definovat vlastní CRS. Chcete-li
definovat CRS, zvolte vlastní CRS… z menu Nastavení. Vlastní uživatelské systémy jsou uloženy ve vaší vlastní
uživatelské QGIS databázi. Kromě vašich CRS obsahuje tato databáze vaše prostorové záložky a další vlastní data.
Defining a custom CRS in QGIS requires a good understanding of the PROJ projection library. To begin, refer to
„Cartographic Projection Procedures for the UNIX Environment - A User’s Manual“ by Gerald I. Evenden, U.S.
Geological Survey Open-File Report 90-284, 1990 (available at https://pubs.usgs.gov/of/1990/of90-284/ofr90-284.
pdf).
This manual describes the use of proj and related command line utilities. The cartographic parameters used with
proj are described in the user manual and are the same as those used by QGIS.
Dialog Vlastní definice souřadnicového referenčního systému vyžaduje pouze dva parametry pro definování
uživatelského SRS:
1. Popisný název
2. The cartographic parameters in PROJ or WKT format
To create a new CRS:
1. Click the Add new CRS
button
2. Enter a descriptive name
3. Select the format: it can be Proj String or WKT
4. Add the CRS Parameters.
Poznámka: Prefer storing the CRS definition in WKT format
Although both Proj String and WKT formats are supported, it’s highly recommended to store projection
definitions in the WKT format. Therefore, if the available definition is in the proj format, select that format,
enter the parameters and then switch to WKT format. QGIS will convert the definition to the WKT format that
you can later save.
5. Click Validate to test whether the CRS definition is an acceptable projection definition.
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Obr. 10.3: Dialog vlastní CRS
You can test your CRS parameters to see if they give sane results. To do this, enter known WGS 84 latitude and
longitude values in North and East fields, respectively. Click on Calculate, and compare the results with the known
values in your coordinate reference system.
10.5.1 Integrate an NTv2-transformation in QGIS
To integrate an NTv2 transformation file in QGIS you need one more step:
1. Place the NTv2 file (.gsb) in the CRS/Proj folder that QGIS uses (e.g. C:\OSGeo4W64\share\proj for
windows users)
2. Add nadgrids (+nadgrids=nameofthefile.gsb) to the Proj definition in the Parameters field of the
Custom Coordinate Reference System Definition (Settings ► Custom Projections…).
Obr. 10.4: Setting an NTv2 transformation
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10.6 Datum Transformations
In QGIS, ‚on-the-fly‘ CRS transformation is enabled by default, meaning that whenever you use layers with different
coordinate systems QGIS transparently reprojects them to the project CRS. For some CRS, there are a number of
possible transforms available to reproject to the project’s CRS!
By default, QGIS will attempt to use the most accurate transformation available. However, in some cases this may not
be possible, e.g. whenever additional support files are required to use a transformation. Whenever a more accurate
transformation is available, but is not currently usable, QGIS will show an informative warning message advising
you of the more accurate transformation and how to enable it on your system. Usually, this requires download of
an external package of transformation support files, and extracting these to the proj folder under your QGIS user
profile folder.
If desired, QGIS can also prompt you whenever multiple possible transformations can be made between two CRSs,
and allow you to make an informed selection of which is the most appropriate transformation to use for your data.
This customization is done in the Settings ► Options ► Transformations tab menu under the Default datum
transformations group:
• using Ask for datum transformation if several are available: when more than one appropriate datum
transformation exist for a source/destination CRS combination, a dialog will automatically be opened prompting
users to choose which of these datum transformations to use for the project. If the Make default checkbox
is ticked when selecting a transformation from this dialog, then the choice is remembered and automatically
applied to any newly created QGIS projects.
• or defining a list of appropriate datum transformations to use as defaults when loading a layer to a project or
reprojecting a layer.
Use the button to open the Select Datum Transformations dialog. Then:
1. Choose the Source CRS of the layer, using the drop-down menu or the Select CRS
widget.
2. Provide the Destination CRS in the same way.
3. A list of available transformations from source to destination will be shown in the table. Clicking a row
shows details on the settings applied and the corresponding accuracy and area of use of the transformation.
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Obr. 10.5: Selecting a preferred default datum transformation
In some cases a transformation may not be available for use on your system. In this case, the transformation
will still be shown (greyed) in this list but can not be picked until you install the required package of
transformation support. Usually, a button is provided to download and install the corresponding grid,
which is then stored under the proj folder in the active user profile directory.
4. Find your preferred transformation and select it
5. Set whether you Allow fallback transforms if preferred operation fails
6. Click OK.
A row is added to the table under Default Datum Transformations with information about the Source CRS,
the Destination CRS, the Operation applied for the transformation and whether Allow fallback Transforms
is enabled.
From now, QGIS automatically uses the selected datum transformations for further transformation between
these two CRSs until you remove it ( ) from the list or change the entry ( ) in the list.
Datum transformations set in the Settings ► Options ► Transformations tab will be inherited by all new QGIS
projects created on the system. Additionally, a particular project may have its own specific set of transformations
specified via the CRS tab of the Project properties dialog (Project ► Properties…). These settings apply to the current
project only.
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KAPITOLA 11
Obecné nástroje
11.1 Kontextová nápověda
Whenever you need help on a specific topic, you can access the corresponding page in the current User Manual via the
Help button available in most dialogs — please note that third-party plugins can point to dedicated web pages.
11.2 Panely
By default, QGIS provides many panels to work with. Some of these panels are described below while others may
be found in different parts of the document. A complete list of default panels provided by QGIS is available via the
View ► Panels ► menu and mentioned at Panely.
11.2.1 Layers Panel
The Layers panel (also called the map legend) lists all the layers in the project and helps you manage their visibility.
You can show or hide it by pressing Ctrl+1. A layer can be selected and dragged up or down in the legend to change
the Z-ordering. Z-ordering means that layers listed nearer the top of the legend are drawn over layers listed lower
down in the legend.
Poznámka: The Z-ordering behavior can be overridden by the Layer Order panel.
At the top of the Layers panel, a toolbar allows you to:
• Open the layer styling dock (F7)
: toggle the layer styling panel on and off.
• Add new group
• Manage Map Themes
: control visibility of layers and arrange them in different map themes.
• Filter Legend by Map Content
: only the layers that are set visible and whose features intersect the current map
canvas have their style rendered in the layers panel. Otherwise, a generic NULL symbol is applied to the layer.
Based on the layer symbology, this is a convenient way to identify which kind of features from which layers
cover your area of interest.
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• Filter Legend by Expression
: apply an expression to remove styles from the selected layer tree that have no feature
satisfying the condition. This can be used to highlight features that are within a given area/feature of another
layer. From the drop-down list, you can edit and clear the expression currently applied.
• Expand All
or Collapse All
layers and groups in the layers panel.
• Remove Layer/Group
currently selected.
Obr. 11.1: Layer Toolbar in Layers Panel
Poznámka: Tools to manage the layers panel are also available for map and legend items in print layouts
Configuring map themes
The Manage Map Themes
drop-down button provides access to convenient shortcuts to manipulate visibility of the
layers in the Layers panel:
• Zobrazit všechny vrstvy
• Skrýt všechny vrstvy
• Show Selected Layers
• Hide Selected Layers
• Toggle Selected Layers: changes the visibility of the first selected layer in the panel, and applies that state
to the other selected layers. Also accesible through Space shortcut.
• Toggle Selected Layers Independently: changes the visibility status of each selected layer
• Hide Deselected Layers
Beyond the simple control of layer visibility, the Manage Map Themes
menu allows you to configure Map Themes in
the legend and switch from one map theme to another. A map theme is a snapshot of the current map legend that
records:
• the layers set as visible in the Layers panel
• and for each visible layer:
– the reference to the style applied to the layer
– the visible classes of the style, ie the layer checked node items in the Layers panel. This applies to
symbologies other than the single symbol rendering
– the collapsed/expanded state of the layer node(s) and the group(s) it’s placed inside
To create a map theme:
1. Check a layer you want to show
2. Configure the layer properties (symbology, diagram, labels…) as usual
3. Expand the Style ► menu at the bottom and click on Add… to store the settings as a new style embedded in the
project
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Poznámka: A map theme does not remember the current details of the properties: only a reference to the
style name is saved, so whenever you apply modifications to the layer while this style is enabled (eg change the
symbology rendering), the map theme is updated with new information.
4. Repeat the previous steps as necessary for the other layers
5. If applicable, expand or collapse groups or visible layer nodes in the Layers panel
6. Click on the Manage Map Themes
button on top of the panel, and Add Theme…
7. Enter the map theme’s name and click OK
The new theme is listed in the lower part of the drop-down menu.
You can create as many map themes as you need: whenever the current combination in the map legend (visible layers,
their active style, the map legend nodes) does not match any existing map theme contents as defined above, click on
Add Theme… to create a new map theme, or use Replace Theme ► to update a map theme. You can rename the active
map theme with Rename Current Theme… or use the Remove Current Theme button to delete it.
Map themes are helpful to switch quickly between different preconfigured combinations: select a map theme in the
list to restore its combination. All configured themes are also accessible in the print layout, allowing you to create
different map items based on specific themes and independent of the current main canvas rendering (see Map item
layers).
Overview of the context menu of the Layers panel
At the bottom of the toolbar, the main component of the Layers panel is the frame listing vector or raster layers
added to the project, optionally organized in groups. Depending on the item selected in the panel, a right-click shows
a dedicated set of options presented below.
Option Vektorová vrstva Rastrová vrstva Group
Zoom to Layer/Group
Zoom to Selection
Show in Overview
Show Feature Count
Copy Layer/Group
Rename Layer/Group
Zoom to Native Resolution (100%)
Stretch Using Current Extent
Update SQL Layer…
Add Group
Duplicate Layer
Remove Layer/Group…
Move Out of Group
Move to Top
Move to Bottom
Check and all its Parents
Group Selected
Otevřít atributovou tabulku
continues on next page
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Tabulka 11.1 – pokračujte na předchozí stránce
Option Vektorová vrstva Rastrová vrstva Group
Přepnout editaci
Aktuální změny ►
Filtrovat…
Change Data Source…
Repair Data Source…
Actions on selections ► (in edit mode)
► Duplicate Feature
► Duplicate Feature and Digitize
Set Layer Scale Visibility…
Zoom to Visible Scale
Set CRS ►
► Set Layer/Group CRS…
► Set Project CRS from Layer
Set Group WMS Data…
Mutually Exclusive Group
Check and all its children (Ctrl-click)
Uncheck and all its children (Ctrl-click)
Make Permanent
Export ►
► Save As…
► Save Features As…
► Save Selected Features As…
► Save As Layer Definition File…
► Save As QGIS Layer Style File…
Styles ►
► Copy Style
► Paste Style
► Add…
► Rename Current…
► Edit symbol…
► Copy Symbol
► Paste Symbol
Vlastnosti…
Table: Context menu from Layers Panel items
For GRASS vector layers, Toggle editing
is not available. See section Digitizing and editing a GRASS vector layer for
information on editing GRASS vector layers.
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Interact with groups and layers
Layers in the legend window can be organized into groups. There are two ways to do this:
1. Press the icon to add a new group. Type in a name for the group and press Enter. Now click on an
existing layer and drag it onto the group.
2. Select some layers, right-click in the legend window and choose Group Selected. The selected layers will
automatically be placed in a new group.
To move a layer out of a group, drag it out, or right-click on it and choose Move Out of Group: the layer is moved
from the group and placed above it. Groups can also be nested inside other groups. If a layer is placed in a nested
group, Move Out of Group will move the layer out of all nested groups.
To move a group or layer to the top of the layer panel, either drag it to the top, or choose Move to Top. If you use
this option on a layer nested in a group, the layer is moved to the top in its current group. The Move to Bottom option
follows the same logic to move layers and groups down.
The checkbox for a group will show or hide the checked layers in the group with one click. With Ctrl pressed, the
checkbox will also turn on or off all the layers in the group and its sub-groups.
Ctrl-click on a checked / unchecked layer will uncheck / check the layer and all its parents.
Enabling the Mutually Exclusive Group option means you can make a group have only one layer visible at the same
time. Whenever a layer within the group is set visible the others will be toggled not visible.
It is possible to select more than one layer or group at the same time by holding down the Ctrl key while clicking
additional layers. You can then move all selected layers to a new group at the same time.
You may also delete more than one layer or group at once by selecting several items with the Ctrl key and then
pressing Ctrl+D: all selected layers or groups will be removed from the layers list.
More information on layers and groups using indicator icon
In some circumstances, icons appears next to the layer or group in the Layers panel to give more information about
the layer/group. These symbols are:
• to indicate that the layer is in edit mode and you can modify the data
• to indicate that the layer being edited has some unsaved changes
• to indicate a filter applied to the layer. Hover over the icon to see the filter expression and double-click to
update the setting
• to identify layers that are required in the project, hence non removable
• to identify an embedded group or layer and the path to their original project file
• to identify a layer whose data source was not available at the project file opening (see Handling broken file
paths). Click the icon to update the source path or select Repair Data Source… entry from the layer contextual
menu.
• to remind you that the layer is a temporary scratch layer and its content will be discarded when you close
this project. To avoid data loss and make the layer permanent, click the icon to store the layer in any of the
OGR vector formats supported by QGIS.
• to identify a layer that has no/unknown CRS
• to identify a temporal layer controlled by canvas animation
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Editing vector layer style
From the Layers panel, you have shortcuts to change the layer rendering quickly and easily. Right-click on a vector
layer and select Styles ► in the list in order to:
• see the styles currently applied to the layer. If you defined many styles for the layer, you can switch from one
to another and your layer rendering will automatically be updated on the map canvas.
• copy part or all of the current style, and when applicable, paste a copied style from another layer
Tip: Quickly share a layer style
From the context menu, copy the style of a layer and paste it to a group or a selection of layers: the style
is applied to all the layers that are of the same type (vector/raster) as the original layer and, for vector layers,
have the same geometry type (point, line or polygon).
• rename the current style, add a new style (which is actually a copy of the current one) or delete the current style
(when multiple styles are available).
Poznámka: The previous options are also available for raster or mesh layers.
• update the symbol color using a Color Wheel. For convenience, the recently used colors are also available at
the bottom of the color wheel.
• Edit Symbol…: open the Symbol Selector dialog and change feature symbol (symbol, size, color…).
When using a classification symbology type (based on categorized, graduated or rule-based), the aforementioned
symbol-level options are available from the class entry context menu. Also provided are the Toggle Items,
Show All Items and Hide All Items entries to switch the visibility of all the classes of features. These avoid
(un)checking items one by one.
Tip: Double-clicking a class leaf entry also opens the Symbol Selector dialog.
11.2.2 Layer Styling Panel
The Layer Styling panel (also enabled with Ctrl+3) is a shortcut to some of the functionalities of the Layer Properties
dialog. It provides a quick and easy way to define the rendering and the behavior of a layer, and to visualize its effects
without having to open the layer properties dialog.
In addition to avoiding the blocking (or „modal“) layer properties dialog, the layer styling panel also avoids
cluttering the screen with dialogs, and contains most style functions (color selector, effects properties, rule edit, label
substitution…): e.g., clicking color buttons inside the layer style panel causes the color selector dialog to be opened
inside the layer style panel itself rather than as a separate dialog.
From a drop-down list of current layers in the layer panel, select an item and:
• Depending on the layer type, set:
– Symbology, Transparency, and Histogram properties for raster layer. These options are the
same as in the Raster Properties Dialog.
– Symbology, Labels, Mask and 3D View properties for vector layer. These options are
the same as in the The Vector Properties Dialog and can be extended by custom properties introduced by
third-party plugins.
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– Symbology and 3D View properties for mesh layer. These options are the same as in the Mesh
Dataset Properties.
• Manage the associated style(s) in the Style Manager (more details at Managing Custom Styles).
• See the History of changes you applied to the layer style in the current project: you can therefore cancel or
restore to any state by selecting it in the list and clicking Apply.
For Vector Tile layers there is an option to show Visible rules only. This is very useful if you just want to work
with rules that fall inside the current map canvas zoom level.
Another powerful feature of this panel is the Live update checkbox. Tick it to render your changes immediately
on the map canvas: you no longer need to click the Apply button.
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Obr. 11.2: Defining a layer’s symbology from the layer styling panel
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11.2.3 Layer Order Panel
By default, layers shown on the QGIS map canvas are drawn following their order in the Layers panel: the higher
a layer is in the panel, the higher (hence, more visible) it’ll be in the map view.
You can define a drawing order for the layers independent of the order in the layers panel with the Layer Order
panel enabled in View ► Panels ► menu or with Ctrl+9. Check Control rendering order underneath the list
of layers and reorganize the layers in the panel as you want. This order becomes the one applied to the map canvas.
For example, in Obr. 11.3, you can see that the airports features are displayed over the alaska polygon despite
those layers‘ respective placement in the Layers panel.
Unchecking Control rendering order will revert to default behavior.
Obr. 11.3: Define a layer order independent of the legend
11.2.4 Overview Panel
The Overview panel (Ctrl+8) displays a map with a full extent view of some of the layers. The Overview map
is filled with layers using the Show in Overview option from the Layer menu or in the layer contextual menu. Within
the view, a red rectangle shows the current map canvas extent, helping you quickly to determine which area of the
whole map you are currently viewing. If you click-and-drag the red rectangle in the overview frame, the main map
view extent will update accordingly.
Note that labels are not rendered to the map overview even if the layers used in the map overview have been set up
for labeling.
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11.2.5 Log Messages Panel
When loading or processing some operations, you can track and follow messages that appear in different tabs using
the Log Messages Panel. It can be activated using the most right icon in the bottom status bar.
11.2.6 Undo/Redo Panel
For each layer being edited, the Undo/Redo (Ctrl+5) panel shows the list of actions carried out, allowing you quickly
to undo a set of actions by selecting the action listed above. More details at Undo and Redo edits.
11.2.7 Statistical Summary Panel
The Statistics panel (Ctrl+6) provides summarized information on any vector layer. This panel allows you to select:
• the vector layer to compute the statistics on
• the column to use, or an expression
• the statistics to return using the drop-down button at the bottom-right of the dialog. Depending on the field’s
(or expression’s values) type, available statistics are:
Statistics Řetězec Integer Float Datum
Count
Count Distinct Value
Count Missing value
Sum
Mean
Standard Deviation
Standard Deviation on Sample
Minimal value
Maximal value
Rozsah
Minority
Majority
Variety
First Quartile
Third Quartile
Inter Quartile Range
Minimum Length
Maximum Length
Mean Length
Table: Statistics available for each field type
The statistical summary can be:
• returned for the whole layer or selected features only
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• recalculated using the button when the underlying data source changes (eg, new or removed features/fields,
attribute modification)
• copied to the clipboard and pasted as a table in another application
Obr. 11.4: Show statistics on a field
11.3 Vnořování projektů
Sometimes, you’d like to keep some layers in different projects, but with the same style. You can either create a default
style for these layers or embed them from another project to save time and effort.
Embed layers and groups from an existing project has some advantages over styling:
• All types of layers (vector or raster, local or online…) can be added
• Fetching groups and layers, you can keep the same tree structure of the „background“ layers in your different
projects
• While the embedded layers are editable, you can’t change their properties such as symbology, labels, forms,
default values and actions, ensuring consistency across projects
• Modify the items in the original project and changes are propagated to all the other projects
If you want to embed content from other project files into your project, select Layer ► Embed Layers and Groups:
1. Click the … button to look for a project: you can see the content of the project (see Obr. 11.5)
2. Hold down Ctrl ( or Cmd) and click on the layers and groups you wish to retrieve
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3. Click OK
The selected layers and groups are embedded in the Layers panel and displayed on the map canvas. An icon
is added next to their name for recognition and hovering over displays a tooltip with the original project file path.
Obr. 11.5: Vyberte vrstvy a skupiny pro připojení
Like any other layer, an embedded layer can be removed from the project by right-clicking on the layer and clicking
Remove
.
Tip: Change rendering of an embedded layer
It’s not possible to change the rendering of an embedded layer, unless you make the changes in the original project file.
However, right-clicking on a layer and selecting Duplicate creates a layer which is fully-featured and not dependent
on the original project. You can then safely remove the linked layer.
11.4 Working with the map canvas
11.4.1 Vykreslování
By default, QGIS renders all visible layers whenever the map canvas is refreshed. The events that trigger a refresh of
the map canvas include:
• adding a layer
• panning or zooming
• resizing the QGIS window
• changing the visibility of a layer or layers
QGIS vám umožňuje kontrolovat proces vykreslování mnohými cestami.
Vykreslování v závislosti na měřítku
Scale-dependent rendering allows you to specify the minimum and maximum scales at which a layer (raster or vector)
will be visible. To set scale-dependent rendering, open the Properties dialog by double-clicking on the layer in the
legend. On the Rendering tab, tick Scale dependent visibility and enter the Minimum (exclusive) and Maximum
(inclusive) scale values.
You can also activate scale dependent visibility on a layer from the Layers panel. Right-click on the layer and in the
context menu, select Set Layer Scale Visibility.
The Set to current canvas scale
button allow you to use the current map canvas scale as boundary of the range visibility.
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Poznámka: When a layer is not rendered in the map canvas because the map scale is out of its visibility scale range,
the layer is greyed in the Layers panel and a new option Zoom to Visible Scale appears in the layer context menu.
Select it and the map is zoomed to the layer’s nearest visibility scale.
Kontrolování vykreslení mapy
Vykreslování mapy může být ovládáno různými způsoby, které jsou popsány níže.
Pozastavení vykreslování
To suspend rendering, click the Render checkbox in the bottom-right corner of the status bar. When Render
is not checked, QGIS does not redraw the canvas in response to any of the events described in the section Vykreslování.
Examples of when you might want to suspend rendering include:
• adding many layers and symbolizing them prior to drawing
• adding one or more large layers and setting scale dependency before drawing
• adding one or more large layers and zooming to a specific view before drawing
• any combination of the above
Zaškrtnutí Render checkboxu umožní vykreslení a způsobí okamžité obnovování mapového okna.
Nastavení možnosti přidání vrstvy
You can set an option to always load new layers without drawing them. This means the layer will be added to the map,
but its visibility checkbox in the legend will be unchecked by default. To set this option, choose menu option Settings
► Options and click on the Rendering tab. Uncheck By default new layers added to the map should be displayed.
Any layer subsequently added to the map will be off (invisible) by default.
Zastavení vykreslování
To stop the map drawing, press the Esc key. This will halt the refresh of the map canvas and leave the map partially
drawn. It may take a bit of time between pressing Esc for the map drawing to halt.
Ovlivnění kvality vykreslení
QGIS has an option to influence the rendering quality of the map. Choose menu option Settings ► Options, click on
the Rendering tab and select or deselect Make lines appear less jagged at the expense of some drawing performance.
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Zrychlení vykreslování
There are some settings that allow you to improve rendering speed. Open the QGIS options dialog using Settings ►
Options, go to the Rendering tab and select or deselect the following checkboxes:
• Use render caching where possible to speed up redraws.
• Render layers in parallel using many CPU cores and then set the Max cores to use.
• The map renders in the background onto a separate image and each Map Update interval, the content from
this (off-screen) image will be taken to update the visible screen representation. However, if rendering finishes
faster than this duration, it will be shown instantaneously.
• With Enable Feature simplification by default for newly added layers, you simplify features‘ geometry (fewer
nodes) and as a result, they display more quickly. Be aware that this can cause rendering inconsistencies.
11.4.2 Zooming and Panning
There are multiple ways to zoom and pan to an area of interest. You can use the Map Navigation toolbar, the mouse
and keyboard on the map canvas and also the menu actions from the View menu and the layers‘ contextual menu in
the Layers panel.
Icon Label Usage View
menu
Map
Navigation
Toolbar
Layer
Contextual
Menu
Pan Map When activated, left click anywhere on the map canvas to pan the map at
the cursor position. You can also pan the map by holding down the left
mouse button and dragging the map canvas.
Zoom In When activated, left click anywhere on the map canvas to zoom in one
level. The mouse cursor position will be the center of the zoomed area of
interest. You can also zoom in to an area by dragging a rectangle on the
map canvas with the left mouse button.
Zoom Out When activated, left click anywhere on the map canvas to zoom out one
level. The mouse cursor position will be the center of the zoomed area
of interest. You can also zoom out from an area by dragging a rectangle
on the map canvas with the left mouse button.
Pan Map to
Selection
Pan the map to the active layer’s selected features.
Zoom To
Selection
Zoom to the active layer’s selected features.
Zoom To
Layer
Zoom to the active layer’s extent.
Zoom Full Zoom to the extent of all the layers in the project.
Zoom Last Zoom the map to the previous extent in history.
Zoom Next Zoom the map to the next extent in history.
Zoom to
Native
Resolution
Zoom the map to a level where one pixel of the active raster layer covers
one screen pixel.
A Zoom factor can be set under the Settings ► Options ► Map tools menu to define the scale behavior while
zooming. There, you can also set a list of Predefined Scales that will be available at the bottom of the map canvas.
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With the Mouse on the Map Canvas
In addition to using the Pan Zoom In
and Zoom Out
tools described above, you can hold the mouse wheel
inside of the map canvas and drag the mouse cursor (on macOS, you may need to hold down the cmd key). You can
also roll the mouse wheel to zoom in and out on the map. The mouse cursor position will be the center of the zoomed
area of interest. Holding down Ctrl while rolling the mouse wheel results in a finer zoom.
With the Keyboard on the Map Canvas
Holding down spacebar on the keyboard and moving the mouse cursor will pan the map the same way dragging
the map canvas with Pan
does.
Panning the map is possible with the arrow keys. Place the mouse cursor inside the map area, and press on the arrow
keys to pan up, down, left and right.
The PgUp and PgDown keys on the keyboard will cause the map display to zoom in or out following the zoom factor
set. Pressing Ctrl++ or Ctrl+- also performs an immediate zoom in/out on the map canvas.
When certain map tools are active (Identify, Measure…), you can perform a zoom by holding down Shift and
dragging a rectangle on the map to zoom to that area. This is not enabled for selection tools (since they use Shift
for adding to selection) or edit tools.
11.4.3 Prostorové záložky
Spatial Bookmarks allow you to „bookmark“ a geographic location and return to it later. By default, bookmarks are
saved in the user’s profile (as User Bookmarks), meaning that they are available from any project the user opens. They
can also be saved for a single project (named Project Bookmarks) and stored within the project file, which can be
helpful if the project is to be shared with other users.
Tvoření záložek
Abyste vytvořili záložku:
1. Zoom and pan to the area of interest.
2. Select the menu option View ► New Spatial Bookmark…, press Ctrl+B or right-click the Spatial
Bookmarks entry in the Browser panel and select New Spatial Bookmark. The Bookmark Editor dialog opens.
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Obr. 11.6: The Bookmark Editor Dialog
3. Enter a descriptive name for the bookmark
4. Enter or select a group name in which to store related bookmarks
5. Select the extent of the area you wish to save, using the extent selector; the extent can be calculated from
a loaded layer extent, the current map canvas or drawn over the current map canvas.
6. Indicate the CRS to use for the extent
7. Select whether the bookmark will be Saved in User Bookmarks or Project Bookmarks
8. Press Save to add the bookmark to the list
Můžete mít více záložek se stejným názvem.
Práce se záložkami
To use and manage bookmarks, you can either use the Spatial Bookmarks panel or Browser.
Select View ► Show Spatial Bookmark Manager or press Ctrl+7 to open the Spatial Bookmarks Manager panel.
Select View ► Show Bookmarks or Ctrl+Shift+B to show the Spatial Bookmarks entry in the Browser
panel.
You can perform the following tasks:
Task Spatial Bookmark Manager Browser
Zoom to
a Bookmark
Double-click on it, or select the bookmark
and press the Zoom to bookmark
button.
Double-click on it, drag and drop it to the
map canvas, or right-click the bookmark
and select Zoom to Bookmark.
Delete
a bookmark
Select the bookmark and click the
Delete bookmark button. Confirm your
choice.
Right-click the bookmark and select Delete
Spatial Bookmark. Confirm your choice.
continues on next page
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Tabulka 11.3 – pokračujte na předchozí stránce
Task Spatial Bookmark Manager Browser
Export
bookmarks to
XML
Click the Import/Export Bookmarks
button and select Export. All the
bookmarks (user or project) are saved in an
xml file.
Select one or more folders (user or project)
or subfolders (groups), then right-click and
select Export Spatial Bookmarks…. The
selected bookmark subset is saved.
Import
bookmarks from
XML
Click the Import/Export Bookmarks
button and select Import. All
bookmarks in the XML file are imported
as user bookmarks.
Right-click the Spatial Bookmarks entry
or one of its folders (user or project) or
subfolders (groups) to determine where
to import the bookmarks, then select
Import Spatial Bookmarks. If performed
on the Spatial Bookmarks entry, the
bookmarks are added to User Bookmarks.
Edit bookmark You can change a bookmark by changing
the values in the table. You can edit the
name, the group, the extent and if it is stored
in the project or not.
Right-click the desired bookmark and
select Edit Spatial Bookmark…. The
Bookmark Editor will open, allowing you
to redefine every aspect of the bookmark
as if you were creating it for the first time.
You can also drag and drop the bookmark
between folders (user and project) and
subfolders (groups).
You can also zoom to bookmarks by typing the bookmark name in the locator.
11.4.4 Dekorace
Decorations include Grid, Title Label, Copyright Label, Image, North Arrow, Scale Bar and Layout Extents. They
are used to ‚decorate‘ the map by adding cartographic elements.
Mřížka
Grid allows you to add a coordinate grid and coordinate annotations to the map canvas.
1. Select menu option View ► Decorations ► Grid… to open the dialog.
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Obr. 11.7: Dialog mřížky
2. Tick Enable grid and set grid definitions according to the layers loaded in the map canvas:
• The Grid type: it can be Line or Marker
• The associated Line symbol or marker symbol used to represent the grid marks
• The Interval X and Interval Y between the grid marks, in map units
• An Offset X and Offset Y distance of the grid marks from the bottom left corner of the map canvas, in
map units
• The interval and offset parameters can be set based on the:
– Canvas Extents: generates a grid with an interval that is approximatively 1/5 of the canvas width
– Active Raster Layer resolution
3. Tick Draw annotations to display the coordinates of the grid marks and set:
• The Annotation direction, ie how the labels would be placed relative to their grid line. It can be:
– Horizontal or Vertical for all the labels
– Horizontal and Vertical, ie each label is parallel to the grid mark it refers to
– Boundary direction, ie each label follows the canvas boundary, and is perpendicular to the grid mark
it refers to
• The Annotation font (text formatting, buffer, shadow…) using the font selector widget
• The Distance to map frame, margin between annotations and map canvas limits. Convenient when
exporting the map canvas eg to an image format or PDF, and avoid annotations to be on the „paper“
limits.
• The Coordinate precision
4. Click Apply to verify that it looks as expected or OK if you’re satisfied.
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Title Label
Title Label allows you to decorate your map with a Title.
To add a Title Label decoration:
1. Select menu option View ► Decorations ► Title Label… to open the dialog.
Obr. 11.8: The Title Decoration Dialog
2. Make sure Enable Title Label is checked
3. Enter the title text you want to place on the map. You can make it dynamic using the Insert or Edit an
Expression… button.
4. Choose the Font for the label using the font selector widget with full access to QGIS text formatting options.
Quickly set the font color and opacity by clicking the black arrow to the right of the font combo box.
5. Select the color to apply to the title’s Background bar color.
6. Choose the Placement of the label in the canvas: options are Top left, Top Center (default), Top Right, Bottom
left, Bottom Center and Bottom Right.
7. Refine the placement of the item by setting a horizontal and/or vertical Margin from Edge. These values can
be in Millimeters or Pixels or set as a Percentage of the width or height of the map canvas.
8. Click Apply to verify that it looks as expected or OK if you’re satisfied.
Copyright Label
Copyright Label can be used to decorate your map with a Copyright label.
To add this decoration:
1. Select menu option View ► Decorations ► Copyright Label… to open the dialog.
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Obr. 11.9: The Copyright Decoration Dialog
2. Make sure Enable Copyright Label is checked
3. Enter the copyright text you want to place on the map. You can make it dynamic using the Insert or Edit an
Expression… button.
4. Choose the Font for the label using the font selector widget with full access to QGIS text formatting options.
Quickly set the font color and opacity by clicking the black arrow to the right of the font combo box.
5. Choose the Placement of the label in the canvas: options are Top left, Top Center, Top Right, Bottom left, Bottom
Center, and Bottom Right (default for Copyright decoration)
6. Refine the placement of the item by setting a horizontal and/or vertical Margin from Edge. These values can
be in Millimeters or Pixels or set as a Percentage of the width or height of the map canvas.
7. Click Apply to verify that it looks as expected or OK if you’re satisfied.
Image Decoration
Image allows you to add an image (logo, legend, ..) on the map canvas.
To add an image:
1. Select menu option View ► Decorations ► Image… to open the dialog.
Obr. 11.10: The Image Decoration Dialog
2. Make sure Enable Image is checked
3. Select a bitmap (e.g. png or jpg) or SVG image using the … Browse
button
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4. If you have chosen a parameter enabled SVG then you can also set a Fill or Stroke (outline) color. For bitmap
images, the color settings are disabled.
5. Set a Size of the image in mm. The width of selected image is used to resize it to given Size.
6. Choose where you want to place the image on the map canvas with the Placement combo box. The default
position is Top Left.
7. Set the Horizontal and Vertical Margin from (Canvas) Edge. These values can be set in Millimeters, Pixels or
as a Percentage of the width or height of the map canvas.
8. Click Apply to verify that it looks as expected and OK if you’re satisfied.
Směrová růžice
North Arrow allows you to add a north arrow on the map canvas.
To add a north arrow:
1. Select menu option View ► Decorations ► North Arrow… to open the dialog.
Obr. 11.11: The North Arrow Dialog
2. Make sure Enable north arrow is checked
3. Optionally change the color and size, or choose a custom SVG
4. Optionally change the angle or choose Automatic to let QGIS determine the direction
5. Optionally choose the placement from the Placement combo box
6. Optionally refine the placement of the arrow by setting a horizontal and/or vertical Margin from (Canvas) Edge.
These values can be in Millimeters or Pixels or set as a Percentage of the width or height of the map canvas.
7. Click Apply to verify that it looks as expected and OK if you’re satisfied.
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Měřítko
Scale Bar adds a simple scale bar to the map canvas. You can control the style and placement, as well as the
labelling of the bar.
QGIS only supports displaying the scale in the same units as your map frame. So, if the units of your project’s CRS
are meters, you can’t create a scale bar in feet. Likewise, if you are using decimal degrees, you can’t create a scale
bar to display distance in meters.
Přidání měřítka
1. Select menu option View ► Decorations ► Scale Bar… to open the dialog
Obr. 11.12: Dialog měřítka
2. Make sure Enable scale bar is checked
3. Choose a style from the Scale bar style combo box
4. Select the Color of bar by choosing a fill color (default: black) and an outline color (default:
white). The scale bar fill and outline can be made opaque by clicking on the down arrow to the right of the
color input.
5. Select the font for the scale bar from the Font of bar combo box
6. Set the Size of bar
7. Optionally check Automatically snap to round number on resize to display easy-to-read values
8. Choose the placement from the Placement combo box
9. You can refine the placement of the item by setting a horizontal and/or vertical Margin from (Canvas) Edge.
These values can be in Millimeters or Pixels or set as a Percentage of the width or height of the map canvas.
10. Click Apply to verify that it looks as expected or OK if you’re satisfied.
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Layout Extents
Layout Extents adds the extents of map item(s) in print layout(s) to the canvas. When enabled, the extents of all
map items within all print layouts are shown using a lightly dotted border labeled with the name of the print layout
and map item. You can control the style and labeling of the displayed layout extents. This decoration is useful when
you are tweaking the positioning of map elements such as labels, and need to know the actual visible region of print
layouts.
Obr. 11.13: Example of layout extents displayed in a QGIS project with two print layouts. The print layout named
‚Sights‘ contains two map items, while the other print layout contains one map item.
To add layout extent(s):
1. Select View ► Decorations ► Layout Extents to open the dialog
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Obr. 11.14: The Layout Extents Dialog
2. Make sure Show layout extents is checked.
3. Optionally change the symbol and labeling of the extents.
4. Click Apply to verify that it looks as expected and OK if you’re satisfied.
Tip: Decorations Settings
When you save a QGIS project file, any changes you have made to Grid, North Arrow, Scale Bar, Copyright and
Layout Extents will be saved in the project and restored the next time you load the project.
11.4.5 Anotační nástroje
Annotations are information added to the map canvas and shown within a balloon. This information can be of different
types and annotations are added using the corresponding tools in the Attributes Toolbar:
• Text Annotation
for custom formatted text
• HTML Annotation
to place the content of an html file
• SVG Annotation
to add an SVG symbol
• Form Annotation
: useful to display attributes of a vector layer in a customized ui file (see Obr. 11.15). This
is similar to the custom attribute forms, but displayed in an annotation item. Also see this video https://www.
youtube.com/watch?v=0pDBuSbQ02o&feature=youtu.be&t=2m25s from Tim Sutton for more information.
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Obr. 11.15: Customized QT Designer annotation form
To add an annotation, select the corresponding tool and click on the map canvas. An empty balloon is added. Double-click
on it and a dialog opens with various options. This dialog is almost the same for all the annotation types:
• At the top, a file selector to fill with the path to an html, svg or ui file depending on the type of annotation.
For text annotation, you can enter your message in a text box and set its rendering with the normal font tools.
• Fixed map position: when unchecked, the balloon placement is based on a screen position (instead of the
map), meaning that it’s always shown regardless the map canvas extent.
• Linked layer: associates the annotation with a map layer, making it visible only when that layer is visible.
• Map marker: using QGIS symbols, sets the symbol to display at the balloon anchor position (shown only when
Fixed map position is checked).
• Frame style: sets the frame background color, transparency, stroke color or width of the balloon using QGIS
symbols.
• Contents margins: sets interior margins of the annotation frame.
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Obr. 11.16: Dialog textové anotace
Annotations can be selected when an annotation tool is enabled. They can then be moved by map position (by dragging
the map marker) or by moving only the balloon. The Move Annotation
tool also allows you to move the balloon on
the map canvas.
To delete an annotation, select it and either press the Del or Backspace button, or double-click it and press the
Delete button in the properties dialog.
Poznámka: If you press Ctrl+T while an Annotation tool (move annotation, text annotation, form annotation)
is active, the visibility states of the items are inverted.
Tip: Layout the map with annotations
You can print or export annotations with your map to various formats using:
• map canvas export tools available in the Project menu
• print layout, in which case you need to check Draw map canvas items in the corresponding map item properties
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11.4.6 Měření
General information
QGIS provides four means of measuring geometries:
• interactive measurement tools
• measuring in the Field Calculator
• derived measurements in the Identifying Features tool
• the vector analysis tool: Vector ► Geometry Tools ► Export/Add Geometry Columns
Measuring works within projected coordinate systems (e.g., UTM) and unprojected data. The first three measuring
tools behave equally to global project settings:
• Unlike most other GIS, the default measurement metric is ellipsoidal, using the ellipsoid defined in Project ►
Properties… ► General. This is true both when geographic and projected coordinate systems are defined for
the project.
• If you want to calculate the projected/planimetric area or distance using cartesian maths, the measurement
ellipsoid has to be set to „None/Planimetric“ (Project ► Properties… ► General). However, with a geographic
(ie unprojected) CRS defined for the data and project, area and distance measurement will be ellipsoidal.
However, neither the identify tool nor the field calculator will transform your data to the project CRS before measuring.
If you want to achieve this, you have to use the vector analysis tool: Vector ► Geometry Tools ► Add Geometry
Attributes…. Here, measurement is planimetric, unless you choose the ellipsoidal measurement.
Measure length, areas and angles interactively
Click the icon in the Attribute toolbar to begin measurements. The down arrow near the icon switches between
length, area or angle. The default unit used in the dialog is the one set in Project ► Properties… ►
General menu.
Poznámka: Configuring the measure tool
While measuring length or area, clicking the Configuration button at the bottom of the widget opens the Settings ►
Options ► Map Tools menu, where you can select the rubberband color, the precision of the measurements and the
unit behavior. You can also choose your preferred measurement or angle units, but keep in mind that those values
are overridden in the current project by the selection made in the Project ► Properties… ► General menu, and by the
selection made in the measurement widget.
All measuring modules use the snapping settings from the digitizing module (see section Nastavení přichytávací
tolerance a vyhledání poloměru). So, if you want to measure exactly along a line feature, or around a polygon feature,
first set its layer snapping tolerance. Now, when using the measuring tools, each mouse click (within the tolerance
setting) will snap to that layer.
By default, Measure Line
measures real distances between given points according to a defined ellipsoid. The tool then
allows you to click points on the map. Each segment length, as well as the total, shows up in the measure window.
To stop measuring, click the right mouse button. Now it is possible to copy all your line measurements at once to the
clipboard using the Copy All button.
Note that you can use the drop-down list near the total to change the measurement units interactively while working
with the measure tool (‚Meters‘, ‚Kilometers‘, ‚Feet‘, ‚Yards‘, ‚Miles‘, ‚Nautical miles‘, ‚Centimeters‘, ‚Millimeters‘,
‚Degrees‘, ‚Map units‘). This unit is retained for the widget until a new project is created or another project is opened.
The Info section in the dialog explains how calculations are made according to the CRS settings available.
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Obr. 11.17: Measure Distance
Measure Area
: Areas can also be measured. In the measure window, the accumulated area size appears. Right-click
to stop drawing. The Info section is also available as well as the ability to switch between different area units (‚Square
meters‘, ‚Square kilometers‘, ‚Square feet‘, ‚Square yards‘, ‚Square miles‘, ‚Hectares‘, ‚Acres‘, ‚Square centimeters‘,
‚Square millimeters‘, ‚Square nautical miles‘, ‚Square degrees‘, ‚Map units‘).
Obr. 11.18: Measure Area
Measure Angle
: You can also measure angles. The cursor becomes cross-shaped. Click to draw the first segment of
the angle you wish to measure, then move the cursor to draw the desired angle. The measurement is displayed in
a pop-up dialog.
Obr. 11.19: Measure Angle
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11.5 Interacting with features
11.5.1 Selecting features
QGIS provides several tools to select features on the map canvas. Selection tools are available in the Edit ► Select
menu or in the Selection Toolbar.
Poznámka: Selection tools work with the currently active layer.
Selecting manually on the map canvas
To select one or more features with the mouse, you can use one of the following tools:
• Select Features by area or single click
• Select Features by Polygon
• Select Features by Freehand
• Select Features by Radius
Poznámka: Other than Select Features by Polygon
, these manual selection tools allow you to select feature(s) on the
map canvas with a single click.
Poznámka: Use the Select Features by Polygon
tool to use an existing polygon feature (from any layer) to select
overlapping features in the active layer. Right-click in the polygon and choose it from the context menu that shows
a list of all the polygons that contain the clicked point. All the overlapping features from the active layer are selected.
Tip: Use the Edit ► Select ► Reselect Features tool to redo your latest selection. Very useful when you have
painstakingly made a selection, and then click somewhere else accidentally and clear your selection.
While using the Select Feature(s) tool, holding Shift or Ctrl toggles whether a feature is selected (ie either
adds to the current selection or remove from it).
For the other tools, different behaviors can be performed by holding down:
• Shift: add features to the current selection
• Ctrl: substract features from the current selection
• Ctrl+Shift: intersect with current selection, ie only keep overlapping features from the current selection
• Alt: select features that are totally within the selection shape. Combined with Shift or Ctrl keys, you can
add or substract features to/from the current selection.
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Automatic selection
The other selection tools, most of them available from the Attribute table, perform a selection based on a feature’s
attribute or its selection state (note that attribute table and map canvas show the same information, so if you select
one feature in the attribute table, it will be selected on the map canvas too):
• Select By Expression…
select features using expression dialog
• Select Features By Value…
or press F3
• Deselect Features from All Layers
or press Ctrl+Alt+A to deselect all selected features in all layers
• Deselect Features from the Current Active Layer
or press Ctrl+Shift+A
• Select All Features
or press Ctrl+A to select all features in the current layer
• Invert Feature Selection
to invert the selection in the current layer
• Select by Location
to select the features based on their spatial relationship with other features (in the same or
another layer - see Select by location)
For example, if you want to find regions that are boroughs from regions.shp of the QGIS sample data, you can:
1. Use the Select features using an Expression
icon
2. Expand the Fields and Values group
3. Double-click the field that you want to query („TYPE_2“)
4. Click All Unique in the panel that shows up on the right
5. From the list, double-click ‚Borough‘. In the Expression editor field, write the following query:
"TYPE_2" = 'Borough'
6. Click Select Features
From the expression builder dialog, you can also use Function list ► Recent (Selection) to make a selection that you
have used before. The dialog remembers the last 20 expressions used. See Výrazy for more information and examples.
Tip: Save your selection into a new file
Users can save selected features into a New Temporary Scratch Layer or a New Vector Layer using Edit ► Copy
Features and Edit ► Paste Features as in the desired format.
Select Features By Value
This selection tool opens the layer’s feature form allowing the user to choose which value to look for for each field,
whether the search should be case-sensitive, and the operation that should be used. The tool has also autocompletes,
automatically filling the search box with existing values.
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Obr. 11.20: Filter/Select features using form dialog
Alongside each field, there is a drop-down list with options to control the search behaviour:
Field search option Řetězec Numeric Datum
Exclude Field from the search
Equal to (=)
Not equal to (̸=)
Greater than (>)
Less than (<)
Greater than or equal to (≥)
Less than or equal to (≤)
Between (inclusive)
Not between (inclusive)
Contains
Does not contain
Is missing (null)
Is not missing (not null)
Starts with
Ends with
For string comparisons, it is also possible to use the Case sensitive option.
After setting all search options, click Select features to select the matching features. The drop-down options are:
• Select features
• Add to current selection
• Remove from current selection
• Filter current selection
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You can also clear all search options using the Reset form button.
Once the conditions are set, you can also either:
• Zoom to features on the map canvas without the need of a preselection
• Flash features, highlighting the matching features. This is a handy way to identify a feature without selection
or using the Identify tool. Note that the flash does not alter the map canvas extent and would be visible only if
the feature is within the bounds of the current map canvas.
11.5.2 Identifying Features
The Identify tool allows you to interact with the map canvas and get information on features in a pop-up window. To
identify features, use:
• View ► Identify Features
• Ctrl+Shift+I (or Cmd+Shift+I),
• Identify Features
icon on the Attributes toolbar
Using the Identify Features tool
QGIS offers several ways to identify features with the Identify Features
tool:
• left click identifies features according to the selection mode and the selection mask set in the Identify Results
panel
• right click with Identify Feature(s) as selection mode set in the Identify Results panel fetches all snapped features
from all visible layers. This opens a context menu, allowing the user to choose more precisely the features to
identify or the action to execute on them.
• right click with Identify Features by Polygon as selection mode in the Identify Results panel identifies the features
that overlap with the chosen existing polygon, according to the selection mask set in the Identify Results panel
Tip: Filter the layers to query with the Identify Features tool
Under Layer Capabilities in Project ► Properties… ► Data Sources, uncheck the Identifiable column next to a layer
to avoid it being queried when using the Identify Features
tool in a mode other than Current Layer. This is a handy
way to return features from only layers that are of interest for you.
If you click on feature(s), the Identify Results dialog will list information about the feature(s) clicked. The default view
is a tree view in which the first item is the name of the layer and its children are its identified feature(s). Each feature
is described by the name of a field along with its value. This field is the one set in Layer Properties ► Display. All the
other information about the feature follows.
Feature information
The Identify Results dialog can be customized to display custom fields, but by default it will display the following
information:
• The feature display name;
• Actions: Actions can be added to the identify feature windows. The action is run by clicking on the action
label. By default, only one action is added, namely View feature form for editing. You can define more
actions in the layer’s properties dialog (see Actions Properties).
• Derived: This information is calculated or derived from other information. It includes:
– general information about the feature’s geometry:
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∗ depending on the geometry type, the cartesian measurements of length, perimeter or area in the
layer’s CRS units. For 3D line vectors the cartesian line length is available.
∗ depending on the geometry type and if an ellipsoid is set in the project properties dialog for
Measurements, the ellipsoidal values of length, perimeter or area using the specified units
∗ the count of geometry parts in the feature and the number of the part clicked
∗ the count of vertices in the feature
– coordinate information, using the project properties Coordinates display settings:
∗ X and Y coordinate values of the point clicked
∗ the number of the closest vertex to the point clicked
∗ X and Y coordinate values of the closest vertex (and Z/M if applicable)
∗ if you click on a curved segment, the radius of that section is also displayed.
• Data attributes: This is the list of attribute fields and values for the feature that has been clicked.
• information about the related child feature if you defined a relation:
– the name of the relation
– the entry in reference field, e.g. the name of the related child feature
– Actions: lists actions defined in the layer’s properties dialog (see Actions Properties) and the default action
is View feature form.
– Data attributes: This is the list of attributes fields and values of the related child feature.
Poznámka: Links in the feature’s attributes are clickable from the Identify Results panel and will open in your default
web browser.
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Obr. 11.21: Identify Results dialog
The Identify Results dialog
At the top of the window, you have a handful of tools:
• Open Form
of the current feature
• Expand tree
• Collapse tree
• Expand New Results by Default
to define whether the next identified feature’s information should be collapsed or
expanded
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• Clear Results
• Copy selected feature to clipboard
• Print selected HTML response
• selection mode to use to fetch features to identify:
– Identify Features by area or single click
– Identify Features by Polygon
– Identify Features by Freehand
– Identify Features by Radius
Poznámka: When using Identify Features by Polygon
, you can right-click any existing polygon and use it to
identify overlapping features in another layer.
At the bottom of the window are the Mode and View combo boxes. Mode defines from which layers features should
be identified:
• Current layer: only features from the selected layer are identified. The layer need not be visible in the canvas.
• Top down, stop at first: only features from the upper visible layer.
• Top down: all features from the visible layers. The results are shown in the panel.
• Layer selection: opens a context menu where the user selects the layer to identify features from, similar to
a right-click. Only the chosen features will be shown in the result panel.
The View can be set as Tree, Table or Graph. ‚Table‘ and ‚Graph‘ views can only be set for raster layers.
The identify tool allows you to Auto open form for single feature results, found under Identify Settings
. If checked,
each time a single feature is identified, a form opens showing its attributes. This is a handy way to quickly edit
a feature’s attributes.
Další funkce lze nalézt v kontextovém menu identifikovaného prvku. Například, z kontextového menu můžete:
• Zobrazit tvar prvku
• Přiblížit na prvek
• Kopírovat prvek: zkopírovat všechnu geometrii a atributy prvku
• Toggle feature selection: Add identified feature to selection
• Kopírovat hodnotu atributu: zkopírovat pouze hodnotu atributu, na který kliknete
• Copy feature attributes: Copy the attributes of the feature
• Vymazat výsledek: odstranit výsledky v okně
• Vymazat zvýrazněné: odstranit z mapy zvýraznění prvků
• Zvýraznit všechny
• Zvýraznit vrstvu
• Aktivovat vrstvu: zvolit vrstvu, aby byla aktivní
• Vlastnosti vrstvy: otevřít okno s vlastnostmi vrstvy
• Rozbalit vše
• Sbalit vše
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11.6 Save and Share Layer Properties
11.6.1 Managing Custom Styles
When a vector layer is added to the map canvas, QGIS by default uses a random symbol/color to render its features.
However, you can set a default symbol in Project ► Properties… ► Default styles that will be applied to each newly
added layer according to its geometry type.
Most of the time, though, you’d rather have a custom and more complex style that can be applied automatically or
manually to the layers (with less effort). You can achieve this by using the Style menu at the bottom of the Layer
Properties dialog. This menu provides you with functions to create, load and manage styles.
A style stores any information set in the layer properties dialog to render or interact with the layer (including
symbology, labeling, fields and form definitions, actions, diagrams…) for vector layers, or the pixels (band or color
rendering, transparency, pyramids, histogram …) for raster.
Obr. 11.22: Vector layer style combo box options
By default, the style applied to a loaded layer is named default. Once you have got the ideal and appropriate
rendering for your layer, you can save it by clicking the Style combo box and choosing:
• Rename Current: The active style is renamed and updated with the current options
• Add: A new style is created using the current options. By default, it will be saved in the QGIS project file. See
below to save the style in another file or a database
• Remove: Delete unwanted style, in case you have more than one style defined for the layer.
At the bottom of the Style drop-down list, you can see the styles set for the layer with the active one checked.
Note that each time you validate the layer properties dialog, the active style is updated with the changes you’ve made.
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You can create as many styles as you wish for a layer but only one can be active at a time. In combination with Map
Themes, this offers a quick and powerful way to manage complex projects without the need to duplicate any layer in
the map legend.
Poznámka: Given that whenever you apply modifications to the layer properties, changes are stored in the active
style, always ensure you are editing the right style to avoid mistakenly altering a style used in a map theme.
Tip: Manage styles from layer context menu
Right-click on the layer in the Layers panel to copy, paste, add or rename layer styles.
11.6.2 Storing Styles in a File or a Database
While styles created from the Style combo box are by default saved inside the project and can be copied and pasted
from layer to layer in the project, it’s also possible to save them outside the project so that they can be loaded in
another project.
Save as text file
Clicking the Style ► Save Style, you can save the style as a:
• QGIS layer style file (.qml)
• SLD file (.sld), only available for vector layers
Used on file-based format layers (.shp, .tab…), Save as Default generates a .qml file for the layer (with the
same name). SLDs can be exported from any type of renderer – single symbol, categorized, graduated or rule-based
– but when importing an SLD, either a single symbol or rule-based renderer is created. This means that categorized
or graduated styles are converted to rule-based. If you want to preserve those renderers, you have to use the QML
format. On the other hand, it can be very handy sometimes to have this easy way of converting styles to rule-based.
Save in database
Vector layer styles can also be stored in a database if the layer datasource is a database provider. Supported
formats are PostGIS, GeoPackage, SpatiaLite, MSSQL and Oracle. The layer style is saved inside a table (named
layer_styles) in the database. Click on Save Style… ► Save in database then fill in the dialog to define a style
name, add a description, a .ui file if applicable and to check if the style should be the default style.
You can save several styles for a single table in the database. However, each table can have only one default style.
Default styles can be saved in the layer database or in qgis.db, a local SQLite database in the active user profile
directory.
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Obr. 11.23: Save Style in database Dialog
Tip: Sharing style files between databases
You can only save your style in a database if the layer comes from such a database. You can’t mix databases (layer
in Oracle and style in MSSQL for instance). Use instead a plain text file if you want the style to be shared among
databases.
Poznámka: You may encounter issues restoring the layer_styles table from a PostgreSQL database backup.
Follow QGIS layer_style table and database backup to fix that.
Load style
When loading a layer in QGIS, if a default style already exists for this layer, QGIS loads the layer with this style. Also
Style ► Restore Default looks for and loads that file, replacing the layer’s current style.
Style ► Load Style helps you apply any saved style to a layer. While text-file styles (.sld or .qml) can be applied to
any layer whatever its format, loading styles stored in a database is only possible if the layer is from the same database
or the style is stored in the QGIS local database.
The Database Styles Manager dialog displays a list of styles related to the layer found in the database and all the other
styles saved in it, with name and description.
Tip: Quickly share a layer style within the project
You can also share layer styles within a project without importing a file or database style: right-click on the layer in
the Layers Panel and, from the Styles combo box , copy the style of a layer and paste it to a group or a selection of
layers: the style is applied to all the layers that are of the same type (vector vs raster) as the original layer and, in the
case of vector layers, have the same geometry type (point, line or polygon).
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11.6.3 Layer definition file
Layer definitions can be saved as a Layer Definition File (.qlr) using Export ► Save As Layer Definition
File… in the active layers‘ context menu. A layer definition file (.qlr) includes references to the data source of the
layers and their styles. .qlr files are shown in the Browser Panel and can be used to add the layers (with the saved
style) to the Layers Panel. You can also drag and drop .qlr files from the system file manager into the map canvas.
11.7 Storing values in Variables
In QGIS, you can use variables to store useful recurrent values (e.g. the project’s title, or the user’s full name) that
can be used in expressions. Variables can be defined at the application’s global level, project level, layer level, layout
level, and layout item’s level. Just like CSS cascading rules, variables can be overwritten - e.g., a project level variable
will overwrite any application global level variables set with the same name. You can use these variables to build
text strings or other custom expressions using the @ character before the variable name. For example in print layout
creating a label with this content:
This map was made using QGIS [% @qgis_version %]. The project file for this
map is: [% @project_path %]
Will render the label like this:
This map was made using QGIS 3.4.4-Madeira. The project file for this map is:
/gis/qgis-user-conference-2019.qgs
Besides the preset read-only variables, you can define your own custom variables for any of the levels mentioned
above. You can manage:
• global variables from the Settings ► Options menu
• project variables from the Project Properties dialog (see Vlastnosti projektu)
• vector layer variables from the Layer Properties dialog (see The Vector Properties Dialog);
• layout variables from the Layout panel in the Print layout (see The Layout Panel);
• and layout item variables from the Item Properties panel in the Print layout (see Layout Items Common
Options).
To differentiate from editable variables, read-only variable names and values are displayed in italic. On the other
hand, higher level variables overwritten by lower level ones are strike through.
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Obr. 11.24: Variables editor at the project level
Poznámka: You can read more about variables and find some examples in Nyall Dawson’s Exploring variables in
QGIS 2.12, part 1, part 2 and part 3 blog posts.
11.8 Authentication
QGIS has the facility to store/retrieve authentication credentials in a secure manner. Users can securely save
credentials into authentication configurations, which are stored in a portable database, can be applied to server or
database connections, and are safely referenced by their ID tokens in project or settings files. For more information
see Ověřovací systém.
A master password needs to be set up when initializing the authentication system and its portable database.
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11.9 Common widgets
In QGIS, there are some options you’ll often have to work with. For convenience, QGIS provides you with special
widgets that are presented below.
11.9.1 Výběr barvy
The color dialog
The Select Color dialog will appear whenever you click the icon to choose a color. The features
of this dialog depend on the state of the Use native color chooser dialogs parameter checkbox in Settings ► Options…
► General. When checked, the color dialog used is the native one of the OS on which QGIS is running. Otherwise,
the QGIS custom color chooser is used.
The custom color chooser dialog has four different tabs which allow you to select colors by Color ramp
, Color wheel
,
Color swatches
or Color picker
. With the first two tabs, you can browse to all possible color combinations and apply
your choice to the item.
Obr. 11.25: Tabulka rozsahu výběru barvy
In the Color swatches
tab, you can choose from a list of color palettes (see Colors Settings for details). All but the
Recent colors palette can be modified with the Add current color
and Remove selected color
buttons at the bottom of
the frame.
The … button next to the palette combo box also offers several options to:
• copy, paste, import or export colors
• create, import or remove color palettes
• add the custom palette to the color selector widget with the Show in Color Buttons item (see Obr. 11.27)
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Obr. 11.26: Color selector swatches tab
Another option is to use the Color picker
which allows you to sample a color from under your mouse cursor at any
part of the QGIS UI or even from another application: press the space bar while the tab is active, move the mouse
over the desired color and click on it or press the space bar again. You can also click the Sample Color button to
activate the picker.
Whatever method you use, the selected color is always described through color sliders for HSV (Hue, Saturation,
Value) and RGB (Red, Green, Blue) values. The color is also identifiable in HTML notation.
Modifying a color is as simple as clicking on the color wheel or ramp or on any of the color parameters sliders. You
can adjust such parameters with the spinbox beside or by scrolling the mouse wheel over the corresponding slider.
You can also type the color in HTML notation. Finally, there is an Opacity slider to set transparency level.
The dialog also provides a visual comparison between the Old color (applied to object) and the Current one (being
selected). Using drag-and-drop or pressing the Add color to swatch
button, any of these colors can be saved in a slot
for easy access.
Tip: Quick color modification
Drag-and-drop a color selector widget onto another one to apply its color.
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The color drop-down shortcut
Click the drop-down arrow to the right of the color button to display a widget for quick color
selection. This shortcut provides access to:
• a color wheel to pick a color from
• an alpha slider to change color opacity
• the color palettes previously set to Show in Color Buttons
• copy the current color and paste it into another widget
• pick a color from anywhere on your computer display
• choose a color from the color selector dialog
• drag-and-drop the color from one widget to another for quick modification
Poznámka: When the color widget is set to a project color through the data-defined override properties, the above
functions for changing the color are unavailable. You’d first need to Unlink color or Clear the definition.
Obr. 11.27: Quick color selector menu
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The color ramp drop-down shortcut
Color ramps are a practical way to apply a set of colors to one or many features. Their creation is described in the Setting
a Color Ramp section. As for the colors, pressing the color ramp button opens the corresponding color
ramp type dialog allowing you to change its properties.
Obr. 11.28: Customizing a colorbrewer ramp
The drop-down menu to the right of the button gives quick access to a wider set of color ramps and options:
• Invert Color Ramp
• a preview of the gradient or catalog: cpt-city color ramps flagged as Favorites in the Style
Manager dialog
• All Color Ramps to access the compatible color ramps database
• Create New Color Ramp… of any supported type that could be used in the current widget (note that this color
ramp will not be available elsewhere unless you save it in the library)
• Edit Color Ramp…, the same as clicking the whole color ramp button
• Save Color Ramp…, to save the current color ramp with its customizations in the style library
Obr. 11.29: Quick color ramp selection widget
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11.9.2 Symbol Widget
The Symbol selector widget is a convenient shortcut when you want to set symbol properties of a feature. Clicking
the drop-down arrow shows the following symbol options, together with the features of the color drop-down widget:
• Configure Symbol…: the same as pressing the symbol selector widget. It opens a dialog to set the symbol
parameters.
• Copy Symbol from the current item
• Paste Symbol to the current item, speeding configuration
11.9.3 Font Selector
The Font selector widget is a convenient shortcut when you want to set font properties for textual information (feature
labels, decoration labels, map legend text, …). Clicking the drop-down arrow shows some or all of the following
options:
Obr. 11.30: Font selector drop-down menu
• Font Size in the associated unit
• Recent Fonts ► menu with the active font checked (at the top)
• Configure Format…: same as pressing the font selector widget. It opens a dialog to set text format parameters.
Depending on the context, it can be the OS default Text format dialog or the QGIS custom dialog with advanced
formatting options (opacity, orientation, buffer, background, shadow, …) as described in section Formatting
the label text.
• Copy Format of the text
• Paste Format to the text, speeding configuration
• the color widget for quick color setting
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11.9.4 Unit Selector
Size properties of the items (labels, symbols, layout elements, …) in QGIS are not necessarily bound to either the
project units or the units of a particular layer. For a large set of properties, the Unit selector drop-down menu allows
you to tweak their values according to the rendering you want (based on screen resolution, paper size, or the terrain).
Available units are:
• Millimeters
• Points
• Pixels
• Inches
• Meters at Scale: This allows you to always set the size in meters, regardless of what the underlying map units are
(e.g. they can be in inches, feet, geographic degrees, …). The size in meters is calculated based on the current
project ellipsoid setting and a projection of the distances in meters at the center of the current map extent.
• and Map Units: The size is scaled according to the map view scale. Because this can lead to too big or too small
values, use the button next to the entry to constrain the size to a range of values based on:
– The Minimum scale and the Maximum scale: The value is scaled based on the map view scale until you
reach any of these scale limits. Out of the range of scale, the value at the nearest scale limit is kept.
– and/or The Minimum size and the Maximum size in mm: The value is scaled based on the map view scale
until it reaches any of these limits; Then the limit size is kept.
Obr. 11.31: Adjust scaling range dialog
11.9.5 Number Formatting
Numeric formatters allow formatting of numeric values for display, using a variety of different formatting techniques
(for instance scientific notation, currency values, percentage values, etc). One use of this is to set text in a layout scale
bar or fixed table.
Different categories of formats are supported. For most of them, you can set part or all of the following numeric
options:
• Show thousands separator
• Show plus sign
• Show trailing zeros
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But they can also have their custom settings. Provided categories are:
• General, the default category: has no setting and displays values as set in the parent widget properties or using
the global settings.
• Number
– The value can be Round to a self defined number of Decimal places or their Significant figures
– customize the Thousands separator and Decimal separator
• Bearing for a text representation of a direction/bearing using:
– Format: possible ranges of values are 0 to 180°, with E/W suffix, -180 to +180° and
0 to 360°
– number of Decimal places
• Currency for a text representation of a currency value.
– Prefix
– Suffix
– number of Decimal places
• Fraction for a vulgar fractional representation of a decimal value (e.g. 1/2 instead of 0.5)
– Use unicode super/subscript to show. For example 1/2
instead of 1/2
– Use dedicated Unicode characters
– customize the Thousands separator
• Percentage - appends % to the values, with setting of:
– number of Decimal places
– Scaling to indicate whether the actual values already represent percentages (then they will be kept as is)
or fractions (then they are converted)
• Scientific notation in the form 2.56e+03. The number of Decimal places can be set.
A live preview of the settings is displayed under the Sample section.
11.9.6 Režim míchání
QGIS offers different options for special rendering effects with these tools that you may previously only know from
graphics programs. Blending modes can be applied on layers and features, and also on print layout items:
• Normal: This is the standard blend mode, which uses the alpha channel of the top pixel to blend with the pixel
beneath it. The colors aren’t mixed.
• Lighten: This selects the maximum of each component from the foreground and background pixels. Be aware
that the results tend to be jagged and harsh.
• Screen: Light pixels from the source are painted over the destination, while dark pixels are not. This mode
is most useful for mixing the texture of one item with another item (such as using a hillshade to texture another
layer).
• Dodge: Brighten and saturate underlying pixels based on the lightness of the top pixel. Brighter top pixels cause
the saturation and brightness of the underlying pixels to increase. This works best if the top pixels aren’t too
bright. Otherwise the effect is too extreme.
• Addition: Adds pixel values of one item to the other. In case of values above the maximum value (in the case
of RGB), white is displayed. This mode is suitable for highlighting features.
• Darken: Retains the lowest values of each component of the foreground and background pixels. Like lighten,
the results tend to be jagged and harsh.
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• Multiply: Pixel values of the top item are multiplied with the corresponding values for the bottom item. The
results are darker.
• Burn: Darker colors in the top item cause the underlying items to darken. Burn can be used to tweak and
colorize underlying layers.
• Overlay: Combines multiply and screen blending modes. Light parts become lighter and dark parts become
darker.
• Soft light: Very similar to overlay, but instead of using multiply/screen it uses color burn/dodge. This
is supposed to emulate shining a soft light onto an image.
• Hard light: Hard light is also very similar to the overlay mode. It’s supposed to emulate projecting a very
intense light onto an image.
• Difference: Subtracts the top pixel from the bottom pixel, or the other way around, in order always to get
a positive value. Blending with black produces no change, as the difference with all colors is zero.
• Subtract: Subtracts pixel values of one item from the other. In the case of negative values, black is displayed.
11.9.7 Data defined override setup
Next to many options in the vector layer properties dialog or settings in the print layout, you will find a
Data defined override
icon. Using expressions based on layer attributes or item settings, prebuilt or custom functions and
variables, this tool allows you to set dynamic values for parameters. When enabled, the value returned by this widget
is applied to the parameter regardless of its normal value (checkbox, textbox, slider…).
The data defined override widget
Clicking the Data defined override
icon shows the following entries:
• Description… that indicates if the option is enabled, which input is expected, the valid input type and the current
definition. Hovering over the widget also pops up this information.
• Store data in the project: a button allowing the property to be stored using to the Auxiliary Storage Properties
mechanism.
• Field type: an entry to select from the layer’s fields that match the valid input type.
• Color: when the widget is linked to a color property, this menu gives access to the colors defined as part of the
current project’s colors scheme.
• Variable: a menu to access the available user-defined variables
• Edit… button to create or edit the expression to apply, using the Expression String Builder dialog. To help you
correctly fill in the expression, a reminder of the expected output’s format is provided in the dialog.
• Paste and Copy buttons.
• Clear button to remove the setup.
• For numeric and color properties, Assistant… to rescale how the feature data is applied to the property (more
details below)
Tip: Use right-click to (de)activate the data override
When the data-defined override option is set up correctly the icon is yellow or . If it is broken, the icon is red
or .
You can enable or disable a configured data-defined override
button by simply clicking the widget with the right mouse
button.
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Using the data-defined assistant interface
When the Data-defined override
button is associated with a numeric or color parameter, it has an Assistant… option
that allows you to change how the data is applied to the parameter for each feature. The assistant allows you to:
• Define the Input data, ie:
– the attribute to represent, using the Field listbox or the Set column expression
function (see Výrazy)
– the range of values to represent: you can manually enter the values or use the Fetch value range from layer
button to fill these fields automatically with the minimum and maximum values returned by the chosen
attribute or the expression applied to your data
• Apply transform curve: by default, output values (see below for setting) are applied to input features
following a linear scale. You can override this logic: enable the transform option, click on the graphic to add
break point(s) and drag the point(s) to apply a custom distribution.
• Define the Output values: the options vary according to the parameter to define. You can globally set:
– the minimum and maximum values to apply to the selected property (n case of a color setting, you’ll need
to provide a color ramp)
– the Scale method of representation which can be Flannery, Exponential, Surface or Radius
– the Exponent to use for data scaling
– the output value or color to represent features with NULL values
When compatible with the property, a live-update preview is displayed in the right-hand side of the dialog to help
you control the value scaling.
Obr. 11.32: The data-defined size assistant
The values presented in the varying size assistant above will set the size ‚Data-defined override‘ with:
coalesce(scale_exp(Importance, 1, 20, 2, 10, 0.57), 1)
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KAPITOLA 12
The Style Library
12.1 The Style Manager
12.1.1 The Style Manager dialog
The Style Manager is the place where you can manage and create generic style items. These are symbols, color ramps,
text formats or label settings that can be used to symbolize features, layers or print layouts. They are stored in the
symbology-style.db database under the active user profile and shared with all the project files opened with
that profile. Style items can also be shared with others thanks to the export/import capabilities of the Style Manager
dialog.
You can open that modeless dialog either:
• from the Settings ► Style Manager… menu
• with the Style Manager
button from the Project toolbar
• or with the Style Manager
button from a vector Layer Properties ► menu (while configuring a symbol or
formatting a text).
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Obr. 12.1: The Style Manager
Organizing style items
The Style Manager dialog displays in its center a frame with previewed items organized into tabs:
• All for a complete collection of point, linear and surface symbols and label settings as well as predefined color
ramps and text formats;
• Marker for point symbols only;
• Line for linear symbols only;
• Fill for surface symbols only;
• Color ramp;
• Text format to manage text formats, which store the font, color, buffers, shadows, and backgrounds of texts
(i.e. all the formatting parts of the label settings, which for instance can be used in layouts);
• Label settings to manage label settings, which include the text formats and some layer-type specific settings
such as label placement, priority, callouts, rendering…
• 3D Symbols to configure symbols with 3D properties (extrusion, shading, altitude, …) for the features to
render in a 3D Map view
For each family of items, you can organize the elements into different categories, listed in the panel on the left:
• Favorites: displayed by default when configuring an item, it shows an extensible set of items;
• All: lists all the available items for the active type;
• Tags: shows a list of labels you can use to identify the items. An item can be tagged more than once. Select
a tag in the list and the tabs are updated to show only their items that belong to it. To create a new tag you could
later attach to a set of items, use the Add Tag… button or select the Add Tag… from any tag contextual
menu;
• Smart Group: a smart group dynamically fetches its symbols according to conditions set (see eg, Obr. 12.2).
Click the Add Smart Group… button to create smart groups. The dialog box allows you to enter an expression
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to filter the items to select (has a particular tag, have a string in its name, etc.). Any symbol, color ramp, text
format or label setting that satisfies the entered condition(s) is automatically added to the smart group.
Obr. 12.2: Creating a Smart Group
Tags and smart groups are not mutually exclusive: they are simply two different ways to organize your style elements.
Unlike the smart groups that automatically fetch their belonged items based on the input constraints, tags are filled
by the user. To edit any of those categories, you can either:
• select the items, right-click and choose Add to Tag ► and then select the tag name or create a new tag;
• select the tag and press Modify group… ► Attach Selected Tag to Symbols. A checkbox appears next to each
item to help you select or deselect it. When selection is finished, press Modify group… ► Finish Tagging.
• select the smart group, press Modify group… ► Edit smart group… and configure a new set of constraints in
the Smart Group Editor dialog. This option is also available in the contextual menu of the smart group.
To remove a tag or a smart group, right-click on it and select the Remove button. Note that this does not delete
the items grouped in the category.
Adding, editing or removing an item
As seen earlier, style elements are listed under different tabs whose contents depend on the active category (tag, smart
group, favorites…). When a tab is enabled, you can:
• Add new items: press the Add item
button and configure the item following symbols, color ramps or text
format and label builder description.
• Modify an existing item: select an item and press Edit item
button and configure as mentioned above.
• Delete existing items: to delete an element you no longer need, select it and click Remove item
(also available
through right-click). The item will be deleted from the local database.
Note that the All tab provides access to these options for every type of item.
Right-clicking over a selection of items also allows you to:
• Add to Favorites;
• Remove from Favorites;
• Add to Tag ► and select the appropriate tag or create a new one to use; the currently assigned tags are checked;
• Clear Tags: detaching the symbols from any tag;
• Remove Item(s);
• Edit Item: applies to the item you right-click over;
• Copy Item;
• Paste Item …: pasting to one of the categories of the style manager or elsewhere in QGIS (symbol or color
buttons)
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• Export Selected Symbol(s) as PNG… (only available with symbols);
• Export Selected Symbol(s) as SVG… (only available with symbols);
Sharing style items
The Import/Export tool, at the left bottom of the Style Manager dialog, offers options to easily share symbols,
color ramps, text formats and label settings with others. These options are also available through right-click over the
items.
Exporting items
You can export a set of items to an .XML file:
1. Expand the Import/Export drop-down menu and select Export Item(s)…
2. Choose the items you’d like to integrate. Selection can be done with the mouse or using a tag or a group
previously set.
3. Press Export when ready. You’ll be prompted to indicate the destination of the saved file. The XML format
generates a single file containing all the selected items. This file can then be imported in another user’s style
library.
Obr. 12.3: Exporting style items
When symbols are selected, you can also export them to .PNG or .SVG. Exporting to .PNG or .SVG (both not
available for other style item types) creates a file for each selected symbol in a given folder. The SVG folder can be
added to the SVG paths in Settings ► Options ► System menu of another user, allowing him direct access to all these
symbols.
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Importing items
You can extend your style library by importing new items:
1. Expand the Import/Export drop-down menu and select Import Item(s) at the left bottom of the dialog.
2. In the new dialog, indicate the source of the style items (it can be an .xml file on the disk or a url).
3. Set whether to Add to favorites the items to import.
4. Check Do not import embedded tags to avoid the import of tags associated to the items being imported.
5. Give the name of any Additional tag(s) to apply to the new items.
6. Select from the preview the symbols you want to add to your library.
7. And press Import.
Obr. 12.4: Importing style items
Using the Browser panel
It’s also possible to import style items into the active user profile style database directly from the Browser panel:
1. Select the style .xml file in the browser
2. Drag-and-drop it over the map canvas or right-click and select Import Style…
3. Fill the Import Items dialog following Importing items
4. Press Import and the selected style items are added to the style database
Double-clicking the style file in the browser opens the Style Manager dialog showing the items in the file. You can
select them and press Copy to Default Style… to import them into the active style database. Tags can be assigned to
items. Also available through right-click, Open Style… command.
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Obr. 12.5: Opening a style items file
The dialog also allows to export single symbols as .PNG or .SVG files.
12.1.2 Setting a Color Ramp
The Color ramp tab in the Style Manager dialog helps you preview different color ramps based on the category selected
in the left panel.
To create a custom color ramp, activate the Color ramp tab and click the Add item
button. The button reveals
a drop-down list to choose the ramp type:
• Gradient: given a start and end colors, generate a color ramp which can be continuous or discrete. With
double-clicking the ramp preview, you can add as many intermediate color stops as you want.
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Obr. 12.6: Example of custom gradient color ramp with multiple stops
• Color presets: allows to create a color ramp consisting of a list of colors selected by the user;
• Random: creates a random set of colors based on range of values for Hue, Saturation, Value and Opacity and
a number of colors (Classes);
• Catalog: ColorBrewer: a set of predefined discrete color gradients you can customize the number of colors in
the ramp;
• or Catalog: cpt-city: an access to a whole catalog of color gradients to locally save as standard gradient. The
cpt-city option opens a new dialog with hundreds of themes included ‚out of the box‘.
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Obr. 12.7: cpt-city dialog with hundreds of color ramps
Tip: Easily adjust the color stops of the gradient color ramp
Double-clicking the ramp preview or drag-and-drop a color from the color spot onto the ramp preview adds a new
color stop. Each color stop can be tweaked using the Výběr barvy widgets or by plotting each of its parameters. You
can also reposition it using the mouse, the arrow keys (combine with Shift key for a larger move) or the Relative
position spinbox. Pressing Delete stop as well as DEL key removes the selected color stop.
12.2 The Symbol Selector
The Symbol selector is the main dialog to design a symbol. You can create or edit Marker, Line or Fill Symbols.
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Obr. 12.8: Designing a Line symbol
Two main components structure the symbol selector dialog:
• the symbol tree, showing symbol layers that are combined afterwards to shape a new global symbol
• and settings to configure the selected symbol layer in the tree.
12.2.1 The symbol layer tree
A symbol can consist of several Symbol layers. The symbol tree shows the overlay of these symbol layers that are
combined afterwards to shape a new global symbol. Besides, a dynamic symbol representation is updated as soon
as symbol properties change.
Depending on the level selected in the symbol tree items, various tools are made available to help you manage the
tree:
• add new symbol layer: you can stack as many symbols as you want
• remove the selected symbol layer
• lock colors of symbol layer: a locked color stays unchanged when user changes the color at the global (or
upper) symbol level
• duplicate a (group of) symbol layer(s)
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• move up or down the symbol layer
12.2.2 Configuring a symbol
In QGIS, configuring a symbol is done in two steps: the symbol and then the symbol layer.
The symbol
At the top level of the tree, it depends on the layer geometry and can be of Marker, Line or Fill type. Each symbol
can embed one or more symbols (including, of any other type) or symbol layers.
You can setup some parameters that apply to the global symbol:
• Unit: it can be Millimeters, Points, Pixels, Meters at Scale, Map units or Inches (see Unit Selector for more
details)
• Opacity
• Color: when this parameter is changed by the user, its value is echoed to all unlocked sub-symbols color
• Size and Rotation for marker symbols
• Width for line symbols
Tip: Use the Size (for marker symbols) or the Width (for line symbols) properties at the symbol level to
proportionally resize all of its embedded symbol layers dimensions.
Poznámka: The Data-defined override button next to the width, size or rotation parameters is inactive when
setting the symbol from the Style manager dialog. When the symbol is connected to a map layer, this button
helps you create proportional or multivariate analysis rendering.
• A preview of the symbols library: Symbols of the same type are shown and, through the editable drop-down
list just above, can be filtered by free-form text or by categories. You can also update the list of symbols using
the Style Manager
button and open the eponym dialog. There, you can use any capabilities as exposed in The
Style Manager section.
The symbols are displayed either:
– in an icon list (with thumbnail, name and associated tags) using the List View
button below the frame;
– or as icon preview using the Icon View
button.
• Press the Save Symbol button to add the symbol being edited to the symbols library.
• With the Advanced option, you can:
– for line and fill symbols, Clip features to canvas extent.
– for fill symbols, Force right-hand rule orientation: allows forcing rendered fill symbols to follow the
standard „right hand rule“ for ring orientation (i.e, polygons where the exterior ring is clockwise, and
the interior rings are all counter-clockwise).
The orientation fix is applied while rendering only, and the original feature geometry is unchanged. This
allows for creation of fill symbols with consistent appearance, regardless of the dataset being rendered
and the ring orientation of individual features.
– Depending on the symbology of the layer a symbol is being applied to, additional settings are available in
the Advanced menu:
∗ Symbol levels… to define the order of symbols rendering
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∗ Data-defined Size Legend
∗ Match to Saved Symbols… and Match to Symbols from File… to automatically assign symbols to
classes
The symbol layer
At a lower level of the tree, you can customize the symbol layers. The available symbol layer types depend on the
upper symbol type. You can apply on the symbol layer paint effects to enhance its rendering.
Because describing all the options of all the symbol layer types would not be possible, only particular and significant
ones are mentioned below.
Common parameters
Some common options and widgets are available to build a symbol layer, regardless it’s of marker, line or fill sub-type:
• the color selector widget to ease color manipulation
• Units: it can be Millimeters, Points, Pixels, Meters at Scale, Map units or Inches (see Unit Selector for
more details)
• the data-defined override
widget near almost all options, extending capabilities of customizing each symbol (see
Data defined override setup for more information)
• the Enable symbol layer option controls the symbol layer’s visibility. Disabled symbol layers are not drawn
when rendering the symbol but are saved in the symbol. Being able to hide symbol layers is convenient when
looking for the best design of your symbol as you don’t need to remove any for the testing. The data-defined
override then makes it possible to hide or display different symbol layers based on expressions (using, for
instance, feature attributes).
• the Draw effects button for effects rendering.
Poznámka: While the description below assumes that the symbol layer type is bound to the feature geometry,
keep in mind that you can embed symbol layers in each others. In that case, the lower level symbol layer parameter
(placement, offset…) might be bound to the upper-level symbol, and not to the feature geometry itself.
Marker Symbols
Appropriate for point geometry features, marker symbols have several Symbol layer types:
• Simple marker (default)
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Obr. 12.9: Designing a Simple Marker Symbol
• Ellipse marker: a simple marker symbol layer, with customizable width and height
• Filled marker: similar to the simple marker symbol layer, except that it uses a fill sub symbol to render the
marker. This allows use of all the existing QGIS fill (and stroke) styles for rendering markers, e.g. gradient or
shapeburst fills.
• Font marker: similar to the simple marker symbol layer, except that it uses installed fonts to render the marker.
Its additional properties are:
– Font family
– Font style
– Character(s), representing the text to display as symbol. They can be typed in or selected from the font
characters collection widget and you can live Preview them with the selected settings.
• Geometry generator (see The Geometry Generator)
• Mask: its sub-symbol defines a mask shape whose color property will be ignored and only the opacity will be
used. This is convenient when the marker symbol overlaps with labels or other symbols whose colors are close,
making it hard to decipher. More details at Masks Properties.
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• Raster image marker: use an image (PNG, JPG, BMP …) as marker symbol. The image can be a file on the
disk, a remote URL or embedded in the style database (more details). Width and height of the image can be set
independently or using the Lock aspect ratio
. The size can be set using any of the common units or as a percentage
of the image’s original size (scaled by the width).
• Vector Field marker (see The Vector Field Marker)
• SVG marker: provides you with images from your SVG paths (set in Settings ► Options… ► System menu) to
render as marker symbol. Width and height of the symbol can be set independently or using the Lock aspect ratio
.
Each SVG file colors and stroke can also be adapted. The image can be a file on the disk, a remote URL or
embedded in the style database (more details).
Poznámka: SVG version requirements
QGIS renders SVG files that follow the SVG Tiny 1.2 profile, intended for implementation on a range of
devices, from cellphones and PDAs to laptop and desktop computers, and thus includes a subset of the features
included in SVG 1.1 Full, along with new features to extend the capabilities of SVG.
Some features not included in these specifications might not be rendered correctly in QGIS.
Tip: Enable SVG marker symbol customization
To have the possibility to change the colors of a SVG marker, you have to add the placeholders param(fill)
for fill color, param(outline) for stroke color and param(outline-width) for stroke width. These
placeholders can optionally be followed by a default value, e.g.:
<svg width="100%" height="100%">
<rect fill="param(fill) #ff0000" stroke="param(outline) #00ff00" stroke-width=
→"param(outline-width) 10" width="100" height="100">
</rect>
</svg>
Line Symbols
Appropriate for line geometry features, line symbols have the following symbol layer types:
• Simple line (default): available settings are:
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Obr. 12.10: Designing a Simple Line Symbol
The simple line symbol layer type has many of the same properties as the simple marker symbol, and in addition:
– Cap style
– Use custom dash pattern: overrides the Stroke style setting with a custom dash.
– Align dash pattern to line length: the dash pattern length will be adjusted so that the line will end with
a complete dash element, instead of a gap.
– Tweak dash pattern at sharp corners: dynamically adjusts the dash pattern placement so that sharp
corners are represented by a full dash element coming into and out of the sharp corner. Dependent on
Align dash pattern to line length.
– Draw line only inside polygon
• Arrow: draws lines as curved (or not) arrows with a single or a double head with configurable (and data-defined):
– Head type
– Arrow type
– Arrow width
– Arrow width at start
– Head length
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– Head thickness
– Offset
It is possible to create Curved arrows (the line feature must have at least three vertices) and Repeat
arrow on each segment. It also uses a fill symbol such as gradients or shapeburst to render the arrow body.
Combined with the geometry generator, this type of layer symbol helps you representing flow maps.
• Geometry generator (see The Geometry Generator)
• Marker line: repeats a marker symbol over the length of a line.
– The markers placement can be at a regular distance or based on the line geometry: first, last or each
vertex, on the central point of the line or of each segment, or on every curve point.
– The markers placement can also be given an offset along the line
– The Rotate marker to follow line direction option sets whether each marker symbol should be oriented
relative to the line direction or not.
Because a line is often a succession of segments of different directions, the rotation of the marker
is calculated by averaging over a specified distance along the line. For example, setting the Average angle
over property to 4mm means that the two points along the line that are 2mm before and after the symbol
placement are used to calculate the line angle for that marker symbol. This has the effect of smoothing
(or removing) any tiny local deviations from the overall line direction, resulting in much nicer visual
orientations of the marker line symbols.
– The marker line can also be offset from the line itself.
• Hashed line: repeats a line segment (a hash) over the length of a line symbol, with a line sub-symbol used to
render each individual segment. In other words, a hashed line is like a marker line in which marker symbols
are replaced with segments. As such, the hashed lines have the same properties as marker line symbols, along
with:
– Hash length
– Hash rotation
– Rotate hash to follow line direction
Obr. 12.11: Examples of hashed lines
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Fill Symbols
Appropriate for polygon geometry features, fill symbols have also several symbol layer types:
• Simple fill (default): fills a polygon with a uniform color
Obr. 12.12: Designing a Simple Fill Symbol
• Centroid fill: places a marker symbol at the centroid of the visible feature. The position of the marker may
not be the real centroid of the feature, because calculation takes into account the polygon(s) clipped to area
visible in map canvas for rendering and ignores holes. Use the geometry generator symbol if you want the exact
centroid.
You can:
– Force point inside polygon
– Draw point on every part of multi-part feature or place the point only on its biggest part
– display the marker symbol(s) in whole or in part, keeping parts overlapping the current feature geometry
(Clip markers to polygon boundary) or the geometry part the symbol belongs to (Clip markers to current
part boundary only)
• Geometry generator (see The Geometry Generator)
• Gradient fill: uses a radial, linear or conical gradient, based on either simple two color gradients or a predefined
gradient color ramp to fill polygons. The gradient can be rotated and applied on a single feature basis or across
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the whole map extent. Also start and end points can be set via coordinates or using the centroid (of feature or
map). A data-defined offset can be defined;
• Line pattern fill: fills the polygon with a hatching pattern of line symbol layer. You can set a rotation, the
spacing between lines and an offset from the feature boundary;
• Point pattern fill: fills the polygon with a hatching pattern of marker symbol layer. You can set the distance
and a displacement between rows of markers, and an offset from the feature boundary;
• Random marker fill: fills the polygon with a marker symbol placed at random locations within the polygon
boundary. You can set:
– the number of marker symbols to render, either as an absolute count or as density-based (the fill density
will remain the same on different scale / zoom levels)
– an optional random number seed, to give consistent placement of markers whenever maps are refreshed
(also allows random placement to play nice with QGIS server and tile-based rendering)
– whether markers rendered near the edges of polygons should be clipped to the polygon boundary or not
• Raster image fill: fills the polygon with tiles from a raster image (PNG JPG, BMP …). The image can be
a file on the disk, a remote URL or an embedded file encoded as a string (more details). Options include (data
defined) opacity, image width, coordinate mode (object or viewport), rotation and offset. The image width can
be set using any of the common units or as a percentage of the original size.
• SVG fill: fills the polygon using SVG markers;
• Shapeburst fill: buffers a gradient fill, where a gradient is drawn from the boundary of a polygon towards the
polygon’s centre. Configurable parameters include distance from the boundary to shade, use of color ramps or
simple two color gradients, optional blurring of the fill and offsets;
• Outline: Arrow: uses a line arrow symbol layer to represent the polygon boundary. The settings for the outline
arrow are the same as for line symbols.
• Outline: Hashed line: uses a hash line symbol layer to represent the polygon boundary (the interior rings, the
exterior ring or all the rings). The settings for the outline hashed line are the same as for line symbols.
• Outline: Marker line: uses a marker line symbol layer to represent the polygon boundary (the interior rings,
the exterior ring or all the rings). The settings for the outline marker line are same as for line symbols.
• Outline: simple line: uses a simple line symbol layer to represent the polygon boundary (the interior rings,
the exterior ring or all the rings). The settings for the outline simple line are the same as for line symbols.
The Draw line only inside polygon option displays the polygon borders inside the polygon and can be useful to
clearly represent adjacent polygon boundaries.
Poznámka: When geometry type is polygon, you can choose to disable the automatic clipping of lines/polygons to
the canvas extent. In some cases this clipping results in unfavourable symbology (e.g. centroid fills where the centroid
must always be the actual feature’s centroid).
The Geometry Generator
Available with all types of symbols, the geometry generator symbol layer allows to use expression syntax to generate
a geometry on the fly during the rendering process. The resulting geometry does not have to match with the original
geometry type and you can add several differently modified symbol layers on top of each other.
Some examples:
-- render the centroid of a feature
centroid( $geometry )
-- visually overlap features within a 100 map units distance from a point
-- feature, i.e generate a 100m buffer around the point
(continues on next page)
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(pokračujte na předchozí stránce)
buffer( $geometry, 100 )
-- Given polygon layer1( id1, layer2_id, ...) and layer2( id2, fieldn...)
-- render layer1 with a line joining centroids of both where layer2_id = id2
make_line( centroid( $geometry ),
centroid( geometry( get_feature( 'layer2', 'id2', attribute(
$currentfeature, 'layer2_id') ) )
)
-- Create a nice radial effect of points surrounding the central feature
-- point when used as a MultiPoint geometry generator
collect_geometries(
array_foreach(
generate_series( 0, 330, 30 ),
project( $geometry, .2, radians( @element ) )
)
)
The Vector Field Marker
The vector field marker is used to display vector field data such as earth deformation, tidal flows, and the like. It
displays the vectors as lines (preferably arrows) that are scaled and oriented according to selected attributes of data
points. It can only be used to render point data; line and polygon layers are not drawn by this symbology.
The vector field is defined by attributes in the data, which can represent the field either by:
• cartesian components (x and y components of the field)
• or polar coordinates: in this case, attributes define Length and Angle. The angle may be measured either
clockwise from north, or Counterclockwise from east, and may be either in degrees or radians.
• or as height only data, which displays a vertical arrow scaled using an attribute of the data. This is appropriate
for displaying the vertical component of deformation, for example.
The magnitude of field can be scaled up or down to an appropriate size for viewing the field.
12.3 Setting a label
Labels are textual information you can display on vector features or maps. They add details you could not necessarily
represent using symbols. Two types of text-related items are available in QGIS:
• Text Format: defines the appearance of the text, including font, size, colors, shadow, background, buffer, …
They can be used to render texts over the map (layout/map title, decorations, scale bar, …), usually through
the font widget.
To create a Text Format item:
1. Open the Style Manager dialog
2. Activate the Text format tab
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Obr. 12.13: Text formats in Style Manager dialog
3. Press the Add item
button. The Text Format dialog opens for configuration. As usual, these properties
are data-definable.
• Label Settings: extend the text format settings with properties related to the location or the interaction with
other texts or features (callouts, placement, overlay, scale visibility, mask …).
They are used to configure smart labelling for vector layers through the Labels tab of the vector Layer
Properties dialog or Layer Styling panel or using the Layer Labeling Options
button of the Label toolbar.
To create a Label Settings item:
1. Open the Style Manager dialog
2. Activate the Label Settings tab
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Obr. 12.14: Label Settings in Style Manager dialog
3. Press the Add item
menu and select the entry corresponding to the geometry type of the features you
want to label.
The Label Settings dialog opens with the following properties. As usual, these properties are data-definable.
12.3.1 Formatting the label text
Most of the following properties are common to Text Format and Label Settings items.
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Text tab
Obr. 12.15: Labels settings - Text tab
In the Text tab, you can set:
• the Font, from the ones available on your machine
• the Style: along with the common styles of the font, you can set whether the text should be underlined or striked
through
• the Size in any supported unit
• the Color
• and the Opacity.
At the bottom of the tab, a widget shows a filterable list of compatible items stored in your style manager database.
This allows you to easily configure the current text format or label setting based on an existing one, and also save
a new item to the style database: Press the Save format… or Save settings… button and provide a name and tag(s).
Poznámka: When configuring a Label Settings item, text format items are also available in this widget. Select one
to quickly overwrite the current textual properties of the label. Likewise, you can create/overwrite a text format from
there.
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Formatting tab
Obr. 12.16: Label settings - Formatting tab
In the Formatting tab, you can:
• Use the Type case option to change the capitalization style of the text. You have the possibility to render the
text as:
– No change
– All uppercase
– All lowercase
– Title case: modifies the first letter of each word into capital, and turns the other letters into lower case if
the original text is using a single type case. In case of mixed type cases in the text, the other letters are
left untouched.
– Force first letter to capital: modifies the first letter of each word into capital and leaves the other letters in
the text untouched.
• Under Spacing, change the space between words and between individual letters.
• Enable kerning of the text font
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• Set the Text orientation which can be Horizontal or Vertical. It can also be Rotation-based when setting a label
(e.g., to properly label line features in parallel placement mode).
• Use the Blend mode option to determine how your labels will mix with the map features below them (more
details at Režim míchání).
• The Apply label text substitutes option allows you to specify a list of texts to substitute to texts in feature
labels (e.g., abbreviating street types). Replacement texts are used when displaying labels on the map. Users
can also export and import lists of substitutes to make reuse and sharing easier.
• Configure Multiple lines:
– Set a character that will force a line break in the text with the Wrap on character option
– Set an ideal line size for auto-wrapping using the Wrap lines to option. The size can represent either the
Maximum line length or the Minimum line length.
– Decide the Line Height
– Format the Alignment: typical values available are Left, Right, Justify and Center.
When setting point labels properties, the text alignment can also be Follow label placement. In that case,
the alignment will depend on the final placement of the label relative to the point. E.g., if the label is placed
to the left of the point, then the label will be right aligned, while if it is placed to the right, it will be left
aligned.
Poznámka: The Multiple lines formatting is not yet supported by curve based label placement. The options
will then be deactivated.
• For line labels you can include Line direction symbol to help determine the line directions, with symbols to
use to indicate the Left or Right. They work particularly well when used with the curved or Parallel placement
options from the Placement tab. There are options to set the symbols position, and to Reverse direction.
• Use the Formatted numbers option to format numeric texts. You can set the number of Decimal places. By
default, 3 decimal places will be used. Use the Show plus sign if you want to show the plus sign for positive
numbers.
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Buffer tab
Obr. 12.17: Label settings - Buffer tab
To create a buffer around the label, activate the Draw text buffer checkbox in the Buffer tab. Then you can:
• Set the buffer’s Size in any supported unit
• Select the buffer’s Color
• Color buffer’s fill: The buffer expands from the label’s outline, so, if the option is activated, the label’s
interior is filled. This may be relevant when using partially transparent labels or with non-normal blending
modes, which will allow seeing behind the label’s text. Unchecking the option (while using totally transparent
labels) will allow you to create outlined text labels.
• Define the buffer’s Opacity
• Apply a Pen join style: it can be Round, Miter or Bevel
• Use the Blend mode option to determine how your label’s buffer will mix with the map components below them
(more details at Režim míchání).
• Check Draw effects to add advanced paint effects for improving text readability, eg through outer glows
and blurs.
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Background tab
The Background tab allows you to configure a shape that stays below each label. To add a background, activate
the Draw Background checkbox and select the Shape type. It can be:
• a regular shape such as Rectangle, Square, Circle or Ellipse
• an SVG symbol from a file, a URL or embedded in the project or style database (more details)
• or a Marker Symbol you can create or select from the symbol library.
Obr. 12.18: Label settings - Background tab
Depending on the selected shape, you need to configure some of the following properties:
• The Size type of the frame, which can be:
– Fixed: using the same size for all the labels, regardless the size of the text
– or a Buffer over the text’s bounding box
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• The Size of the frame in X and Y directions, using any supported units
• A Rotation of the background, between Sync with label, Offset of label and Fixed. The last two require an angle
in degrees.
• An Offset X,Y to shift the background item in the X and/or Y directions
• A Radius X,Y to round the corners of the background shape (applies to rectangle and square shapes only)
• An Opacity of the background
• A Blend mode to mix the background with the other items in the rendering (see Režim míchání).
• The Fill color, Stroke color and Stroke width for shape types other than the marker symbol. Use the Load symbol
parameters to revert changes on an SVG symbol to its default settings.
• A Pen join style: it can be Round, Miter or Bevel (applies to rectangle and square shapes only)
• Draw effects to add advanced paint effects for improving text readability, eg through outer glows and
blurs.
Shadow tab
Obr. 12.19: Label settings - Shadow tab
To add a shadow to the text, enable the Shadow tab and activate the Draw drop shadow. Then you can:
• Indicate the item used to generate the shadow with Draw under. It can be the Lowest label component or
a particular component such as the Text itself, the Buffer or the Background.
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• Set the shadow’s Offset from the item being shadowded, ie:
– The angle: clockwise, it depends on the underlying item orientation
– The distance of offset from the item being shadowded
– The units of the offset
If you tick the Use global shadow checkbox, then the zero point of the angle is always oriented to the north
and doesn’t depend on the orientation of the label’s item.
• Influence the appearance of the shadow with the Blur radius. The higher the number, the softer the shadows,
in the units of your choice.
• Define the shadow’s Opacity
• Rescale the shadow’s size using the Scale factor
• Choose the shadow’s Color
• Use the Blend mode option to determine how your label’s shadow will mix with the map components below
them (more details at Režim míchání).
12.3.2 Configuring interaction with labels
Other than the text formatting settings exposed above, you can also set how labels interact with each others or with
the features.
Mask tab
The Mask tab allows you to define a mask area around the labels. This feature is very useful when you have
overlapping symbols and labels with similar colors, and you want to make the labels visible.
Obr. 12.20: Labels settings - Mask tab
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To create masking effects on labels:
1. Activate the Enable mask checkbox in the tab.
2. Then you can set:
• the mask’s Size in the supported units
• the Opacity of the mask area around the label
• a Pen Join Style
• paint effects through the Draw effects checkbox.
3. Select this mask shape as a mask source in the overlapping layer properties Mask tab (see Masks Properties).
Callouts tab
A common practice when placing labels on a crowded map is to use callouts - labels which are placed outside (or
displaced from) their associated feature are identified with a dynamic line connecting the label and the feature. If one
of the two endings (either the label or the feature) is moved, the shape of the connector is recomputed.
Obr. 12.21: Labels with various callouts settings
To add a callout to a label, enable the Callouts tab and activate the Draw callouts. Then you can:
1. Select the Style of connector, one of:
• Simple lines: a straight line, the shortest path
• Manhattan style: a 90° broken line
2. Select the Line style with full capabilities of a line symbol including layer effects, and data-defined settings
3. Set the Minimum length of callout lines
4. Set the Offset from feature option: controls the distance from the feature (or its anchor point if a polygon) where
callout lines end. Eg, this avoids drawing lines right up against the edges of the features.
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5. Set the Offset from label area option: controls the distance from the label anchor point (where the callout line
ends). This avoids drawing lines right up against the text.
6. Draw lines to all feature parts from the feature’s label
7. Set the Anchor point for the (polygon) feature (the end point of the connector line). Available options:
• Pole of inaccessibility
• Point on exterior
• Point on surface
• Centroid
8. Set the Label anchor point: controls where the connector line should join to the label text. Available options:
• Closest point
• Centroid
• Fixed position at the edge (Top left, Top center, Top right, Left middle, Right middle, Bottom left, Bottom
center and Bottom right).
Placement tab
Choose the Placement tab for configuring label placement and labeling priority. Note that the placement options
differ according to the type of vector layer, namely point, line or polygon, and are affected by the global PAL setting.
Placement for point layers
Point labels placement modes available are:
• Cartographic: point labels are generated with a better visual relationship with the point feature, following ideal
cartographic placement rules. Labels can be placed:
– at a set Distance in supported units, either from the point feature itself or from the bounds of the symbol
used to represent the feature (set in Distance offset from). The latter option is especially useful when the
symbol size isn’t fixed, e.g. if it’s set by a data defined size or when using different symbols in a categorized
renderer.
– following a Position priority that can be customized or set for an individual feature using a data defined list
of prioritised positions. This also allows only certain placements to be used, so e.g. for coastal features
you can prevent labels being placed over the land.
By default, cartographic mode placements are prioritised in the following order (respecting the guidelines
from Krygier and Wood (2011) and other cartographic textbooks):
1. top right
2. top left
3. bottom right
4. bottom left
5. middle right
6. middle left
7. top, slightly right
8. bottom, slightly left.
• Around Point: labels are placed in a circle around the feature. equal radius (set in Distance) circle around the
feature. The placement priority is clockwise from the „top right“. The position can be constrained using the
data-defined Quadrant option.
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• Offset from Point: labels are placed at an Offset X,Y distance from the point feature, in various units, or preferably
over the feature. You can use a data-defined Quadrant to constrain the placement and can assign a Rotation to
the label.
Placement for line layers
Label modes for line layers include:
• Parallel: draws the label parallel to a generalised line representing the feature, with preference for placement
over straighter portions of the line. You can define:
– Allowed positions: Above line, On line, Below line and Line orientation dependent position (placing the
label at the left or the right of the line). It’s possible to select several options at once. In that case, QGIS
will look for the optimal label position.
– Distance between the label and the line
• Curved: draws the label following the curvature of the line feature. In addition to the parameters available with
the Parallel mode, you can set the Maximum angle between curved characters, either inside or outside.
• Horizontal: draws labels horizontally along the length of the line feature.
Obr. 12.22: Label placement examples for lines
Next to placement modes, you can set:
• Repeating Labels Distance to display multiple times the label over the length of the feature. The distance can
be in Millimeters, Points, Pixels, Meters at scale, Map Units and Inches.
• A Label Overrun Distance (not available for horizontal mode): specifies the maximal allowable distance a label
may run past the end (or start) of line features. Increasing this value can allow for labels to be shown for shorter
line features.
• Label Anchoring: controls the placement of the labels along the line feature they refer to. Click on Settings …
to choose:
– the position along the line (as a ratio) which labels will be placed close to. It can be data-defined and
possible values are:
∗ Center of Line
∗ Start of Line
∗ End of Line
∗ or Custom….
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– Placement Behavior: use Preferred Placement Hint to treat the label anchor only as a hint for the label
placement. By choosing Strict, labels are placed exactly on the label anchor.
Placement for polygon layers
You can choose one of the following modes for placing labels of polygons:
Obr. 12.23: Label placement examples for polygons
• Offset from Centroid: labels are placed over the feature centroid or at a fixed Offset X,Y distance (in supported
units) from the centroid. The reference centroid can be determined based on the part of the polygon rendered
in the map canvas (visible polygon) or the whole polygon, no matter if you can see it. You can also:
– force the centroid point to lay inside their polygon
– place the label within a specific quadrant
– assign a rotation
– Allow placing labels outside of polygons when it is not possible to place them inside the polygon. Thanks
to data-defined properties, this makes possible to either allow outside labels, prevent outside labels, or
force outside labels on a feature-by-feature basis.
• Around Centroid: places the label within a preset distance around the centroid, with a preference for the
placement directly over the centroid. Again, you can define whether the centroid is the one of the visible polygon
or the whole polygon, and whether to force the centroid point inside the polygon.
• Horizontal: places at the best position a horizontal label inside the polygon. The preferred placement is further
from the edges of the polygon. It’s possible to Allow placing labels outside of polygons.
• Free (Angled): places at the best position a rotated label inside the polygon. The rotation respects the polygon’s
orientation and the preferred placement is further from the edges of the polygon. It’s possible to Allow placing
labels outside of polygons.
• Using Perimeter: draws the label parallel to a generalised line representing the polygon boundary, with
preference for straighter portions of the perimeter. You can define:
– Allowed positions: Above line, On line, Below line and Line orientation dependent position (placing the
label at the left or the right of the polygon’s boundary). It’s possible to select several options at once. In
that case, QGIS will look for the optimal label position.
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– Distance between the label and the polygon’s outline
– the Repeating Labels Distance to display multiple times the label over the length of the perimeter.
• Using Perimeter (Curved): draws the label following the curvature of the polygon’s boundary. In addition to the
parameters available with the Using Perimeter mode, you can set the Maximum angle between curved characters
polygon, either inside or outside.
• Outside Polygons: always places labels outside the polygons, at a set Distance
Common placement settings
Some label placement settings are available for all layer geometry types:
Data Defined
The Data Defined group provides direct control on labels placement, on a feature-by-feature basis. It relies on their
attributes or an expression to set:
• the X and Y coordinate
• the text alignment over the custom position set above:
– Horizontal: it can be Left, Center or Right
– the text Vertical: it can be Bottom, Base, Half, Cap or Top
• the text Rotation. Check the Preserve data rotation values entry if you want to keep the rotation value in the
associated field and apply it to the label, whether the label is pinned or not. If unchecked, unpinning the label
rotation is reset and its value cleared from the attribute table.
Poznámka: Data-defined rotation with polygon features is currently supported only with the Around centroid
placement mode.
Poznámka: Expressions can not be used in combination with the labels map tools (ie the Rotate label and Move label
tools) to data-define labels placement. The widget will be reset to the corresponding auxiliary storage field.
Priority
In the Priority section you can define the placement priority rank of each label, ie if there are different diagrams or
labels candidates for the same location, the item with the higher priority will be displayed and the others could be left
out.
The priority rank is also used to evaluate whether a label could be omitted due to a greater weighted obstacle feature.
Obstacles
In some contexts (eg, high density labels, overlapping features…), the labels placement can result in labels being
placed over unrelated features.
An obstacle is a feature over which QGIS avoids placing other features‘ labels or diagrams. This can be controlled
from the Obstacles section:
1. Activate the Features act as obstacles option to decide that features of the layer should act as obstacles for
any label and diagram (including items from other features in the same layer).
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Instead of the whole layer, you can select a subset of features to use as obstacles, using the data-defined override
control next to the option.
2. Use the Settings button to tweak the obstacle’s weighting.
• For every potential obstacle feature you can assign an Obstacle weight: any label or diagram whose
placement priority rank is greater than this value can be placed over. Labels or diagrams with lower
rank will be omitted if no other placement is possible.
This weighting can also be data-defined, so that within the same layer, certain features are more likely to
be covered than others.
• For polygon layers, you can choose the kind of obstacle the feature is:
– over the feature’s interior: avoids placing labels over the interior of the polygon (prefers placing
labels totally outside or just slightly inside the polygon)
– or over the feature’s boundary: avoids placing labels over the boundary of the polygon (prefers
placing labels outside or completely inside the polygon). This can be useful for layers where the
features cover the whole area (administrative units, categorical coverages, …). In this case, it
is impossible to avoid placing labels within these features, and it looks much better when placing
them over the boundaries between features is avoided.
Rendering tab
In the Rendering tab, you can tune when the labels can be rendered and their interaction with other labels and
features.
Label options
Under Label options:
• You find the scale-based and the Pixel size-based visibility settings.
• The Label z-index determines the order in which labels are rendered, as well in relation with other feature labels
in the layer (using data-defined override expression), as with labels from other layers. Labels with a higher zindex
are rendered on top of labels (from any layer) with lower z-index.
Additionally, the logic has been tweaked so that if two labels have matching z-indexes, then:
– if they are from the same layer, the smaller label will be drawn above the larger label
– if they are from different layers, the labels will be drawn in the same order as their layers themselves (ie
respecting the order set in the map legend).
Poznámka: This setting doesn’t make labels to be drawn below the features from other layers, it just controls
the order in which labels are drawn on top of all the layers‘ features.
• While rendering labels and in order to display readable labels, QGIS automatically evaluates the position of the
labels and can hide some of them in case of collision. You can however choose to Show all labels for this
layer (including colliding labels) in order to manually fix their placement (see The Label Toolbar).
• With data-defined expressions in Show label and Always Show you can fine tune which labels should be
rendered.
• Allow to Show upside-down labels: alternatives are Never, when rotation defined or always.
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Feature options
Under Feature options:
• You can choose to Label every part of a multi-part features and Limit number of features to be labeled to.
• Both line and polygon layers offer the option to set a minimum size for the features to be labeled, using Suppress
labeling of features smaller than.
• For polygon features, you can also filter the labels to show according to whether they completely fit within their
feature or not.
• For line features, you can choose to Merge connected lines to avoid duplicate labels, rendering a quite airy map
in conjunction with the Distance or Repeat options in the Placement tab.
12.4 Creating 3D Symbols
The Style Manager helps you create and store 3D symbols for every geometry type to render in the 3D map view.
As of the other items, enable the 3D Symbols tab and expand the button menu to create:
• 3D point symbols
• 3D line symbols
• 3D polygon symbols
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12.4.1 Point Layers
Obr. 12.24: Properties of a 3D point symbol
• You can define different simple 3D shapes like Sphere, Cylinder, Cube, Cone, Plane and Torus defined by their
Radius, Size or Length. The unit of size of the 3D shapes refers to the CRS of the project.
• The shading of the 3D shapes can be defined by the menus Diffuse, Ambient, Specular and Shininess (see
https://en.wikipedia.org/wiki/Phong_reflection_model#Description)
• If you choose 3D Model, the location will be determined by a simple point coordinate.
• For visualizing 3D point clouds you can use Billboard Shapes defined by the Billboard Height, Billboard symbol
and Altitude clamping. The symbol will have a stable size.
• Altitude clamping can be set to Absolute, Relative or Terrain. The Absolute setting can be used when height
values of the 3d vectors are provided as absolute measures from 0. Relative and Terrain add given elevation
values to the underlying terrain elevation.
• Translation can be used to move objects in x, y and z axis.
• You can define a Scale factor for the 3D shape as well as a Rotation around the x-, y- and z-axis.
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12.4.2 Line layers
Obr. 12.25: Properties of a 3D line symbol
• Beneath the Width and Height settings you can define the Extrusion of the vector lines. If the lines do not have
z-values, you can define the 3d volumes with this setting.
• With the Altitude clamping you define the position of the 3D lines relative to the underlying terrain surface, if
you have included raster elevation data or other 3D vectors.
• The Altitude binding defines how the feature is clamped to the terrain. Either every Vertex of the feature will
be clamped to the terrain or this will be done by the Centroid.
• It is possible to Render as simple 3D lines.
• The shading can be defined in the menus Diffuse, Ambient, Specular and Shininess.
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12.4.3 Polygon Layers
Obr. 12.26: Properties of a 3D polygon symbol
• As for the other ones, Height can be defined in CRS units. You can also use the button to overwrite the
value with a custom expression, a variable or an entry of the attribute table
• Again, Extrusion is possible for missing z-values. Also for the extrusion you can use the button in order to
use the values of the vector layer and have different results for each polygon:
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Obr. 12.27: Data Defined Extrusion
• The Altitude clamping, Altitude binding can be defined as explained above.
• There is an additional option to Add back faces and Invert normals.
• You can define Edges by Width and Color.
12.4.4 Application example
To go through the settings explained above you can have a look at https://public.cloudmergin.com/projects/saber/
luxembourg/tree.
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Managing Data Source
13.1 Opening Data
As part of an Open Source Software ecosystem, QGIS is built upon different libraries that, combined with its own
providers, offer capabilities to read and often write a lot of formats:
• Vector data formats include GeoPackage, GML, GeoJSON, GPX, KML, Comma Separated Values, ESRI
formats (Shapefile, Geodatabase…), MapInfo and MicroStation file formats, AutoCAD DWG/DXF, GRASS
and many more… Read the complete list of supported vector formats.
• Raster data formats include GeoTIFF, JPEG, ASCII Gridded XYZ, MBTiles, R or Idrisi rasters, GDAL
Virtual, SRTM, Sentinel Data, ERDAS IMAGINE, ArcInfo Binary Grid, ArcInfo ASCII Grid, and many
more… Read the complete list of supported raster formats.
• Database formats include PostgreSQL/PostGIS, SQLite/SpatiaLite, Oracle, DB2 or MSSQL Spatial,
MySQL…
• Web map and data services (WM(T)S, WFS, WCS, CSW, XYZ tiles, ArcGIS services, …) are also handled
by QGIS providers. See Working with OGC / ISO protocols for more information about some of these.
• You can read supported files from archived folders and use QGIS native formats such as QML files (QML The
QGIS Style File Format) and virtual and memory layers.
More than 80 vector and 140 raster formats are supported by GDAL and QGIS native providers.
Poznámka: Not all of the listed formats may work in QGIS for various reasons. For example, some require external
proprietary libraries, or the GDAL/OGR installation of your OS may not have been built to support the format you
want to use. To see the list of available formats, run the command line ogrinfo --formats (for vector) and
gdalinfo --formats (for raster), or check the Settings ► Options ► GDAL menu in QGIS.
In QGIS, depending on the data format, there are different tools to open a dataset, mainly available in the Layer ► Add
Layer ► menu or from the Manage Layers toolbar (enabled through View ► Toolbars menu). However, all these tools
point to a unique dialog, the Data Source Manager dialog, that you can open with the Open Data Source Manager
button,
available on the Data Source Manager Toolbar, or by pressing Ctrl+L. The Data Source Manager dialog(Obr. 13.1)
offers a unified interface to open vector or raster file-based data as well as databases or web services supported by
QGIS. It can be set modal or not with the Modeless data source manager dialog in the Settings ► Options ►
General menu.
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Obr. 13.1: QGIS Data Source Manager dialog
Beside this main entry point, you also have the DB Manager plugin that offers advanced capabilities to analyze
and manipulate connected databases. More information on DB Manager capabilities can be found in DB Manager
Plugin.
There are many other tools, native or third-party plugins, that help you open various data formats.
This chapter will describe only the tools provided by default in QGIS for loading data. It will mainly focus on the Data
Source Manager dialog but more than describing each tab, it will also explore the tools based on the data provider or
format specificities.
13.1.1 The Browser Panel
The Browser is one of the main ways to quickly and easily add your data to projects. It’s available as:
• a Data Source Manager tab, enabled pressing the Open Data Source Manager
button (Ctrl+L);
• as a QGIS panel you can open from the menu View ► Panels (or Settings ► Panels) or by pressing Ctrl+2.
In both cases, the Browser helps you navigate in your file system and manage geodata, regardless the type of layer
(raster, vector, table), or the datasource format (plain or compressed files, databases, web services).
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Exploring the Interface
At the top of the Browser panel, you find some buttons that help you to:
• Add Selected Layers
: you can also add data to the map canvas by selecting Add selected layer(s) from the layer’s
context menu;
• Refresh
the browser tree;
• Filter Browser
to search for specific data. Enter a search word or wildcard and the browser will filter the tree
to only show paths to matching DB tables, filenames or folders – other data or folders won’t be displayed. See
the Browser Panel(2) example in Obr. 13.2. The comparison can be case-sensitive or not. It can also be set to:
– Normal: show items containing the search text
– Wildcard(s): fine tune the search using the ? and/or * characters to specify the position of the search text
– Regular expression
• Collapse All
the whole tree;
• Enable/disable properties widget
: when toggled on, a new widget is added at the bottom of the panel showing, if
applicable, metadata for the selected item.
The entries in the Browser panel are organised hierarchically, and there are several top level entries:
1. Favorites where you can place shortcuts to often used locations
2. Spatial Bookmarks where you can store often used map extents (see Prostorové záložky)
3. Project Home: for a quick access to the folder in which (most of) the data related to your project are stored.
The default value is the directory where your project file resides.
4. Home directory in the file system and the filesystem root directory.
5. Connected local or network drives
6. Then comes a number of container / database types and service protocols, depending on your platform and
underlying libraries:
• GeoPackage
• SpatiaLite
• PostGIS
• MSSQL
• Oracle
• DB2
• WMS/WMTS
• Vector Tiles
• XYZ Tiles
• WCS
• WFS/OGC API-Features
• OWS
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• ArcGIS Map Service
• ArcGIS Feature Service
• GeoNode
Interacting with the Browser items
The browser supports drag and drop within the browser, from the browser to the canvas and Layers panel, and from
the Layers panel to layer containers (e.g. GeoPackage) in the browser.
Project file items inside the browser can be expanded, showing the full layer tree (including groups) contained within
that project. Project items are treated the same way as any other item in the browser, so they can be dragged and
dropped within the browser (for example to copy a layer item to a geopackage file) or added to the current project
through drag and drop or double click.
The context menu for an element in the Browser panel is opened by right-clicking on it.
For file system directory entries, the context menu offers the following:
• New ► to create in the selected entry a:
– Directory…
– GeoPackage…
– ShapeFile…
• Add as a Favorite: favorite folders can be renamed (Rename favorite…) or removed (Remove favorite) any time.
• Hide from Browser: hidden folders can be toggled to visible from the Settings ► Options ► Data Sources ►
Hidden browser paths setting
• Fast Scan this Directory
• Open Directory
• Open in Terminal
• Vlastnosti…
• Directory Properties…
For leaf entries that can act as layers in the project, the context menu will have supporting entries. For example, for
non-database, non-service-based vector, raster and mesh data sources:
• Delete File „<name of file>“…
• Export Layer –> To File…
• Add Layer to Project
• Layer Properties
• File Properties
In the Layer properties entry, you will find (similar to what you will find in the vector and raster layer properties once
the layers have been added to the project):
• Metadata for the layer. Metadata groups: Information from provider (if possible, Path will be a hyperlink to
the source), Identification, Extent, Access, Fields (for vector layers), Bands (for raster layers), Contacts, Links
(for vector layers), References (for raster layers), History.
• A Preview panel
• The attribute table for vector sources (in the Attributes panel).
To add a layer to the project using the Browser:
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1. Enable the Browser as described above. A browser tree with your file system, databases and web services
is displayed. You may need to connect databases and web services before they appear (see dedicated sections).
2. Find the layer in the list.
3. Use the context menu, double-click its name, or drag-and-drop it into the map canvas. Your layer is now added
to the Layers panel and can be viewed on the map canvas.
Tip: Open a QGIS project directly from the browser
You can also open a QGIS project directly from the Browser panel by double-clicking its name or by drag-and-drop
into the map canvas.
Once a file is loaded, you can zoom around it using the map navigation tools. To change the style of a layer, open
the Layer Properties dialog by double-clicking on the layer name or by right-clicking on the name in the legend
and choosing Properties from the context menu. See section Symbology Properties for more information on setting
symbology for vector layers.
Right-clicking an item in the browser tree helps you to:
• for a file or a table, display its metadata or open it in your project. Tables can even be renamed, deleted or
truncated.
• for a folder, bookmark it into your favourites or hide it from the browser tree. Hidden folders can be managed
from the Settings ► Options ► Data Sources tab.
• manage your spatial bookmarks: bookmarks can be created, exported and imported as XML files.
• create a connection to a database or a web service.
• refresh, rename or delete a schema.
You can also import files into databases or copy tables from one schema/database to another with a simple drag-and-drop.
There is a second browser panel available to avoid long scrolling while dragging. Just select the file and
drag-and-drop from one panel to the other.
Obr. 13.2: QGIS Browser panels side-by-side
Tip: Add layers to QGIS by simple drag-and-drop from your OS file browser
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You can also add file(s) to the project by drag-and-dropping them from your operating system file browser to the
Layers Panel or the map canvas.
13.1.2 The DB Manager
The DB Manager Plugin is another tool for integrating and managing spatial database formats supported by QGIS
(PostGIS, SpatiaLite, GeoPackage, Oracle Spatial, MSSQL, DB2, Virtual layers). It can be activated from the Plugins
► Manage and Install Plugins… menu.
The DB Manager
Plugin provides several features:
• connect to databases and display their structure and contents
• preview tables of databases
• add layers to the map canvas, either by double-clicking or drag-and-drop.
• add layers to a database from the QGIS Browser or from another database
• create SQL queries and add their output to the map canvas
• create virtual layers
More information on DB Manager capabilities is found in DB Manager Plugin.
Obr. 13.3: DB Manager dialog
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13.1.3 Provider-based loading tools
Beside the Browser Panel and the DB Manager, the main tools provided by QGIS to add layers, you’ll also find tools
that are specific to data providers.
Poznámka: Some external plugins also provide tools to open specific format files in QGIS.
Loading a layer from a file
To load a layer from a file:
1. Open the layer type tab in the Data Source Manager dialog, ie click the Open Data Source Manager
button (or
press Ctrl+L) and enable the target tab or:
• for vector data (like GML, ESRI Shapefile, Mapinfo and DXF layers): press Ctrl+Shift+V, select
the Layer ► Add Layer ► Add Vector Layer menu option or click on the Add Vector Layer
toolbar
button.
Obr. 13.4: Add Vector Layer Dialog
• for raster data (like GeoTiff, MBTiles, GRIdded Binary and DWG layers): press Ctrl+Shift+R,
select the Layer ► Add Layer ► Add Raster Layer menu option or click on the Add Raster Layer
toolbar button.
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Obr. 13.5: Add Raster Layer Dialog
2. Check File source type
3. Click on the … Browse
button
4. Navigate the file system and load a supported data source. More than one layer can be loaded at the same time
by holding down the Ctrl key and clicking on multiple items in the dialog or holding down the Shift key
to select a range of items by clicking on the first and last items in the range. Only formats that have been well
tested appear in the formats filter. Other formats can be loaded by selecting All files (the top item in the
pull-down menu).
5. Press Open to load the selected file into Data Source Manager dialog
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Obr. 13.6: Loading a Shapefile with open options
6. Press Add to load the file in QGIS and display them in the map view. Obr. 13.7 shows QGIS after loading the
alaska.shp file.
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Obr. 13.7: QGIS with Shapefile of Alaska loaded
Poznámka: For loading vector files the GDAL driver offers to define open actions. These will be shown when the
vector file is selected. Options are described in detail on https://gdal.org/drivers/vector/ .
Poznámka: Because some formats like MapInfo (e.g., .tab) or Autocad (.dxf) allow mixing different types of
geometry in a single file, loading such datasets opens a dialog to select geometries to use in order to have one geometry
per layer.
The Add Vector Layer
and Add Raster Layer
tabs allow loading of layers from source types other than File:
• You can load specific vector formats like ArcInfo Binary Coverage, UK. National Transfer
Format, as well as the raw TIGER format of the US Census Bureau or OpenfileGDB. To do that,
you select Directory as Source type. In this case, a directory can be selected in the dialog after pressing …
Browse
.
• With the Database source type you can select an existing database connection or create one to the selected
database type. Some possible database types are ODBC, Esri Personal Geodatabase, MSSQL as well
as PostgreSQL or MySQL .
Pressing the New button opens the Create a New OGR Database Connection dialog whose parameters are among
the ones you can find in Creating a stored Connection. Pressing Open lets you select from the available tables,
for example of PostGIS enabled databases.
• The Protocol: HTTP(S), cloud, etc. source type opens data stored locally or on the network, either publicly
accessible, or in private buckets of commercial cloud storage services. Supported protocol types are:
– HTTP/HTTPS/FTP, with a URI and, if required, an authentication.
– Cloud storage such as AWS S3, Google Cloud Storage, Microsoft Azure Blob, Alibaba
OSS Cloud, Open Stack Swift Storage. You need to fill in the Bucket or container and the
Object key.
– service supporting OGC WFS 3 (still experimental), using GeoJSON or GEOJSON - Newline
Delimited format or based on CouchDB database. A URI is required, with optional authentication.
– For all vector source types it is possible to define the Encoding or to use the Automatic ► setting.
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Loading a mesh layer
A mesh is an unstructured grid usually with temporal and other components. The spatial component contains
a collection of vertices, edges and faces in 2D or 3D space. More information on mesh layers at Working with Mesh
Data.
To add a mesh layer to QGIS:
1. Open the Data Source Manager dialog, either by selecting it from the Layer ► menu or clicking the
Open Data Source Manager
button.
2. Enable the Mesh tab on the left panel
3. Press the … Browse
button to select the file. Various formats are supported.
4. Select the layer and press Add. The layer will be added using the native mesh rendering.
Obr. 13.8: Mesh tab in Data Source Manager
Importing a delimited text file
Delimited text files (e.g. .txt, .csv, .dat, .wkt) can be loaded using the tools described above. This way, they
will show up as simple tables. Sometimes, delimited text files can contain coordinates / geometries that you could
want to visualize. This is what Add Delimited Text Layer is designed for.
1. Click the Open Data Source Manager
icon to open the Data Source Manager dialog
2. Enable the Delimited Text tab
3. Select the delimited text file to import (e.g., qgis_sample_data/csv/elevp.csv) by clicking on the
… Browse
button.
4. In the Layer name field, provide the name to use for the layer in the project (e.g. Elevation).
5. Configure the settings to meet your dataset and needs, as explained below.
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Obr. 13.9: Delimited Text Dialog
File format
Once the file is selected, QGIS attempts to parse the file with the most recently used delimiter, identifying fields
and rows. To enable QGIS to correctly parse the file, it is important to select the right delimiter. You can specify
a delimiter by choosing between:
• CSV (comma separated values) to use the comma character.
• Regular expression delimiter and enter text into the Expression field. For example, to change the delimiter
to tab, use \t (this is used in regular expressions for the tab character).
• Custom delimiters, choosing among some predefined delimiters like comma, space, tab, semicolon,
… .
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Records and fields
Some other convenient options can be used for data recognition:
• Number of header lines to discard: convenient when you want to avoid the first lines in the file in the import,
either because those are blank lines or with another formatting.
• First record has field names: values in the first line are used as field names, otherwise QGIS uses the field
names field_1, field_2…
• Detect field types: automatically recognizes the field type. If unchecked then all attributes are treated as text
fields.
• Decimal separator is comma: you can force decimal separator to be a comma.
• Trim fields: allows you to trim leading and trailing spaces from fields.
• Discard empty fields.
As you set the parser properties, a sample data preview updates at the bottom of the dialog.
Geometry definition
Once the file is parsed, set Geometry definition to
• Point coordinates and provide the X field, Y field, Z field (for 3-dimensional data) and M field (for the
measurement dimension) if the layer is of point geometry type and contains such fields. If the coordinates
are defined as degrees/minutes/seconds, activate the DMS coordinates checkbox. Provide the appropriate
Geometry CRS using the Select CRS
widget.
• Well known text (WKT) option if the spatial information is represented as WKT: select the Geometry field
containing the WKT geometry and choose the approriate Geometry field or let QGIS auto-detect it. Provide
the appropriate Geometry CRS using the Select CRS
widget.
• If the file contains non-spatial data, activate No geometry (attribute only table) and it will be loaded as an
ordinary table.
Layer settings
Additionally, you can enable:
• Use spatial index to improve the performance of displaying and spatially selecting features.
• Use subset index to improve performance of subset filters (when defined in the layer properties).
• Watch file to watch for changes to the file by other applications while QGIS is running.
At the end, click Add to add the layer to the map. In our example, a point layer named Elevation is added to the
project and behaves like any other map layer in QGIS. This layer is the result of a query on the .csv source file
(hence, linked to it) and would require to be saved in order to get a spatial layer on disk.
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Importing a DXF or DWG file
DXF and DWG files can be added to QGIS by simple drag-and-drop from the Browser Panel. You will be prompted
to select the sublayers you would like to add to the project. Layers are added with random style properties.
Poznámka: For DXF files containing several geometry types (point, line and/or polygon), the name of the layers
will be generated as <filename.dxf> entities <geometry type>.
To keep the dxf/dwg file structure and its symbology in QGIS, you may want to use the dedicated Project ►
Import/Export ► Import Layers from DWG/DXF… tool which allows you to:
1. import elements from the drawing file into a GeoPackage database.
2. add imported elements to the project.
In the DWG/DXF Import dialog, to import the drawing file contents:
1. Input the location of the Target package, i.e. the new GeoPackage file that will store the data. If an existing file
is provided, then it will be overwritten.
2. Specify the coordinate reference system of the data in the drawing file.
3. Check Expand block references to import the blocks in the drawing file as normal elements.
4. Check Use curves to promote the imported layers to a curved geometry type.
5. Use the Import button to select the DWG/DXF file to use (one per geopackage). The GeoPackage database
will be automatically populated with the drawing file content. Depending on the size of the file, this can take
some time.
After the .dwg or .dxf data has been imported into the GeoPackage database, the frame in the lower half of the
dialog is populated with the list of layers from the imported file. There you can select which layers to add to the QGIS
project:
1. At the top, set a Group name to group the drawing files in the project.
2. Check layers to show: Each selected layer is added to an ad hoc group which contains vector layers for the
point, line, label and area features of the drawing layer. The style of the layers will resemble the look they
originally had in *CAD.
3. Choose if the layer should be visible at opening.
4. Checking the Merge layers option places all layers in a single group.
5. Press OK to open the layers in QGIS.
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Obr. 13.10: Import dialog for DWG/DXF files
Importing OpenStreetMap Vectors
The OpenStreetMap project is popular because in many countries no free geodata such as digital road maps are
available. The objective of the OSM project is to create a free editable map of the world from GPS data, aerial
photography and local knowledge. To support this objective, QGIS provides support for OSM data.
Using the Browser Panel, you can load an .osm file to the map canvas, in which case you’ll get a dialog to select
sublayers based on the geometry type. The loaded layers will contain all the data of that geometry type in the .osm
file, and keep the osm file data structure.
SpatiaLite Layers
The first time you load data from a SpatiaLite database, begin by:
• clicking on the Add SpatiaLite Layer
toolbar button
• selecting the Add SpatiaLite Layer… option from the Layer ► Add Layer menu
• or by typing Ctrl+Shift+L
This will bring up a window that will allow you either to connect to a SpatiaLite database already known to QGIS
(which you choose from the drop-down menu) or to define a new connection to a new database. To define a new
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connection, click on New and use the file browser to point to your SpatiaLite database, which is a file with a .sqlite
extension.
QGIS also supports editable views in SpatiaLite.
GPS
Loading GPS data in QGIS can be done using the core plugin GPS Tools. Instructions are found in section GPS
Plugin.
GRASS
Working with GRASS vector data is described in section GRASS GIS Integration.
Database related tools
Creating a stored Connection
In order to read and write tables from a database format QGIS supports you have to create a connection to that
database. While QGIS Browser Panel is the simplest and recommanded way to connect to and use databases, QGIS
provides other tools to connect to each of them and load their tables:
• Add PostGIS Layer… or by typing Ctrl+Shift+D
• Add MSSQL Spatial Layer
• Add Oracle Spatial Layer… or by typing Ctrl+Shift+O
• Add DB2 Spatial Layer… or by typing Ctrl+Shift+2
These tools are accessible either from the Manage Layers Toolbar and the Layer ► Add Layer ► menu. Connecting
to SpatiaLite database is described at SpatiaLite Layers.
Tip: Create connection to database from the QGIS Browser Panel
Selecting the corresponding database format in the Browser tree, right-clicking and choosing connect will provide
you with the database connection dialog.
Most of the connection dialogs follow a common basis that will be described below using the PostgreSQL database
tool as an example. For additional settings specific to other providers, you can find corresponding descriptions at:
• Connecting to MSSQL Spatial;
• Connecting to Oracle Spatial;
• Connecting to DB2 Spatial.
The first time you use a PostGIS data source, you must create a connection to a database that contains the data. Begin
by clicking the appropriate button as exposed above, opening an Add PostGIS Table(s) dialog (see Obr. 13.12). To
access the connection manager, click on the New button to display the Create a New PostGIS Connection dialog.
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Obr. 13.11: Create a New PostGIS Connection Dialog
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The parameters required for a PostGIS connection are explained below. For the other database types, see their
differences at Particular Connection requirements.
• Name: A name for this connection. It can be the same as Database.
• Service: Service parameter to be used alternatively to hostname/port (and potentially database). This can be
defined in pg_service.conf. Check the PostgreSQL Service connection file section for more details.
• Host: Name of the database host. This must be a resolvable host name such as would be used to open a TCP/IP
connection or ping the host. If the database is on the same computer as QGIS, simply enter localhost here.
• Port: Port number the PostgreSQL database server listens on. The default port for PostGIS is 5432.
• Database: Name of the database.
• SSL mode: SSL encryption setup The following options are available:
– Prefer (the default): I don’t care about encryption, but I wish to pay the overhead of encryption if the
server supports it.
– Require: I want my data to be encrypted, and I accept the overhead. I trust that the network will make
sure I always connect to the server I want.
– Verify CA: I want my data encrypted, and I accept the overhead. I want to be sure that I connect to a server
that I trust.
– Verify Full: I want my data encrypted, and I accept the overhead. I want to be sure that I connect to
a server I trust, and that it’s the one I specify.
– Allow: I don’t care about security, but I will pay the overhead of encryption if the server insists on it.
– Disable: I don’t care about security, and I don’t want to pay the overhead of encryption.
• Authentication, basic.
– User name: User name used to log in to the database.
– Password: Password used with Username to connect to the database.
You can save any or both of the User name and Password parameters, in which case they will be used
by default each time you need to connect to this database. If not saved, you’ll be prompted to supply the
credentials to connect to the database in next QGIS sessions. The connection parameters you entered are stored
in a temporary internal cache and returned whenever a username/password for the same database is requested,
until you end the current QGIS session.
Varování: QGIS User Settings and Security
In the Authentication tab, saving username and password will keep unprotected credentials in the
connection configuration. Those credentials will be visible if, for instance, you share the project file
with someone. Therefore, it is advisable to save your credentials in an Authentication configuration instead
(Configurations tab - See Ověřovací systém for more details) or in a service connection file (see PostgreSQL
Service connection file for example).
• Authentication, configurations. Choose an authentication configuration. You can add configurations using the
button. Choices are:
– Basic authentication
– PKI PKCS#12 authentication
– PKI paths authentication
– PKI stored identity certificate
Optionally, depending on the type of database, you can activate the following checkboxes:
• Only show layers in the layer registries
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• Don’t resolve type of unrestricted columns (GEOMETRY)
• Only look in the ‚public‘ schema
• Also list tables with no geometry
• Use estimated table metadata
• Allow saving/loading QGIS projects in the database - more details here
Tip: Use estimated table metadata to speed up operations
When initializing layers, various queries may be needed to establish the characteristics of the geometries stored in the
database table. When the Use estimated table metadata option is checked, these queries examine only a sample of the
rows and use the table statistics, rather than the entire table. This can drastically speed up operations on large datasets,
but may result in incorrect characterization of layers (e.g. the feature count of filtered layers will not be accurately
determined) and may even cause strange behaviour if columns that are supposed to be unique actually are not.
Once all parameters and options are set, you can test the connection by clicking the Test Connection button or apply
it by clicking the OK button. From Add PostGIS Table(s), click now on Connect, and the dialog is filled with tables
from the selected database (as shown in Obr. 13.12).
Particular Connection requirements
Because of database type particularities, provided options are not the same. Database specific options are described
below.
PostgreSQL Service connection file
The service connection file allows PostgreSQL connection parameters to be associated with a single service name.
That service name can then be specified by a client and the associated settings will be used.
It’s called .pg_service.conf under *nix systems (GNU/Linux, macOS etc.) and pg_service.conf on
Windows.
The service file can look like this:
[water_service]
host=192.168.0.45
port=5433
dbname=gisdb
user=paul
password=paulspass
[wastewater_service]
host=dbserver.com
dbname=water
user=waterpass
Poznámka: There are two services in the above example: water_service and wastewater_service. You
can use these to connect from QGIS, pgAdmin, etc. by specifying only the name of the service you want to connect
to (without the enclosing brackets). If you want to use the service with psql you need to do something like export
PGSERVICE=water_service before doing your psql commands.
You can find all the PostgreSQL parameters here
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Poznámka: If you don’t want to save the passwords in the service file you can use the .pg_pass option.
On *nix operating systems (GNU/Linux, macOS etc.) you can save the .pg_service.conf file in the user’s
home directory and PostgreSQL clients will automatically be aware of it. For example, if the logged user is web, .
pg_service.conf should be saved in the /home/web/ directory in order to directly work (without specifying
any other environment variables).
You can specify the location of the service file by creating a PGSERVICEFILE environment variable (e.g.
run the export PGSERVICEFILE=/home/web/.pg_service.conf command under your *nix OS to
temporarily set the PGSERVICEFILE variable)
You can also make the service file available system-wide (all users) either by placing the .pg_service.conf file
in pg_config --sysconfdir or by adding the PGSYSCONFDIR environment variable to specify the directory
containing the service file. If service definitions with the same name exist in the user and the system file, the user file
takes precedence.
Varování: There are some caveats under Windows:
• The service file should be saved as pg_service.conf and not as .pg_service.conf.
• The service file should be saved in Unix format in order to work. One way to do it is to open it with
Notepad++ and Edit ► EOL Conversion ► UNIX Format ► File save.
• You can add environmental variables in various ways; a tested one, known to work reliably, is Control
Panel ► System and Security ► System ► Advanced system settings ► Environment Variables adding
PGSERVICEFILE with the path - e.g. C:\Users\John\pg_service.conf
• After adding an environment variable you may also need to restart the computer.
Connecting to Oracle Spatial
The spatial features in Oracle Spatial aid users in managing geographic and location data in a native type within an
Oracle database. In addition to some of the options in Creating a stored Connection, the connection dialog proposes:
• Database: SID or SERVICE_NAME of the Oracle instance;
• Port: Port number the Oracle database server listens on. The default port is 1521;
• Options: Oracle connection specific options (e.g. OCI_ATTR_PREFETCH_ROWS,
OCI_ATTR_PREFETCH_MEMORY). The format of the options string is a semicolon separated list
of option names or option=value pairs;
• Workspace: Workspace to switch to;
• Schema: Schema in which the data are stored
Optionally, you can activate the following checkboxes:
• Only look in metadata table: restricts the displayed tables to those that are in the
all_sdo_geom_metadata view. This can speed up the initial display of spatial tables.
• Only look for user’s tables: when searching for spatial tables, restricts the search to tables that are owned by
the user.
• Also list tables with no geometry: indicates that tables without geometry should also be listed by default.
• Use estimated table statistics for the layer metadata: when the layer is set up, various metadata are required
for the Oracle table. This includes information such as the table row count, geometry type and spatial extents
of the data in the geometry column. If the table contains a large number of rows, determining this metadata
can be time-consuming. By activating this option, the following fast table metadata operations are done:
Row count is determined from all_tables.num_rows. Table extents are always determined with the
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SDO_TUNE.EXTENTS_OF function, even if a layer filter is applied. Table geometry is determined from the
first 100 non-null geometry rows in the table.
• Only existing geometry types: only lists the existing geometry types and don’t offer to add others.
• Include additional geometry attributes.
Tip: Oracle Spatial Layers
Normally, an Oracle Spatial layer is defined by an entry in the USER_SDO_METADATA table.
To ensure that selection tools work correctly, it is recommended that your tables have a primary key.
Connecting to DB2 Spatial
In addition to some of the options described in Creating a stored Connection, the connection to a DB2 database (see
DB2 Spatial Layers for more information) can be specified using either a Service/DSN name defined to ODBC or
Driver, Host and Port.
An ODBC Service/DSN connection requires the service name defined to ODBC.
A driver/host/port connection requires:
• Driver: Name of the DB2 driver. Typically this would be IBM DB2 ODBC DRIVER.
• DB2 Host: Name of the database host. This must be a resolvable host name such as would be used to open
a TCP/IP connection or ping the host. If the database is on the same computer as QGIS, simply enter localhost
here.
• DB2 Port: Port number the DB2 database server listens on. The default DB2 LUW port is 50000. The default
DB2 z/OS port is 446.
Tip: DB2 Spatial Layers
A DB2 Spatial layer is defined by a row in the DB2GSE.ST_GEOMETRY_COLUMNS view.
Poznámka: In order to work effectively with DB2 spatial tables in QGIS, it is important that tables have an INTEGER
or BIGINT column defined as PRIMARY KEY and if new features are going to be added, this column should also
have the GENERATED characteristic.
It is also helpful for the spatial column to be registered with a specific spatial reference identifier (most often 4326
for WGS84 coordinates). A spatial column can be registered by calling the ST_Register_Spatial_Column
stored procedure.
Connecting to MSSQL Spatial
In addition to some of the options in Creating a stored Connection, creating a new MSSQL connection dialog proposes
you to fill a Provider/DSN name. You can also display available databases.
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Loading a Database Layer
Once you have one or more connections defined to a database (see section Creating a stored Connection), you can
load layers from it. Of course, this requires that data are available. See section Importing Data into PostgreSQL for
a discussion on importing data into a PostGIS database.
To load a layer from a database, you can perform the following steps:
1. Open the „Add <database> table(s)“ dialog (see Creating a stored Connection).
2. Choose the connection from the drop-down list and click Connect.
3. Select or unselect Also list tables with no geometry.
4. Optionally, use some Search Options to reduce the list of tables to those matching your search. You can
also set this option before you hit the Connect button, speeding up the database fetching.
5. Find the layer(s) you wish to add in the list of available layers.
6. Select it by clicking on it. You can select multiple layers by holding down the Shift or Ctrl key while
clicking.
7. If applicable, use the Set Filter button (or double-click the layer) to start the Query Builder dialog (see section
Query Builder) and define which features to load from the selected layer. The filter expression appears in the
sql column. This restriction can be removed or edited in the Layer Properties ► General ► Provider Feature
Filter frame.
8. The checkbox in the Select at id column that is activated by default gets the feature ids without the
attributes and generally speeds up the data loading.
9. Click on the Add button to add the layer to the map.
Obr. 13.12: Add PostGIS Table(s) Dialog
Tip: Use the Browser Panel to speed up loading of database table(s)
Adding DB tables from the Data Source Manager may sometimes be time consuming as QGIS fetches statistics and
properties (e.g. geometry type and field, CRS, number of features) for each table beforehand. To avoid this, once the
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connection is set, it is better to use the Browser Panel or the DB Manager to drag and drop the database tables into
the map canvas.
13.1.4 QGIS Custom formats
QGIS proposes two custom formats:
• Temporary Scratch Layer: a memory layer that is bound to the project (see Creating a new Temporary Scratch
Layer for more information)
• Virtual Layers: a layer resulting from a query on other layer(s) (see Creating virtual layers for more information)
13.1.5 QLR - QGIS Layer Definition File
Layer definitions can be saved as a Layer Definition File (QLR - .qlr) using Export ► Save As Layer Definition
File… in the layer context menu.
The QLR format makes it possible to share „complete“ QGIS layers with other QGIS users. QLR files contain links
to the data sources and all the QGIS style information necessary to style the layer.
QLR files are shown in the Browser Panel and can be used to add layers (with their saved styles) to the Layers Panel.
You can also drag and drop QLR files from the system file manager into the map canvas.
13.1.6 Connecting to web services
With QGIS you can get access to different types of OGC web services (WM(T)S, WFS(-T), WCS, CSW, …). Thanks
to QGIS Server, you can also publish such services. QGIS-Server-manual contains descriptions of these capabilities.
Using Vector Tiles services
Vector Tiles services can be found in the Vector Tiles top level entry in the Browser. You can add a service by opening
the context menu with a right-click and choosing New Generic Connection …. You set up a service by adding a Name
and a URL. The Vector Tiles Service must provide tiles in .pbf format. The dialog provides two menus to define the
Min. Zoom Level and the Max. Zoom Level. Vector Tiles have a pyramid structure. By using these options you
have the opportunity to individually generate layers from the tile pyramid. These layers will then be used to render
the Vector Tile in QGIS. For Mercator projection (used by OpenStreetMap Vector Tiles) Zoom Level 0 represents
the whole world at a scale of 1:500.000.000. Zoom Level 14 represents the scale 1:35.000. Obr. 13.13 shows the
dialog with the MapTiler planet Vector Tiles service configuration.
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Obr. 13.13: Vector Tiles - Maptiler Planet configuration
By using New ArcGIS Vector Tile Service Connection … you can connect to ArcGIS Vector Tile Services.
Using XYZ Tile services
XYZ Tile services can be found in the XYZ Tiles top level entry in the Browser. By default, the OpenStreetMap XYZ
Tile service is configured. You can add other services that use the XYZ Tile protocol by choosing New Connection in
the XYZ Tiles context menu (right-click to open). Obr. 13.14 shows the dialog with the OpenStreetMap XYZ Tile
service configuration.
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Obr. 13.14: XYZ Tiles - OpenStreetMap configuration
Configurations can be saved (Save Connections) to XML and loaded (Load Connections) through the context menu.
Authentication configuration is supported. The XML file for OpenStreetMap looks like this:
<!DOCTYPE connections>
<qgsXYZTilesConnections version="1.0">
<xyztiles url="https://tile.openstreetmap.org/{z}/{x}/{y}.png"
zmin="0" zmax="19" tilePixelRatio="0" password="" name="OpenStreetMap"
username="" authcfg="" referer=""/>
</qgsXYZTilesConnections>
Once a connection to a XYZ tile service is set, right-click over the entry to:
• Edit… the XYZ connection settings
• Delete the connection
• Export layer… ► To File, saving it as a raster
• Add layer to project: a double-click also adds the layer
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• View the Layer Properties… and get access to metadata and a preview of the data provided by the service. More
settings are available when the layer has been loaded into the project.
Examples of XYZ Tile services:
• OpenStreetMap Monochrome: URL: http://tiles.wmflabs.org/bw-mapnik/{z}/{x}/{y}.
png, Min. Zoom Level: 0, Max. Zoom Level: 19.
• Google Maps: URL: https://mt1.google.com/vt/lyrs=m&x={x}&y={y}&z={z}, Min. Zoom
Level: 0, Max. Zoom Level: 19.
• Open Weather Map Temperature: URL: http://tile.openweathermap.org/map/temp_new/
{z}/{x}/{y}.png?appid={api_key} Min. Zoom Level: 0, Max. Zoom Level: 19.
13.2 Creating Layers
Layers can be created in many ways, including:
• empty layers from scratch
• layers from existing layers
• layers from the clipboard
• layers as a result of an SQL-like query based on one or many layers (virtual layers)
QGIS also provides tools to import/export from/to different formats.
13.2.1 Creating new vector layers
QGIS allows you to create new layers in different formats. It provides tools for creating GeoPackage, Shapefile,
SpatiaLite, GPX format and Temporary Scratch layers (aka memory layers). Creation of a new GRASS layer
is supported within the GRASS plugin.
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Creating a new GeoPackage layer
To create a new GeoPackage layer, press the New GeoPackage Layer… button in the Layer ► Create Layer ►
menu or from the Data Source Manager toolbar. The New GeoPackage Layer dialog will be displayed as shown in
Obr. 13.15.
Obr. 13.15: Creating a New GeoPackage layer dialog
1. The first step is to indicate the database file location. This can be done by pressing the … button to the right of
the Database field and select an existing GeoPackage file or create a new one. QGIS will automatically add the
right extension to the name you provide.
2. Give the new layer / table a name (Table name)
3. Define the Geometry type. If not a geometryless layer, you can specify whether it should Include Z dimension
and/or Include M values.
4. Specify the coordinate reference system using the button
To add fields to the layer you are creating:
1. Enter the Name of the field
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2. Select the data Type. Supported types are Text data, Whole number (both integer and integer64), Decimal
number, Date and Date and time, Binary (BLOB) and Boolean.
3. Depending on the selected data format, enter the Maximum length of values.
4. Click on the Add to Fields List button
5. Reproduce the steps above for each field you need to add
6. Once you are happy with the attributes, click OK. QGIS will add the new layer to the legend, and you can edit
it as described in section Digitizing an existing layer.
By default, when creating a GeoPackage layer, QGIS generates a Feature id column called fid which acts as the
primary key of the layer. The name can be changed. The geometry field, if availabe, is named geometry, and you
can choose to Create a spatial index on it. These options can be found under the Advanced Options together with the
Layer identifier (short human readable name of the layer) and the Layer description.
Further management of GeoPackage layers can be done with the DB Manager.
Creating a new Shapefile layer
To create a new ESRI Shapefile format layer, press the New Shapefile Layer… button in the Layer ► Create Layer
► menu or from the Data Source Manager toolbar. The New Shapefile Layer dialog will be displayed as shown in
Obr. 13.16.
1. Provide a path and file name using the … button next to File name. QGIS will automatically add the right
extension to the name you provide.
2. Next, indicate the File encoding of the data
3. Choose the Geometry type of the layer: No Geometry (resulting in a .DBF format file), point, multipoint, line
or polygon
4. Specify whether the geometry should have additional dimensions: None, Z (+ M values) or M values
5. Specify the coordinate reference system using the button
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Obr. 13.16: Creating a new Shapefile layer dialog
To add fields to the layer you are creating:
1. Enter the Name of the field
2. Select the data Type. Only Decimal number, Whole number, Text data and Date attributes are supported.
3. Depending on the selected data format, enter the Length and Precision.
4. Click on the Add to Fields List button
5. Reproduce the steps above for each field you need to add
6. Once you are happy with the attributes, click OK. QGIS will add the new layer to the legend, and you can edit
it as described in section Digitizing an existing layer.
By default, a first integer id column is added but can be removed.
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Creating a new SpatiaLite layer
To create a new SpatiaLite layer, press the New SpatiaLite Layer… button in the Layer ► Create Layer ► menu
or from the Data Source Manager toolbar. The New SpatiaLite Layer dialog will be displayed as shown in Obr. 13.17.
Obr. 13.17: Creating a New SpatiaLite layer dialog
1. The first step is to indicate the database file location. This can be done by pressing the … button to the right of
the Database field and select an existing SpatiaLite file or create a new one. QGIS will automatically add the
right extension to the name you provide.
2. Provide a name (Layer name) for the new layer
3. Define the Geometry type. If not a geometryless layer, you can specify whether it should Include Z dimension
and/or Include M values.
4. Specify the coordinate reference system using the button.
To add fields to the layer you are creating:
1. Enter the Name of the field
2. Select the data Type. Supported types are Text data, Whole number and Decimal number.
3. Click on the Add to Fields List button
4. Reproduce the steps above for each field you need to add
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5. Once you are happy with the attributes, click OK. QGIS will add the new layer to the legend, and you can edit
it as described in section Digitizing an existing layer.
If desired, you can select Create an autoincrementing primary key under the guilabel:Advanced Options section.
You can also rename the Geometry column (geometry by default).
Further management of SpatiaLite layers can be done with DB Manager.
Creating a new GPX layer
To create a new GPX file, you first need to load the GPS plugin. Plugins ► Plugin Manager… opens the Plugin
Manager Dialog. Activate the GPS Tools checkbox.
When this plugin is loaded, choose Create Layer ► Create new GPX Layer… from the Layer menu. In the dialog,
choose where to save the new file and press Save. Three new layers are added to the Layers Panel: waypoints,
routes and tracks.
Creating a new Temporary Scratch Layer
Temporary Scratch Layers are in-memory layers, meaning that they are not saved on disk and will be discarded
when QGIS is closed. They can be handy for storing features you temporarily need or as intermediate layers during
geoprocessing operations.
To create a new Temporary Scratch layer, choose the New Temporary Scratch Layer… entry in the Layer ► Create
Layer ► menu or in the Data Source Manager toolbar. The New Temporary Scratch Layer dialog will be displayed
as shown in Obr. 13.18. Then:
1. Provide the Layer name
2. Select the Geometry type. Here you can create a:
• No geometry type layer, served as simple table,
• Point or MultiPoint layer,
• LineString/CompoundCurve or MultiLineString/MultiCurve layer,
• Polygon/CurvePolygon or MultiPolygon/MultiSurface layer.
3. For geometric types, specify the dimensions of the dataset: check whether it should Include Z dimension and/or
Include M values
4. Specify the coordinate reference system using the button.
5. Add fields to the layer. Note that unlike many formats, temporary layers can be created without any fields. This
step is thus optional.
1. Enter the Name of the field
2. Select the data Type: Text, Whole number, Decimal number, Boolean, Date, Time, Date & Time and Binary
(BLOB) are supported.
3. Depending on the selected data format, enter the Length and Precision
4. Click on the Add to Fields List button
5. Repeat the steps above for each field you need to add
6. Once you are happy with the settings, click OK. QGIS will add the new layer to the Layers panel, and you can
edit it as described in section Digitizing an existing layer.
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Obr. 13.18: Creating a new Temporary Scratch layer dialog
You can also create prepopulated temporary scratch layers using e.g. the clipboard (see Creating new layers from the
clipboard) or as a result of a Processing algorithm.
Tip: Permanently store a memory layer on disk
To avoid data loss when closing a project with temporary scratch layers, you can save these layers to any vector format
supported by QGIS:
• clicking the indicator icon next to the layer;
• selecting the Make permanent entry in the layer contextual menu;
• using the Export ► entry from the contextual menu or the Layer ► Save As… menu.
Each of these commands opens the Save Vector Layer as dialog described in the Creating new layers from an existing
layer section and the saved file replaces the temporary one in the Layers panel.
13.2.2 Creating new layers from an existing layer
Both raster and vector layers can be saved in a different format and/or reprojected to a different coordinate reference
system (CRS) using the Layer ► Save As… menu or right-clicking on the layer in the Layers panel and selecting:
• Export ► Save As… for raster layers
• Export ► Save Features As… or Export ► Save Selected Features As… for vector layers.
• Drag and drop the layer from the layer tree to the PostGIS entry in the Browser Panel. Note that you must have
a PostGIS connection in the Browser Panel.
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Common parameters
The Save Layer as… dialog shows several parameters to change the behavior when saving the layer. Among the
common parameters for raster and vector are:
• File name: the location of the file on the disk. It can refer to the output layer or to a container that stores the
layer (for example database-like formats such as GeoPackage, SpatiaLite or Open Document Spreadsheets).
• CRS: can be changed to reproject the data
• Extent (possible values are layer, Map view or user-defined extent)
• Add saved file to map: to add the new layer to the canvas
However, some parameters are specific to raster and vector formats:
Raster specific parameters
Depending on the format of export, some of these options may not be available:
• Output mode (it can be raw data or rendered image)
• Format: exports to any raster format GDAL can write to, such as GeoTiff, GeoPackage, MBTiles, Geospatial
PDF, SAGA GIS Binary Grid, Intergraph Raster, ESRI .hdr Labelled…
• Resolution
• Create Options: use advanced options (file compression, block sizes, colorimetry…) when generating files, either
from the predefined create profiles related to the output format or by setting each parameter.
• Pyramids creation
• VRT Tiles in case you opted to Create VRT
• No data values
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Obr. 13.19: Saving as a new raster layer
Vector specific parameters
Depending on the format of export, some of these options may be available:
• Format: exports to any vector format GDAL can write to, such as GeoPackage, GML, ESRI Shapefile,
AutoCAD DXF, ESRI FileGDB, Mapinfo TAB or MIF, SpatiaLite, CSV, KML, ODS, …
• Layer name: available when the File name refers to a container-like format, this entry represents the output
layer.
• Encoding
• Save only selected features
• Select fields to export and their export options. In case you set your fields behavior with some Edit widgets, e.g.
value map, you can keep the displayed values in the layer by checking Replace all selected raw fields
values by displayed values.
• Symbology export: can be used mainly for DXF export and for all file formats who manage OGR feature styles
(see note below) as DXF, KML, tab file formats:
– No symbology: default style of the application that reads the data
– Feature symbology: save style with OGR Feature Styles (see note below)
– Symbol Layer symbology: save with OGR Feature Styles (see note below) but export the same geometry
multiple times if there are multiple symbology symbol layers used
– A Scale value can be applied to the latest options
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Poznámka: OGR Feature Styles are a way to store style directly in the data as a hidden attribute. Only some formats
can handle this kind of information. KML, DXF and TAB file formats are such formats. For advanced details, you
can read the OGR Feature Styles specification document.
• Geometry: you can configure the geometry capabilities of the output layer
– geometry type: keeps the original geometry of the features when set to Automatic, otherwise removes or
overrides it with any type. You can add an empty geometry column to an attribute table and remove the
geometry column of a spatial layer.
– Force multi-type: forces creation of multi-geometry features in the layer.
– Include z-dimension to geometries.
Tip: Overriding layer geometry type makes it possible to do things like save a geometryless table (e.g. .csv file)
into a shapefile WITH any type of geometry (point, line, polygon), so that geometries can then be manually added to
rows with the Add Part
tool.
• Datasource Options, Layer Options or Custom Options which allow you to configure advanced parameters
depending on the output format. Some are described in Exploring Data Formats and Fields but for full details,
see the GDAL driver documentation. Each file format has its own custom parameters, e.g. for the GeoJSON
format have a look at the GDAL GeoJSON documentation.
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Obr. 13.20: Saving as a new vector layer
When saving a vector layer into an existing file, depending on the capabilities of the output format (Geopackage,
SpatiaLite, FileGDB…), the user can decide whether to:
• overwrite the whole file
• overwrite only the target layer (the layer name is configurable)
• append features to the existing target layer
• append features, add new fields if there are any.
For formats like ESRI Shapefile, MapInfo .tab, feature append is also available.
13.2.3 Creating new DXF files
Besides the Save As… dialog which provides options to export a single layer to another format, including *.
DXF, QGIS provides another tool to export multiple layers as a single DXF layer. It’s accessible in the Project ►
Import/Export ► Export Project to DXF… menu.
In the DXF Export dialog:
1. Provide the destination file.
2. Choose the symbology mode and scale (see the OGR Feature Styles note), if applicable.
3. Select the data Encoding.
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4. Select the CRS to apply: the selected layers will be reprojected to the given CRS.
5. Select the layers to include in the DXF files either by checking them in the table widget or automatically picking
them from an existing map theme. The Select All and Deselect All buttons can help to quickly set the data to
export.
For each layer, you can choose whether to export all the features in a single DXF layer or rely on a field whose
values are used to split the features into layers in the DXF output.
Optionally, you can also choose to:
• Use the layer title as name if set instead of the layer name itself;
• Export features intersecting the current map extent;
• Force 2d output (eg. to support polyline width);
• Export label as MTEXT elements or TEXT elements.
Obr. 13.21: Exporting a project to DXF dialog
13.2.4 Creating new layers from the clipboard
Features that are on the clipboard can be pasted into a new layer. To do this, Select some features, copy them to the
clipboard, and then paste them into a new layer using Edit ► Paste Features as ► and choosing:
• New Vector Layer…: the Save vector layer as… dialog appears (see Creating new layers from an existing layer
for parameters)
• or Temporary Scratch Layer…: you need to provide a name for the layer
A new layer, filled with selected features and their attributes is created (and added to map canvas).
Poznámka: Creating layers from the clipboard is possible with features selected and copied within QGIS as well
as features from another application, as long as their geometries are defined using well-known text (WKT).
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13.2.5 Creating virtual layers
A virtual layer is a special kind of vector layer. It allows you to define a layer as the result of an SQL query involving
any number of other vector layers that QGIS is able to open. Virtual layers do not carry data by themselves and can
be seen as views.
To create a virtual layer, open the virtual layer creation dialog by:
• choosing the Add/Edit Virtual Layer entry in the Layer ► Add Layer ► menu;
• enabling the Add Virtual Layer tab in the Data Source Manager dialog;
• or using the DB Manager dialog tree.
The dialog allows you to specify a Layer name and an SQL Query. The query can use the name (or id) of loaded
vector layers as tables, as well as their field names as columns.
For example, if you have a layer called airports, you can create a new virtual layer called public_airports
with an SQL query like:
SELECT *
FROM airports
WHERE USE = "Civilian/Public"
The SQL query will be executed, regardless of the underlying provider of the airports layer, even if this provider
does not directly support SQL queries.
Obr. 13.22: Create virtual layers dialog
Joins and complex queries can also be created, for example, to join airports and country information:
SELECT airports.*, country.population
FROM airports
JOIN country
ON airports.country = country.name
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Poznámka: It’s also possible to create virtual layers using the SQL window of DB Manager Plugin.
Embedding layers for use in queries
Besides the vector layers available in the map canvas, the user can add layers to the Embedded layers list, which can
be used in queries without the need to have them showing in the map canvas or Layers panel.
To embed a layer, click Add and provide the Local name, Provider, Encoding and the path to the Source.
The Import button allows adding layers in the map canvas into the Embedded layers list. Those layers can then be
removed from the Layers panel without breaking existent queries.
Supported query language
The underlying engine uses SQLite and SpatiaLite to operate.
It means you can use all of the SQL your local installation of SQLite understands.
Functions from SQLite and spatial functions from SpatiaLite can also be used in a virtual layer query. For instance,
creating a point layer out of an attribute-only layer can be done with a query similar to:
SELECT id, MakePoint(x, y, 4326) as geometry
FROM coordinates
Functions of QGIS expressions can also be used in a virtual layer query.
To refer the geometry column of a layer, use the name geometry.
Contrary to a pure SQL query, all the fields of a virtual layer query must be named. Don’t forget to use the as keyword
to name your columns if they are the result of a computation or a function call.
Performance issues
With default parameters, the virtual layer engine will try its best to detect the type of the different columns of the
query, including the type of the geometry column if one is present.
This is done by introspecting the query when possible or by fetching the first row of the query (LIMIT 1) as a last
resort. Fetching the first row of the result just to create the layer may be undesirable for performance reasons.
The creation dialog parameters:
• Unique identifier column: specifies a field of the query that represents unique integer values that QGIS can use
as row identifiers. By default, an autoincrementing integer value is used. Defining a unique identifier column
speeds up the selection of rows by id.
• No geometry: forces the virtual layer to ignore any geometry field. The resulting layer is an attribute-only layer.
• Geometry Column: specifies the name of the geometry column.
• Geometry Type: specifies the type of the geometry.
• Geometry CRS: specifies the coordinate reference system of the virtual layer.
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Special comments
The virtual layer engine tries to determine the type of each column of the query. If it fails, the first row of the query
is fetched to determine column types.
The type of a particular column can be specified directly in the query by using some special comments.
The syntax is the following: /*:type*/. It has to be placed just after the name of a column. type can be either
int for integers, real for floating point numbers or text.
For instance:
SELECT id+1 as nid /*:int*/
FROM table
The type and coordinate reference system of the geometry column can also be set thanks to special comments with the
following syntax /*:gtype:srid*/ where gtype is the geometry type (point, linestring, polygon,
multipoint, multilinestring or multipolygon) and srid an integer representing the EPSG code of
a coordinate reference system.
Use of indexes
When requesting a layer through a virtual layer, the source layer indices will be used in the following ways:
• if an = predicate is used on the primary key column of the layer, the underlying data provider will be asked for
a particular id (FilterFid)
• for any other predicates (>, <=, !=, etc.) or on a column without a primary key, a request built from an
expression will be used to request the underlying vector data provider. It means indexes may be used on database
providers if they exist.
A specific syntax exists to handle spatial predicates in requests and triggers the use of a spatial index: a hidden column
named _search_frame_ exists for each virtual layer. This column can be compared for equality to a bounding
box. Example:
SELECT *
FROM vtab
WHERE _search_frame_=BuildMbr(-2.10,49.38,-1.3,49.99,4326)
Spatial binary predicates like ST_Intersects are sped up significantly when used in conjunction with this spatial
index syntax.
13.3 Exploring Data Formats and Fields
13.3.1 Raster data
GIS raster data are matrices of discrete cells that represent features / phenomena on, above or below the earth’s
surface. Each cell in the raster grid has the same size, and cells are usually rectangular (in QGIS they will always be
rectangular). Typical raster datasets include remote sensing data, such as aerial photography, or satellite imagery and
modelled data, such as elevation or temperature.
Unlike vector data, raster data typically do not have an associated database record for each cell. They are geocoded
by pixel resolution and the X/Y coordinate of a corner pixel of the raster layer. This allows QGIS to position the data
correctly on the map canvas.
The GeoPackage format is convenient for storing raster data when working with QGIS. The popular and powerful
GeoTiff format is a good alternative.
QGIS makes use of georeference information inside the raster layer (e.g., GeoTiff) or an associated world file to
properly display the data.
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13.3.2 Vektorová data
Many of the features and tools available in QGIS work the same, regardless the vector data source. However, because
of the differences in format specifications (GeoPackage, ESRI Shapefile, MapInfo and MicroStation file formats,
AutoCAD DXF, PostGIS, SpatiaLite, DB2, Oracle Spatial, MSSQL Spatial databases, and many more), QGIS may
handle some of their properties differently. Support is provided by the OGR Simple Feature Library. This section
describes how to work with these specificities.
Poznámka: QGIS supports (multi)point, (multi)line, (multi)polygon, CircularString, CompoundCurve,
CurvePolygon, MultiCurve, MultiSurface feature types, all optionally with Z and/or M values.
You should also note that some drivers don’t support some of these feature types, like CircularString,
CompoundCurve, CurvePolygon, MultiCurve, MultiSurface feature type. QGIS will convert them.
GeoPackage
The GeoPackage (GPKG) format is platform-independent, and is implemented as a SQLite database container, and
can be used to store both vector and raster data. The format was defined by the Open Geospatial Consortium (OGC),
and was published in 2014.
GeoPackage can be used to store the following in a SQLite database:
• vector features
• tile matrix sets of imagery and raster maps
• attributes (non-spatial data)
• extensions
Since QGIS version 3.8, GeoPackage can also store QGIS projects. GeoPackage layers can have JSON fields.
GeoPackage is the default format for vector data in QGIS.
ESRI Shapefile format
The ESRI Shapefile format is still one of the most used vector file formats, even if it has some limitations compared
to for instance GeoPackage and SpatiaLite.
An ESRI Shapefile format dataset consists of several files. The following three are required:
1. .shp file containing the feature geometries
2. .dbf file containing the attributes in dBase format
3. .shx index file
An ESRI Shapefile format dataset can also include a file with a .prj suffix, which contains projection information.
While it is very useful to have a projection file, it is not mandatory. A Shapefile format dataset can contain additional
files. For further details, see the the ESRI technical specification at https://www.esri.com/library/whitepapers/pdfs/
shapefile.pdf.
GDAL 3.1 has read-write support for compressed ESRI Shapefile format (shz and shp.zip).
Improving Performance for ESRI Shapefile format datasets
To improve the drawing performance for an ESRI Shapefile format dataset, you can create a spatial index. A spatial
index will improve the speed of both zooming and panning. Spatial indexes used by QGIS have a .qix extension.
Use these steps to create the index:
1. Load an ESRI Shapefile format dataset (see The Browser Panel)
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2. Open the Layer Properties dialog by double-clicking on the layer name in the legend or by right-clicking and
choosing Properties… from the context menu
3. In the Source tab, click the Create Spatial Index button
Problem loading a .prj file
If you load an ESRI Shapefile format dataset with a .prj file and QGIS is not able to read the coordinate reference
system from that file, you will need to define the proper projection manually in the Layer Properties ► Source tab of
the layer by clicking the Select CRS
button. This is due to the fact that .prj files often do not provide the complete
projection parameters as used in QGIS and listed in the CRS dialog.
For the same reason, if you create a new ESRI Shapefile format dataset with QGIS, two different projection files are
created: a .prj file with limited projection parameters, compatible with ESRI software, and a .qpj file, providing
all the parameters of the CRS. Whenever QGIS finds a .qpj file, it will be used instead of the .prj.
Delimited Text Files
Delimited text files are very common and widely used because of their simplicity and readability – data can be viewed
and edited in a plain text editor. A delimited text file is tabular data with columns separated by a defined character
and rows separated by line breaks. The first row usually contains the column names. A common type of delimited text
file is a CSV (Comma Separated Values), with columns separated by commas. Delimited text files can also contain
positional information (see Storing geometry information in delimited text files).
QGIS allows you to load a delimited text file as a layer or an ordinary table (see The Browser Panel or Importing
a delimited text file). First check that the file meets the following requirements:
1. The file must have a delimited header row of field names. This must be the first line of the data (ideally the first
row in the text file).
2. If geometry should be enabled, the file must contain field(s) that define the geometry. These field(s) can have
any name.
3. The X and Y coordinates fields (if geometry is defined by coordinates) must be specified as numbers. The
coordinate system is not important.
4. If you have a CSV file with non-string columns, you must have an accompanying CSVT file (see section Using
CSVT file to control field formatting).
The elevation point data file elevp.csv in the QGIS sample dataset (see section Downloading sample data) is an
example of a valid text file:
X;Y;ELEV
-300120;7689960;13
-654360;7562040;52
1640;7512840;3
[...]
Some things to note about the text file:
1. The example text file uses ; (semicolon) as delimiter (any character can be used to delimit the fields).
2. The first row is the header row. It contains the fields X, Y and ELEV.
3. No quotes (") are used to delimit text fields
4. The X coordinates are contained in the X field
5. The Y coordinates are contained in the Y field
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Storing geometry information in delimited text files
Delimited text files can contain geometry information in two main forms:
• As coordinates in separate columns (eg. Xcol, Ycol… ), for point geometry data;
• As well-known text (WKT) representation of geometry in a single column, for any geometry type.
Features with curved geometries (CircularString, CurvePolygon and CompoundCurve) are supported. Here are some
examples of geometry types in a delimited text file with geometries coded as WKT:
Label;WKT_geom
LineString;LINESTRING(10.0 20.0, 11.0 21.0, 13.0 25.5)
CircularString;CIRCULARSTRING(268 415,227 505,227 406)
CurvePolygon;CURVEPOLYGON(CIRCULARSTRING(1 3, 3 5, 4 7, 7 3, 1 3))
CompoundCurve;COMPOUNDCURVE((5 3, 5 13), CIRCULARSTRING(5 13, 7 15,
9 13), (9 13, 9 3), CIRCULARSTRING(9 3, 7 1, 5 3))
Delimited text files also support Z and M coordinates in geometries:
LINESTRINGZ(10.0 20.0 30.0, 11.0 21.0 31.0, 11.0 22.0 30.0)
Using CSVT file to control field formatting
When loading CSV files, the OGR driver assumes all fields are strings (i.e. text) unless it is told otherwise. You can
create a CSVT file to tell OGR (and QGIS) the data type of the different columns:
Type Název Example
Whole number Integer 4
Decimal number Real 3.456
Datum Date (YYYY-MM-DD) 2016-07-28
Time Time (HH:MM:SS+nn) 18:33:12+00
Date & Time DateTime (YYYY-MM-DD HH:MM:SS+nn) 2016-07-28 18:33:12+00
The CSVT file is a ONE line plain text file with the data types in quotes and separated by commas, e.g.:
"Integer","Real","String"
You can even specify width and precision of each column, e.g.:
"Integer(6)","Real(5.5)","String(22)"
This file is saved in the same folder as the .csv file, with the same name, but .csvt as the extension.
You can find more information at GDAL CSV Driver.
PostGIS Layers
PostGIS layers are stored in a PostgreSQL database. The advantages of PostGIS are spatial indexing, filtering and
querying capabilities. Using PostGIS, vector functions such as select and identify work more accurately than they do
with OGR layers in QGIS.
Tip: PostGIS Layers
Normally, a PostGIS layer is identified by an entry in the geometry_columns table. QGIS can load layers that do not
have an entry in the geometry_columns table. This includes both tables and views. Refer to your PostgreSQL manual
for information on creating views.
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This section contains some details on how QGIS accesses PostgreSQL layers. Most of the time, QGIS should simply
provide you with a list of database tables that can be loaded, and it will load them on request. However, if you have
trouble loading a PostgreSQL table into QGIS, the information below may help you understand QGIS messages and
give you directions for modifying the PostgreSQL table or view definition to allow QGIS to load it.
Primary key
QGIS requires that PostgreSQL layers contain a column that can be used as a unique key for the layer. For tables, this
usually means that the table needs a primary key, or a column with a unique constraint on it. In QGIS, this column
needs to be of type int4 (an integer of size 4 bytes). Alternatively, the ctid column can be used as primary key. If
a table lacks these items, the oid column will be used instead. Performance will be improved if the column is indexed
(note that primary keys are automatically indexed in PostgreSQL).
QGIS offers a checkbox Select at id that is activated by default. This option gets the ids without the attributes, which
is faster in most cases.
Zobrazit
If the PostgreSQL layer is a view, the same requirement exists, but views do not always have primary keys or columns
with unique constraints on them. You have to define a primary key field (has to be integer) in the QGIS dialog before
you can load the view. If a suitable column does not exist in the view, QGIS will not load the layer. If this occurs,
the solution is to alter the view so that it does include a suitable column (a type of integer and either a primary key or
with a unique constraint, preferably indexed).
As for table, a checkbox Select at id is activated by default (see above for the meaning of the checkbox). It can make
sense to disable this option when you use expensive views.
QGIS layer_style table and database backup
If you want to make a backup of your PostGIS database using the pg_dump and pg_restore commands, and
the default layer styles as saved by QGIS fail to restore afterwards, you need to set the XML option to DOCUMENT
before the restore command:
SET XML OPTION DOCUMENT;
Filter database side
QGIS allows to filter features already on server side. Check Settings ► Options ► Data Sources ► Execute
expressions on server-side if possible to do so. Only supported expressions will be sent to the database. Expressions
using unsupported operators or functions will gracefully fallback to local evaluation.
Support of PostgreSQL data types
Data types supported by the PostgreSQL provider include: integer, float, boolean, binary object, varchar, geometry,
timestamp, array, hstore and json.
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Importing Data into PostgreSQL
Data can be imported into PostgreSQL/PostGIS using several tools, including the DB Manager plugin and the
command line tools shp2pgsql and ogr2ogr.
Správce databází
QGIS comes with a core plugin named DB Manager
. It can be used to load data, and it includes support for schemas.
See section DB Manager Plugin for more information.
shp2pgsql
PostGIS includes a utility called shp2pgsql, that can be used to import Shapefile format datasets into a PostGIS-enabled
database. For example, to import a Shapefile format dataset named lakes.shp into a PostgreSQL
database named gis_data, use the following command:
shp2pgsql -s 2964 lakes.shp lakes_new | psql gis_data
This creates a new layer named lakes_new in the gis_data database. The new layer will have a spatial reference
identifier (SRID) of 2964. See section Práce s projekcemi for more information about spatial reference systems and
projections.
Tip: Exporting datasets from PostGIS
There is also a tool for exporting PostGIS datasets to Shapefile format: pgsql2shp. It is shipped within your PostGIS
distribution.
ogr2ogr
In addition to shp2pgsql and DB Manager, there is another tool for feeding geographical data in PostGIS: ogr2ogr.
It is part of your GDAL installation.
To import a Shapefile format dataset into PostGIS, do the following:
ogr2ogr -f "PostgreSQL" PG:"dbname=postgis host=myhost.de user=postgres
password=topsecret" alaska.shp
This will import the Shapefile format dataset alaska.shp into the PostGIS database postgis using the user postgres
with the password topsecret on the host server myhost.de.
Note that OGR must be built with PostgreSQL to support PostGIS. You can verify this by typing (in ):
ogrinfo --formats | grep -i post
If you prefer to use the PostgreSQL’s COPY command instead of the default INSERT INTO method, you can
export the following environment variable (at least available on and ):
export PG_USE_COPY=YES
ogr2ogr does not create spatial indexes like shp2pgsl does. You need to create them manually, using the normal SQL
command CREATE INDEX afterwards, as an extra step (as described in the next section Improving Performance).
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Improving Performance
Retrieving features from a PostgreSQL database can be time-consuming, especially over a network. You can improve
the drawing performance of PostgreSQL layers by ensuring that a PostGIS spatial index exists on each layer in the
database. PostGIS supports creation of a GiST (Generalized Search Tree) index to speed up spatial searching (GiST
index information is taken from the PostGIS documentation available at https://postgis.net).
Tip: You can use the DBManager to create an index for your layer. You should first select the layer and click on
Table ► Edit table, go to Indexes tab and click on Add Spatial Index.
The syntax for creating a GiST index is:
CREATE INDEX [indexname] ON [tablename]
USING GIST ( [geometryfield] GIST_GEOMETRY_OPS );
Note that for large tables, creating the index can take a long time. Once the index is created, you should perform
a VACUUM ANALYZE. See the PostGIS documentation (POSTGIS-PROJECT in Literature and Web References)
for more information.
The following example creates a GiST index:
gsherman@madison:~/current$ psql gis_data
Welcome to psql 8.3.0, the PostgreSQL interactive terminal.
Type: \copyright for distribution terms
\h for help with SQL commands
\? for help with psql commands
\g or terminate with semicolon to execute query
\q to quit
gis_data=# CREATE INDEX sidx_alaska_lakes ON alaska_lakes
gis_data-# USING GIST (the_geom GIST_GEOMETRY_OPS);
CREATE INDEX
gis_data=# VACUUM ANALYZE alaska_lakes;
VACUUM
gis_data=# \q
gsherman@madison:~/current$
Vector layers crossing 180° longitude
Many GIS packages don’t wrap vector maps with a geographic reference system (lat/lon) crossing the 180 degrees
longitude line (http://postgis.refractions.net/documentation/manual-2.0/ST_Shift_Longitude.html). As result, if we
open such a map in QGIS, we could see two widely separated locations, that should appear near each other. In Obr.
13.23, the tiny point on the far left of the map canvas (Chatham Islands) should be within the grid, to the right of the
New Zealand main islands.
Obr. 13.23: Map in lat/lon crossing the 180° longitude line
A work-around is to transform the longitude values using PostGIS and the ST_Shift_Longitude function. This
function reads every point/vertex in every component of every feature in a geometry, and if the longitude coordinate
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is < 0°, it adds 360° to it. The result is a 0° - 360° version of the data to be plotted in a 180°-centric map.
Obr. 13.24: Crossing 180° longitude applying the ST_Shift_Longitude function
Použití
• Import data into PostGIS (Importing Data into PostgreSQL) using, for example, the DB Manager plugin.
• Use the PostGIS command line interface to issue the following command (in this example,
„TABLE“ is the actual name of your PostGIS table): gis_data=# update TABLE set
the_geom=ST_Shift_Longitude(the_geom);
• If everything went well, you should receive a confirmation about the number of features that were updated.
Then you’ll be able to load the map and see the difference (Figure_vector_crossing_map).
SpatiaLite Layers
If you want to save a vector layer using the SpatiaLite format, you can do this by following instructions at Creating
new layers from an existing layer. You select SpatiaLite as Format and enter both File name and Layer name.
Also, you can select SQLite as format and then add SPATIALITE=YES in the Custom Options ► Data source
field. This tells GDAL to create a SpatiaLite database. See also https://gdal.org/drivers/vector/sqlite.html.
QGIS also supports editable views in SpatiaLite. For SpatiaLite data management, you can also use the core plugin
DB Manager.
If you want to create a new SpatiaLite layer, please refer to section Creating a new SpatiaLite layer.
GeoJSON specific parameters
When exporting layers to GeoJSON, there are some specific Layer Options available. These options come from GDAL
which is responsible for the writing of the file:
• COORDINATE_PRECISION the maximum number of digits after the decimal separator to write in coordinates.
Defaults to 15 (note: for Lat Lon coordinates 6 is considered enough). Truncation will occur to remove trailing
zeros.
• RFC7946 by default GeoJSON 2008 will be used. If set to YES, the updated RFC 7946 standard
will be used. Default is NO (thus GeoJSON 2008). See https://gdal.org/drivers/vector/geojson.html#
rfc-7946-write-support for the main differences, in short: only EPSG:4326 is allowed, other crs’s will be
transformed, polygons will be written such as to follow the right-hand rule for orientation, values of a „bbox“
array are [west, south, east, north], not [minx, miny, maxx, maxy]. Some extension member names are
forbidden in FeatureCollection, Feature and Geometry objects, the default coordinate precision is 7 decimal
digits
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• WRITE_BBOX set to YES to include the bounding box of the geometries at the feature and feature collection
level
Besides GeoJSON there is also an option to export to „GeoJSON - Newline Delimited“ (see https://gdal.org/drivers/
vector/geojsonseq.html). Instead of a FeatureCollection with Features, you can stream one type (probably only
Features) sequentially separated with newlines.
GeoJSON - Newline Delimited has some specific Layer options availabe too:
• COORDINATE_PRECISION see above (same as for GeoJSON)
• RS whether to start records with the RS=0x1E character. The difference is how the features are separated: only
by a newline (LF) character (Newline Delimited JSON, geojsonl) or by also prepending a record-separator (RS)
character (giving GeoJSON Text Sequences, geojsons). Default to NO. Files are given the .json extension if
extension is not provided.
DB2 Spatial Layers
IBM DB2 for Linux, Unix and Windows (DB2 LUW), IBM DB2 for z/OS (mainframe) and IBM DashDB products
allow users to store and analyse spatial data in relational table columns. The DB2 provider for QGIS supports the full
range of visualization, analysis and manipulation of spatial data in these databases.
User documentation on these capabilities can be found at the DB2 z/OS KnowledgeCenter, DB2 LUW
KnowledgeCenter and DB2 DashDB KnowledgeCenter.
For more information about working with the DB2 spatial capabilities, check out the DB2 Spatial Tutorial on IBM
DeveloperWorks.
The DB2 provider currently only supports the Windows environment through the Windows ODBC driver.
The client running QGIS needs to have one of the following installed:
• DB2 LUW
• IBM Data Server Driver Package
• IBM Data Server Client
To open a DB2 data in QGIS, see the The Browser Panel or Loading a Database Layer section.
If you are accessing a DB2 LUW database on the same machine or using DB2 LUW as a client, the DB2 executables
and supporting files need to be included in the Windows path. This can be done by creating a batch file like the
following with the name db2.bat and including it in the directory %OSGEO4W_ROOT%/etc/ini:
@echo off
REM Point the following to where DB2 is installed
SET db2path=C:\Program Files (x86)\sqllib
REM This should usually be ok - modify if necessary
SET gskpath=C:\Program Files (x86)\ibm\gsk8
SET Path=%db2path%\BIN;%db2path%\FUNCTION;%gskpath%\lib64;%gskpath%\lib;%path%
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Working with Vector Data
14.1 The Vector Properties Dialog
The Layer Properties dialog for a vector layer provides general settings to manage appearance of layer features in the
map (symbology, labeling, diagrams), interaction with the mouse (actions, map tips, form design). It also provides
information about the layer.
To access the Layer Properties dialog:
• In the Layers panel, double-click the layer or right-click and select Properties… from the pop-up menu;
• Go to Layer ► Layer Properties… menu when the layer is selected.
The vector Layer Properties dialog provides the following sections:
Information Source Symbology[1]
Labels[1]
Mask[1]
3D View[1]
Diagrams Fields Attributes Form
Joins Auxiliary Storage Actions
Display Rendering Temporal
Variables Metadata Dependencies
Legend QGIS Server Digitizing
External plugins[2]
tabs
[1]
Also available in the Layer styling panel
[2]
External plugins you install can optionally add tabs to this dialog. Those are not presented in this document. Refer
to their documentation.
Tip: Share full or partial properties of the layer styles
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The Style menu at the bottom of the dialog allows you to import or export these or part of these properties from/to
several destination (file, clipboard, database). See Managing Custom Styles.
Poznámka: Because properties (symbology, label, actions, default values, forms…) of embedded layers (see
Vnořování projektů) are pulled from the original project file and to avoid changes that may break this behavior, the
layer properties dialog is made unavailable for these layers.
14.1.1 Information Properties
The Information tab is read-only and represents an interesting place to quickly grab summarized information and
metadata on the current layer. Provided information are:
• based on the provider of the layer (format of storage, path, geometry type, data source encoding, extent…);
• picked from the filled metadata (access, links, contacts, history…);
• or related to its geometry (spatial extent, CRS…) or its attributes (number of fields, characteristics of each…).
14.1.2 Source Properties
Use this tab to define general settings for the vector layer.
Obr. 14.1: Source tab in vector Layer Properties dialog
Other than setting the Layer name to display in the Layers Panel, available options include:
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Coordinate Reference System
• Displays the layer’s Coordinate Reference System (CRS). You can change the layer’s CRS, selecting a recently
used one in the drop-down list or clicking on Select CRS
button (see Coordinate Reference System Selector).
Use this process only if the CRS applied to the layer is a wrong one or if none was applied. If you wish to
reproject your data into another CRS, rather use layer reprojection algorithms from Processing or Save it into
another layer.
• Create spatial index (only for OGR-supported formats).
• Update extents information for a layer.
Query Builder
The Query Builder dialog is accessible through the eponym button at the bottom of the Source tab in the Layer
Properties dialog, under the Provider feature filter group.
The Query Builder provides an interface that allows you to define a subset of the features in the layer using a SQL-like
WHERE clause and to display the result in the main window. As long as the query is active, only the features
corresponding to its result are available in the project.
You can use one or more layer attributes to define the filter in the Query Builder. The use of more than one
attribute is shown in Obr. 14.2. In the example, the filter combines the attributes
• toa (DateTime field: cast("toa" as character) > '2017-05-17' and cast("toa"
as character) < '2019-12-24T18:00:00'),
• name (String field: "name" > 'S') and
• FID (Integer field: FID > 10)
using the AND, OR and NOT operators and parenthesis. This syntax (including the DateTime format for the toa
field) works for GeoPackage datasets.
The filter is made at the data provider (OGR, PostgreSQL, MSSQL…) level. So the syntax depends on the data
provider (DateTime is for instance not supported for the ESRI Shapefile format). The complete expression:
cast("toa" as character) > '2017-05-17' AND
cast("toa" as character) < '2019-12-24T18:00:00' AND
NOT ("name" > 'S' OR FID > 10)
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Obr. 14.2: Query Builder
You can also open the Query Builder dialog using the Filter… option from the Layer menu or the layer contextual
menu. The Fields, Values and Operators sections in the dialog help you to construct the SQL-like query exposed in
the Provider specific filter expression box.
The Fields list contains all the fields of the layer. To add an attribute column to the SQL WHERE clause field,
double-click its name or just type it into the SQL box.
The Values frame lists the values of the currently selected field. To list all unique values of a field, click the All button.
To instead list the first 25 unique values of the column, click the Sample button. To add a value to the SQL WHERE
clause field, double click its name in the Values list. You can use the search box at the top of the Values frame to
easily browse and find attribute values in the list.
The Operators section contains all usable operators. To add an operator to the SQL WHERE clause field, click the
appropriate button. Relational operators ( = , > , …), string comparison operator (LIKE), and logical operators (AND,
OR, …) are available.
The Test button helps you check your query and displays a message box with the number of features satisfying the
current query. Use the Clear button to wipe the SQL query and revert the layer to its original state (ie, fully load all
the features).
When a filter is applied, QGIS treats the resulting subset acts as if it were the entire layer. For example if you applied
the filter above for ‚Borough‘ ("TYPE_2" = 'Borough'), you can not display, query, save or edit Anchorage,
because that is a ‚Municipality‘ and therefore not part of the subset.
Tip: Filtered layers are indicated in the Layers Panel
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In the Layers panel, filtered layer is listed with a Filter
icon next to it indicating the query used when the mouse
hovers over the button. Double-click the icon opens the Query Builder dialog for edit.
14.1.3 Symbology Properties
The Symbology tab provides you with a comprehensive tool for rendering and symbolizing your vector data.
You can use tools that are common to all vector data, as well as special symbolizing tools that were designed for
the different kinds of vector data. However all types share the following dialog structure: in the upper part, you have
a widget that helps you prepare the classification and the symbol to use for features and at the bottom the Layer
rendering widget.
Tip: Switch quickly between different layer representations
Using the Styles ► Add menu at the bottom of the Layer Properties dialog, you can save as many styles as needed.
A style is the combination of all properties of a layer (such as symbology, labeling, diagram, fields form, actions…)
as you want. Then, simply switch between styles from the context menu of the layer in Layers Panel to automatically
get different representations of your data.
Tip: Export vector symbology
You have the option to export vector symbology from QGIS into Google *.kml, *.dxf and MapInfo *.tab files. Just
open the right mouse menu of the layer and click on Save As… to specify the name of the output file and its format.
In the dialog, use the Symbology export menu to save the symbology either as Feature symbology ► or as Symbol layer
symbology ►. If you have used symbol layers, it is recommended to use the second setting.
Features rendering
The renderer is responsible for drawing a feature together with the correct symbol. Regardless layer geometry type,
there are four common types of renderers: single symbol, categorized, graduated and rule-based. For point layers,
there are a point displacement and a heatmap renderers available while polygon layers can also be rendered with the
inverted polygons and 2.5 D renderers.
There is no continuous color renderer, because it is in fact only a special case of the graduated renderer. The
categorized and graduated renderers can be created by specifying a symbol and a color ramp - they will set the colors
for symbols appropriately. For each data type (points, lines and polygons), vector symbol layer types are available.
Depending on the chosen renderer, the dialog provides different additional sections.
Poznámka: If you change the renderer type when setting the style of a vector layer the settings you made for the
symbol will be maintained. Be aware that this procedure only works for one change. If you repeat changing the
renderer type the settings for the symbol will get lost.
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Single Symbol Renderer
The Single Symbol renderer is used to render all features of the layer using a single user-defined symbol. See The
Symbol Selector for further information about symbol representation.
Obr. 14.3: Single symbol line properties
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No Symbols Renderer
The No Symbols renderer is a special use case of the Single Symbol renderer as it applies the same rendering to
all features. Using this renderer, no symbol will be drawn for features, but labeling, diagrams and other non-symbol
parts will still be shown.
Selections can still be made on the layer in the canvas and selected features will be rendered with a default symbol.
Features being edited will also be shown.
This is intended as a handy shortcut for layers which you only want to show labels or diagrams for, and avoids the
need to render symbols with totally transparent fill/border to achieve this.
Categorized Renderer
The Categorized renderer is used to render the features of a layer, using a user-defined symbol whose aspect
reflects the discrete values of a field or an expression.
Obr. 14.4: Categorized Symbolizing options
To use categorized symbology for a layer:
1. Select the Value of classification: it can be an existing field or an expression you can type in the box or build
using the associated button. Using expressions for categorizing avoids the need to create an ad hoc field
for symbology purposes (eg, if your classification criteria are derived from one or more attributes).
The expression used to classify features can be of any type; eg, it can:
• be a comparison. In this case, QGIS returns values 1 (True) and 0 (False). Some examples:
myfield >= 100
$id = @atlas_featureid
(continues on next page)
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(pokračujte na předchozí stránce)
myfield % 2 = 0
within( $geometry, @atlas_geometry )
• combine different fields:
concat( field_1, ' ', field_2 )
• be a calculation on fields:
myfield % 2
year( myfield )
field_1 + field_2
substr( field_1, -3 )
• be used to transform linear values to discrete classes, e.g.:
CASE WHEN x > 1000 THEN 'Big' ELSE 'Small' END
• combine several discrete values into a single category, e.g.:
CASE
WHEN building IN ('residence', 'mobile home') THEN 'residential'
WHEN building IN ('commercial', 'industrial') THEN 'Commercial and␣
→Industrial'
END
Tip: While you can use any kind of expression to categorize features, for some complex expressions it might
be simpler to use rule-based rendering.
2. Configure the Symbol, which will be used as base symbol for all the classes;
3. Indicate the Color ramp, ie the range of colors from which the color applied to each symbol is selected.
Besides the common options of the color ramp widget, you can apply a Random Color Ramp to the
categories. You can click the Shuffle Random Colors entry to regenerate a new set of random colors if you
are not satisfied.
4. Then click on the Classify button to create classes from the distinct values of the provided field or expression.
5. Apply the changes if the live update is not in use and each feature on the map canvas will be rendered with the
symbol of its class.
By default, QGIS appends an all other values class to the list. While empty at the beginning, this class is used
as a default class for any feature not falling into the other classes (eg, when you create features with new values
for the classification field / expression).
Further tweaks can be done to the default classification:
• You can Add
new categories, Remove
selected categories or Delete All of them.
• A class can be disabled by unchecking the checkbox to the left of the class name; the corresponding features
are hidden on the map.
• Drag-and-drop the rows to reorder the classes
• To change the symbol, the value or the legend of a class, double click the item.
Right-clicking over selected item(s) shows a contextual menu to:
• Copy Symbol and Paste Symbol, a convenient way to apply the item’s representation to others
• Change Color… of the selected symbol(s)
• Change Opacity… of the selected symbol(s)
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• Change Output Unit… of the selected symbol(s)
• Change Width… of the selected line symbol(s)
• Change Size… of the selected point symbol(s)
• Change Angle… of the selected point symbol(s)
• Merge Categories: Groups multiple selected categories into a single one. This allows simpler styling of layers
with a large number of categories, where it may be possible to group numerous distinct categories into a smaller
and more manageable set of categories which apply to multiple values.
Tip: Since the symbol kept for the merged categories is the one of the topmost selected category in the list,
you may want to move the category whose symbol you wish to reuse to the top before merging.
• Unmerge Categories that were previously merged
The Advanced menu gives access to options to speed classification or fine-tune the symbols rendering:
• Match to saved symbols: Using the symbols library, assigns to each category a symbol whose name represents
the classification value of the category
• Match to symbols from file…: Provided a file with symbols, assigns to each category a symbol whose name
represents the classification value of the category
• Symbol levels… to define the order of symbols rendering.
Tip: Edit categories directly from the Layers panel
When a layer symbology is based on a categorized, graduated or rule-based symbology mode, you can edit each of
the categories from the Layers Panel. Right-click on a sub-item of the layer and you will:
• Toggle items visibility
• Show all items
• Hide all items
• Modify the symbol color thanks to the color selector wheel
• Edit symbol… from the symbol selector dialog
• Copy symbol
• Paste symbol
Graduated Renderer
The Graduated renderer is used to render all the features from a layer, using an user-defined symbol whose color
or size reflects the assignment of a selected feature’s attribute to a class.
Like the Categorized Renderer, the Graduated Renderer allows you to define rotation and size scale from specified
columns.
Also, analogous to the Categorized Renderer, it allows you to select:
• The value (using the fields listbox or the Set value expression
function)
• The symbol (using the Symbol selector dialog)
• The legend format and the precision
• The method to use to change the symbol: color or size
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• The colors (using the color Ramp list) if the color method is selected
• The size (using the size domain and its unit)
Then you can use the Histogram tab which shows an interactive histogram of the values from the assigned field or
expression. Class breaks can be moved or added using the histogram widget.
Poznámka: You can use Statistical Summary panel to get more information on your vector layer. See Statistical
Summary Panel.
Back to the Classes tab, you can specify the number of classes and also the mode for classifying features within the
classes (using the Mode list). The available modes are:
• Equal Count (Quantile): each class will have the same number of elements (the idea of a boxplot).
• Equal Interval: each class will have the same size (e.g. with the values from 1 to 16 and four classes, each class
will have a size of four).
• Logarithmic scale: suitable for data with a wide range of values. Narrow classes for low values and wide classes
for large values (e.g. for decimal numbers with range [0..100] and two classes, the first class will be from 0 to
10 and the second class from 10 to 100).
• Natural Breaks (Jenks): the variance within each class is minimized while the variance between classes
is maximized.
• Pretty Breaks: computes a sequence of about n+1 equally spaced nice values which cover the range of the
values in x. The values are chosen so that they are 1, 2 or 5 times a power of 10. (based on pretty from the R
statistical environment https://www.rdocumentation.org/packages/base/topics/pretty).
• Standard Deviation: classes are built depending on the standard deviation of the values.
The listbox in the center part of the Symbology tab lists the classes together with their ranges, labels and symbols that
will be rendered.
Click on Classify button to create classes using the chosen mode. Each classes can be disabled unchecking the
checkbox at the left of the class name.
To change symbol, value and/or label of the class, just double click on the item you want to change.
Right-clicking over selected item(s) shows a contextual menu to:
• Copy Symbol and Paste Symbol, a convenient way to apply the item’s representation to others
• Change Color… of the selected symbol(s)
• Change Opacity… of the selected symbol(s)
• Change Output Unit… of the selected symbol(s)
• Change Width… of the selected line symbol(s)
• Change Size… of the selected point symbol(s)
• Change Angle… of the selected point symbol(s)
The example in Obr. 14.5 shows the graduated rendering dialog for the major_rivers layer of the QGIS sample dataset.
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Obr. 14.5: Graduated Symbolizing options
Tip: Thematic maps using an expression
Categorized and graduated thematic maps can be created using the result of an expression. In the properties dialog
for vector layers, the attribute chooser is extended with a Set column expression
function. So you don’t need to write the
classification attribute to a new column in your attribute table if you want the classification attribute to be a composite
of multiple fields, or a formula of some sort.
Proportional Symbol and Multivariate Analysis
Proportional Symbol and Multivariate Analysis are not rendering types available from the Symbology rendering drop-down
list. However with the data-defined override options applied over any of the previous rendering options, QGIS
allows you to display your point and line data with such representation.
Creating proportional symbol
To apply a proportional rendering:
1. First apply to the layer the single symbol renderer.
2. Then set the symbol to apply to the features.
3. Select the item at the upper level of the symbol tree, and use the Data-defined override
button next to the Size
(for point layer) or Width (for line layer) option.
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4. Select a field or enter an expression, and for each feature, QGIS will apply the output value to the property and
proportionally resize the symbol in the map canvas.
If need be, use the Size assistant… option of the menu to apply some transformation (exponential,
flannery…) to the symbol size rescaling (see Using the data-defined assistant interface for more details).
You can choose to display the proportional symbols in the Layers panel and the print layout legend item: unfold
the Advanced drop-down list at the bottom of the main dialog of the Symbology tab and select Data-defined size
legend… to configure the legend items (see Data-defined size legend for details).
Obr. 14.6: Scaling airports size based on elevation of the airport
Creating multivariate analysis
A multivariate analysis rendering helps you evaluate the relationship between two or more variables e.g., one can be
represented by a color ramp while the other is represented by a size.
The simplest way to create multivariate analysis in QGIS is to:
1. First apply a categorized or graduated rendering on a layer, using the same type of symbol for all the classes.
2. Then, apply a proportional symbology on the classes:
1. Click on the Change button above the classification frame: you get the The Symbol Selector dialog.
2. Rescale the size or width of the symbol layer using the data defined override widget as seen above.
Like the proportional symbol, the scaled symbology can be added to the layer tree, on top of the categorized or
graduated classes symbols using the data defined size legend feature. And both representation are also available in the
print layout legend item.
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Obr. 14.7: Multivariate example with scaled size legend
Rule-based Renderer
The Rule-based renderer is used to render all the features from a layer, using rule-based symbols whose aspect
reflects the assignment of a selected feature’s attribute to a class. The rules are based on SQL statements and can be
nested. The dialog allows rule grouping by filter or scale, and you can decide if you want to enable symbol levels or
use only the first-matched rule.
To create a rule:
1. Activate an existing row by double-clicking it (by default, QGIS adds a symbol without a rule when the rendering
mode is enabled) or click the Edit rule
or Add rule
button.
2. In the Edit Rule dialog that opens, you can define a label to help you identify each rule. This is the label that
will be displayed in the Layers Panel and also in the print composer legend.
3. Manually enter an expression in the text box next to the Filter option or press the button next to it to
open the expression string builder dialog.
4. Use the provided functions and the layer attributes to build an expression to filter the features you’d like to
retrieve. Press the Test button to check the result of the query.
5. You can enter a longer label to complete the rule description.
6. You can use the Scale Range option to set scales at which the rule should be applied.
7. Finally, configure the symbol to use for these features.
8. And press OK.
A new row summarizing the rule is added to the Layer Properties dialog. You can create as many rules as necessary
following the steps above or copy pasting an existing rule. Drag-and-drop the rules on top of each other to nest them
and refine the upper rule features in subclasses.
Selecting a rule, you can also organize its features in subclasses using the Refine selected rules drop-down menu.
Automated rule refinement can be based on:
• scales;
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• categories: applying a categorized renderer;
• or ranges: applying a graduated renderer.
Refined classes appear like sub-items of the rule, in a tree hierarchy and like above, you can set symbology of each
class.
In the Edit rule dialog, you can avoid writing all the rules and make use of the Else option to catch all the features
that do not match any of the other rules, at the same level. This can also be achieved by writing Else in the Rule
column of the Layer Properties ► Symbology ► Rule-based dialog.
Right-clicking over selected item(s) shows a contextual menu to:
• Copy and Paste, a convenient way to create new item(s) based on existing item(s)
• Copy Symbol and Paste Symbol, a convenient way to apply the item’s representation to others
• Change Color… of the selected symbol(s)
• Change Opacity… of the selected symbol(s)
• Change Output Unit… of the selected symbol(s)
• Change Width… of the selected line symbol(s)
• Change Size… of the selected point symbol(s)
• Change Angle… of the selected point symbol(s)
• Refine Current Rule: open a submenu that allows to refine the current rule with scales, categories (categorized
renderer) or Ranges (graduated renderer).
The created rules also appear in a tree hierarchy in the map legend. Double-click the rules in the map legend and the
Symbology tab of the layer properties appears showing the rule that is the background for the symbol in the tree.
The example in Obr. 14.8 shows the rule-based rendering dialog for the rivers layer of the QGIS sample dataset.
Obr. 14.8: Rule-based Symbolizing options
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Point displacement Renderer
The Point Displacement renderer works to visualize all features of a point layer, even if they have the same
location. To do this, the renderer takes the points falling in a given Distance tolerance from each other and places
them around their barycenter following different Placement methods:
• Ring: places all the features on a circle whose radius depends on the number of features to display.
• Concentric rings: uses a set of concentric circles to show the features.
• Grid: generates a regular grid with a point symbol at each intersection.
The Center symbol widget helps you customize the symbol and color of the middle point. For the distributed points
symbols, you can apply any of the No symbols, Single symbol, Categorized, Graduated or Rule-based renderer using
the Renderer drop-down list and customize them using the Renderer Settings… button.
While the minimal spacing of the Displacement lines depends on the point symbol renderer’s, you can still customize
some of its settings such as the Stroke width, Stroke color and Size adjustment (eg, to add more spacing between the
rendered points).
Use the Labels group options to perform points labeling: the labels are placed near the displaced position of the
symbol, and not at the feature real position. Other than the Label attribute, Label font and Label color, you can set
the Minimum map scale to display the labels.
Obr. 14.9: Point displacement dialog
Poznámka: Point Displacement renderer does not alter feature geometry, meaning that points are not moved from
their position. They are still located at their initial place. Changes are only visual, for rendering purpose. Use instead
the Processing Points displacement algorithm if you want to create displaced features.
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Point Cluster Renderer
Unlike the Point Displacement renderer which blows up nearest or overlaid point features placement, the
Point Cluster renderer groups nearby points into a single rendered marker symbol. Based on a specified Distance,
points that fall within from each others are merged into a single symbol. Points aggregation is made based on the
closest group being formed, rather than just assigning them the first group within the search distance.
From the main dialog, you can:
• set the symbol to represent the point cluster in the Cluster symbol; the default rendering displays the number of
aggregated features thanks to the @cluster_size variable on Font marker symbol layer.
• use the Renderer drop-down list to apply any of the other feature rendering types to the layer (single,
categorized, rule-based…). Then, push the Renderer Settings… button to configure features‘ symbology as usual.
Note that this renderer is only visible on features that are not clustered. Also, when the symbol color is the same
for all the point features inside a cluster, that color sets the @cluster_color variable of the cluster.
Obr. 14.10: Point Cluster dialog
Poznámka: Point Cluster renderer does not alter feature geometry, meaning that points are not moved from their
position. They are still located at their initial place. Changes are only visual, for rendering purpose. Use instead the
Processing K-means clustering or DBSCAN clustering algorithm if you want to create cluster-based features.
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Inverted Polygon Renderer
The Inverted Polygon renderer allows user to define a symbol to fill in outside of the layer’s polygons. As above
you can select subrenderers, namely Single symbol, Graduated, Categorized, Rule-Based or 2.5D renderer.
Obr. 14.11: Inverted Polygon dialog
Heatmap Renderer
With the Heatmap renderer you can create live dynamic heatmaps for (multi)point layers. You can specify the
heatmap radius in millimeters, points, pixels, map units or inches, choose and edit a color ramp for the heatmap style
and use a slider for selecting a trade-off between render speed and quality. You can also define a maximum value limit
and give a weight to points using a field or an expression. When adding or removing a feature the heatmap renderer
updates the heatmap style automatically.
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Obr. 14.12: Heatmap dialog
2.5D Renderer
Using the 2.5D renderer it’s possible to create a 2.5D effect on your layer’s features. You start by choosing a Height
value (in map units). For that you can use a fixed value, one of your layer’s fields, or an expression. You also need
to choose an Angle (in degrees) to recreate the viewer position (0° means west, growing in counter clock wise). Use
advanced configuration options to set the Roof Color and Wall Color. If you would like to simulate solar radiation on
the features walls, make sure to check the Shade walls based on aspect option. You can also simulate a shadow
by setting a Color and Size (in map units).
Obr. 14.13: 2.5D dialog
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Tip: Using 2.5D effect with other renderers
Once you have finished setting the basic style on the 2.5D renderer, you can convert this to another renderer (single,
categorized, graduated). The 2.5D effects will be kept and all other renderer specific options will be available for you
to fine tune them (this way you can have for example categorized symbols with a nice 2.5D representation or add
some extra styling to your 2.5D symbols). To make sure that the shadow and the „building“ itself do not interfere with
other nearby features, you may need to enable Symbols Levels ( Advanced ► Symbol levels…). The 2.5D height and
angle values are saved in the layer’s variables, so you can edit it afterwards in the variables tab of the layer’s properties
dialog.
Layer rendering
From the Symbology tab, you can also set some options that invariably act on all features of the layer:
• Opacity : You can make the underlying layer in the map canvas visible with this tool. Use
the slider to adapt the visibility of your vector layer to your needs. You can also make a precise definition of
the percentage of visibility in the menu beside the slider.
• Blending mode at the Layer and Feature levels: You can achieve special rendering effects with these tools that
you may previously only know from graphics programs. The pixels of your overlaying and underlaying layers
are mixed through the settings described in Režim míchání.
• Apply paint effects on all the layer features with the Draw Effects button.
• Control feature rendering order allows you, using features attributes, to define the z-order in which they shall
be rendered. Activate the checkbox and click on the button beside. You then get the Define Order dialog
in which you:
1. Choose a field or build an expression to apply to the layer features.
2. Set in which order the fetched features should be sorted, i.e. if you choose Ascending order, the features
with lower value are rendered under those with higher value.
3. Define when features returning NULL value should be rendered: first (bottom) or last (top).
4. Repeat the above steps as many times as rules you wish to use.
The first rule is applied to all the features in the layer, z-ordering them according to their returned value. Then,
within each group of features with the same value (including those with NULL value) and thus the same z-level,
the next rule is applied to sort them. And so on…
Obr. 14.14: Layer rendering options
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Other Settings
Symbol levels
For renderers that allow stacked symbol layers (only heatmap doesn’t) there is an option to control the rendering order
of each symbol’s levels.
For most of the renderers, you can access the Symbols levels option by clicking the Advanced button below the saved
symbols list and choosing Symbol levels. For the Rule-based Renderer the option is directly available through Symbols
Levels… button, while for Point displacement Renderer renderer the same button is inside the Rendering settings dialog.
To activate symbols levels, select the Enable symbol levels. Each row will show up a small sample of the combined
symbol, its label and the individual symbols layer divided into columns with a number next to it. The numbers represent
the rendering order level in which the symbol layer will be drawn. Lower values levels are drawn first, staying at the
bottom, while higher values are drawn last, on top of the others.
Obr. 14.15: Symbol levels dialog
Poznámka: If symbols levels are deactivated, the complete symbols will be drawn according to their respective
features order. Overlapping symbols will simply obfuscate to other below. Besides, similar symbols won’t „merge“
with each other.
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Obr. 14.16: Symbol levels activated (A) and deactivated (B) difference
Data-defined size legend
When a layer is rendered with the proportional symbol or the multivariate rendering or when a scaled size diagram
is applied to the layer, you can allow the display of the scaled symbols in both the Layers panel and the print layout
legend.
To enable the Data-defined Size Legend dialog to render symbology, select the eponym option in the Advanced button
below the saved symbols list. For diagrams, the option is available under the Legend tab. The dialog provides the
following options to:
• select the type of legend: Legend not enabled, Separated legend items and Collapsed legend. For
the latter option, you can select whether the legend items are aligned at the Bottom or at the Center;
• set the symbol to use for legend representation;
• insert the title in the legend;
• resize the classes to use: by default, QGIS provides you with a legend of five classes (based on natural pretty
breaks) but you can apply your own classification using the Manual size classes option. Use the and
buttons to set your custom classes values and labels.
A preview of the legend is displayed in the right panel of the dialog and updated as you set the parameters. For
collapsed legend, a leader line from the horizontal center of the symbol to the corresponding legend text is drawn.
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Obr. 14.17: Setting size scaled legend
Poznámka: Currently, data-defined size legend for layer symbology can only be applied to point layer using single,
categorized or graduated symbology.
Draw effects
In order to improve layer rendering and avoid (or at least reduce) the resort to other software for final rendering
of maps, QGIS provides another powerful functionality: the Draw Effects options, which adds paint effects for
customizing the visualization of vector layers.
The option is available in the Layer Properties ► Symbology dialog, under the Layer rendering group (applying to the
whole layer) or in symbol layer properties (applying to corresponding features). You can combine both usage.
Paint effects can be activated by checking the Draw effects option and clicking the Customize effects
button. That
will open the Effect Properties Dialog (see Obr. 14.18). The following effect types, with custom options are available:
• Source: Draws the feature’s original style according to the configuration of the layer’s properties. The Opacity
of its style can be adjusted as well as the Blend mode and Draw mode. These are common properties for all
types of effects.
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Obr. 14.18: Draw Effects: Source dialog
• Blur: Adds a blur effect on the vector layer. The custom options that you can change are the Blur type (Stack
blur (fast) or Gaussian blur (quality)) and the Blur strength.
Obr. 14.19: Draw Effects: Blur dialog
• Colorise: This effect can be used to make a version of the style using one single hue. The base will always be
a grayscale version of the symbol and you can:
– Use the Grayscale to select how to create it: options are ‚By lightness‘, ‚By luminosity‘, ‚By average‘
and ‚Off‘.
– If Colorise is selected, it will be possible to mix another color and choose how strong it should be.
– Control the Brightness, Contrast and Saturation levels of the resulting symbol.
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Obr. 14.20: Draw Effects: Colorize dialog
• Drop Shadow: Using this effect adds a shadow on the feature, which looks like adding an extra dimension.
This effect can be customized by changing the Offset angle and distance, determining where the shadow shifts
towards to and the proximity to the source object. Drop Shadow also has the option to change the Blur radius
and the Color of the effect.
Obr. 14.21: Draw Effects: Drop Shadow dialog
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• Inner Shadow: This effect is similar to the Drop Shadow effect, but it adds the shadow effect on the inside of
the edges of the feature. The available options for customization are the same as the Drop Shadow effect.
Obr. 14.22: Draw Effects: Inner Shadow dialog
• Inner Glow: Adds a glow effect inside the feature. This effect can be customized by adjusting the Spread (width)
of the glow, or the Blur radius. The latter specifies the proximity from the edge of the feature where you want
any blurring to happen. Additionally, there are options to customize the color of the glow using a Single color
or a Color ramp.
Obr. 14.23: Draw Effects: Inner Glow dialog
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• Outer Glow: This effect is similar to the Inner Glow effect, but it adds the glow effect on the outside of the
edges of the feature. The available options for customization are the same as the Inner Glow effect.
Obr. 14.24: Draw Effects: Outer Glow dialog
• Transform: Adds the possibility of transforming the shape of the symbol. The first options available for
customization are the Reflect horizontal and Reflect vertical, which actually create a reflection on the horizontal
and/or vertical axes. The other options are:
– Shear X,Y: Slants the feature along the X and/or Y axis.
– Scale X,Y: Enlarges or minimizes the feature along the X and/or Y axis by the given percentage.
– Rotation: Turns the feature around its center point.
– and Translate X,Y changes the position of the item based on a distance given on the X and/or Y axis.
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Obr. 14.25: Draw Effects: Transform dialog
One or more effect types can be used at the same time. You (de)activate an effect using its checkbox in the effects list.
You can change the selected effect type by using the Effect type option. You can reorder the effects using
Move up
and Move down
buttons, and also add/remove effects using the Add new effect
and Remove effect
buttons.
There are some common options available for all draw effect types. Opacity and Blend mode options work similar to
the ones described in Layer rendering and can be used in all draw effects except for the transform one.
There is also a Draw mode option available for every effect, and you can choose whether to render and/or
modify the symbol, following some rules:
• Effects render from top to bottom.
• Render only mode means that the effect will be visible.
• Modifier only mode means that the effect will not be visible but the changes that it applies will be passed to the
next effect (the one immediately below).
• The Render and Modify mode will make the effect visible and pass any changes to the next effect. If the effect
is at the top of the effects list or if the immediately above effect is not in modify mode, then it will use the
original source symbol from the layers properties (similar to source).
14.1.4 Labels Properties
The Labels properties provides you with all the needed and appropriate capabilities to configure smart labeling
on vector layers. This dialog can also be accessed from the Layer Styling panel, or using the Layer Labeling Options
button of the Labels toolbar.
The first step is to choose the labeling method from the drop-down list. Available methods are:
• No labels: the default value, showing no labels from the layer
• Single labels: Show labels on the map using a single attribute or an expression
• Rule-based labeling
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• and Blocking: allows to set a layer as just an obstacle for other layer’s labels without rendering any labels
of its own.
The next steps assume you select the Single labels option, opening the following dialog.
Obr. 14.26: Layer labeling settings - Single labels
At the top of the dialog, a Value drop-down list is enabled. You can select an attribute column to use for labeling. By
default, the display field is used. Click if you want to define labels based on expressions - See Define labels based
on expressions.
Below are displayed options to customize the labels, under various tabs:
• Text
• Formatting
• Buffer
• Mask
• Background
• Shadow
• Callouts
• Placement
• Rendering
Description of how to set each property is exposed at Setting a label.
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Setting the automated placement engine
You can use the automated placement settings to configure a project-level automated behavior of the labels. In the
top right corner of the Labels tab, click the Automated placement settings (applies to all layers)
button, opening a dialog with
the following options:
Obr. 14.27: The labels automated placement engine
• Number of candidates: calculates and assigns to line and polygon features the number of possible labels
placement based on their size. The longer or wider a feature is, the more candidates it has, and its labels
can be better placed with less risk of collision.
• Text rendering: sets the default value for label rendering widgets when exporting a map canvas or a layout to
PDF or SVG. If Always render labels as text is selected then labels can be edited in external applications (e.g.
Inkscape) as normal text. BUT the side effect is that the rendering quality is decreased, and there are issues
with rendering when certain text settings like buffers are in place. That’s why Always render labels as paths
(recommended) which exports labels as outlines, is recommended.
• Allow truncated labels on edges of map: controls whether labels which fall partially outside of the map
extent should be rendered. If checked, these labels will be shown (when there’s no way to place them fully
within the visible area). If unchecked then partially visible labels will be skipped. Note that this setting has no
effects on labels‘ display in the layout map item.
• Show all labels for all layers (i.e. including colliding objects). Note that this option can be also set per layer
(see Rendering tab)
• Show unplaced labels: allows to determine whether any important labels are missing from the maps (e.g.
due to overlaps or other constraints). They are displayed using a customizable color.
• Show candidates (for debugging): controls whether boxes should be drawn on the map showing all the
candidates generated for label placement. Like the label says, it’s useful only for debugging and testing the
effect different labeling settings have. This could be handy for a better manual placement with tools from the
label toolbar.
• Project labeling version: QGIS supports two different versions of label automatic placement:
– Version 1: the old system (used by QGIS versions 3.10 and earlier, and when opening projects created
in these versions in QGIS 3.12 or later). Version 1 treats label and obstacle priorities as „rough guides“
only, and it’s possible that a low-priority label will be placed over a high-priority obstacle in this version.
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Accordingly, it can be difficult to obtain the desired labeling results when using this version and it is thus
recommended only for compatibility with older projects.
– Version 2 (recommended): this is the default system in new projects created in QGIS 3.12 or later. In
version 2, the logic dictating when labels are allowed to overlap obstacles has been reworked. The newer
logic forbids any labels from overlapping any obstacles with a greater obstacle weight compared to the
label’s priority. As a result, this version results in much more predictable and easier to understand labeling
results.
Rule-based labeling
With rule-based labeling multiple label configurations can be defined and applied selectively on the base of expression
filters and scale range, as in Rule-based rendering.
To create a rule, select the Rule-based labeling option in the main drop-down list from the Labels tab and click
the button at the bottom of the dialog. Then fill the new dialog with a description and an expression to filter
features. You can also set a scale range in which the label rule should be applied. The other options available in this
dialog are the common settings seen beforehand.
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Obr. 14.28: Rule settings
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A summary of existing rules is shown in the main dialog (see Obr. 14.29). You can add multiple rules, reorder or
imbricate them with a drag-and-drop. You can as well remove them with the button or edit them with button
or a double-click.
Obr. 14.29: Rule based labeling panel
Define labels based on expressions
Whether you choose single or rule-based labeling type, QGIS allows using expressions to label features.
Assuming you are using the Single labels method, click the button near the Value drop-down list in the Labels
tab of the properties dialog.
In Obr. 14.30, you see a sample expression to label the alaska trees layer with tree type and area, based on the field
‚VEGDESC‘, some descriptive text, and the function $area in combination with format_number() to make it
look nicer.
Obr. 14.30: Using expressions for labeling
Expression based labeling is easy to work with. All you have to take care of is that:
• You may need to combine all elements (strings, fields, and functions) with a string concatenation function such
as concat, + or ||. Be aware that in some situations (when null or numeric value are involved) not all of
these tools will fit your need.
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• Strings are written in ‚single quotes‘.
• Fields are written in „double quotes“ or without any quote.
Let’s have a look at some examples:
1. Label based on two fields ‚name‘ and ‚place‘ with a comma as separator:
"name" || ', ' || "place"
Returns:
John Smith, Paris
2. Label based on two fields ‚name‘ and ‚place‘ with other texts:
'My name is ' + "name" + 'and I live in ' + "place"
'My name is ' || "name" || 'and I live in ' || "place"
concat('My name is ', name, ' and I live in ', "place")
Returns:
My name is John Smith and I live in Paris
3. Label based on two fields ‚name‘ and ‚place‘ with other texts combining different concatenation functions:
concat('My name is ', name, ' and I live in ' || place)
Returns:
My name is John Smith and I live in Paris
Or, if the field ‚place‘ is NULL, returns:
My name is John Smith
4. Multi-line label based on two fields ‚name‘ and ‚place‘ with a descriptive text:
concat('My name is ', "name", '\n' , 'I live in ' , "place")
Returns:
My name is John Smith
I live in Paris
5. Label based on a field and the $area function to show the place’s name and its rounded area size in a converted
unit:
'The area of ' || "place" || ' has a size of '
|| round($area/10000) || ' ha'
Returns:
The area of Paris has a size of 10500 ha
6. Create a CASE ELSE condition. If the population value in field population is <= 50000 it is a town, otherwise
it is a city:
concat('This place is a ',
CASE WHEN "population" <= 50000 THEN 'town' ELSE 'city' END)
Returns:
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This place is a town
7. Display name for the cities and no label for the other features (for the „city“ context, see example above):
CASE WHEN "population" > 50000 THEN "NAME" END
Returns:
Paris
As you can see in the expression builder, you have hundreds of functions available to create simple and very complex
expressions to label your data in QGIS. See Výrazy chapter for more information and examples on expressions.
Using data-defined override for labeling
With the Data defined override
function, the settings for the labeling are overridden by entries in the attribute table or
expressions based on them. This feature can be used to set values for most of the labeling options described above.
For example, using the Alaska QGIS sample dataset, let’s label the airports layer with their name, based on their
militarian USE, i.e. whether the airport is accessible to :
• military people, then display it in gray color, size 8;
• others, then show in blue color, size 10.
To do this, after you enabled the labeling on the NAME field of the layer (see Setting a label):
1. Activate the Text tab.
2. Click on the icon next to the Size property.
3. Select Edit… and type:
CASE
WHEN "USE" like '%Military%' THEN 8 -- because compatible values are
→'Military'
-- and 'Joint Military/Civilian'
ELSE 10
END
4. Press OK to validate. The dialog closes and the button becomes meaning that an rule is being run.
5. Then click the button next to the color property, type the expression below and validate:
CASE
WHEN "USE" like '%Military%' THEN '150, 150, 150'
ELSE '0, 0, 255'
END
Likewise, you can customize any other property of the label, the way you want. See more details on the
Data-define override
widget’s description and manipulation in Data defined override setup section.
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Obr. 14.31: Airports labels are formatted based on their attributes
Tip: Use the data-defined override to label every part of multi-part features
There is an option to set the labeling for multi-part features independently from your label properties. Choose the
Rendering, Feature options, go to the Data-define override
button next to the checkbox Label every part of
multipart-features and define the labels as described in Data defined override setup.
The Label Toolbar
The Label Toolbar provides some tools to manipulate label or diagram properties.
Obr. 14.32: The Label toolbar
While for readability, label has been used below to describe the Label toolbar, note that when mentioned in their
name, the tools work almost the same way with diagrams:
• Highlight Pinned Labels and Diagrams
. If the vector layer of the label is editable, then the highlighting is green,
otherwise it’s blue.
• Toggles Display of Unplaced Labels
: Allows to determine whether any important labels are missing from the maps
(e.g. due to overlaps or other constraints). They are displayed with a customizable color (see Setting the
automated placement engine).
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• Pin/Unpin Labels and Diagrams
. By clicking or draging an area, you pin label(s). If you click or drag an area holding
Shift, label(s) are unpinned. Finally, you can also click or drag an area holding Ctrl to toggle the pin status
of label(s).
• Show/Hide Labels and Diagrams
. If you click on the labels, or click and drag an area holding Shift, they are
hidden. When a label is hidden, you just have to click on the feature to restore its visibility. If you drag an area,
all the labels in the area will be restored.
• Moves a Label or Diagram
. You just have to drag the label to the desired place.
• Rotates a Label
. Click the label and move around and you get the text rotated.
• Change Label Properties
. It opens a dialog to change the clicked label properties; it can be the label itself, its
coordinates, angle, font, size, multiline alignment … as long as this property has been mapped to a field. Here
you can set the option to Label every part of a feature.
Varování: Label tools overwrite current field values
Using the Label toolbar to customize the labeling actually writes the new value of the property in the mapped
field. Hence, be careful to not inadvertently replace data you may need later!
Poznámka: The Auxiliary Storage Properties mechanism may be used to customize labeling (position, and so on)
without modifying the underlying data source.
Customize the labels from the map canvas
Combined with the Label Toolbar, the data defined override setting helps you manipulate labels in the map canvas
(move, edit, rotate). We now describe an example using the data-defined override function for the Move label
function
(see Obr. 14.33).
1. Import lakes.shp from the QGIS sample dataset.
2. Double-click the layer to open the Layer Properties. Click on Labels and Placement. Select Offset from
centroid.
3. Look for the Data defined entries. Click the icon to define the field type for the Coordinate. Choose
xlabel for X and ylabel for Y. The icons are now highlighted in yellow.
Obr. 14.33: Labeling of vector polygon layers with data-defined override
4. Zoom into a lake.
5. Set editable the layer using the Toggle Editing
button.
6. Go to the Label toolbar and click the icon. Now you can shift the label manually to another position (see
Obr. 14.34). The new position of the label is saved in the xlabel and ylabel columns of the attribute table.
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7. It’s also possible to add a line connecting each lake to its moved label using:
• the label’s callout property
• or the geometry generator symbol layer with the expression below:
make_line( centroid( $geometry ), make_point( "xlabel", "ylabel" ) )
Obr. 14.34: Moved labels
Poznámka: The Auxiliary Storage Properties mechanism may be used with data-defined properties without having
an editable data source.
14.1.5 Diagrams Properties
The Diagrams tab allows you to add a graphic overlay to a vector layer (see Obr. 14.35).
The current core implementation of diagrams provides support for:
• No diagrams: the default value with no diagram displayed over the features;
• Pie chart, a circular statistical graphic divided into slices to illustrate numerical proportion. The arc length
of each slice is proportional to the quantity it represents;
• Text diagram, a horizontaly divided circle showing statistics values inside;
• Histogram, bars of varying colors for each attribute aligned next to each other
• Stacked bars, Stacks bars of varying colors for each attribute on top of each other vertically or horizontally
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In the top right corner of the Diagrams tab, the Automated placement settings (applies to all layers)
button provides means to
control diagram labels placement on the map canvas.
Tip: Switch quickly between types of diagrams
Given that the settings are almost common to the different types of diagram, when designing your diagram, you can
easily change the diagram type and check which one is more appropriate to your data without any loss.
For each type of diagram, the properties are divided into several tabs:
• Attributes
• Rendering
• Size
• Placement
• Options
• Legend
Attributes
Attributes defines which variables to display in the diagram. Use add item
button to select the desired fields into the
‚Assigned Attributes‘ panel. Generated attributes with Výrazy can also be used.
You can move up and down any row with click and drag, sorting how attributes are displayed. You can also change
the label in the ‚Legend‘ column or the attribute color by double-clicking the item.
This label is the default text displayed in the legend of the print layout or of the layer tree.
Obr. 14.35: Diagram properties - Attributes tab
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Vykreslování
Rendering defines how the diagram looks like. It provides general settings that do not interfere with the statistic values
such as:
• the graphic’s opacity, its outline width and color;
• depending on the type of diagram:
– for histogram and stacked bars, the width of the bar and the spacing between the bars. You may want
to set the spacing to 0 for stacked bars. Moreover, the Axis line symbol can be made visible on the map
canvas and customized using line symbol properties.
– for text diagram, the circle background color and the font used for texts;
– for pie charts, the Start angle of the first slice and their Direction (clockwise or not).
• the use of paint effects on the graphics.
In this tab, you can also manage and fine tune the diagram visibility with different options:
• Diagram z-index: controls how diagrams are drawn on top of each other and on top of labels. A diagram with
a high index is drawn over diagrams and labels;
• Show all diagrams: shows all the diagrams even if they overlap each other;
• Show diagram: allows only specific diagrams to be rendered;
• Always Show: selects specific diagrams to always render, even when they overlap other diagrams or map labels;
• setting the Scale dependent visibility;
Obr. 14.36: Diagram properties - Rendering tab
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Size
Size is the main tab to set how the selected statistics are represented. The diagram size units can be ‚Millimeters‘,
‚Points‘, ‚Pixels‘, ‚Map Units‘ or ‚Inches‘. You can use:
• Fixed size, a unique size to represent the graphic of all the features (not available for histograms)
• or Scaled size, based on an expression using layer attributes:
1. In Attribute, select a field or build an expression
2. Press Find to return the Maximum value of the attribute or enter a custom value in the widget.
3. For histogram and stacked bars, enter a Bar length value, used to represent the Maximum value of the
attributes. For each feature, the bar lenght will then be scaled linearly to keep this matching.
4. For pie chart and text diagram, enter a Size value, used to represent the Maximum value of the attributes.
For each feature, the circle area or diameter will then be scaled linearly to keep this matching (from 0).
A Minimum size can however be set for small diagrams.
Obr. 14.37: Diagram properties - Size tab
Placement
Placement defines the diagram position. Depending on the layer geometry type, it offers different options for the
placement (more details at Placement):
• Around point or Over point for point geometry. The former variable requires a radius to follow.
• Around line or Over line for line geometry. Like point feature, the first variable requires a distance to respect
and you can specify the diagram placement relative to the feature (‚above‘, ‚on‘ and/or ‚below‘ the line) It’s
possible to select several options at once. In that case, QGIS will look for the optimal position of the diagram.
Remember that you can also use the line orientation for the position of the diagram.
• Around centroid (at a set Distance), Over centroid, Using perimeter and Inside polygon are the options for polygon
features.
The Coordinate group provides direct control on diagram placement, on a feature-by-feature basis, using their
attributes or an expression to set the X and Y coordinate. The information can also be filled using the Move labels
and diagrams tool.
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In the Priority section, you can define the placement priority rank of each diagram, ie if there are different diagrams
or labels candidates for the same location, the item with the higher priority will be displayed and the others could be
left out.
Discourage diagrams and labels from covering features defines features to use as obstacles, ie QGIS will try to not
place diagrams nor labels over these features. The priority rank is then used to evaluate whether a diagram could be
omitted due to a greater weighted obstacle feature.
Obr. 14.38: Vector properties dialog with diagram properties, Placement tab
Možnosti
The Options tab has settings for histograms and stacked bars. You can choose whether the Bar orientation should be
Up, Down, Right or Left, for horizontal and vertical diagrams.
Legend
From the Legend tab, you can choose to display items of the diagram in the Layers panel, and in the print layout
legend, next to the layer symbology:
• check Show legend entries for diagram attributes to display in the legends the Color and Legend properties,
as previously assigned in the Attributes tab;
• and, when a scaled size is being used for the diagrams, push the Legend Entries for Diagram Size… button to
configure the diagram symbol aspect in the legends. This opens the Data-defined Size Legend dialog whose
options are described in Data-defined size legend.
When set, the diagram legend items (attributes with color and diagram size) are also displayed in the print layout
legend, next to the layer symbology.
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14.1.6 Masks Properties
The Masks tab helps you configure the current layer symbols overlay with other symbol layers or labels, from
any layer. This is meant to improve the readability of symbols and labels whose colors are close and can be hard to
decipher when overlapping; it adds a custom and transparent mask around the items to „hide“ parts of the symbol
layers of the current layer.
To apply masks on the active layer, you first need to enable in the project either mask symbol layers or mask labels.
Then, from the Masks tab, check:
• the Masked symbol layers: lists in a tree structure all the symbol layers of the current layer. There you can select
the symbol layer item you would like to transparently „cut out“ when they overlap the selected mask sources
• the Mask sources tab: list all the mask labels and mask symbol layers defined in the project. Select the items
that would generate the mask over the selected masked symbol layers
Obr. 14.39: Layer properties - Masks tab
14.1.7 3D View Properties
The 3D View tab provides settings for vector layers that should be depicted in the 3D Map view tool.
For better performance, data from vector layers are loaded in the background, using multithreading, and rendered in
tiles whose size can be controlled from the Layer rendering section of the tab:
• Zoom levels count: determines how deep the quadtree will be. For example, one zoom level means there will
be a single tile for the whole layer. Three zoom levels means there will be 16 tiles at the leaf level (every extra
zoom level multiplies that by 4). The default is 3 and the maximum is 8.
• Show bounding boxes of tiles: especially useful if there are issues with tiles not showing up when they should
To display a layer in 3D, select from the combobox at the top of the tab, either:
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• Single symbol: features are rendered using a common 3D symbol whose properties can be data-defined or not.
Read details on setting a 3D symbol for each layer geometry type.
• Rule-based: multiple symbol configurations can be defined and applied selectively based on expression filters
and scale range. More details on how-to at Rule-based rendering.
Obr. 14.40: 3D properties of a point layer
14.1.8 Fields Properties
The Fields tab provides information on fields related to the layer and helps you organize them.
The layer can be made editable using the Toggle editing mode
. At this moment, you can modify its structure using the
New field
and Delete field
buttons.
You can also rename fields by double-clicking its name. This is only supported for data providers like PostgreSQL,
Oracle, Memory layer and some OGR layer depending on the OGR data format and version.
If set in the underlying data source or in the forms properties, the field’s alias is also displayed. An alias is a human
readable field name you can use in the feature form or the attribute table. Aliases are saved in the project file.
Depending on the data provider, you can associate a comment with a field, for example at its creation. This information
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is retrieved and shown in the Comment column and is later displayed when hovering over the field label in a feature
form.
Other than the fields contained in the dataset, virtual fields and Auxiliary Storage included, the Fields tab also lists
fields from any joined layers. Depending on the origin of the field, a different background color is applied to it.
For each listed field, the dialog also lists read-only characteristics such as its type, type name, length and
precision. When serving the layer as WMS or WFS, you can also check here which fields could be retrieved.
Obr. 14.41: Fields properties tab
14.1.9 Attributes Form Properties
The Attributes Form tab helps you set up the form to display when creating new features or querying existing one.
You can define:
• the look and the behavior of each field in the feature form or the attribute table (label, widget, constraints…);
• the form’s structure (custom or autogenerated):
• extra logic in Python to handle interaction with the form or field widgets.
At the top right of the dialog, you can set whether the form is opened by default when creating new features. This can
be configured per layer or globally with the Suppress attribute form pop-up after feature creation option in the Settings
► Options ► Digitizing menu.
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Customizing a form for your data
By default, when you click on a feature with the Identify Features
tool or switch the attribute table to the form
view mode, QGIS displays a basic form with predefined widgets (generally spinboxes and textboxes — each field
is represented on a dedicated row by its label next to the widget). If relations are set on the layer, fields from the
referencing layers are shown in an embedded frame at the bottom of the form, following the same basic structure.
This rendering is the result of the default Autogenerate value of the Attribute editor layout setting in the Layer
properties ► Attributes Form tab. This property holds three different values:
• Autogenerate: keeps the basic structure of „one row - one field“ for the form but allows to customize each
corresponding widget.
• Drag-and-drop designer: other than widget customization, the form structure can be made more
complex eg, with widgets embedded in groups and tabs.
• Provide ui file: allows to use a Qt designer file, hence a potentially more complex and fully featured
template, as feature form.
The autogenerated form
When the Autogenerate option is on, the Available widgets panel shows lists of fields (from the layer and its
relations) that would be shown in the form. Select a field and you can configure its appearance and behavior in the
right panel:
• adding custom label and automated checks to the field;
• setting a particular widget to use.
The drag and drop designer
The drag and drop designer allows you to create a form with several containers (tabs or groups) to present the attribute
fields, as shown for example in Obr. 14.42.
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Obr. 14.42: Resulting built-in form with tabs and named groups
1. Choose Drag and drop designer from the Select attribute layout editor combobox. This enables the
Form Layout panel next to the Available widgets panel, filled with existing fields. The selected field displays its
properties in a third panel.
2. Select fields you do not want to use in your Form Layout panel and hit the button to remove them. Drag
and drop fields from the other panel to re-add them. The same field can be added multiple times.
3. Drag and drop fields within the Form Layout panel to reorder their position.
4. Add containers (tab or group frames) to associate fields that belong to the same category and better structure
the form.
1. The first step is to use the icon to create a tab in which fields and groups will be displayed
2. Then set the properties of the container, ie:
• the name
• the type, ie a tab or a group in container (a group inside a tab or another group)
• and the number of columns the embedded fields should be distributed over
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Obr. 14.43: Dialog to create containers with the Attribute editor layout
These, and other properties can later be updated by selecting the item and, from the third panel:
• hide or show the container’s label
• display the container as a group box (only available for tabs).
• rename the container
• set the number of columns
• enter an expression to control the container’s visibility. The expression will be re-evaluated every
time values in the form change, and the tab or group box shown/hidden accordingly
• add a background color
3. You can create as many containers as you want; press the icon again to create another tab or a group
frame under an existing tab.
5. The next step is to assign the relevant fields to each container, by simple drag and drop. Groups and tabs can
also be moved in the same way.
6. Customize the widget of the fields in use
7. In case the layer is involved in a one or many to many relation, drag-and-drop the relation name from the
Available widgets panel to the Form Layout panel. The associated layer attribute form will be embedded at
the chosen place in the current layer’s form. As for the other items, select the relation label to configure some
properties:
• hide or show the relation label
• show the link button
• show the unlink button
8. Apply the layer’s properties dialog
9. Open a feature attribute form (eg, using the Identify features
tool) and it should display the new form.
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Using custom ui-file
The Provide ui-file option allows you to use complex dialogs made with Qt-Designer. Using a UI-file allows
a great deal of freedom in creating a dialog. Note that, in order to link the graphical objects (textbox, combobox…)
to the layer’s fields, you need to give them the same name.
Use the Edit UI to define the path to the file to use.
UI-files can also be hosted on a remote server. In this case, you provide the URL of the form instead of the file path
in Edit UI.
You’ll find some example in the Creating a new form lesson of the QGIS-training-manual-index-reference.
For more advanced information, see https://woostuff.wordpress.com/2011/09/05/
qgis-tips-custom-feature-forms-with-python-logic/.
Enhance your form with custom functions
QGIS forms can have a Python function that is called when the dialog is opened. Use this function to add extra logic
to your dialogs. The form code can be specified in three different ways:
• load from the environment: use a function, for example in startup.py or from an installed
plugin
• load from an external file: a file chooser will let you select a Python file from your filesystem or
enter a URL for a remote file.
• provide code in this dialog: a Python editor will appear where you can directly type the function
to use.
In all cases you must enter the name of the function that will be called (open in the example below).
An example is (in module MyForms.py):
def open(dialog,layer,feature):
geom = feature.geometry()
control = dialog.findChild(QWidget,"My line edit")
Reference in Python Init Function like so: open
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Configure the field behavior
The main part of the Attributes Form tab helps you set the type of widget used to fill or display values of the field, in
the attribute table or the feature form: you can define how user interacts with each field and the values or range of
values that are allowed to be added to each.
Obr. 14.44: Dialog to select an edit widget for an attribute column
Common settings
Regardless the type of widget applied to the field, there are some common properties you can set to control whether
and how a field can be edited.
Widget display
Show label: indicates whether the field name should be displayed in the form (only in the Drag and drop designer
mode).
General options
• Alias: a human readable name to use for fields. The alias will be displayed in the feature form, the attribute
table, or in the Identify results panel. It can also be used as field name replacement in the expression builder,
easing expressions understanding and reviews. Aliases are saved in project file.
• Comment: displays the field’s comment as shown in the Fields tab, in a read-only state. This information is shown
as tooltip when hovering over the field label in a feature form.
• Editable: uncheck this option to set the field read-only (not manually modifiable) even when the layer is in
edit mode. Note that checking this setting doesn’t override any edit limitation from the provider.
• Label on top: places the field name above or beside the widget in the feature form.
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Default values
• Default value: for new features, automatically populates by default the field with a predefined value or an
expression-based one. For example, you can:
– use $x, $length, $area to automatically populate a field with the feature’s X coordinate, length, area
or any geometric information at its creation;
– increment a field by 1 for each new feature using maximum("field")+1;
– save the feature creation datetime using now();
– use variables in expressions, making it easier to e.g. insert the operator name (@user_full_name),
the project file path (@project_path), …
A preview of the resulting default value is displayed at the bottom of the widget.
Poznámka: The Default value option is not aware of the values in any other field of the feature being
created so it won’t be possible to use an expression combining any of those values i.e using an expression like
concat(field1, field2) may not work.
• Apply default value on update: whenever the feature attribute or geometry is changed, the default value
is recalculated. This could be handy to save values like last user that modifies data, last time it was changed…
Constraints
You can constrain the value to insert in the field. This constraint can be:
• Not null: requires the user to provide a value;
• Unique: guarantee the inserted value to be unique throughout the field;
• based on a custom expression: e.g. not regexp_match(col0,'[^A-Za-z]') will ensure that the
value of the field col0 has only alphabet letters. A short description can be added to help you remember the
constraint.
Whenever a value is added or edited in a field, it’s submitted to the existing constraints and:
• if it meets all the requirements, a green check is shown beside the field in the form;
• if it does not meet all the requirements, then the field is colored in yellow or orange and a corresponding cross
is displayed next to the widget. You can hover over the cross to remind which constraints are applied to the
field and fix the value:
– A yellow cross appears when the unmet constraint is an unenforced one and it does not prevent you to
save the changes with the „wrong“ values;
– An orange cross can not be ignored and does not allow you to save your modifications until they meet the
constraints. It appears when the Enforce constraint option is checked.
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Edit widgets
Based on the field type, QGIS automatically determines and assigns a default widget type to it. You can then replace
the widget with any other compatible with the field type. The available widgets are:
• Checkbox: Displays a checkbox whose state defines the value to insert.
• Classification: Only available when a categorized symbology is applied to the layer, displays a combo box with
the values of the classes.
• Color: Displays a color widget allowing to select a color; the color value is stored as a html notation in the
attribute table.
• Date/Time: Displays a line field which can open a calendar widget to enter a date, a time or both. Column type
must be text. You can select a custom format, pop-up a calendar, etc.
• Enumeration: Opens a combo box with predefined values fetched from the database. This is currently only
supported by the PostgreSQL provider, for fields of enum type.
• Attachment: Uses a „Open file“ dialog to store file path in a relative or absolute mode. It can also be used to
display a hyperlink (to document path), a picture or a web page.
• Hidden: A hidden attribute column is invisible. The user is not able to see its contents.
• Key/Value: Displays a two-columns table to store sets of key/value pairs within a single field. This is currently
supported by the PostgreSQL provider, for fields of hstore type.
• List: Displays a single column table to add different values within a single field. This is currently supported by
the PostgreSQL provider, for fields of array type.
• Range: Allows you to set numeric values from a specific range. The edit widget can be either a slider or a spin
box.
• Relation Reference: This is the default widget assigned to the referencing field (i.e., the foreign key in the
child layer) when a relation is set. It provides direct access to the parent feature’s form which in turn embeds
the list and form of its children.
• Text Edit (default): This opens a text edit field that allows simple text or multiple lines to be used. If you choose
multiple lines you can also choose html content.
• Unique Values: You can select one of the values already used in the attribute table. If ‚Editable‘ is activated,
a line edit is shown with autocompletion support, otherwise a combo box is used.
• Uuid Generator: Generates a read-only UUID (Universally Unique Identifiers) field, if empty.
• Value Map: A combo box with predefined items. The value is stored in the attribute, the description is shown
in the combo box. You can define values manually or load them from a layer or a CSV file.
• Value Relation: Offers values from a related table in a combobox. You can select layer, key column and value
column. Several options are available to change the standard behaviors: allow null value, order by value, allow
multiple selections and use of auto-completer. The forms will display either a drop-down list or a line edit field
when completer checkbox is enabled.
Tip: Relative Path in Attachment widget
If the path which is selected with the file browser is located in the same directory as the .qgs project file or below,
paths are converted to relative paths. This increases portability of a .qgs project with multimedia information
attached.
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14.1.10 Joins Properties
The Joins tab allows you to associate features of the current layer (called Target layer) to features from
another loaded vector layer (or table). The join is based on an attribute that is shared by the layers. The layers can be
geometryless (tables) or not but their join attribute should be of the same type.
To create a join:
1. Click the Add new join
button. The Add vector join dialog appears.
2. Select the Join layer you want to connect with the target vector layer
3. Specify the Join field and the Target field that are common to both the join layer and the target layer
4. Press OK and a summary of selected parameters is added to the Join panel.
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Obr. 14.45: Join an attribute table to an existing vector layer
The steps above will create a join, where ALL the attributes of the first matching feature in the join layer is added
to the target layer’s feature. QGIS provides more options to tweak the join:
• Cache join layer in virtual memory: allows you to cache values in memory (without geometries) from the
joined layer in order to speed up lookups.
• Create attribute index on the join field
• Dynamic form: helps to synchronize join fields on the fly, according to the Target field. This way, constraints
for join fields are also correctly updated. Note that it’s deactivated by default because it may be very time
consuming if you have a lot of features or a myriad of joins.
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• If the target layer is editable, then some icons will be displayed in the attribute table next to fields, in order to
inform about their status:
– : the join layer is not configured to be editable. If you want to be able to edit join features from the
target attribute table, then you have to check the option Editable join layer.
– : the join layer is well configured to be editable, but its current status is read only.
– : the join layer is editable, but synchronization mechanisms are not activated. If you want to
automatically add a feature in the join layer when a feature is created in the target layer, then you have
to check the option Upsert on edit. Symmetrically, the option Delete cascade may be activated if
you want to automatically delete join features.
• Joined fields: instead of adding all the fields from the joined layer, you can specify a subset.
• Custom field name prefix for joined fields, in order to avoid name collision
QGIS currently has support for joining non-spatial table formats supported by OGR (e.g., CSV, DBF and Excel),
delimited text and the PostgreSQL provider.
14.1.11 Auxiliary Storage Properties
The regular way to customize styling and labeling is to use data-defined properties as described in Data defined
override setup. However, it may not be possible if the underlying data is read only. Moreover, configuring these data-defined
properties may be very time consuming or not desirable! For example, if you want to fully use map tools
coming with The Label Toolbar, then you need to add and configure more than 20 fields in your original data source
(X and Y positions, rotation angle, font style, color and so on).
The Auxiliary Storage mechanism provides the solution to these limitations and awkward configurations. Auxiliary
fields are a roundabout way to automatically manage and store these data-defined properties (labels, diagram,
symbology…) in a SQLite database thanks to editable joins. This allows you to store properties for layers that aren’t
editable.
A tab is available in vector layer properties dialog to manage auxiliary storage:
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Obr. 14.46: Auxiliary Storage tab
Labeling
Considering that the data source may be customized thanks to data-defined properties without being editable, labeling
map tools described in The Label Toolbar are always available as soon as labeling is activated.
Actually, the auxiliary storage system needs an auxiliary layer to store these properties in a SQLite database (see
Auxiliary storage database). Its creation process is run the first time you click on the map while a labeling map tool
is currently activated. Then, a window is displayed, allowing you to select the primary key to use for joining (to ensure
that features are uniquely identified):
Obr. 14.47: Auxiliary Layer creation dialog
As soon as an auxiliary layer is configured for the current data source, you can retrieve its information in the tab:
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Obr. 14.48: Auxiliary Layer key
The auxiliary layer now has these characteristics:
• the primary key is ID,
• there are 0 features using an auxiliary field,
• there are 0 auxiliary fields.
Now that the auxiliary layer is created, you can edit the layer labels. Click on a label while the Change Label
map
tool is activated, then you can update styling properties like sizes, colors, and so on. The corresponding data-defined
properties are created and can be retrieved:
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Obr. 14.49: Auxiliary Fields
As you can see in the figure above, 21 fields are automatically created and configured for labeling. For example, the
FontStyle auxiliary field type is a String and is named labeling_fontstyle in the underlying SQLite
database. There is also 1 feature which is currently using these auxiliary fields.
Notice that the icon is displayed in the Labels properties tab indicating that the data-defined override options are
set correctly:
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Obr. 14.50: Data-defined properties automatically created
Otherwise, there’s another way to create an auxiliary field for a specific property thanks to the data-defined override
button. By clicking on Store data in the project, an auxiliary field is automatically created for the Opacity field. If you
click on this button and the auxiliary layer is not created yet, a window (Obr. 14.47) is first displayed to select the
primary key to use for joining.
Symbologie
Like the method described above for customizing labels, auxiliary fields can also be used to stylize symbols and
diagrams. To do this, click on Data-defined override
and select Store data in the project for a specific property. For
example, the Fill color field:
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Obr. 14.51: Data-defined property menu for symbol
There are different attributes for each symbol (e.g. fill style, fill color, stroke color, etc…), so each auxiliary field
representing an attribute requires a unique name to avoid conflicts. After selecting Store data in the project, a window
opens and displays the Type of the field and prompts you to enter a unique name for the auxiliary field. For example,
when creating a Fill color auxiliary field the following window opens:
Obr. 14.52: Name of the auxiliary field for a symbol
Once created, the auxiliary field can be retrieved in the auxiliary storage tab:
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Obr. 14.53: Auxiliary field symbol
Attribute table and widgets
Auxiliary fields can be edited using the attribute table. However, not all auxiliary fields are initially visible in the
attribute table.
Auxiliary fields representing attributes of a layer’s symbology, labeling, appearance, or diagrams will appear
automatically in the attribute table. The exception are attributes that can be modified using the Label Toolbar which
are hidden by default. Auxiliary fields representing a Color have a widget Color set by default, otherwise auxiliary
fields default to the Text Edit widget.
Auxiliary fields that represent attributes that can be modified using the Label toolbar are Hidden in the attribute table
by default. To make a field visible, open the Attribute Form properties tab and change the value of an auxiliary field
Widget Type from Hidden to another relevant value. For example, change the auxiliary_storage_labeling_size to
Text Edit or change auxiliary_storage_labeling_color to the Color widget. Those fields will now be visible in the
attribute table.
Auxiliary fields in the attribute table will appear like the following image:
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Obr. 14.54: Form with auxiliary fields
Management
The Auxiliary Layer menu allows you to manage the auxiliary fields:
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Obr. 14.55: Auxiliary layer management
The first item Create is disabled in this case because the auxiliary layer is already created. But in case of a fresh work,
you can use this action to create an auxiliary layer. As explained in Labeling, a primary key will be needed then.
The Clear action allows to keep all auxiliary fields, but remove their contents. This way, the number of features using
these fields will fall to 0.
The Delete action completely removes the auxiliary layer. In other words, the corresponding table is deleted from the
underlying SQLite database and properties customization are lost.
Finally, the Export action allows to save the auxiliary layer as a new vector layer. Note that geometries are not stored
in auxiliary storage. However, in this case, geometries are exported from the original data source too.
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Auxiliary storage database
When you save your project with the .qgs format, the SQLite database used for auxiliary storage is saved at the
same place but with the extension .qgd.
For convenience, an archive may be used instead thanks to the .qgz format. In this case, .qgd and .qgs files are
both embedded in the archive.
14.1.12 Actions Properties
QGIS provides the ability to perform an action based on the attributes of a feature. This can be used to perform
any number of actions, for example, running a program with arguments built from the attributes of a feature or passing
parameters to a web reporting tool.
Obr. 14.56: Overview action dialog with some sample actions
Actions are useful when you frequently want to run an external application or view a web page based on one or more
values in your vector layer. They are divided into six types and can be used like this:
• Generic, Mac, Windows and Unix actions start an external process.
• Python actions execute a Python expression.
• Generic and Python actions are visible everywhere.
• Mac, Windows and Unix actions are visible only on the respective platform (i.e., you can define three ‚Edit‘
actions to open an editor and the users can only see and execute the one ‚Edit‘ action for their platform to run
the editor).
There are several examples included in the dialog. You can load them by clicking on Create Default Actions. To edit
any of the examples, double-click its row. One example is performing a search based on an attribute value. This
concept is used in the following discussion.
The Show in Attribute Table allows you to display in the attribute table dialog the checked feature-scoped actions,
either as Combo Box or as Separate Buttons (see Configuring the columns).
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Defining Actions
To define an attribute action, open the vector Layer Properties dialog and click on the Actions tab. In the Actions tab,
click the Add a new action
to open the Edit Action dialog.
Select the action Type and provide a descriptive name for the action. The action itself must contain the name of
the application that will be executed when the action is invoked. You can add one or more attribute field values
as arguments to the application. When the action is invoked, any set of characters that start with a % followed by the
name of a field will be replaced by the value of that field. The special characters %% will be replaced by the value of
the field that was selected from the identify results or attribute table (see using_actions below). Double quote marks
can be used to group text into a single argument to the program, script or command. Double quotes will be ignored
if preceded by a backslash.
The Action Scopes allows you to define where the action should be available. You have 4 different choices:
1. Feature Scope: action is available when right click in the cell within the attribute table.
2. Field Scope: action is available when right click in the cell within the attribute table, in the feature form and in
the default action button of the main toolbar.
3. Layer Scope: action is available in the action button in the attribute table toolbar. Be aware that this type of
action involves the entire layer and not the single features.
4. Canvas: action is available in the main action button in the toolbar.
If you have field names that are substrings of other field names (e.g., col1 and col10), you should indicate that
by surrounding the field name (and the % character) with square brackets (e.g., [%col10]). This will prevent the
%col10 field name from being mistaken for the %col1 field name with a 0 on the end. The brackets will be
removed by QGIS when it substitutes in the value of the field. If you want the substituted field to be surrounded by
square brackets, use a second set like this: [[%col10]].
Using the Identify Features tool, you can open the Identify Results dialog. It includes a (Derived) item that contains
information relevant to the layer type. The values in this item can be accessed in a similar way to the other fields
by proceeding the derived field name with (Derived).. For example, a point layer has an X and Y field, and the
values of these fields can be used in the action with %(Derived).X and %(Derived).Y. The derived attributes
are only available from the Identify Results dialog box, not the Attribute Table dialog box.
Two example actions are shown below:
• konqueror https://www.google.com/search?q=%nam
• konqueror https://www.google.com/search?q=%%
In the first example, the web browser konqueror is invoked and passed a URL to open. The URL performs a Google
search on the value of the nam field from our vector layer. Note that the application or script called by the action
must be in the path, or you must provide the full path. To be certain, we could rewrite the first example as: /
opt/kde3/bin/konqueror https://www.google.com/search?q=%nam. This will ensure that the
konqueror application will be executed when the action is invoked.
The second example uses the %% notation, which does not rely on a particular field for its value. When the action
is invoked, the %% will be replaced by the value of the selected field in the identify results or attribute table.
Using Actions
QGIS offers many ways to execute actions you enabled on a layer. Depending on their settings, they can be available:
• in the drop-down menu of Run Feature Action
button from the Attributes toolbar or Attribute table dialog;
• when right-clicking a feature with the Identify Features
tool (see Identifying Features for more information);
• from the Identify Results panel, under the Actions section;
• as items of an Actions column in the Attribute Table dialog.
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If you are invoking an action that uses the %% notation, right-click on the field value in the Identify Results dialog or
the Attribute Table dialog that you wish to pass to the application or script.
Here is another example that pulls data out of a vector layer and inserts it into a file using bash and the echo command
(so it will only work on or perhaps ). The layer in question has fields for a species name taxon_name, latitude
lat and longitude long. We would like to be able to make a spatial selection of localities and export these field
values to a text file for the selected record (shown in yellow in the QGIS map area). Here is the action to achieve this:
bash -c "echo \"%taxon_name %lat %long\" >> /tmp/species_localities.txt"
After selecting a few localities and running the action on each one, opening the output file will show something like
this:
Acacia mearnsii -34.0800000000 150.0800000000
Acacia mearnsii -34.9000000000 150.1200000000
Acacia mearnsii -35.2200000000 149.9300000000
Acacia mearnsii -32.2700000000 150.4100000000
As an exercise, we can create an action that does a Google search on the lakes layer. First, we need to determine
the URL required to perform a search on a keyword. This is easily done by just going to Google and doing a simple
search, then grabbing the URL from the address bar in your browser. From this little effort, we see that the format
is https://www.google.com/search?q=QGIS, where QGIS is the search term. Armed with this information, we can
proceed:
1. Make sure the lakes layer is loaded.
2. Open the Layer Properties dialog by double-clicking on the layer in the legend, or right-click and choose
Properties from the pop-up menu.
3. Click on the Actions tab.
4. Click Add a new action
.
5. Choose the Open action type,
6. Enter a name for the action, for example Google Search.
7. Additionally you can add a Short Name or even an Icon.
8. Choose the action Scope. See Defining Actions for further information. Leave the default settings for this
example.
9. For the action, we need to provide the name of the external program to run. In this case, we can use Firefox.
If the program is not in your path, you need to provide the full path.
10. Following the name of the external application, add the URL used for doing a Google search, up to but not
including the search term: https://www.google.com/search?q=
11. The text in the Action field should now look like this: https://www.google.com/search?q=
12. Click on the drop-down box containing the field names for the lakes layer. It’s located just to the left of the
Insert button.
13. From the drop-down box, select ‚NAMES‘ and click Insert.
14. Your action text now looks like this:
https://www.google.com/search?q=[%NAMES%]
15. To finalize and add the action, click the OK button.
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Obr. 14.57: Edit action dialog configured with the example
This completes the action, and it is ready to use. The final text of the action should look like this:
https://www.google.com/search?q=[%NAMES%]
We can now use the action. Close the Layer Properties dialog and zoom in to an area of interest. Make sure the lakes
layer is active and identify a lake. In the result box you’ll now see that our action is visible:
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Obr. 14.58: Select feature and choose action
When we click on the action, it brings up Firefox and navigates to the URL https://www.google.com/search?q=
Tustumena. It is also possible to add further attribute fields to the action. Therefore, you can add a + to the end of
the action text, select another field and click on Insert Field. In this example, there is just no other field available that
would make sense to search for.
You can define multiple actions for a layer, and each will show up in the Identify Results dialog.
You can also invoke actions from the attribute table by selecting a row and right-clicking, then choosing the action
from the pop-up menu.
There are all kinds of uses for actions. For example, if you have a point layer containing locations of images or photos
along with a file name, you could create an action to launch a viewer to display the image. You could also use actions
to launch web-based reports for an attribute field or combination of fields, specifying them in the same way we did
in our Google search example.
We can also make more complex examples, for instance, using Python actions.
Usually, when we create an action to open a file with an external application, we can use absolute paths, or eventually
relative paths. In the second case, the path is relative to the location of the external program executable file. But what
about if we need to use relative paths, relative to the selected layer (a file-based one, like Shapefile or SpatiaLite)?
The following code will do the trick:
command = "firefox"
imagerelpath = "images_test/test_image.jpg"
layer = qgis.utils.iface.activeLayer()
import os.path
layerpath = layer.source() if layer.providerType() == 'ogr'
else (qgis.core.QgsDataSourceURI(layer.source()).database()
if layer.providerType() == 'spatialite' else None)
path = os.path.dirname(str(layerpath))
image = os.path.join(path,imagerelpath)
import subprocess
subprocess.Popen( [command, image ] )
We just have to remember that the action is one of type Python and the command and imagerelpath variables must
be changed to fit our needs.
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But what about if the relative path needs to be relative to the (saved) project file? The code of the Python action would
be:
command = "firefox"
imagerelpath = "images_test/test_image.jpg"
projectpath = qgis.core.QgsProject.instance().fileName()
import os.path
path = os.path.dirname(str(projectpath)) if projectpath != '' else None
image = os.path.join(path, imagerelpath)
import subprocess
subprocess.Popen( [command, image ] )
Another Python action example is the one that allows us to add new layers to the project. For instance, the following
examples will add to the project respectively a vector and a raster. The names of the files to be added to the project
and the names to be given to the layers are data driven (filename and layername are column names of the table of
attributes of the vector where the action was created):
qgis.utils.iface.addVectorLayer('/yourpath/[% "filename" %].shp',
'[% "layername" %]', 'ogr')
To add a raster (a TIF image in this example), it becomes:
qgis.utils.iface.addRasterLayer('/yourpath/[% "filename" %].tif',
'[% "layername" %]')
14.1.13 Display Properties
The Display tab helps you configure fields to use for feature identification:
• The Display name: based on a field or an expression. This is:
– the label shown on top of the feature information in the Identify tool results
– the field used in the locator bar when looking for features in all layers
– the feature identifier in the attribute table form view
– the feature identifier when the map or layout is exported to a layered output format such as GeoPDF
– the map tip information, i.e. the message displayed in the map canvas when hovering over a feature of
the active layer with the Show Map Tips
icon pressed. Applicable when no HTML Map Tip is set.
• The HTML Map Tip is specifically created for the map tips: it’s a more complex and full HTML text mixing
fields, expressions and html tags (multiline, fonts, images, hyperlink…).
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Obr. 14.59: HTML code for map tip
To activate map tips, select the menu option View ► Show Map Tips or click on the Show Map Tips
icon of the
Attributes Toolbar. Map tip is a cross-session feature meaning that once activated, it stays on and apply to any layer
in any project, even in future QGIS sessions until it’s toggled off.
Obr. 14.60: Map tip made with HTML code
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14.1.14 Rendering Properties
Scale dependent visibility
You can set the Maximum (inclusive) and Minimum (exclusive) scale, defining a range of scale in which features will
be visible. Out of this range, they are hidden. The Set to current canvas scale
button helps you use the current map canvas
scale as boundary of the range visibility. See Vykreslování v závislosti na měřítku for more information.
Simplify geometry
QGIS offers support for on-the-fly feature generalisation. This can improve rendering times when drawing many
complex features at small scales. This feature can be enabled or disabled in the layer settings using the Simplify
geometry option. There is also a global setting that enables generalisation by default for newly added layers (see global
simplification for more information).
Obr. 14.61: Layer Geometry Simplification dialog
Poznámka: Feature generalisation may introduce artefacts into your rendered output in some cases. These may
include slivers between polygons and inaccurate rendering when using offset-based symbol layers.
While rendering extremely detailed layers (e.g. polygon layers with a huge number of nodes), this can cause layout
exports in PDF/SVG format to be huge as all nodes are included in the exported file. This can also make the resultant
file very slow to work with/open in other programs.
Checking Force layer to render as raster forces these layers to be rasterised so that the exported files won’t have
to include all the nodes contained in these layers and the rendering is therefore sped up.
You can also do this by forcing the layout to export as a raster, but that is an all-or-nothing solution, given that the
rasterisation is applied to all layers.
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Refresh layer at interval (seconds): set a timer to automatically refresh individual layers at a matching interval. Canvas
updates are deferred in order to avoid refreshing multiple times if more than one layer has an auto update interval set.
Depending on the data provider (e.g. PostgreSQL), notifications can be sent to QGIS when changes are applied to
the data source, out of QGIS. Use the Refresh layer on notification option to trigger an update. You can also limit
the layer refresh to a specific message set in the Only if message is text box.
14.1.15 Variables Properties
The Variables tab lists all the variables available at the layer’s level (which includes all global and project’s
variables).
It also allows the user to manage layer-level variables. Click the button to add a new custom layer-level variable.
Likewise, select a custom layer-level variable from the list and click the button to remove it.
More information on variables usage in the General Tools Storing values in Variables section.
14.1.16 Metadata Properties
The Metadata tab provides you with options to create and edit a metadata report on your layer. Information to fill
concern:
• the data Identification: basic attribution of the dataset (parent, identifier, title, abstract, language…);
• the Categories the data belongs to. Alongside the ISO categories, you can add custom ones;
• the Keywords to retrieve the data and associated concepts following a standard based vocabulary;
• the Access to the dataset (licenses, rights, fees, and constraints);
• the Extent of the dataset, either spatial one (CRS, map extent, altitudes) or temporal;
• the Contact of the owner(s) of the dataset;
• the Links to ancillary resources and related information;
• the History of the dataset.
A summary of the filled information is provided in the Validation tab and helps you identify potential issues related
to the form. You can then either fix them or ignore them.
Metadata are currently saved in the project file. They can also be saved in a .qmd file alongside file based layers or
in a local .sqlite database for remote layers (e.g. PostGIS).
14.1.17 Dependencies Properties
The Dependencies tab allows to declare data dependencies between layers. A data dependency occurs when a data
modification in a layer, not by direct user manipulation, may modify data of other layers. This is the case for instance
when geometry of a layer is updated by a database trigger or custom PyQGIS scripting after modification of another
layer’s geometry.
In the Dependencies tab, you can select any layers which may externally alter the data in the current layer. Correctly
specifying dependent layers allows QGIS to invalidate caches for this layer when the dependent layers are altered.
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14.1.18 Legend Properties
The Legend properties tab provides you with advanced settings for the Layers panel and/or the print layout legend.
These options include:
• Text on symbols: In some cases it can be useful to add extra information to the symbols in the legend. With
this frame, you can affect to any of the symbols used in the layer symbology a text that is displayed over the
symbol, in both Layers panel and print layout legend. This mapping is done by typing each text next to the
symbol in the table widget or filling the table using the Set Labels from Expression button. Text appearance
is handled through the font and color selector widgets of the Text Format button.
Obr. 14.62: Setting text on symbols (left) and its rendering in the Layers panel (right)
• a list of widgets you can embed within the layer tree in the Layers panel. The idea is to have a way to quickly
access some actions that are often used with the layer (setup transparency, filtering, selection, style or other
stuff…).
By default, QGIS provides transparency widget but this can be extended by plugins registering their own widgets
and assign custom actions to layers they manage.
14.1.19 QGIS Server Properties
The QGIS Server tab consists of Description, Attribution, MetadataURL, and LegendUrl sections.
From the Description section, you can change the Short name used to reference the layer in requests (to learn more
about short names, read server_short_name). You can also add or edit a Title and Abstract for the layer, or define
a Keyword list here. These keyword lists can be used in a metadata catalog. If you want to use a title from an XML
metadata file, you have to fill in a link in the DataUrl field.
Use Attribution to get attribute data from an XML metadata catalog.
In MetadataUrl, you can define the general path to the XML metadata catalog. This information will be saved in the
QGIS project file for subsequent sessions and will be used for QGIS server.
In the LegendUrl section, you can provide the url of a legend image in the url field. You can use the Format drop-down
option to apply the appropriate format of the image. Currently png, jpg and jpeg image formats are supported.
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Obr. 14.63: QGIS Server tab in vector layers properties dialog
To learn more about QGIS Server, read the QGIS-Server-manual.
14.1.20 Digitizing Properties
The Digitizing tab gives access to options that help to ensure the quality of digitized geometries.
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Obr. 14.64: The QGIS Digitizing tab in the vector layers properties dialog
Automatic Fixes
Options in the Automatic Fixes section will directly affect the vertices of any geometry which is added or modified.
If the Remove duplicate nodes option is checked, any two subsequent vertices with exactly the same coordinates
will be removed. If the Geometry precision is set, all vertices will be rounded to the closest multiple of the configured
geometry precision. The rounding will happen in the layer coordinate reference system. Z and M values are not
rounded. With many map tools, a grid is shown on the canvas while digitizing.
Geometry Checks
In the Geometry checks section, additional validations on a per geometry basis can be activated. Immediately after
any geometry modification, failures in these checks are reported to the user in the geometry validation panel. As long
as a check is failing, it is not possible to save the layer. The Is valid check will run basic validity checks like self
intersection on geometries.
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Topology Checks
In the Topology checks section, additional topology validation checks can be activated. Topology checks will be
executed when the user saves the layer. Check errors will be reported in the geometry validation panel. As long
as validation errors are present, the layer can not be saved. Topology checks are executed in the area of the bounding
box of the modified features. Since other features may be present in the same area, topological errors concerning
these features are reported as well as errors introduced in the current edit session.
Topology check option Illustration
The Gap check will check for gaps between neighbouring
polygons.
The Overlap check will check for overlaps between
neighbouring polygons.
The Missing vertex check will check for shared boundaries
of neighbouring polygons where one border misses a vertex
which is present on the other one.
Gap check exceptions
Sometimes it is desirable to keep gaps inside an area in a polygon layer that otherwise is fully covered by polygons.
For example, a land use layer may have acceptable holes for lakes. It is possible to define areas that are ignored in the
gap check. Since gaps inside these areas are allowed, we will refer to them as Allowed Gaps areas.
In the options for the gap checks under Allowed Gaps, an Allowed Gaps layer can be configured.
Whenever the gap check is executed, gaps which are covered by one or more polygons in the Allowed Gaps Layer are
not reported as topology errors.
It is also possible to configure an additional Buffer. This buffer is applied to each polygon on the Allowed Gaps Layer.
This makes it possible to make the tests less susceptible to small changes in the outlines at the borders of gaps.
When Allowed Gaps are enabled, an additional button (Add Allowed Gap) for detected gap errors is available in the
geometry validation dock, where gaps are reported during digitizing. If the Add Allowed Gap button is pushed, a new
polygon with the geometry of the detected gap is inserted into the Allowed Gaps Layer. This makes it possible to
quickly flag gaps as allowed.
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14.2 Výrazy
Based on layer data and prebuilt or user defined functions, Expressions offer a powerful way to manipulate attribute
value, geometry and variables in order to dynamically change the geometry style, the content or position of the label,
the value for diagram, the height of a layout item, select some features, create virtual field, …
Poznámka: A list of the default functions and variables for writing expressions can be found at List of functions,
with detailed information and examples.
14.2.1 The Expression string builder
Main dialog to build expressions, the Expression string builder is available from many parts in QGIS and, can
particularly be accessed when:
• clicking the button;
• selecting features with the Select By Expression…
tool;
• editing attributes with e.g. the Field calculator
tool;
• manipulating symbology, label or layout item parameters with the Data defined override
tool (see Data defined
override setup);
• building a geometry generator symbol layer;
• doing some geoprocessing.
The Expression builder dialog offers access to the:
• Expression tab which, thanks to a list of predefined functions, helps to write and check the expression to use;
• Function Editor tab which helps to extend the list of functions by creating custom ones.
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The Interface
The Expression tab provides the main interface to write expressions using functions, layer fields and values. It contains
the following widgets:
Obr. 14.65: The Expression tab
• An expression editor area for typing or pasting expressions. Autocompletion is available to speed expression
writing:
– Corresponding variables, function names and field names to the input text are shown below: use the Up
and Down arrows to browse the items and press Tab to insert in the expression or simply click on the
wished item.
– Function parameters are shown while filling them.
QGIS also checks the expression rightness and highlights all the errors using:
– Underline: for unknown functions, wrong or invalid arguments;
– Marker: for every other error (eg, missing parenthesis, unexpected character) at a single location.
Tip: Document your expression with comments
When using complex expression, it is good practice to add text either as a multiline comment or inline comments
to help you remember.
/*
Labels each region with its highest (in altitude) airport(s)
and altitude, eg 'AMBLER : 264m' for the 'Northwest Artic' region
*/
with_variable(
'airport_alti', -- stores the highest altitude of the region
aggregate(
'airports',
'max',
"ELEV", -- the field containing the altitude
-- and limit the airports to the region they are within
filter := within( $geometry, geometry( @parent ) )
),
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(pokračujte na předchozí stránce)
aggregate( -- finds airports at the same altitude in the region
'airports',
'concatenate',
"NAME",
filter := within( $geometry, geometry( @parent ) )
and "ELEV" = @airport_alti
)
|| ' : ' || @airport_alti || 'm'
-- using || allows regions without airports to be skipped
)
• Above the expression editor, a set of tools helps you:
– Clear the expression editor
– create and manage user expressions
• Under the expression editor, you find:
– a set of basic operators to help you build the expression
– an indication of the expected format of output when you are data-defining feature properties
– a live Output preview of the expression, evaluated on the first feature of the Layer by default. You can
browse and evaluate other features of the layer using the Feature combobox (the values are taken from
the display name property of the layer).
In case of error, it indicates it and you can access the details with the provided hyperlink.
• A function selector displays the list of functions, variables, fields… organized in groups. A search box
is available to filter the list and quickly find a particular function or field. Double-clicking an item adds it
to the expression editor.
• A help panel displays help for each selected item in the function selector.
Tip: Press Ctrl+Click when hovering a function name in an expression to automatically display its help
in the dialog.
A field’s values widget shown when a field is selected in the function selector helps to fetch features attributes:
– Look for a particular field value
– Display the list of All Unique or 10 Samples values. Also available from right-click.
When the field is mapped with another layer or a set of values, i.e. if the field widget is of
RelationReference, ValueRelation or ValueMap type, it’s possible to list all the values of the mapped
field (from the referenced layer, table or list). Moreover, you can filter this list to Only show values in
use in the current field.
Double-clicking a field value in the widget adds it to the expression editor.
Tip: The right panel, showing functions help or field values, can be collapsed (invisible) in the dialog. Press
the Show Values or Show Help button to get it back.
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Writing an expression
QGIS expressions are used to select features or set values. Writing an expression in QGIS follows some rules:
1. The dialog defines the context: if you are used to SQL, you probably know queries of the type select features
from layer where condition or update layer set field = new_value where condition. A QGIS expression also
needs all these information but the tool you use to open the expression builder dialog provides parts of them.
For example, giving a layer (building) with a field (height):
• pressing the Select by expression
tool means that you want to „select features from buildings“. The
condition is the only information you need to provide in the expression text widget, e.g. type "height"
> 20 to select buildings that are higher than 20.
• with this selection made, pressing the Field calculator
button and choosing „height“ as Update existing
field, you already provide the command „update buildings set height = ??? where height > 20“. The only
remaining bits you have to provide in this case is the new value, e.g. just enter 50 to set the height of
the previously selected buildings.
2. Pay attention to quotes: single quotes return a literal, so a text placed between single quotes ('145')
is interpreted as a string. Double quotes will give you the value of that text so use them for fields ("myfield").
Fields can also be used without quotes (myfield). No quotes for numbers (3.16).
Poznámka: Functions normally take as argument a string for field name. Do:
attribute( @atlas_feature, 'height' ) -- returns the value stored in the
→"height" attribute of the current atlas feature
And not:
attribute( @atlas_feature, "height" ) -- fetches the value of the attribute␣
→named "height" (e.g. 100), and use that value as a field
-- from which to return the atlas␣
→feature value. Probably wrong as a field named "100" may not exist.
Tip: Use named parameters to ease expression reading
Some functions require many parameters to be set. The expression engine supports the use of named parameters.
This means that instead of writing the cryptic expression clamp( 1, 2, 9), you can use clamp( min:=1,
value:=2, max:=9). This also allows arguments to be switched, e.g. clamp( value:=2, max:=9,
min:=1). Using named parameters helps clarify what the arguments for an expression function refer to, which
is helpful when you are trying to interpret an expression later!
Some use cases of expressions
• From the Field Calculator, calculate a „pop_density“ field using the existing „total_pop“ and „area_km2“ fields:
"total_pop" / "area_km2"
• Label or categorize features based on their area:
CASE WHEN $area > 10 000 THEN 'Larger' ELSE 'Smaller' END
• Update the field „density_level“ with categories according to the „pop_density“ values:
CASE WHEN "pop_density" < 50 THEN 'Low population density'
WHEN "pop_density" >= 50 and "pop_density" < 150 THEN 'Medium population␣
→density'
(continues on next page)
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(pokračujte na předchozí stránce)
WHEN "pop_density" >= 150 THEN 'High population density'
END
• Apply a categorized style to all the features according to whether their average house price is smaller or higher
than 10000€ per square metre:
"price_m2" > 10000
• Using the „Select By Expression…“ tool, select all the features representing areas of “High population density”
and whose average house price is higher than 10000€ per square metre:
"density_level" = 'High population density' and "price_m2" > 10000
The previous expression could also be used to define which features to label or show on the map.
• Create a different symbol (type) for the layer, using the geometry generator:
point_on_surface( $geometry )
• Given a point feature, generate a closed line (using make_line) around its geometry:
make_line(
-- using an array of points placed around the original
array_foreach(
-- list of angles for placing the projected points (every 90°)
array:=generate_series( 0, 360, 90 ),
-- translate the point 20 units in the given direction (angle)
expression:=project( $geometry, distance:=20, azimuth:=radians( @element )␣
→)
)
)
• In a print layout label, display the name of the „airports“ features that are within the layout „Map 1“ item:
with_variable( 'extent',
map_get( item_variables( 'Map 1' ), 'map_extent' ),
aggregate( 'airports', 'concatenate', "NAME",
intersects( $geometry, @extent ), ' ,'
)
)
Saving Expressions
Using the Add current expression to user expressions
button above the expression editor frame, you can save important
expressions you want to have quick access to. These are available from the User expressions group in the middle
panel. They are saved under the user profile (<userprofile>/QGIS/QGIS3.ini file) and available in all
expression dialogs inside all projects of the current user profile.
A set of tools available above the expression editor frame helps you manage the user expressions:
• Add the current expression to user expressions
: store the expression in the user profile. A label and a help text can be
added for easy identification.
• Edit selected expression from user expressions
, as well as their help and label
• Remove selected expression from user expressions
• Import user expressions
from a .json file into the active user profile folder
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• Export user expressions
as a .json file; all the user expressions in the user profile QGIS3.ini file are shared
14.2.2 Function Editor
With the Function Editor tab, you are able to write your own functions in Python language. This provides a handy and
comfortable way to address particular needs that would not be covered by the predefined functions.
Obr. 14.66: The Function Editor tab
To create a new function:
1. Press the New File
button.
2. Enter a name to use in the form that pops up and press OK.
A new item of the name you provide is added in the left panel of the Function Editor tab; this is a Python .py
file based on QGIS template file and stored in the /python/expressions folder under the active user
profile directory.
3. The right panel displays the content of the file: a python script template. Update the code and its help according
to your needs.
4. Press the Save and Load Functions button. The function you wrote is added to the functions tree in the
Expression tab, by default under the Custom group.
5. Enjoy your new function.
6. If the function requires improvements, enable the Function Editor tab, do the changes and press again the
Save and Load Functions button to make them available in the file, hence in any expression tab.
Custom Python functions are stored under the user profile directory, meaning that at each QGIS startup, it will
auto load all the functions defined with the current user profile. Be aware that new functions are only saved in the
/python/expressions folder and not in the project file. If you share a project that uses one of your custom
functions you will need to also share the .py file in the /python/expressions folder.
To delete a custom function:
1. Enable the Function Editor tab
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2. Select the function in the list
3. Press the Remove selected function
. The function is removed from the list and the corresponding .py file deleted
from the user profile folder.
Example
Here’s a short example on how to create your own my_sum function that will operate with two values.
from qgis.core import *
from qgis.gui import *
@qgsfunction(args='auto', group='Custom')
def my_sum(value1, value2, feature, parent):
"""
Calculates the sum of the two parameters value1 and value2.
<h2>Example usage:</h2>
<ul>
<li>my_sum(5, 8) -> 13</li>
<li>my_sum("field1", "field2") -> 42</li>
</ul>
"""
return value1 + value2
When using the args='auto' function argument the number of function arguments required will be calculated
by the number of arguments the function has been defined with in Python (minus 2 - feature, and parent). The
group='Custom' argument indicates the group in which the function should be listed in the Expression dialog.
It is also possible to add keywords arguments like:
• usesgeometry=True if the expression requires access to the features geometry. By default False.
• handlesnull=True if the expression has custom handling for NULL values. If False (default), the result
will always be NULL as soon as any parameter is NULL.
• referenced_columns=[list]: An array of attribute names that are required to the function. Defaults
to [QgsFeatureRequest.ALL_ATTRIBUTES].
The previous example function can then be used in expressions:
Obr. 14.67: Custom Function added to the Expression tab
Further information about creating Python code can be found in the PyQGIS-Developer-Cookbook.
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14.3 List of functions
The functions, operators and variables available in QGIS are listed below, grouped by categories.
14.3.1 Aggregates Functions
This group contains functions which aggregate values over layers and fields.
• aggregate
• array_agg
• collect
• concatenate
• concatenate_unique
• count
• count_distinct
• count_missing
• iqr
• majority
• max_length
• maximum
• mean
• median
• min_length
• minimum
• minority
• q1
• q3
• range
• relation_aggregate
• stdev
• sum
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aggregate
Returns an aggregate value calculated using features from another layer.
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Syntax aggregate(layer, aggregate, expression, [filter], [concatenator=‘‘], [order_by])
[] marks optional arguments
Arguments
• layer - a string, representing either a layer name or layer ID
• aggregate - a string corresponding to the aggregate to calculate. Valid options are:
– count
– count_distinct
– count_missing
– min
– max
– sum
– mean
– median
– stdev
– stdevsample
– range
– minority
– majority
– q1: first quartile
– q3: third quartile
– iqr: inter quartile range
– min_length: minimum string length
– max_length: maximum string length
– concatenate: join strings with a concatenator
– concatenate_unique: join unique strings with a concatenator
– collect: create an aggregated multipart geometry
– array_agg: create an array of aggregated values
• expression - sub expression or field name to aggregate
• filter - optional filter expression to limit the features used for calculating the aggregate.
Fields and geometry are from the features on the joined layer. The source feature can be
accessed with the variable @parent.
• concatenator - optional string to use to join values for ‚concatenate‘ aggregate
• order_by - optional filter expression to order the features used for calculating the
aggregate. Fields and geometry are from the features on the joined layer. By default, the
features will be returned in an unspecified order.
Examples
• aggregate(layer:='rail_stations',aggregate:='sum',
expression:="passengers") → sum of all values from the passengers
field in the rail_stations layer
• aggregate('rail_stations','sum', "passengers"/7) → calculates
a daily average of „passengers“ by dividing the „passengers“ field by 7 before summing
the values
• aggregate(layer:='rail_stations',aggregate:='sum',
expression:="passengers",filter:="class">3) → sums up all
values from the „passengers“ field from features where the „class“ attribute is greater than
3 only
• aggregate(layer:='rail_stations',aggregate:='concatenate',
expression:="name", concatenator:=',') → comma separated list of
the name field for all features in the rail_stations layer
• aggregate(layer:='countries', aggregate:='max',
expression:="code", filter:=intersects( $geometry,
geometry(@parent) ) ) → The country code of an intersecting country
on the layer ‚countries‘
• aggregate(layer:='rail_stations',aggregate:='sum',
expression:="passengers",filter:=contains(
@atlas_geometry, $geometry ) ) → sum of all values from the passengers
field in the rail_stations within the current atlas feature
• aggregate(layer:='rail_stations', aggregate:='collect',
expression:=centroid($geometry), filter:="region_name" =
attribute(@parent,'name') ) → aggregates centroid geometries of the
rail_stations of the same region as current feature
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array_agg
Returns an array of aggregated values from a field or expression.
Syntax array_agg(expression, [group_by], [filter], [order_by])
[] marks optional arguments
Arguments
• expression - sub expression of field to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
• order_by - optional expression to use to order features used to calculate aggregate. By
default, the features will be returned in an unspecified order.
Examples
• array_agg("name",group_by:="state") → list of name values, grouped by
state field
collect
Returns the multipart geometry of aggregated geometries from an expression
Syntax collect(expression, [group_by], [filter])
[] marks optional arguments
Arguments
• expression - geometry expression to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
Examples
• collect( $geometry ) → multipart geometry of aggregated geometries
• collect( centroid($geometry), group_by:="region", filter:=
"use" = 'civilian' ) → aggregated centroids of the civilian features based on
their region value
concatenate
Returns all aggregated strings from a field or expression joined by a delimiter.
Syntax concatenate(expression, [group_by], [filter], [concatenator], [order_by])
[] marks optional arguments
Arguments
• expression - sub expression of field to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
• concatenator - optional string to use to join values. Empty by default.
• order_by - optional expression to use to order features used to calculate aggregate. By
default, the features will be returned in an unspecified order.
Examples
• concatenate("town_name",group_by:="state",
concatenator:=',') → comma separated list of town_names, grouped by
state field
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concatenate_unique
Returns all unique strings from a field or expression joined by a delimiter.
Syntax concatenate_unique(expression, [group_by], [filter], [concatenator], [order_by])
[] marks optional arguments
Arguments
• expression - sub expression of field to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
• concatenator - optional string to use to join values. Empty by default.
• order_by - optional expression to use to order features used to calculate aggregate. By
default, the features will be returned in an unspecified order.
Examples
• concatenate_unique("town_name",group_by:="state",
concatenator:=',') → comma separated list of unique town_names, grouped by
state field
count
Returns the count of matching features.
Syntax count(expression, [group_by], [filter])
[] marks optional arguments
Arguments
• expression - sub expression of field to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
Examples
• count("stations",group_by:="state") → count of stations, grouped by
state field
count_distinct
Returns the count of distinct values.
Syntax count_distinct(expression, [group_by], [filter])
[] marks optional arguments
Arguments
• expression - sub expression of field to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
Examples
• count_distinct("stations",group_by:="state") → count of distinct
stations values, grouped by state field
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count_missing
Returns the count of missing (NULL) values.
Syntax count_missing(expression, [group_by], [filter])
[] marks optional arguments
Arguments
• expression - sub expression of field to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
Examples
• count_missing("stations",group_by:="state") → count of missing
(NULL) station values, grouped by state field
iqr
Returns the calculated inter quartile range from a field or expression.
Syntax iqr(expression, [group_by], [filter])
[] marks optional arguments
Arguments
• expression - sub expression of field to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
Examples
• iqr("population",group_by:="state") → inter quartile range of
population value, grouped by state field
majority
Returns the aggregate majority of values (most commonly occurring value) from a field or expression.
Syntax majority(expression, [group_by], [filter])
[] marks optional arguments
Arguments
• expression - sub expression of field to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
Examples
• majority("class",group_by:="state") → most commonly occurring class
value, grouped by state field
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max_length
Returns the maximum length of strings from a field or expression.
Syntax max_length(expression, [group_by], [filter])
[] marks optional arguments
Arguments
• expression - sub expression of field to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
Examples
• max_length("town_name",group_by:="state") → maximum length of
town_name, grouped by state field
maximum
Returns the aggregate maximum value from a field or expression.
Syntax maximum(expression, [group_by], [filter])
[] marks optional arguments
Arguments
• expression - sub expression of field to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
Examples
• maximum("population",group_by:="state") → maximum population
value, grouped by state field
mean
Returns the aggregate mean value from a field or expression.
Syntax mean(expression, [group_by], [filter])
[] marks optional arguments
Arguments
• expression - sub expression of field to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
Examples
• mean("population",group_by:="state") → mean population value,
grouped by state field
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median
Returns the aggregate median value from a field or expression.
Syntax median(expression, [group_by], [filter])
[] marks optional arguments
Arguments
• expression - sub expression of field to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
Examples
• median("population",group_by:="state") → median population value,
grouped by state field
min_length
Returns the minimum length of strings from a field or expression.
Syntax min_length(expression, [group_by], [filter])
[] marks optional arguments
Arguments
• expression - sub expression of field to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
Examples
• min_length("town_name",group_by:="state") → minimum length of
town_name, grouped by state field
minimum
Returns the aggregate minimum value from a field or expression.
Syntax minimum(expression, [group_by], [filter])
[] marks optional arguments
Arguments
• expression - sub expression of field to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
Examples
• minimum("population",group_by:="state") → minimum population
value, grouped by state field
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minority
Returns the aggregate minority of values (least occurring value) from a field or expression.
Syntax minority(expression, [group_by], [filter])
[] marks optional arguments
Arguments
• expression - sub expression of field to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
Examples
• minority("class",group_by:="state") → least occurring class value,
grouped by state field
q1
Returns the calculated first quartile from a field or expression.
Syntax q1(expression, [group_by], [filter])
[] marks optional arguments
Arguments
• expression - sub expression of field to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
Examples
• q1("population",group_by:="state") → first quartile of population value,
grouped by state field
q3
Returns the calculated third quartile from a field or expression.
Syntax q3(expression, [group_by], [filter])
[] marks optional arguments
Arguments
• expression - sub expression of field to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
Examples
• q3("population",group_by:="state") → third quartile of population value,
grouped by state field
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range
Returns the aggregate range of values (maximum - minimum) from a field or expression.
Syntax range(expression, [group_by], [filter])
[] marks optional arguments
Arguments
• expression - sub expression of field to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
Examples
• range("population",group_by:="state") → range of population values,
grouped by state field
relation_aggregate
Returns an aggregate value calculated using all matching child features from a layer relation.
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Syntax relation_aggregate(relation, aggregate, expression, [concatenator=‘‘], [order_by])
[] marks optional arguments
Arguments
• relation - a string, representing a relation ID
• aggregate - a string corresponding to the aggregate to calculate. Valid options are:
– count
– count_distinct
– count_missing
– min
– max
– sum
– mean
– median
– stdev
– stdevsample
– range
– minority
– majority
– q1: first quartile
– q3: third quartile
– iqr: inter quartile range
– min_length: minimum string length
– max_length: maximum string length
– concatenate: join strings with a concatenator
– concatenate_unique: join unique strings with a concatenator
– collect: create an aggregated multipart geometry
– array_agg: create an array of aggregated values
• expression - sub expression or field name to aggregate
• concatenator - optional string to use to join values for ‚concatenate‘ aggregate
• order_by - optional expression to order the features used for calculating the aggregate.
Fields and geometry are from the features on the joined layer. By default, the features will
be returned in an unspecified order.
Examples
• relation_aggregate(relation:='my_relation',
aggregate:='mean',expression:="passengers") → mean value of
all matching child features using the ‚my_relation‘ relation
• relation_aggregate('my_relation','sum', "passengers"/7) →
sum of the passengers field divided by 7 for all matching child features using the
‚my_relation‘ relation
• relation_aggregate('my_relation','concatenate', "towns",
concatenator:=',') → comma separated list of the towns field for all matching
child features using the ‚my_relation‘ relation
• relation_aggregate('my_relation','array_agg', "id") → array of
the id field from all matching child features using the ‚my_relation‘ relation
Further reading: Creating one or many to many relations
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stdev
Returns the aggregate standard deviation value from a field or expression.
Syntax stdev(expression, [group_by], [filter])
[] marks optional arguments
Arguments
• expression - sub expression of field to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
Examples
• stdev("population",group_by:="state") → standard deviation of
population value, grouped by state field
sum
Returns the aggregate summed value from a field or expression.
Syntax sum(expression, [group_by], [filter])
[] marks optional arguments
Arguments
• expression - sub expression of field to aggregate
• group_by - optional expression to use to group aggregate calculations
• filter - optional expression to use to filter features used to calculate aggregate
Examples
• sum("population",group_by:="state") → summed population value,
grouped by state field
14.3.2 Array Functions
This group contains functions to create and manipulate arrays (also known as list data structures). The order of values
within the array matters, unlike the ‚map‘ data structure, where the order of key-value pairs is irrelevant and values
are identified by their keys.
• array
• array_all
• array_append
• array_cat
• array_contains
• array_distinct
• array_filter
• array_find
• array_first
• array_foreach
• array_get
• array_insert
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• array_intersect
• array_last
• array_length
• array_prepend
• array_remove_all
• array_remove_at
• array_reverse
• array_slice
• array_sort
• array_to_string
• generate_series
• regexp_matches
• string_to_array
array
Returns an array containing all the values passed as parameter.
Syntax array(value1, value2, …)
Arguments
• value - a value
Examples
• array(2,10) → [ 2, 10 ]
array_all
Returns true if an array contains all the values of a given array.
Syntax array_all(array_a, array_b)
Arguments • array_a - an array
• array_b - the array of values to search
Examples
• array_all(array(1,2,3),array(2,3)) → true
• array_all(array(1,2,3),array(1,2,4)) → false
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array_append
Returns an array with the given value added at the end.
Syntax array_append(array, value)
Arguments • array - an array
• value - the value to add
Examples
• array_append(array(1,2,3),4) → [ 1, 2, 3, 4 ]
array_cat
Returns an array containing all the given arrays concatenated.
Syntax array_cat(array1, array2, …)
Arguments • array - an array
Examples
• array_cat(array(1,2),array(2,3)) → [ 1, 2, 2, 3 ]
array_contains
Returns true if an array contains the given value.
Syntax array_contains(array, value)
Arguments • array - an array
• value - the value to search
Examples
• array_contains(array(1,2,3),2) → true
array_distinct
Returns an array containing distinct values of the given array.
Syntax array_distinct(array)
Arguments • array - an array
Examples
• array_distinct(array(1,2,3,2,1)) → [ 1, 2, 3 ]
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array_filter
Returns an array with only the items for which the expression evaluates to true.
Syntax array_filter(array, expression)
Arguments • array - an array
• expression - an expression to evaluate on each item. The variable @element will be
replaced by the current value.
Examples
• array_filter(array(1,2,3),@element < 3) → [ 1, 2 ]
array_find
Returns the index (0 for the first one) of a value within an array. Returns -1 if the value is not found.
Syntax array_find(array, value)
Arguments • array - an array
• value - the value to search
Examples
• array_find(array(1,2,3),2) → 1
array_first
Returns the first value of an array.
Syntax array_first(array)
Arguments • array - an array
Examples
• array_first(array('a','b','c')) → ‚a‘
array_foreach
Returns an array with the given expression evaluated on each item.
Syntax array_foreach(array, expression)
Arguments • array - an array
• expression - an expression to evaluate on each item. The variable @element will be
replaced by the current value.
Examples
• array_foreach(array('a','b','c'),upper(@element)) → [ ‚A‘, ‚B‘,
‚C‘ ]
• array_foreach(array(1,2,3),@element + 10) → [ 11, 12, 13 ]
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array_get
Returns the Nth value (0 for the first one) of an array.
Syntax array_get(array, index)
Arguments • array - an array
• index - the index to get (0 based)
Examples
• array_get(array('a','b','c'),1) → ‚b‘
array_insert
Returns an array with the given value added at the given position.
Syntax array_insert(array, pos, value)
Arguments • array - an array
• pos - the position where to add (0 based)
• value - the value to add
Examples
• array_insert(array(1,2,3),1,100) → [ 1, 100, 2, 3 ]
array_intersect
Returns true if at least one element of array1 exists in array2.
Syntax array_intersect(array1, array2)
Arguments
• array1 - an array
• array2 - another array
Examples
• array_intersect(array(1,2,3,4),array(4,0,2,5)) → true
array_last
Returns the last value of an array.
Syntax array_last(array)
Arguments • array - an array
Examples
• array_last(array('a','b','c')) → ‚c‘
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array_length
Returns the number of elements of an array.
Syntax array_length(array)
Arguments • array - an array
Examples
• array_length(array(1,2,3)) → 3
array_prepend
Returns an array with the given value added at the beginning.
Syntax array_prepend(array, value)
Arguments • array - an array
• value - the value to add
Examples
• array_prepend(array(1,2,3),0) → [ 0, 1, 2, 3 ]
array_remove_all
Returns an array with all the entries of the given value removed.
Syntax array_remove_all(array, value)
Arguments • array - an array
• value - the values to remove
Examples
• array_remove_all(array('a','b','c','b'),'b') → [ ‚a‘, ‚c‘ ]
array_remove_at
Returns an array with the given index removed.
Syntax array_remove_at(array, pos)
Arguments • array - an array
• pos - the position to remove (0 based)
Examples
• array_remove_at(array(1,2,3),1) → [ 1, 3 ]
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array_reverse
Returns the given array with array values in reversed order.
Syntax array_reverse(array)
Arguments • array - an array
Examples
• array_reverse(array(2,4,0,10)) → [ 10, 0, 4, 2 ]
array_slice
Returns a portion of the array. The slice is defined by the start_pos and end_pos arguments.
Syntax array_slice(array, start_pos, end_pos)
Arguments • array - an array
• start_pos - the index of the start position of the slice (0 based). The start_pos index
is included in the slice. If you use a negative start_pos, the index is counted from the end
of the list (-1 based).
• end_pos - the index of the end position of the slice (0 based). The end_pos index
is included in the slice. If you use a negative end_pos, the index is counted from the end
of the list (-1 based).
Examples
• array_slice(array(1,2,3,4,5),0,3) → [ 1, 2, 3, 4 ]
• array_slice(array(1,2,3,4,5),0,-1) → [ 1, 2, 3, 4, 5 ]
• array_slice(array(1,2,3,4,5),-5,-1) → [ 1, 2, 3, 4, 5 ]
• array_slice(array(1,2,3,4,5),0,0) → [ 1 ]
• array_slice(array(1,2,3,4,5),-2,-1) → [ 4, 5 ]
• array_slice(array(1,2,3,4,5),-1,-1) → [ 5 ]
• array_slice(array('Dufour','Valmiera','Chugiak',
'Brighton'),1,2) → [ ‚Valmiera‘, ‚Chugiak‘ ]
• array_slice(array('Dufour','Valmiera','Chugiak',
'Brighton'),-2,-1) → [ ‚Chugiak‘, ‚Brighton‘ ]
array_sort
Returns the provided array with its elements sorted.
Syntax array_sort(array, [ascending=true])
[] marks optional arguments
Arguments • array - an array
• ascending - set this parameter to false to sort the array in descending order
Examples
• array_sort(array(3,2,1)) → [ 1, 2, 3 ]
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array_to_string
Concatenates array elements into a string separated by a delimiter and using optional string for empty values.
Syntax array_to_string(array, [delimiter=‘,‘], [empty_value=‘‘])
[] marks optional arguments
Arguments
• array - the input array
• delimiter - the string delimiter used to separate concatenated array elements
• empty_value - the optional string to use as replacement for empty (zero length) matches
Examples
• array_to_string(array('1','2','3')) → ‚1,2,3‘
• array_to_string(array(1,2,3),'-') → ‚1-2-3‘
• array_to_string(array('1','','3'),',','0') → ‚1,0,3‘
generate_series
Creates an array containing a sequence of numbers.
Syntax generate_series(start, stop, [step=1])
[] marks optional arguments
Arguments
• start - first value of the sequence
• stop - value that ends the sequence once reached
• step - value used as the increment between values
Examples
• generate_series(1,5) → [ 1, 2, 3, 4, 5 ]
• generate_series(5,1,-1) → [ 5, 4, 3, 2, 1 ]
regexp_matches
Returns an array of all strings captured by capturing groups, in the order the groups themselves appear in the supplied
regular expression against a string.
Syntax regexp_matches(string, regex, [empty_value=‘‘])
[] marks optional arguments
Arguments
• string - the string to capture groups from against the regular expression
• regex - the regular expression used to capture groups
• empty_value - the optional string to use as replacement for empty (zero length) matches
Examples
• regexp_matches('QGIS=>rocks','(.*)=>(.*)') → [ ‚QGIS‘, ‚rocks‘ ]
• regexp_matches('key=>','(.*)=>(.*)','empty value') → [ ‚key‘,
‚empty value‘ ]
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string_to_array
Splits string into an array using supplied delimiter and optional string for empty values.
Syntax string_to_array(string, [delimiter=‘,‘], [empty_value=‘‘])
[] marks optional arguments
Arguments
• string - the input string
• delimiter - the string delimiter used to split the input string
• empty_value - the optional string to use as replacement for empty (zero length) matches
Examples
• string_to_array('1,2,3',',') → [ ‚1‘, ‚2‘, ‚3‘ ]
• string_to_array('1,,3',',','0') → [ ‚1‘, ‚0‘, ‚3‘ ]
14.3.3 Funkce barev
Tato skupina obsahuje funkce pro manipulaci s barvami.
• color_cmyk
• color_cmyka
• color_grayscale_average
• color_hsl
• color_hsla
• color_hsv
• color_hsva
• color_mix_rgb
• color_part
• color_rgb
• color_rgba
• create_ramp
• darker
• lighter
• project_color
• ramp_color
• set_color_part
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color_cmyk
Returns a string representation of a color based on its cyan, magenta, yellow and black components
Syntax color_cmyk(cyan, magenta, yellow, black)
Arguments
• cyan - cyan component of the color, as a percentage integer value from 0 to 100
• magenta - magenta component of the color, as a percentage integer value from 0 to 100
• yellow - yellow component of the color, as a percentage integer value from 0 to 100
• black - black component of the color, as a percentage integer value from 0 to 100
Examples
• color_cmyk(100,50,0,10) → ‚0,115,230‘
color_cmyka
Returns a string representation of a color based on its cyan, magenta, yellow, black and alpha (transparency)
components
Syntax color_cmyka(cyan, magenta, yellow, black, alpha)
Arguments
• cyan - cyan component of the color, as a percentage integer value from 0 to 100
• magenta - magenta component of the color, as a percentage integer value from 0 to 100
• yellow - yellow component of the color, as a percentage integer value from 0 to 100
• black - black component of the color, as a percentage integer value from 0 to 100
• alpha - alpha component as an integer value from 0 (completely transparent) to 255
(opaque).
Examples
• color_cmyk(100,50,0,10,200) → ‚0,115,230,200‘
color_grayscale_average
Applies a grayscale filter and returns a string representation from a provided color.
Syntax color_grayscale_average(color)
Arguments
• color - a color string
Examples
• color_grayscale_average('255,100,50') → ‚135,135,135,255‘
color_hsl
Returns a string representation of a color based on its hue, saturation, and lightness attributes.
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Syntax color_hsl(hue, saturation, lightness)
Arguments
• hue - hue of the color, as an integer value from 0 to 360
• saturation - saturation percentage of the color as an integer value from 0 to 100
• lightness - lightness percentage of the color as an integer value from 0 to 100
Examples
• color_hsl(100,50,70) → ‚166,217,140‘
color_hsla
Returns a string representation of a color based on its hue, saturation, lightness and alpha (transparency) attributes
Syntax color_hsla(hue, saturation, lightness, alpha)
Arguments
• hue - hue of the color, as an integer value from 0 to 360
• saturation - saturation percentage of the color as an integer value from 0 to 100
• lightness - lightness percentage of the color as an integer value from 0 to 100
• alpha - alpha component as an integer value from 0 (completely transparent) to 255
(opaque).
Examples
• color_hsla(100,50,70,200) → ‚166,217,140,200‘
color_hsv
Returns a string representation of a color based on its hue, saturation, and value attributes.
Syntax color_hsv(hue, saturation, value)
Arguments
• hue - hue of the color, as an integer value from 0 to 360
• saturation - saturation percentage of the color as an integer value from 0 to 100
• value - value percentage of the color as an integer from 0 to 100
Examples
• color_hsv(40,100,100) → ‚255,170,0‘
color_hsva
Returns a string representation of a color based on its hue, saturation, value and alpha (transparency) attributes.
Syntax color_hsva(hue, saturation, value, alpha)
Arguments
• hue - hue of the color, as an integer value from 0 to 360
• saturation - saturation percentage of the color as an integer value from 0 to 100
• value - value percentage of the color as an integer from 0 to 100
• alpha - alpha component as an integer value from 0 (completely transparent) to 255
(opaque)
Examples
• color_hsva(40,100,100,200) → ‚255,170,0,200‘
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color_mix_rgb
Returns a string representing a color mixing the red, green, blue, and alpha values of two provided colors based on
a given ratio.
Syntax color_mix_rgb(color1, color2, ratio)
Arguments
• color1 - a color string
• color2 - a color string
• ratio - a ratio
Examples
• color_mix_rgb('0,0,0','255,255,255',0.5) → ‚127,127,127,255‘
color_part
Returns a specific component from a color string, e.g., the red component or alpha component.
Syntax color_part(color, component)
Arguments
• color - a color string
• component - a string corresponding to the color component to return. Valid options are:
– red: RGB red component (0-255)
– green: RGB green component (0-255)
– blue: RGB blue component (0-255)
– alpha: alpha (transparency) value (0-255)
– hue: HSV hue (0-360)
– saturation: HSV saturation (0-100)
– value: HSV value (0-100)
– hsl_hue: HSL hue (0-360)
– hsl_saturation: HSL saturation (0-100)
– lightness: HSL lightness (0-100)
– cyan: CMYK cyan component (0-100)
– magenta: CMYK magenta component (0-100)
– yellow: CMYK yellow component (0-100)
– black: CMYK black component (0-100)
Examples
• color_part('200,10,30','green') → 10
color_rgb
Returns a string representation of a color based on its red, green, and blue components.
Syntax color_rgb(red, green, blue)
Arguments
• red - red component as an integer value from 0 to 255
• green - green component as an integer value from 0 to 255
• blue - blue component as an integer value from 0 to 255
Examples
• color_rgb(255,127,0) → ‚255,127,0‘
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color_rgba
Returns a string representation of a color based on its red, green, blue, and alpha (transparency) components.
Syntax color_rgba(red, green, blue, alpha)
Arguments
• red - red component as an integer value from 0 to 255
• green - green component as an integer value from 0 to 255
• blue - blue component as an integer value from 0 to 255
• alpha - alpha component as an integer value from 0 (completely transparent) to 255
(opaque).
Examples
• color_rgba(255,127,0,200) → ‚255,127,0,200‘
create_ramp
Returns a gradient ramp from a map of color strings and steps.
Syntax create_ramp(map, [discrete=false])
[] marks optional arguments
Arguments
• map - a map of color strings and steps
• discrete - set this parameter to true to create a discrete color ramp
Examples
• ramp_color(create_ramp(map(0,'0,0,0',1,'255,0,0')),1) →
‚255,0,0,255‘
darker
Returns a darker (or lighter) color string
Syntax darker(color, factor)
Arguments
• color - a color string
• factor - an integer corresponding to the darkening factor:
– if the factor is greater than 100, this function returns a darker color (e.g., setting
factor to 200 returns a color that is half the brightness);
– if the factor is less than 100, the return color is lighter, but using the lighter() function
for this purpose is recommended;
– if the factor is 0 or negative, the return value is unspecified.
Examples
• darker('200,10,30', 200) → ‚100,5,15,255‘
Further reading: lighter
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lighter
Returns a lighter (or darker) color string
Syntax lighter(color, factor)
Arguments
• color - a color string
• factor - an integer corresponding to the lightening factor:
– if the factor is greater than 100, this function returns a lighter color (e.g., setting
factor to 150 returns a color that is 50% brighter);
– if the factor is less than 100, the return color is darker, but using the darker() function
for this purpose is recommended;
– if the factor is 0 or negative, the return value is unspecified.
Examples
• lighter('200,10,30', 200) → ‚255,158,168,255‘
Further reading: darker
project_color
Returns a color from the project’s color scheme.
Syntax project_color(name)
Arguments
• name - a color name
Examples
• project_color('Logo color') → ‚20,140,50‘
Further reading: setting project colors
ramp_color
Returns a string representing a color from a color ramp.
Saved ramp variant
Returns a string representing a color from a saved ramp
Syntax ramp_color(ramp_name, value)
Arguments
• ramp_name - the name of the color ramp as a string, for example ‚Spectral‘
• value - the position on the ramp to select the color from as a real number between 0 and
1
Examples
• ramp_color('Spectral',0.3) → ‚253,190,115,255‘
Poznámka: The color ramps available vary between QGIS installations. This function may not give the expected
results if you move your QGIS project between installations.
Expression-created ramp variant
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Returns a string representing a color from an expression-created ramp
Syntax ramp_color(ramp, value)
Arguments
• ramp - the color ramp
• value - the position on the ramp to select the color from as a real number between 0 and
1
Examples
• ramp_color(create_ramp(map(0,'0,0,0',1,'255,0,0')),1) →
‚255,0,0,255‘
Further reading: Setting a Color Ramp, The color ramp drop-down shortcut
set_color_part
Sets a specific color component for a color string, e.g., the red component or alpha component.
Syntax set_color_part(color, component, value)
Arguments
• color - a color string
• component - a string corresponding to the color component to set. Valid options are:
– red: RGB red component (0-255)
– green: RGB green component (0-255)
– blue: RGB blue component (0-255)
– alpha: alpha (transparency) value (0-255)
– hue: HSV hue (0-360)
– saturation: HSV saturation (0-100)
– value: HSV value (0-100)
– hsl_hue: HSL hue (0-360)
– hsl_saturation: HSL saturation (0-100)
– lightness: HSL lightness (0-100)
– cyan: CMYK cyan component (0-100)
– magenta: CMYK magenta component (0-100)
– yellow: CMYK yellow component (0-100)
– black: CMYK black component (0-100)
• value - new value for color component, respecting the ranges listed above
Examples
• set_color_part('200,10,30','green',50) → ‚200,50,30,255‘
14.3.4 Conditional Functions
Tato skupina obsahuje funkce pro zpracování podmíněné kontroly ve výrazech.
• CASE
• coalesce
• if
• nullif
• regexp_match
• try
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CASE
CASE is used to evaluate a series of conditions and return a result for the first condition met. The conditions are
evaluated sequentially, and if a condition is true, the evaluation stops, and the corresponding result is returned. If
none of the conditions are true, the value in the ELSE clause is returned. Furthermore, if no ELSE clause is set and
none of the conditions are met, NULL is returned.
CASE
WHEN condition THEN result
[ …n ]
[ ELSE result ]
END
[ ] marks optional components
Arguments
• WHEN condition - A condition expression to evaluate
• THEN result - If condition evaluates to True then result is evaluated and returned.
• ELSE result - If none of the above conditions evaluated to True then result is evaluated
and returned.
Examples
• CASE WHEN "name" IS NULL THEN 'None' END → Returns the string ‚None‘
if the „name“ field is NULL
• CASE WHEN $area > 10000 THEN 'Big property' WHEN $area >
5000 THEN 'Medium property' ELSE 'Small property' END →
Returns the string ‚Big property‘ if the area is bigger than 10000, ‚Medium property‘ if the
area is between 5000 and 10000, and ‚Small property‘ for others
coalesce
Returns the first non-NULL value from the expression list.
This function can take any number of arguments.
Syntax coalesce(expression1, expression2, …)
Arguments
• expression - any valid expression or value, regardless of type.
Examples
• coalesce(NULL, 2) → 2
• coalesce(NULL, 2, 3) → 2
• coalesce(7, NULL, 3*2) → 7
• coalesce("fieldA", "fallbackField", 'ERROR') → value of fieldA if
it is non-NULL else the value of „fallbackField“ or the string ‚ERROR‘ if both are NULL
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if
Tests a condition and returns a different result depending on the conditional check.
Syntax if(condition, result_when_true, result_when_false)
Arguments
• condition - the condition which should be checked
• result_when_true - the result which will be returned when the condition is true or another
value that does not convert to false.
• result_when_false - the result which will be returned when the condition is false or
another value that converts to false like 0 or ‚‘. NULL will also be converted to false.
Examples
• if( 1+1=2, 'Yes', 'No' ) → ‚Yes‘
• if( 1+1=3, 'Yes', 'No' ) → ‚No‘
• if( 5 > 3, 1, 0) → 1
• if( '', 'It is true (not empty)', 'It is false (empty)' )
→ ‚It is false (empty)‘
• if( ' ', 'It is true (not empty)', 'It is false (empty)' )
→ ‚It is true (not empty)‘
• if( 0, 'One', 'Zero' ) → ‚Zero‘
• if( 10, 'One', 'Zero' ) → ‚One‘
nullif
Returns a NULL value if value1 equals value2; otherwise it returns value1. This can be used to conditionally substitute
values with NULL.
Syntax nullif(value1, value2)
Arguments
• value1 - The value that should either be used or substituted with NULL.
• value2 - The control value that will trigger the NULL substitution.
Examples
• nullif('(none)', '(none)') → NULL
• nullif('text', '(none)') → ‚text‘
• nullif("name", '') → NULL, if name is an empty string (or already NULL), the
name in any other case.
regexp_match
Return the first matching position matching a regular expression within an unicode string, or 0 if the substring is not
found.
Syntax regexp_match(input_string, regex)
Arguments
• input_string - the string to test against the regular expression
• regex - The regular expression to test against. Backslash characters must be double escaped
(e.g., „\\s“ to match a white space character or „\\b“ to match a word boundary).
Examples
• regexp_match('QGIS ROCKS','\\sROCKS') → 5
• regexp_match('Budač','udač\\b') → 2
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try
Tries an expression and returns its value if error-free. If the expression returns an error, an alternative value will be
returned when provided otherwise the function will return NULL.
Syntax try(expression, [alternative])
[] marks optional arguments
Arguments
• expression - the expression which should be run
• alternative - the result which will be returned if the expression returns an error.
Examples
• try( to_int( '1' ), 0 ) → 1
• try( to_int( 'a' ), 0 ) → 0
• try( to_date( 'invalid_date' ) ) → NULL
14.3.5 Conversions Functions
This group contains functions to convert one data type to another (e.g., string from/to integer, binary from/to string,
string to date, …).
• from_base64
• hash
• md5
• sha256
• to_base64
• to_date
• to_datetime
• to_decimal
• to_dm
• to_dms
• to_int
• to_interval
• to_real
• to_string
• to_time
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from_base64
Decodes a string in the Base64 encoding into a binary value.
Syntax from_base64(string)
Arguments
• string - the string to decode
Examples
• from_base64('UUdJUw==') → ‚QGIS‘
hash
Creates a hash from a string with a given method. One byte (8 bits) is represented with two hex ‚‘digits‘‘, so ‚md4‘
(16 bytes) produces a 16 * 2 = 32 character long hex string and ‚keccak_512‘ (64 bytes) produces a 64 * 2 = 128
character long hex string.
Syntax hash(string, method)
Arguments
• string - the string to hash
• method - The hash method among ‚md4‘, ‚md5‘, ‚sha1‘, ‚sha224‘, ‚sha384‘,
‚sha512‘, ‚sha3_224‘, ‚sha3_256‘, ‚sha3_384‘, ‚sha3_512‘, ‚keccak_224‘, ‚keccak_256‘,
‚keccak_384‘, ‚keccak_512‘
Examples
• hash('QGIS', 'md4') → ‚c0fc71c241cdebb6e888cbac0e2b68eb‘
• hash('QGIS', 'md5') → ‚57470aaa9e22adaefac7f5f342f1c6da‘
• hash('QGIS', 'sha1') → ‚f87cfb2b74cdd5867db913237024e7001e62b114‘
• hash('QGIS', 'sha224') → ‚4093a619ada631c770f44bc643ead18fb393b93d6a6af1861fcfece0‘
• hash('QGIS', 'sha256') → ‚eb045cba7a797aaa06ac58830846e40c8e8c780bc0676d3393605fae50c
• hash('QGIS', 'sha384') → ‚91c1de038cc3d09fdd512e99f9dd9922efadc39ed21d3922e69a4305cc25
• hash('QGIS', 'sha512') → ‚c2c092f2ab743bf8edbeb6d028a745f30fc720408465ed369421f0a4e20
• hash('QGIS', 'sha3_224') → ‚467f49a5039e7280d5d42fd433e80d203439e338eaabd701f0d6c17d
• hash('QGIS', 'sha3_256') → ‚540f7354b6b8a6e735f2845250f15f4f3ba4f666c55574d9e9354575d
• hash('QGIS', 'sha3_384') → ‚96052da1e77679e9a65f60d7ead961b287977823144786386eb43647
• hash('QGIS', 'sha3_512') → ‚900d079dc69761da113980253aa8ac0414a8bd6d09879a916228f874
• hash('QGIS', 'keccak_224') → ‚5b0ce6acef8b0a121d4ac4f3eaa8503c799ad4e26a3392d1fb20147
• hash('QGIS', 'keccak_256') → ‚991c520aa6815392de24087f61b2ae0fd56abbfeee4a8ca019c1011
• hash('QGIS', 'keccak_384') → ‚c57a3aed9d856fa04e5eeee9b62b6e027cca81ba574116d3cc1f0d4
md5
Creates a md5 hash from a string.
Syntax md5(string)
Arguments
• string - the string to hash
Examples
• md5('QGIS') → ‚57470aaa9e22adaefac7f5f342f1c6da‘
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sha256
Creates a sha256 hash from a string.
Syntax sha256(string)
Arguments
• string - the string to hash
Examples
• sha256('QGIS') → ‚eb045cba7a797aaa06ac58830846e40c8e8c780bc0676d3393605fae50c05309‘
to_base64
Encodes a binary value into a string, using the Base64 encoding.
Syntax to_base64(value)
Arguments
• value - the binary value to encode
Examples
• to_base64('QGIS') → ‚UUdJUw==‘
to_date
Converts a string into a date object. An optional format string can be provided to parse the string; see
QDate::fromString for additional documentation on the format.
Syntax to_date(string, [format], [language])
[] marks optional arguments
Arguments
• string - string representing a date value
• format - format used to convert the string into a date
• language - language (lowercase, two- or three-letter, ISO 639 language code) used to
convert the string into a date
Examples
• to_date('2012-05-04') → 2012-05-04
• to_date('June 29, 2019','MMMM d, yyyy') → 2019-06-29
• to_date('29 juin, 2019','d MMMM, yyyy','fr') → 2019-06-29
to_datetime
Converts a string into a datetime object. An optional format string can be provided to parse the string; see
QDate::fromString and QTime::fromString for additional documentation on the format.
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Syntax to_datetime(string, [format], [language])
[] marks optional arguments
Arguments
• string - string representing a datetime value
• format - format used to convert the string into a datetime
• language - language (lowercase, two- or three-letter, ISO 639 language code) used to
convert the string into a datetime
Examples
• to_datetime('2012-05-04 12:50:00') → 2012-05-04T12:50:00
• to_datetime('June 29, 2019 @ 12:34','MMMM d, yyyy @ HH:mm')
→ 2019-06-29T12:34
• to_datetime('29 juin, 2019 @ 12:34','d MMMM, yyyy @ HH:mm',
'fr') → 2019-06-29T12:34
to_decimal
Converts a degree, minute, second coordinate to its decimal equivalent.
Syntax to_decimal(value)
Arguments
• value - A degree, minute, second string.
Examples
• to_decimal('6°21\'16.445') → 6.3545680555
to_dm
Converts a coordinate to degree, minute.
Syntax to_dm(coordinate, axis, precision, [formatting=])
[] marks optional arguments
Arguments
• coordinate - A latitude or longitude value.
• axis - The axis of the coordinate. Either ‚x‘ or ‚y‘.
• precision - Number of decimals.
• formatting - Designates the formatting type. Acceptable values are NULL (default),
‚aligned‘ or ‚suffix‘.
Examples
• to_dm(6.1545681, 'x', 3) → 6°9.274′
• to_dm(6.1545681, 'y', 4, 'aligned') → 6°09.2741′
N
• to_dm(6.1545681, 'y', 4, 'suffix') → 6°9.2741′
N
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to_dms
Converts a coordinate to degree, minute, second.
Syntax to_dms(coordinate, axis, precision, [formatting=])
[] marks optional arguments
Arguments
• coordinate - A latitude or longitude value.
• axis - The axis of the coordinate. Either ‚x‘ or ‚y‘.
• precision - Number of decimals.
• formatting - Designates the formatting type. Acceptable values are NULL (default),
‚aligned‘ or ‚suffix‘.
Examples
• to_dms(6.1545681, 'x', 3) → 6°9′
16.445′′
• to_dms(6.1545681, 'y', 4, 'aligned') → 6°09′
16.4452′′
N
• to_dms(6.1545681, 'y', 4, 'suffix') → 6°9′
16.4452′′
N
to_int
Converts a string to integer number. Nothing is returned if a value cannot be converted to integer (e.g ‚123asd‘
is invalid).
Syntax to_int(string)
Arguments
• string - string to convert to integer number
Examples
• to_int('123') → 123
to_interval
Converts a string to an interval type. Can be used to take days, hours, month, etc of a date.
Syntax to_interval(string)
Arguments
• string - a string representing an interval. Allowable formats include {n} days {n} hours
{n} months.
Examples
• to_interval('1 day 2 hours') → interval: 1.08333 days
• to_interval( '0.5 hours' ) → interval: 30 minutes
• to_datetime('2012-05-05 12:00:00') - to_interval('1 day 2
hours') → 2012-05-04T10:00:00
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to_real
Converts a string to a real number. Nothing is returned if a value cannot be converted to real (e.g ‚123.56asd‘ is invalid).
Numbers are rounded after saving changes if the precision is smaller than the result of the conversion.
Syntax to_real(string)
Arguments
• string - string to convert to real number
Examples
• to_real('123.45') → 123.45
to_string
Converts a number to string.
Syntax to_string(number)
Arguments
• number - Integer or real value. The number to convert to string.
Examples
• to_string(123) → ‚123‘
to_time
Converts a string into a time object. An optional format string can be provided to parse the string; see
QTime::fromString for additional documentation on the format.
Syntax to_time(string, [format], [language])
[] marks optional arguments
Arguments
• string - string representing a time value
• format - format used to convert the string into a time
• language - language (lowercase, two- or three-letter, ISO 639 language code) used to
convert the string into a time
Examples
• to_time('12:30:01') → 12:30:01
• to_time('12:34','HH:mm') → 12:34:00
• to_time('12:34','HH:mm','fr') → 12:34:00
14.3.6 Custom Functions
This group contains functions created by the user. See Function Editor for more details.
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14.3.7 Funkce dat a časů
This group contains functions for handling date and time data. This group shares several functions with the Conversions
Functions (to_date, to_time, to_datetime, to_interval) and Funkce řetězců (format_date) groups.
Poznámka: Storing date, datetime and intervals on fields
The ability to store date, time and datetime values directly on fields depends on the data source’s provider (e.g.,
Shapefile accepts date format, but not datetime or time format). The following are some suggestions to overcome this
limitation:
• date, datetime and time can be converted and stored in text type fields using the format_date() function.
• Intervals can be stored in integer or decimal type fields after using one of the date extraction functions (e.g.,
day() to get the interval expressed in days)
• age
• datetime_from_epoch
• day
• day_of_week
• epoch
• format_date
• hour
• make_date
• make_datetime
• make_interval
• make_time
• minute
• month
• now
• second
• to_date
• to_datetime
• to_interval
• to_time
• week
• year
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age
Returns the difference between two dates or datetimes.
The difference is returned as an Interval and needs to be used with one of the following functions in order to
extract useful information:
• year
• month
• week
• day
• hour
• minute
• second
Syntax age(datetime1, datetime2)
Arguments
• datetime1 - a string, date or datetime representing the later date
• datetime2 - a string, date or datetime representing the earlier date
Examples
• day(age('2012-05-12','2012-05-02')) → 10
• hour(age('2012-05-12','2012-05-02')) → 240
datetime_from_epoch
Returns a datetime whose date and time are the number of milliseconds, msecs, that have passed since 1970-01-01T00:00:00.000,
Coordinated Universal Time (Qt.UTC), and converted to Qt.LocalTime.
Syntax datetime_from_epoch(int)
Arguments
• int - number (milliseconds)
Examples
• datetime_from_epoch(1483225200000) → 2017-01-01T00:00:00
day
Extracts the day from a date, or the number of days from an interval.
Date variant
Extracts the day from a date or datetime.
Syntax day(date)
Arguments
• date - a date or datetime value
Examples
• day('2012-05-12') → 12
Interval variant
Calculates the length in days of an interval.
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Syntax day(interval)
Arguments
• interval - interval value to return number of days from
Examples
• day(to_interval('3 days')) → 3
• day(to_interval('3 weeks 2 days')) → 23
• day(age('2012-01-01','2010-01-01')) → 730
day_of_week
Returns the day of the week for a specified date or datetime. The returned value ranges from 0 to 6, where 0
corresponds to a Sunday and 6 to a Saturday.
Syntax day_of_week(date)
Arguments
• date - date or datetime value
Examples
• day_of_week(to_date('2015-09-21')) → 1
epoch
Returns the interval in milliseconds between the unix epoch and a given date value.
Syntax epoch(date)
Arguments
• date - a date or datetime value
Examples
• epoch(to_date('2017-01-01')) → 1483203600000
format_date
Formats a date type or string into a custom string format. Uses Qt date/time format strings. See QDateTime::toString.
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Syntax format_date(datetime, format, [language])
[] marks optional arguments
Arguments
• datetime - date, time or datetime value
• format - String template used to format the string.
Výraz Output
d the day as number without a leading zero (1 to 31)
dd the day as number with a leading zero (01 to 31)
ddd the abbreviated localized day name (e.g. ‚Mon‘ to ‚Sun‘)
dddd the long localized day name (e.g. ‚Monday‘ to ‚Sunday‘)
M the month as number without a leading zero (1-12)
MM the month as number with a leading zero (01-12)
MMM the abbreviated localized month name (e.g. ‚Jan‘ to ‚Dec‘)
MMMM the long localized month name (e.g. ‚January‘ to ‚December‘)
yy the year as two digit number (00-99)
yyyy the year as four digit number
These expressions may be used for the time part of the format string:
Výraz Output
h the hour without a leading zero (0 to 23 or 1 to 12 if AM/PM display)
hh the hour with a leading zero (00 to 23 or 01 to 12 if AM/PM display)
H the hour without a leading zero (0 to 23, even with AM/PM display)
HH the hour with a leading zero (00 to 23, even with AM/PM display)
m the minute without a leading zero (0 to 59)
mm the minute with a leading zero (00 to 59)
s the second without a leading zero (0 to 59)
ss the second with a leading zero (00 to 59)
z the milliseconds without trailing zeroes (0 to 999)
zzz the milliseconds with trailing zeroes (000 to 999)
AP or A interpret as an AM/PM time. AP must be either ‚AM‘ or ‚PM‘.
ap or a Interpret as an AM/PM time. ap must be either ‚am‘ or ‚pm‘.
• language - language (lowercase, two- or three-letter, ISO 639 language code) used to
format the date into a custom string
Examples
• format_date('2012-05-15','dd.MM.yyyy') → ‚15.05.2012‘
• format_date('2012-05-15','d MMMM yyyy','fr') → ‚15 mai 2012‘
• format_date('2012-05-15','dddd') → ‚Tuesday‘
• format_date('2012-05-15 13:54:20','dd.MM.yy') → ‚15.05.12‘
• format_date('13:54:20','hh:mm AP') → ‚01:54 PM‘
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hour
Extracts the hour part from a datetime or time, or the number of hours from an interval.
Time variant
Extracts the hour part from a time or datetime.
Syntax hour(datetime)
Arguments
• datetime - a time or datetime value
Examples
• hour( to_datetime('2012-07-22 13:24:57') ) → 13
Interval variant
Calculates the length in hours of an interval.
Syntax hour(interval)
Arguments
• interval - interval value to return number of hours from
Examples
• hour(to_interval('3 hours')) → 3
• hour(age('2012-07-22T13:00:00','2012-07-22T10:00:00')) → 3
• hour(age('2012-01-01','2010-01-01')) → 17520
make_date
Creates a date value from year, month and day numbers.
Syntax make_date(year, month, day)
Arguments
• year - Year number. Years 1 to 99 are interpreted as is. Year 0 is invalid.
• month - Month number, where 1=January
• day - Day number, beginning with 1 for the first day in the month
Examples
• make_date(2020,5,4) → date value 2020-05-04
make_datetime
Creates a datetime value from year, month, day, hour, minute and second numbers.
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Syntax make_datetime(year, month, day, hour, minute, second)
Arguments
• year - Year number. Years 1 to 99 are interpreted as is. Year 0 is invalid.
• month - Month number, where 1=January
• day - Day number, beginning with 1 for the first day in the month
• hour - Hour number
• minute - Minutes
• second - Seconds (fractional values include milliseconds)
Examples
• make_datetime(2020,5,4,13,45,30.5) → datetime value 2020-05-04
13:45:30.500
make_interval
Creates an interval value from year, month, weeks, days, hours, minute and seconds values.
Syntax make_interval([years=0], [months=0], [weeks=0], [days=0], [hours=0], [minutes=0],
[seconds=0])
[] marks optional arguments
Arguments
• years - Number of years (assumes a 365.25 day year length).
• months - Number of months (assumes a 30 day month length)
• weeks - Number of weeks
• days - Number of days
• hours - Number of hours
• minutes - Number of minutes
• seconds - Number of seconds
Examples
• make_interval(hours:=3) → interval: 3 hours
• make_interval(days:=2, hours:=3) → interval: 2.125 days
• make_interval(minutes:=0.5, seconds:=5) → interval: 35 seconds
make_time
Creates a time value from hour, minute and second numbers.
Syntax make_time(hour, minute, second)
Arguments
• hour - Hour number
• minute - Minutes
• second - Seconds (fractional values include milliseconds)
Examples
• make_time(13,45,30.5) → time value 13:45:30.500
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minute
Extracts the minutes part from a datetime or time, or the number of minutes from an interval.
Time variant
Extracts the minutes part from a time or datetime.
Syntax minute(datetime)
Arguments
• datetime - a time or datetime value
Examples
• minute( to_datetime('2012-07-22 13:24:57') ) → 24
Interval variant
Calculates the length in minutes of an interval.
Syntax minute(interval)
Arguments
• interval - interval value to return number of minutes from
Examples
• minute(to_interval('3 minutes')) → 3
• minute(age('2012-07-22T00:20:00','2012-07-22T00:00:00')) →
20
• minute(age('2012-01-01','2010-01-01')) → 1051200
month
Extracts the month part from a date, or the number of months from an interval.
Date variant
Extracts the month part from a date or datetime.
Syntax month(date)
Arguments
• date - a date or datetime value
Examples
• month('2012-05-12') → 05
Interval variant
Calculates the length in months of an interval.
Syntax month(interval)
Arguments
• interval - interval value to return number of months from
Examples
• month(to_interval('3 months')) → 3
• month(age('2012-01-01','2010-01-01')) → 4.03333
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now
Returns the current date and time. The function is static and will return consistent results while evaluating. The time
returned is the time when the expression is prepared.
Syntax now()
Examples
• now() → 2012-07-22T13:24:57
second
Extracts the seconds part from a datetime or time, or the number of seconds from an interval.
Time variant
Extracts the seconds part from a time or datetime.
Syntax second(datetime)
Arguments
• datetime - a time or datetime value
Examples
• second( to_datetime('2012-07-22 13:24:57') ) → 57
Interval variant
Calculates the length in seconds of an interval.
Syntax second(interval)
Arguments
• interval - interval value to return number of seconds from
Examples
• second(to_interval('3 minutes')) → 180
• second(age('2012-07-22T00:20:00','2012-07-22T00:00:00')) →
1200
• second(age('2012-01-01','2010-01-01')) → 63072000
to_date
Converts a string into a date object. An optional format string can be provided to parse the string; see
QDate::fromString for additional documentation on the format.
Syntax to_date(string, [format], [language])
[] marks optional arguments
Arguments
• string - string representing a date value
• format - format used to convert the string into a date
• language - language (lowercase, two- or three-letter, ISO 639 language code) used to
convert the string into a date
Examples
• to_date('2012-05-04') → 2012-05-04
• to_date('June 29, 2019','MMMM d, yyyy') → 2019-06-29
• to_date('29 juin, 2019','d MMMM, yyyy','fr') → 2019-06-29
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to_datetime
Converts a string into a datetime object. An optional format string can be provided to parse the string; see
QDate::fromString and QTime::fromString for additional documentation on the format.
Syntax to_datetime(string, [format], [language])
[] marks optional arguments
Arguments
• string - string representing a datetime value
• format - format used to convert the string into a datetime
• language - language (lowercase, two- or three-letter, ISO 639 language code) used to
convert the string into a datetime
Examples
• to_datetime('2012-05-04 12:50:00') → 2012-05-04T12:50:00
• to_datetime('June 29, 2019 @ 12:34','MMMM d, yyyy @ HH:mm')
→ 2019-06-29T12:34
• to_datetime('29 juin, 2019 @ 12:34','d MMMM, yyyy @ HH:mm',
'fr') → 2019-06-29T12:34
to_interval
Converts a string to an interval type. Can be used to take days, hours, month, etc of a date.
Syntax to_interval(string)
Arguments
• string - a string representing an interval. Allowable formats include {n} days {n} hours
{n} months.
Examples
• to_interval('1 day 2 hours') → interval: 1.08333 days
• to_interval( '0.5 hours' ) → interval: 30 minutes
• to_datetime('2012-05-05 12:00:00') - to_interval('1 day 2
hours') → 2012-05-04T10:00:00
to_time
Converts a string into a time object. An optional format string can be provided to parse the string; see
QTime::fromString for additional documentation on the format.
Syntax to_time(string, [format], [language])
[] marks optional arguments
Arguments
• string - string representing a time value
• format - format used to convert the string into a time
• language - language (lowercase, two- or three-letter, ISO 639 language code) used to
convert the string into a time
Examples
• to_time('12:30:01') → 12:30:01
• to_time('12:34','HH:mm') → 12:34:00
• to_time('12:34','HH:mm','fr') → 12:34:00
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week
Extracts the week number from a date, or the number of weeks from an interval.
Date variant
Extracts the week number from a date or datetime.
Syntax week(date)
Arguments
• date - a date or datetime value
Examples
• week('2012-05-12') → 19
Interval variant
Calculates the length in weeks of an interval.
Syntax week(interval)
Arguments
• interval - interval value to return number of months from
Examples
• week(to_interval('3 weeks')) → 3
• week(age('2012-01-01','2010-01-01')) → 104.285
year
Extracts the year part from a date, or the number of years from an interval.
Date variant
Extracts the year part from a date or datetime.
Syntax year(date)
Arguments
• date - a date or datetime value
Examples
• year('2012-05-12') → 2012
Interval variant
Calculates the length in years of an interval.
Syntax year(interval)
Arguments
• interval - interval value to return number of years from
Examples
• year(to_interval('3 years')) → 3
• year(age('2012-01-01','2010-01-01')) → 1.9986
Některé příklady:
Besides these functions, subtracting dates, datetimes or times using the - (minus) operator will return an interval.
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Adding or subtracting an interval to dates, datetimes or times, using the + (plus) and - (minus) operators, will return
a datetime.
• Get the number of days until QGIS 3.0 release:
to_date('2017-09-29') - to_date(now())
-- Returns <interval: 203 days>
• The same with time:
to_datetime('2017-09-29 12:00:00') - now()
-- Returns <interval: 202.49 days>
• Get the datetime of 100 days from now:
now() + to_interval('100 days')
-- Returns <datetime: 2017-06-18 01:00:00>
14.3.8 Pole a hodnoty
Contains a list of fields from the layer.
Double-click a field name to have it added to your expression. You can also type the field name (preferably inside
double quotes) or its alias.
To retrieve fields values to use in an expression, select the appropriate field and, in the shown widget, choose between
10 Samples and All Unique. Requested values are then displayed and you can use the Search box at the top of the list
to filter the result. Sample values can also be accessed via right-clicking on a field.
To add a value to the expression you are writing, double-click on it in the list. If the value is of a string type, it should
be simple quoted, otherwise no quote is needed.
14.3.9 Files and Paths Functions
This group contains functions which manipulate file and path names.
• base_file_name
• file_exists
• file_name
• file_path
• file_size
• file_suffix
• is_directory
• is_file
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base_file_name
Returns the base name of the file without the directory or file suffix.
Syntax base_file_name(path)
Arguments
• path - a file path
Examples
• base_file_name('/home/qgis/data/country_boundaries.shp') →
‚country_boundaries‘
file_exists
Returns true if a file path exists.
Syntax file_exists(path)
Arguments
• path - a file path
Examples
• file_exists('/home/qgis/data/country_boundaries.shp') → true
file_name
Returns the name of a file (including the file extension), excluding the directory.
Syntax file_name(path)
Arguments
• path - a file path
Examples
• file_name('/home/qgis/data/country_boundaries.shp') →
‚country_boundaries.shp‘
file_path
Returns the directory component of a file path. This does not include the file name.
Syntax file_path(path)
Arguments
• path - a file path
Examples
• file_path('/home/qgis/data/country_boundaries.shp') →
‚/home/qgis/data‘
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file_size
Returns the size (in bytes) of a file.
Syntax file_size(path)
Arguments
• path - a file path
Examples
• file_size('/home/qgis/data/country_boundaries.geojson') →
5674
file_suffix
Returns the file suffix (extension) from a file path.
Syntax file_suffix(path)
Arguments
• path - a file path
Examples
• file_suffix('/home/qgis/data/country_boundaries.shp') →
‚shp‘
is_directory
Returns true if a path corresponds to a directory.
Syntax is_directory(path)
Arguments
• path - a file path
Examples
• is_directory('/home/qgis/data/country_boundaries.shp') →
false
• is_directory('/home/qgis/data/') → true
is_file
Returns true if a path corresponds to a file.
Syntax is_file(path)
Arguments
• path - a file path
Examples
• is_file('/home/qgis/data/country_boundaries.shp') → true
• is_file('/home/qgis/data/') → false
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14.3.10 Form Functions
This group contains functions that operate exclusively under the attribute form context. For example, in field’s widgets
settings.
• current_parent_value
• current_value
current_parent_value
Only usable in an embedded form context, this function returns the current, unsaved value of a field in the parent form
currently being edited. This will differ from the parent feature’s actual attribute values for features which are currently
being edited or have not yet been added to a parent layer. When used in a value-relation widget filter expression, this
function should be wrapped into a ‚coalesce()‘ that can retrieve the actual parent feature from the layer when the form
is not used in an embedded context.
Syntax current_parent_value(field_name)
Arguments
• field_name - a field name in the current parent form
Examples
• current_parent_value( 'FIELD_NAME' ) → The current value of a field
‚FIELD_NAME‘ in the parent form.
current_value
Returns the current, unsaved value of a field in the form or table row currently being edited. This will differ from the
feature’s actual attribute values for features which are currently being edited or have not yet been added to a layer.
Syntax current_value(field_name)
Arguments
• field_name - a field name in the current form or table row
Examples
• current_value( 'FIELD_NAME' ) → The current value of field
‚FIELD_NAME‘.
14.3.11 Fuzzy Matching Functions
This group contains functions for fuzzy comparisons between values.
• hamming_distance
• levenshtein
• longest_common_substring
• soundex
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hamming_distance
Returns the Hamming distance between two strings. This equates to the number of characters at corresponding
positions within the input strings where the characters are different. The input strings must be the same length, and
the comparison is case-sensitive.
Syntax hamming_distance(string1, string2)
Arguments
• string1 - a string
• string2 - a string
Examples
• hamming_distance('abc','xec') → 2
• hamming_distance('abc','ABc') → 2
• hamming_distance(upper('abc'),upper('ABC')) → 0
levenshtein
Returns the Levenshtein edit distance between two strings. This equates to the minimum number of character edits
(insertions, deletions or substitutions) required to change one string to another.
The Levenshtein distance is a measure of the similarity between two strings. Smaller distances mean the strings are
more similar, and larger distances indicate more different strings. The distance is case sensitive.
Syntax levenshtein(string1, string2)
Arguments
• string1 - a string
• string2 - a string
Examples
• levenshtein('kittens','mitten') → 2
• levenshtein('Kitten','kitten') → 1
• levenshtein(upper('Kitten'),upper('kitten')) → 0
longest_common_substring
Returns the longest common substring between two strings. This substring is the longest string that is a substring
of the two input strings. For example, the longest common substring of „ABABC“ and „BABCA“ is „BABC“. The
substring is case sensitive.
Syntax longest_common_substring(string1, string2)
Arguments
• string1 - a string
• string2 - a string
Examples
• longest_common_substring('ABABC','BABCA') → ‚BABC‘
• longest_common_substring('abcDeF','abcdef') → ‚abc‘
• longest_common_substring(upper('abcDeF'),upper('abcdex'))
→ ‚ABCDE‘
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soundex
Returns the Soundex representation of a string. Soundex is a phonetic matching algorithm, so strings with similar
sounds should be represented by the same Soundex code.
Syntax soundex(string)
Arguments
• string - a string
Examples
• soundex('robert') → ‚R163‘
• soundex('rupert') → ‚R163‘
• soundex('rubin') → ‚R150‘
14.3.12 General Functions
This group contains general assorted functions.
• env
• eval
• eval_template
• is_layer_visible
• layer_property
• var
• with_variable
env
Gets an environment variable and returns its content as a string. If the variable is not found, NULL will be returned.
This is handy to inject system specific configuration like drive letters or path prefixes. Definition of environment
variables depends on the operating system, please check with your system administrator or the operating system
documentation how this can be set.
Syntax env(name)
Arguments
• name - The name of the environment variable which should be retrieved.
Examples
• env( 'LANG' ) → ‚en_US.UTF-8‘
• env( 'MY_OWN_PREFIX_VAR' ) → ‚Z:‘
• env( 'I_DO_NOT_EXIST' ) → NULL
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eval
Evaluates an expression which is passed in a string. Useful to expand dynamic parameters passed as context variables
or fields.
Syntax eval(expression)
Arguments
• expression - an expression string
Examples
• eval('\'nice\'') → ‚nice‘
• eval(@expression_var) → [whatever the result of evaluating @expression_var
might be…]
eval_template
Evaluates a template which is passed in a string. Useful to expand dynamic parameters passed as context variables or
fields.
Syntax eval_template(template)
Arguments
• template - a template string
Examples
• eval_template('QGIS [% upper(\'rocks\') %]') → QGIS ROCKS
is_layer_visible
Returns true if a specified layer is visible.
Syntax is_layer_visible(layer)
Arguments
• layer - a string, representing either a layer name or layer ID
Examples
• is_layer_visible('baseraster') → True
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layer_property
Returns a matching layer property or metadata value.
Syntax layer_property(layer, property)
Arguments
• layer - a string, representing either a layer name or layer ID
• property - a string corresponding to the property to return. Valid options are:
– name: layer name
– id: layer ID
– title: metadata title string
– abstract: metadata abstract string
– keywords: metadata keywords
– data_url: metadata URL
– attribution: metadata attribution string
– attribution_url: metadata attribution URL
– source: layer source
– min_scale: minimum display scale for layer
– max_scale: maximum display scale for layer
– is_editable: if layer is in edit mode
– crs: layer CRS
– crs_definition: layer CRS full definition
– crs_description: layer CRS description
– extent: layer extent (as a geometry object)
– distance_units: layer distance units
– type: layer type, e.g., Vector or Raster
– storage_type: storage format (vector layers only)
– geometry_type: geometry type, e.g., Point (vector layers only)
– feature_count: approximate feature count for layer (vector layers only)
– path: File path to the layer data source. Only available for file based layers.
Examples
• layer_property('streets','title') → ‚Basemap Streets‘
• layer_property('airports','feature_count') → 120
• layer_property('landsat','crs') → ‚EPSG:4326‘
Further reading: vector, raster and mesh layer properties
var
Returns the value stored within a specified variable.
Syntax var(name)
Arguments
• name - a variable name
Examples
• var('qgis_version') → ‚2.12‘
Further reading: List of default variables
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with_variable
This function sets a variable for any expression code that will be provided as 3rd argument. This is only useful for
complicated expressions, where the same calculated value needs to be used in different places.
Syntax with_variable(name, value, expression)
Arguments
• name - the name of the variable to set
• value - the value to set
• expression - the expression for which the variable will be available
Examples
• with_variable('my_sum', 1 + 2 + 3, @my_sum * 2 + @my_sum *
5) → 42
14.3.13 Funkce geometrie
This group contains functions that operate on geometry objects (e.g. buffer, transform, $area).
• angle_at_vertex
• $area
• area
• azimuth
• boundary
• bounds
• bounds_height
• bounds_width
• buffer
• buffer_by_m
• centroid
• close_line
• closest_point
• collect_geometries
• combine
• contains
• convex_hull
• crosses
• difference
• disjoint
• distance
• distance_to_vertex
• end_point
• extend
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• exterior_ring
• extrude
• flip_coordinates
• force_rhr
• geom_from_gml
• geom_from_wkb
• geom_from_wkt
• geom_to_wkb
• geom_to_wkt
• $geometry
• geometry
• geometry_n
• hausdorff_distance
• inclination
• interior_ring_n
• intersection
• intersects
• intersects_bbox
• is_closed
• is_empty
• is_empty_or_null
• is_multipart
• is_valid
• $length
• length
• line_interpolate_angle
• line_interpolate_point
• line_locate_point
• line_merge
• line_substring
• m
• m_max
• m_min
• main_angle
• make_circle
• make_ellipse
• make_line
• make_point
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• make_point_m
• make_polygon
• make_rectangle_3points
• make_regular_polygon
• make_square
• make_triangle
• minimal_circle
• nodes_to_points
• num_geometries
• num_interior_rings
• num_points
• num_rings
• offset_curve
• order_parts
• oriented_bbox
• overlaps
• overlay_contains
• overlay_crosses
• overlay_disjoint
• overlay_equals
• overlay_intersects
• overlay_nearest
• overlay_touches
• overlay_within
• $perimeter
• perimeter
• point_n
• point_on_surface
• pole_of_inaccessibility
• project
• relate
• reverse
• rotate
• segments_to_lines
• shortest_line
• simplify
• simplify_vw
• single_sided_buffer
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• smooth
• start_point
• sym_difference
• tapered_buffer
• touches
• transform
• translate
• union
• wedge_buffer
• within
• $x
• x
• $x_at
• x_max
• x_min
• $y
• y
• $y_at
• y_max
• y_min
• z
• z_max
• z_min
angle_at_vertex
Returns the bisector angle (average angle) to the geometry for a specified vertex on a linestring geometry. Angles are
in degrees clockwise from north.
Syntax angle_at_vertex(geometry, vertex)
Arguments
• geometry - a linestring geometry
• vertex - vertex index, starting from 0; if the value is negative, the selected vertex index
will be its total count minus the absolute value
Examples
• angle_at_vertex(geometry:=geom_from_wkt('LineString(0 0,
10 0, 10 10)'),vertex:=1) → 45.0
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$area
Returns the area of the current feature. The area calculated by this function respects both the current project’s ellipsoid
setting and area unit settings. For example, if an ellipsoid has been set for the project then the calculated area will be
ellipsoidal, and if no ellipsoid is set then the calculated area will be planimetric.
Syntax $area
Examples
• $area → 42
area
Returns the area of a geometry polygon object. Calculations are always planimetric in the Spatial Reference System
(SRS) of this geometry, and the units of the returned area will match the units for the SRS. This differs from
the calculations performed by the $area function, which will perform ellipsoidal calculations based on the project’s
ellipsoid and area unit settings.
Syntax area(geometry)
Arguments
• geometry - polygon geometry object
Examples
• area(geom_from_wkt('POLYGON((0 0, 4 0, 4 2, 0 2, 0 0))'))
→ 8.0
azimuth
Returns the north-based azimuth as the angle in radians measured clockwise from the vertical on point_a to point_b.
Syntax azimuth(point_a, point_b)
Arguments
• point_a - point geometry
• point_b - point geometry
Examples
• degrees( azimuth( make_point(25, 45), make_point(75, 100)
) ) → 42.273689
• degrees( azimuth( make_point(75, 100), make_point(25,45) )
) → 222.273689
boundary
Returns the closure of the combinatorial boundary of the geometry (ie the topological boundary of the geometry).
For instance, a polygon geometry will have a boundary consisting of the linestrings for each ring in the polygon. Some
geometry types do not have a defined boundary, e.g., points or geometry collections, and will return NULL.
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Syntax boundary(geometry)
Arguments
• geometry - a geometry
Examples
• geom_to_wkt(boundary(geom_from_wkt('Polygon((1 1, 0 0, -1
1, 1 1))'))) → ‚LineString(1 1,0 0,-1 1,1 1)‘
• geom_to_wkt(boundary(geom_from_wkt('LineString(1 1,0 0,-1
1)'))) → ‚MultiPoint ((1 1),(-1 1))‘
Further reading: Boundary algorithm
bounds
Returns a geometry which represents the bounding box of an input geometry. Calculations are in the Spatial Reference
System of this geometry.
Syntax bounds(geometry)
Arguments
• geometry - a geometry
Examples
• bounds($geometry) → bounding box of the current feature’s geometry
• geom_to_wkt(bounds(geom_from_wkt('Polygon((1 1, 0 0, -1 1,
1 1))'))) → ‚Polygon ((-1 0, 1 0, 1 1, -1 1, -1 0))‘
Further reading: Bounding boxes algorithm
bounds_height
Returns the height of the bounding box of a geometry. Calculations are in the Spatial Reference System of this
geometry.
Syntax bounds_height(geometry)
Arguments
• geometry - a geometry
Examples
• bounds_height($geometry) → height of bounding box of the current feature’s
geometry
• bounds_height(geom_from_wkt('Polygon((1 1, 0 0, -1 1, 1
1))')) → 1
bounds_width
Returns the width of the bounding box of a geometry. Calculations are in the Spatial Reference System of this
geometry.
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Syntax bounds_width(geometry)
Arguments
• geometry - a geometry
Examples
• bounds_width($geometry) → width of bounding box of the current feature’s
geometry
• bounds_width(geom_from_wkt('Polygon((1 1, 0 0, -1 1, 1
1))')) → 2
buffer
Returns a geometry that represents all points whose distance from this geometry is less than or equal to distance.
Calculations are in the Spatial Reference System of this geometry.
Syntax buffer(geometry, distance, [segments=8])
[] marks optional arguments
Arguments
• geometry - a geometry
• distance - buffer distance in layer units
• segments - number of segments to use to represent a quarter circle when a round join
style is used. A larger number results in a smoother buffer with more nodes.
Examples
• buffer($geometry, 10.5) → polygon of the current feature’s geometry buffered
by 10.5 units
Further reading: Buffer algorithm
buffer_by_m
Creates a buffer along a line geometry where the buffer diameter varies according to the m-values at the line vertices.
Syntax buffer_by_m(geometry, [segments=8])
[] marks optional arguments
Arguments
• geometry - input geometry. Must be a (multi)line geometry with m values.
• segments - number of segments to approximate quarter-circle curves in the buffer.
Examples
• buffer_by_m(geometry:=geom_from_wkt('LINESTRINGM(1 2 0.5,
4 2 0.2)'),segments:=8) → A variable width buffer starting with a diameter of
0.5 and ending with a diameter of 0.2 along the linestring geometry.
Further reading: Variable width buffer (by M value) algorithm
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centroid
Returns the geometric center of a geometry.
Syntax centroid(geometry)
Arguments
• geometry - a geometry
Examples
• centroid($geometry) → a point geometry
Further reading: Centroids algorithm
close_line
Returns a closed line string of the input line string by appending the first point to the end of the line, if it is not already
closed. If the geometry is not a line string or multi line string then the result will be NULL.
Syntax close_line(geometry)
Arguments
• geometry - a line string geometry
Examples
• geom_to_wkt(close_line(geom_from_wkt('LINESTRING(0 0, 1 0,
1 1)'))) → ‚LineString (0 0, 1 0, 1 1, 0 0)‘
• geom_to_wkt(close_line(geom_from_wkt('LINESTRING(0 0, 1 0,
1 1, 0 0)'))) → ‚LineString (0 0, 1 0, 1 1, 0 0)‘
closest_point
Returns the point on geometry1 that is closest to geometry2.
Syntax closest_point(geometry1, geometry2)
Arguments
• geometry1 - geometry to find closest point on
• geometry2 - geometry to find closest point to
Examples
• geom_to_wkt(closest_point(geom_from_wkt('LINESTRING (20
80, 98 190, 110 180, 50 75 )'),geom_from_wkt('POINT(100
100)'))) → ‚Point(73.0769 115.384)‘
collect_geometries
Collects a set of geometries into a multi-part geometry object.
List of arguments variant
Geometry parts are specified as separate arguments to the function.
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Syntax collect_geometries(geometry1, geometry2, …)
Arguments
• geometry - a geometry
Examples
• geom_to_wkt(collect_geometries(make_point(1,2),
make_point(3,4), make_point(5,6))) → ‚MultiPoint ((1 2),(3 4),(5
6))‘
Array variant
Geometry parts are specified as an array of geometry parts.
Syntax collect_geometries(array)
Arguments
• array - array of geometry objects
Examples
• geom_to_wkt(collect_geometries(array(make_point(1,2),
make_point(3,4), make_point(5,6)))) → ‚MultiPoint ((1 2),(3 4),(5 6))‘
Further reading: Collect geometries algorithm
combine
Returns the combination of two geometries.
Syntax combine(geometry1, geometry2)
Arguments
• geometry1 - a geometry
• geometry2 - a geometry
Examples
• geom_to_wkt( combine( geom_from_wkt( 'LINESTRING(3 3, 4 4,
5 5)' ), geom_from_wkt( 'LINESTRING(3 3, 4 4, 2 1)' ) ) )
→ ‚MULTILINESTRING((4 4, 2 1), (3 3, 4 4), (4 4, 5 5))‘
• geom_to_wkt( combine( geom_from_wkt( 'LINESTRING(3 3, 4 4)'
), geom_from_wkt( 'LINESTRING(3 3, 6 6, 2 1)' ) ) ) →
‚LINESTRING(3 3, 4 4, 6 6, 2 1)‘
contains
Tests whether a geometry contains another. Returns true if and only if no points of geometry2 lie in the exterior of
geometry1, and at least one point of the interior of geometry2 lies in the interior of geometry1.
Syntax contains(geometry1, geometry2)
Arguments
• geometry1 - a geometry
• geometry2 - a geometry
Examples
• contains( geom_from_wkt( 'POLYGON((0 0, 0 1, 1 1, 1 0, 0
0))' ), geom_from_wkt( 'POINT(0.5 0.5 )' ) ) → true
• contains( geom_from_wkt( 'POLYGON((0 0, 0 1, 1 1, 1 0, 0
0))' ), geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ) ) → false
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Further reading: overlay_contains
convex_hull
Returns the convex hull of a geometry. It represents the minimum convex geometry that encloses all geometries
within the set.
Syntax convex_hull(geometry)
Arguments
• geometry - a geometry
Examples
• geom_to_wkt( convex_hull( geom_from_wkt( 'LINESTRING(3 3,
4 4, 4 10)' ) ) ) → ‚POLYGON((3 3, 4 10, 4 4, 3 3))‘
Further reading: Convex hull algorithm
crosses
Tests whether a geometry crosses another. Returns true if the supplied geometries have some, but not all, interior
points in common.
Syntax crosses(geometry1, geometry2)
Arguments
• geometry1 - a geometry
• geometry2 - a geometry
Examples
• crosses( geom_from_wkt( 'LINESTRING(3 5, 4 4, 5 3)' ),
geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ) ) → true
• crosses( geom_from_wkt( 'POINT(4 5)' ), geom_from_wkt(
'LINESTRING(3 3, 4 4, 5 5)' ) ) → false
Further reading: overlay_crosses
difference
Returns a geometry that represents that part of geometry1 that does not intersect with geometry2.
Syntax difference(geometry1, geometry2)
Arguments
• geometry1 - a geometry
• geometry2 - a geometry
Examples
• geom_to_wkt( difference( geom_from_wkt( 'LINESTRING(3 3, 4
4, 5 5)' ), geom_from_wkt( 'LINESTRING(3 3, 4 4)' ) ) ) →
‚LINESTRING(4 4, 5 5)‘
Further reading: Difference algorithm
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disjoint
Tests whether geometries do not spatially intersect. Returns true if the geometries do not share any space together.
Syntax disjoint(geometry1, geometry2)
Arguments
• geometry1 - a geometry
• geometry2 - a geometry
Examples
• disjoint( geom_from_wkt( 'POLYGON((0 0, 0 1, 1 1, 1 0, 0 0
))' ), geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ) ) → true
• disjoint( geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ),
geom_from_wkt( 'POINT(4 4)' )) → false
Further reading: overlay_disjoint
distance
Returns the minimum distance (based on spatial ref) between two geometries in projected units.
Syntax distance(geometry1, geometry2)
Arguments
• geometry1 - a geometry
• geometry2 - a geometry
Examples
• distance( geom_from_wkt( 'POINT(4 4)' ), geom_from_wkt(
'POINT(4 8)' ) ) → 4
distance_to_vertex
Returns the distance along the geometry to a specified vertex.
Syntax distance_to_vertex(geometry, vertex)
Arguments
• geometry - a linestring geometry
• vertex - vertex index, starting from 0; if the value is negative, the selected vertex index
will be its total count minus the absolute value
Examples
• distance_to_vertex(geometry:=geom_from_wkt('LineString(0
0, 10 0, 10 10)'),vertex:=1) → 10.0
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end_point
Returns the last node from a geometry.
Syntax end_point(geometry)
Arguments
• geometry - geometry object
Examples
• geom_to_wkt(end_point(geom_from_wkt('LINESTRING(4 0, 4 2,
0 2)'))) → ‚Point (0 2)‘
Further reading: Extract specific vertices algorithm
extend
Extends the start and end of a linestring geometry by a specified amount. Lines are extended using the bearing of
the first and last segment in the line. For a multilinestring, all the parts are extended. Distances are in the Spatial
Reference System of this geometry.
Syntax extend(geometry, start_distance, end_distance)
Arguments
• geometry - a (multi)linestring geometry
• start_distance - distance to extend the start of the line
• end_distance - distance to extend the end of the line.
Examples
• geom_to_wkt(extend(geom_from_wkt('LineString(0 0, 1 0, 1
1)'),1,2)) → ‚LineString (-1 0, 1 0, 1 3)‘
• geom_to_wkt(extend(geom_from_wkt('MultiLineString((0 0, 1
0, 1 1), (2 2, 0 2, 0 5))'),1,2)) → ‚MultiLineString ((-1 0, 1 0, 1 3),(3
2, 0 2, 0 7))‘
Further reading: Extend lines algorithm
exterior_ring
Returns a line string representing the exterior ring of a polygon geometry. If the geometry is not a polygon then the
result will be NULL.
Syntax exterior_ring(geometry)
Arguments
• geometry - a polygon geometry
Examples
• geom_to_wkt(exterior_ring(geom_from_wkt('POLYGON((-1 -1, 4
0, 4 2, 0 2, -1 -1),( 0.1 0.1, 0.1 0.2, 0.2 0.2, 0.2, 0.1,
0.1 0.1))'))) → ‚LineString (-1 -1, 4 0, 4 2, 0 2, -1 -1)‘
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extrude
Returns an extruded version of the input (Multi-)Curve or (Multi-)Linestring geometry with an extension specified
by x and y.
Syntax extrude(geometry, x, y)
Arguments
• geometry - a polygon geometry
• x - x extension, numeric value
• y - y extension, numeric value
Examples
• geom_to_wkt(extrude(geom_from_wkt('LineString(1 2, 3 2, 4
3)'), 1, 2)) → ‚Polygon ((1 2, 3 2, 4 3, 5 5, 4 4, 2 4, 1 2))‘
• geom_to_wkt(extrude(geom_from_wkt('MultiLineString((1 2, 3
2), (4 3, 8 3))'), 1, 2)) → ‚MultiPolygon (((1 2, 3 2, 4 4, 2 4, 1 2)),((4 3,
8 3, 9 5, 5 5, 4 3)))‘
flip_coordinates
Returns a copy of the geometry with the x and y coordinates swapped. Useful for repairing geometries which have
had their latitude and longitude values reversed.
Syntax flip_coordinates(geometry)
Arguments
• geometry - a geometry
Examples
• geom_to_wkt(flip_coordinates(make_point(1, 2))) → ‚Point (2 1)‘
Further reading: Swap X and Y coordinates algorithm
force_rhr
Forces a geometry to respect the Right-Hand-Rule, in which the area that is bounded by a polygon is to the right of
the boundary. In particular, the exterior ring is oriented in a clockwise direction and the interior rings in a counter-clockwise
direction.
Syntax force_rhr(geometry)
Arguments
• geometry - a geometry. Any non-polygon geometries are returned unchanged.
Examples
• geom_to_wkt(force_rhr(geometry:=geom_from_wkt('POLYGON((-1
-1, 4 0, 4 2, 0 2, -1 -1))'))) → ‚Polygon ((-1 -1, 0 2, 4 2, 4 0, -1 -1))‘
Further reading: Force right-hand-rule algorithm
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geom_from_gml
Returns a geometry from a GML representation of geometry.
Syntax geom_from_gml(gml)
Arguments
• gml - GML representation of a geometry as a string
Examples
• geom_from_gml('<gml:LineString srsName="EPSG:4326"><gml:coordinates>4,
4 5,5 6,6</gml:coordinates></gml:LineString>') → a line geometry
object
geom_from_wkb
Returns a geometry created from a Well-Known Binary (WKB) representation.
Syntax geom_from_wkb(binary)
Arguments
• binary - Well-Known Binary (WKB) representation of a geometry (as a binary blob)
Examples
• geom_from_wkb( geom_to_wkb( make_point(4,5) ) ) → a point
geometry object
geom_from_wkt
Returns a geometry created from a Well-Known Text (WKT) representation.
Syntax geom_from_wkt(text)
Arguments
• text - Well-Known Text (WKT) representation of a geometry
Examples
• geom_from_wkt( 'POINT(4 5)' ) → a geometry object
geom_to_wkb
Returns the Well-Known Binary (WKB) representation of a geometry
Syntax geom_to_wkb(geometry)
Arguments
• geometry - a geometry
Examples
• geom_to_wkb( $geometry ) → binary blob containing a geometry object
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geom_to_wkt
Returns the Well-Known Text (WKT) representation of the geometry without SRID metadata.
Syntax geom_to_wkt(geometry, [precision=8])
[] marks optional arguments
Arguments
• geometry - a geometry
• precision - numeric precision
Examples
• geom_to_wkt( make_point(6, 50) ) → ‚POINT(6 50)‘
• geom_to_wkt(centroid(geom_from_wkt('Polygon((1 1, 0 0, -1
1, 1 1))'))) → ‚POINT(0 0.66666667)‘
• geom_to_wkt(centroid(geom_from_wkt('Polygon((1 1, 0 0, -1
1, 1 1))')), 2) → ‚POINT(0 0.67)‘
$geometry
Returns the geometry of the current feature. Can be used for processing with other functions.
Syntax $geometry
Examples
• geom_to_wkt( $geometry ) → ‚POINT(6 50)‘
geometry
Returns a feature’s geometry.
Syntax geometry(feature)
Arguments
• feature - a feature object
Examples
• geom_to_wkt( geometry( get_feature( layer, attributeField,
value ) ) ) → ‚POINT(6 50)‘
• intersects( $geometry, geometry( get_feature( layer,
attributeField, value ) ) ) → true
geometry_n
Returns a specific geometry from a geometry collection, or NULL if the input geometry is not a collection.
Syntax geometry_n(geometry, index)
Arguments
• geometry - geometry collection
• index - index of geometry to return, where 1 is the first geometry in the collection
Examples
• geom_to_wkt(geometry_n(geom_from_wkt('GEOMETRYCOLLECTION(POINT(0
1), POINT(0 0), POINT(1 0), POINT(1 1))'),3)) → ‚Point (1 0)‘
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hausdorff_distance
Returns the Hausdorff distance between two geometries. This is basically a measure of how similar or dissimilar 2
geometries are, with a lower distance indicating more similar geometries.
The function can be executed with an optional densify fraction argument. If not specified, an approximation to the
standard Hausdorff distance is used. This approximation is exact or close enough for a large subset of useful cases.
Examples of these are:
• computing distance between Linestrings that are roughly parallel to each other, and roughly equal in length.
This occurs in matching linear networks.
• Testing similarity of geometries.
If the default approximate provided by this method is insufficient, specify the optional densify fraction argument.
Specifying this argument performs a segment densification before computing the discrete Hausdorff distance. The
parameter sets the fraction by which to densify each segment. Each segment will be split into a number of equal-length
subsegments, whose fraction of the total length is closest to the given fraction. Decreasing the densify fraction
parameter will make the distance returned approach the true Hausdorff distance for the geometries.
Syntax hausdorff_distance(geometry1, geometry2, [densify_fraction])
[] marks optional arguments
Arguments
• geometry1 - a geometry
• geometry2 - a geometry
• densify_fraction - densify fraction amount
Examples
• hausdorff_distance( geometry1:= geom_from_wkt('LINESTRING
(0 0, 2 1)'),geometry2:=geom_from_wkt('LINESTRING (0 0, 2
0)')) → 2
• hausdorff_distance( geom_from_wkt('LINESTRING (130 0, 0 0,
0 150)'),geom_from_wkt('LINESTRING (10 10, 10 150, 130
10)')) → 14.142135623
• hausdorff_distance( geom_from_wkt('LINESTRING (130 0, 0 0,
0 150)'),geom_from_wkt('LINESTRING (10 10, 10 150, 130
10)'),0.5) → 70.0
inclination
Returns the inclination measured from the zenith (0) to the nadir (180) on point_a to point_b.
Syntax inclination(point_a, point_b)
Arguments
• point_a - point geometry
• point_b - point geometry
Examples
• inclination( make_point( 5, 10, 0 ), make_point( 5, 10, 5
) ) → 0.0
• inclination( make_point( 5, 10, 0 ), make_point( 5, 10, 0
) ) → 90.0
• inclination( make_point( 5, 10, 0 ), make_point( 50, 100,
0 ) ) → 90.0
• inclination( make_point( 5, 10, 0 ), make_point( 5, 10, -5
) ) → 180.0
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interior_ring_n
Returns a specific interior ring from a polygon geometry, or NULL if the geometry is not a polygon.
Syntax interior_ring_n(geometry, index)
Arguments
• geometry - polygon geometry
• index - index of interior to return, where 1 is the first interior ring
Examples
• geom_to_wkt(interior_ring_n(geom_from_wkt('POLYGON((-1 -1,
4 0, 4 2, 0 2, -1 -1),(-0.1 -0.1, 0.4 0, 0.4 0.2, 0 0.2,
-0.1 -0.1),(-1 -1, 4 0, 4 2, 0 2, -1 -1))'),1)) → ‚LineString
(-0.1 -0.1, 0.4 0, 0.4 0.2, 0 0.2, -0.1 -0.1))‘
intersection
Returns a geometry that represents the shared portion of two geometries.
Syntax intersection(geometry1, geometry2)
Arguments
• geometry1 - a geometry
• geometry2 - a geometry
Examples
• geom_to_wkt( intersection( geom_from_wkt( 'LINESTRING(3 3,
4 4, 5 5)' ), geom_from_wkt( 'LINESTRING(3 3, 4 4)' ) ) )
→ ‚LINESTRING(3 3, 4 4)‘
• geom_to_wkt( intersection( geom_from_wkt( 'LINESTRING(3 3,
4 4, 5 5)' ), geom_from_wkt( 'MULTIPOINT(3.5 3.5, 4 5)' )
) ) → ‚POINT(3.5 3.5)‘
Further reading: Intersection algorithm
intersects
Tests whether a geometry intersects another. Returns true if the geometries spatially intersect (share any portion of
space) and false if they do not.
Syntax intersects(geometry1, geometry2)
Arguments
• geometry1 - a geometry
• geometry2 - a geometry
Examples
• intersects( geom_from_wkt( 'POINT(4 4)' ), geom_from_wkt(
'LINESTRING(3 3, 4 4, 5 5)' ) ) → true
• intersects( geom_from_wkt( 'POINT(4 5)' ), geom_from_wkt(
'POINT(5 5)' ) ) → false
Further reading: overlay_intersects
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intersects_bbox
Tests whether a geometry’s bounding box overlaps another geometry’s bounding box. Returns true if the geometries
spatially intersect the bounding box defined and false if they do not.
Syntax intersects_bbox(geometry1, geometry2)
Arguments
• geometry1 - a geometry
• geometry2 - a geometry
Examples
• intersects_bbox( geom_from_wkt( 'POINT(4 5)' ),
geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ) ) → true
• intersects_bbox( geom_from_wkt( 'POINT(6 5)' ),
geom_from_wkt( 'POLYGON((3 3, 4 4, 5 5, 3 3))' ) ) →
false
is_closed
Returns true if a line string is closed (start and end points are coincident), or false if a line string is not closed. If the
geometry is not a line string then the result will be NULL.
Syntax is_closed(geometry)
Arguments
• geometry - a line string geometry
Examples
• is_closed(geom_from_wkt('LINESTRING(0 0, 1 1, 2 2)')) → false
• is_closed(geom_from_wkt('LINESTRING(0 0, 1 1, 2 2, 0 0)'))
→ true
is_empty
Returns true if a geometry is empty (without coordinates), false if the geometry is not empty and NULL if there is no
geometry. See also is_empty_or_null.
Syntax is_empty(geometry)
Arguments
• geometry - a geometry
Examples
• is_empty(geom_from_wkt('LINESTRING(0 0, 1 1, 2 2)')) → false
• is_empty(geom_from_wkt('LINESTRING EMPTY')) → true
• is_empty(geom_from_wkt('POINT(7 4)')) → false
• is_empty(geom_from_wkt('POINT EMPTY')) → true
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is_empty_or_null
Returns true if a geometry is NULL or empty (without coordinates) or false otherwise. This function is like the
expression ‚$geometry IS NULL or is_empty($geometry)‘
Syntax is_empty_or_null(geometry)
Arguments
• geometry - a geometry
Examples
• is_empty_or_null(NULL) → true
• is_empty_or_null(geom_from_wkt('LINESTRING(0 0, 1 1, 2
2)')) → false
• is_empty_or_null(geom_from_wkt('LINESTRING EMPTY')) → true
• is_empty_or_null(geom_from_wkt('POINT(7 4)')) → false
• is_empty_or_null(geom_from_wkt('POINT EMPTY')) → true
is_multipart
Returns true if the geometry is of Multi type.
Syntax is_multipart(geometry)
Arguments
• geometry - a geometry
Examples
• is_multipart(geom_from_wkt('MULTIPOINT ((0 0),(1 1),(2
2))')) → true
• is_multipart(geom_from_wkt('POINT (0 0)')) → false
is_valid
Returns true if a geometry is valid; if it is well-formed in 2D according to the OGC rules.
Syntax is_valid(geometry)
Arguments
• geometry - a geometry
Examples
• is_valid(geom_from_wkt('LINESTRING(0 0, 1 1, 2 2, 0 0)'))
→ true
• is_valid(geom_from_wkt('LINESTRING(0 0)')) → false
$length
Returns the length of a linestring. If you need the length of a border of a polygon, use $perimeter instead. The length
calculated by this function respects both the current project’s ellipsoid setting and distance unit settings. For example,
if an ellipsoid has been set for the project then the calculated length will be ellipsoidal, and if no ellipsoid is set then
the calculated length will be planimetric.
Syntax $length
Examples
• $length → 42.4711
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length
Returns the number of characters in a string or the length of a geometry linestring.
String variant
Returns the number of characters in a string.
Syntax length(string)
Arguments
• string - string to count length of
Examples
• length('hello') → 5
Geometry variant
Calculate the length of a geometry line object. Calculations are always planimetric in the Spatial Reference System
(SRS) of this geometry, and the units of the returned length will match the units for the SRS. This differs from the
calculations performed by the $length function, which will perform ellipsoidal calculations based on the project’s
ellipsoid and distance unit settings.
Syntax length(geometry)
Arguments
• geometry - line geometry object
Examples
• length(geom_from_wkt('LINESTRING(0 0, 4 0)')) → 4.0
line_interpolate_angle
Returns the angle parallel to the geometry at a specified distance along a linestring geometry. Angles are in degrees
clockwise from north.
Syntax line_interpolate_angle(geometry, distance)
Arguments
• geometry - a linestring geometry
• distance - distance along line to interpolate angle at
Examples
• line_interpolate_angle(geometry:=geom_from_wkt('LineString(0
0, 10 0)'),distance:=5) → 90.0
line_interpolate_point
Returns the point interpolated by a specified distance along a linestring geometry.
Syntax line_interpolate_point(geometry, distance)
Arguments
• geometry - a linestring geometry
• distance - distance along line to interpolate
Examples
• geom_to_wkt(line_interpolate_point(geometry:=geom_from_wkt('LineString(
0, 10 0)'),distance:=5)) → ‚Point (5 0)‘
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Further reading: Interpolate point on line algorithm
line_locate_point
Returns the distance along a linestring corresponding to the closest position the linestring comes to a specified point
geometry.
Syntax line_locate_point(geometry, point)
Arguments
• geometry - a linestring geometry
• point - point geometry to locate closest position on linestring to
Examples
• line_locate_point(geometry:=geom_from_wkt('LineString(0 0,
10 0)'),point:=geom_from_wkt('Point(5 0)')) → 5.0
line_merge
Returns a LineString or MultiLineString geometry, where any connected LineStrings from the input geometry
have been merged into a single linestring. This function will return NULL if passed a geometry which is not
a LineString/MultiLineString.
Syntax line_merge(geometry)
Arguments
• geometry - a LineString/MultiLineString geometry
Examples
• geom_to_wkt(line_merge(geom_from_wkt('MULTILINESTRING((0
0, 1 1),(1 1, 2 2))'))) → ‚LineString(0 0,1 1,2 2)‘
• geom_to_wkt(line_merge(geom_from_wkt('MULTILINESTRING((0
0, 1 1),(11 1, 21 2))'))) → ‚MultiLineString((0 0, 1 1),(11 1, 21 2)‘
line_substring
Returns the portion of a line (or curve) geometry which falls between the specified start and end distances (measured
from the beginning of the line). Z and M values are linearly interpolated from existing values.
Syntax line_substring(geometry, start_distance, end_distance)
Arguments
• geometry - a linestring or curve geometry
• start_distance - distance to start of substring
• end_distance - distance to end of substring
Examples
• geom_to_wkt(line_substring(geometry:=geom_from_wkt('LineString(0
0, 10 0)'),start_distance:=2,end_distance=6)) → ‚LineString (2
0,6 0)‘
Further reading: Line substring algorithm
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m
Returns the m value of a point geometry.
Syntax m(geometry)
Arguments
• geometry - a point geometry
Examples
• m( geom_from_wkt( 'POINTM(2 5 4)' ) ) → 4
m_max
Returns the maximum m (measure) value of a geometry.
Syntax m_max(geometry)
Arguments
• geometry - a geometry containing m values
Examples
• m_max( make_point_m( 0,0,1 ) ) → 1
• m_max(make_line( make_point_m( 0,0,1 ), make_point_m( -1,
-1,2 ), make_point_m( -2,-2,0 ) ) ) → 2
m_min
Returns the minimum m (measure) value of a geometry.
Syntax m_min(geometry)
Arguments
• geometry - a geometry containing m values
Examples
• m_min( make_point_m( 0,0,1 ) ) → 1
• m_min(make_line( make_point_m( 0,0,1 ), make_point_m( -1,
-1,2 ), make_point_m( -2,-2,0 ) ) ) → 0
main_angle
Returns the main angle of a geometry (clockwise, in degrees from North), which represents the angle of the oriented
minimal bounding rectangle which completely covers the geometry.
Syntax main_angle(geometry)
Arguments
• geometry - a geometry
Examples
• main_angle(geom_from_wkt('Polygon ((321577 129614, 321581
129618, 321585 129615, 321581 129610, 321577 129614))')) →
38.66
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make_circle
Creates a circular polygon.
Syntax make_circle(center, radius, [segments=36])
[] marks optional arguments
Arguments
• center - center point of the circle
• radius - radius of the circle
• segments - optional argument for polygon segmentation. By default this value is 36
Examples
• geom_to_wkt(make_circle(make_point(10,10), 5, 4)) → ‚Polygon
((10 15, 15 10, 10 5, 5 10, 10 15))‘
• geom_to_wkt(make_circle(make_point(10,10,5), 5, 4)) →
‚PolygonZ ((10 15 5, 15 10 5, 10 5 5, 5 10 5, 10 15 5))‘
• geom_to_wkt(make_circle(make_point(10,10,5,30), 5, 4)) →
‚PolygonZM ((10 15 5 30, 15 10 5 30, 10 5 5 30, 5 10 5 30, 10 15 5 30))‘
make_ellipse
Creates an elliptical polygon.
Syntax make_ellipse(center, semi_major_axis, semi_minor_axis, azimuth, [segments=36])
[] marks optional arguments
Arguments
• center - center point of the ellipse
• semi_major_axis - semi-major axis of the ellipse
• semi_minor_axis - semi-minor axis of the ellipse
• azimuth - orientation of the ellipse
• segments - optional argument for polygon segmentation. By default this value is 36
Examples
• geom_to_wkt(make_ellipse(make_point(10,10), 5, 2, 90, 4))
→ ‚Polygon ((15 10, 10 8, 5 10, 10 12, 15 10))‘
• geom_to_wkt(make_ellipse(make_point(10,10,5), 5, 2, 90, 4))
→ ‚PolygonZ ((15 10 5, 10 8 5, 5 10 5, 10 12 5, 15 10 5))‘
• geom_to_wkt(make_ellipse(make_point(10,10,5,30), 5, 2, 90,
4)) → ‚PolygonZM ((15 10 5 30, 10 8 5 30, 5 10 5 30, 10 12 5 30, 15 10 5 30))‘
make_line
Creates a line geometry from a series of point geometries.
List of arguments variant
Line vertices are specified as separate arguments to the function.
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Syntax make_line(point1, point2, …)
Arguments
• point - a point geometry (or array of points)
Examples
• geom_to_wkt(make_line(make_point(2,4),make_point(3,5))) →
‚LineString (2 4, 3 5)‘
• geom_to_wkt(make_line(make_point(2,4),make_point(3,5),
make_point(9,7))) → ‚LineString (2 4, 3 5, 9 7)‘
Array variant
Line vertices are specified as an array of points.
Syntax make_line(array)
Arguments
• array - array of points
Examples
• geom_to_wkt(make_line(array(make_point(2,4),make_point(3,
5),make_point(9,7)))) → ‚LineString (2 4, 3 5, 9 7)‘
make_point
Creates a point geometry from an x and y (and optional z and m) value.
Syntax make_point(x, y, [z], [m])
[] marks optional arguments
Arguments
• x - x coordinate of point
• y - y coordinate of point
• z - optional z coordinate of point
• m - optional m value of point
Examples
• geom_to_wkt(make_point(2,4)) → ‚Point (2 4)‘
• geom_to_wkt(make_point(2,4,6)) → ‚PointZ (2 4 6)‘
• geom_to_wkt(make_point(2,4,6,8)) → ‚PointZM (2 4 6 8)‘
make_point_m
Creates a point geometry from an x, y coordinate and m value.
Syntax make_point_m(x, y, m)
Arguments
• x - x coordinate of point
• y - y coordinate of point
• m - m value of point
Examples
• geom_to_wkt(make_point_m(2,4,6)) → ‚PointM (2 4 6)‘
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make_polygon
Creates a polygon geometry from an outer ring and optional series of inner ring geometries.
Syntax make_polygon(outerRing, [innerRing1], [innerRing2], …)
[] marks optional arguments
Arguments
• outerRing - closed line geometry for polygon’s outer ring
• innerRing - optional closed line geometry for inner ring
Examples
• geom_to_wkt(make_polygon(geom_from_wkt('LINESTRING( 0 0, 0
1, 1 1, 1 0, 0 0 )'))) → ‚Polygon ((0 0, 0 1, 1 1, 1 0, 0 0))‘
• geom_to_wkt(make_polygon(geom_from_wkt('LINESTRING( 0 0,
0 1, 1 1, 1 0, 0 0 )'),geom_from_wkt('LINESTRING(
0.1 0.1, 0.1 0.2, 0.2 0.2, 0.2 0.1, 0.1 0.1 )'),
geom_from_wkt('LINESTRING( 0.8 0.8, 0.8 0.9, 0.9 0.9, 0.9
0.8, 0.8 0.8 )'))) → ‚Polygon ((0 0, 0 1, 1 1, 1 0, 0 0),(0.1 0.1, 0.1 0.2, 0.2 0.2,
0.2 0.1, 0.1 0.1),(0.8 0.8, 0.8 0.9, 0.9 0.9, 0.9 0.8, 0.8 0.8))‘
make_rectangle_3points
Creates a rectangle from 3 points.
Syntax make_rectangle_3points(point1, point2, point3, [option=0])
[] marks optional arguments
Arguments
• point1 - First point.
• point2 - Second point.
• point3 - Third point.
• option - An optional argument to construct the rectangle. By default this value is 0. Value
can be 0 (distance) or 1 (projected). Option distance: Second distance is equal to the
distance between 2nd and 3rd point. Option projected: Second distance is equal to the
distance of the perpendicular projection of the 3rd point on the segment or its extension.
Examples
• geom_to_wkt(make_rectangle(make_point(0, 0), make_point(0,
5), make_point(5, 5), 0))) → ‚Polygon ((0 0, 0 5, 5 5, 5 0, 0 0))‘
• geom_to_wkt(make_rectangle(make_point(0, 0), make_point(0,
5), make_point(5, 3), 1))) → ‚Polygon ((0 0, 0 5, 5 5, 5 0, 0 0))‘
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make_regular_polygon
Creates a regular polygon.
Syntax make_regular_polygon(center, radius, number_sides, [circle=0])
[] marks optional arguments
Arguments
• center - center of the regular polygon
• radius - second point. The first if the regular polygon is inscribed. The midpoint of the
first side if the regular polygon is circumscribed.
• number_sides - Number of sides/edges of the regular polygon
• circle - Optional argument to construct the regular polygon. By default this value is 0.
Value can be 0 (inscribed) or 1 (circumscribed)
Examples
• geom_to_wkt(make_regular_polygon(make_point(0,0),
make_point(0,5), 5)) → ‚Polygon ((0 5, 4.76 1.55, 2.94 -4.05, -2.94 -
4.05, -4.76 1.55, 0 5))‘
• geom_to_wkt(make_regular_polygon(make_point(0,0),
project(make_point(0,0), 4.0451, radians(36)), 5)) →
‚Polygon ((0 5, 4.76 1.55, 2.94 -4.05, -2.94 -4.05, -4.76 1.55, 0 5))‘
make_square
Creates a square from a diagonal.
Syntax make_square(point1, point2)
Arguments
• point1 - First point of the diagonal
• point2 - Last point of the diagonal
Examples
• geom_to_wkt(make_square( make_point(0,0), make_point(5,
5))) → ‚Polygon ((0 0, -0 5, 5 5, 5 0, 0 0))‘
• geom_to_wkt(make_square( make_point(5,0), make_point(5,
5))) → ‚Polygon ((5 0, 2.5 2.5, 5 5, 7.5 2.5, 5 0))‘
make_triangle
Creates a triangle polygon.
Syntax make_triangle(point1, point2, point3)
Arguments
• point1 - first point of the triangle
• point2 - second point of the triangle
• point3 - third point of the triangle
Examples
• geom_to_wkt(make_triangle(make_point(0,0), make_point(5,
5), make_point(0,10))) → ‚Triangle ((0 0, 5 5, 0 10, 0 0))‘
• geom_to_wkt(boundary(make_triangle(make_point(0,0),
make_point(5,5), make_point(0,10)))) → ‚LineString (0 0, 5 5, 0
10, 0 0)‘
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minimal_circle
Returns the minimal enclosing circle of a geometry. It represents the minimum circle that encloses all geometries
within the set.
Syntax minimal_circle(geometry, [segments=36])
[] marks optional arguments
Arguments
• geometry - a geometry
• segments - optional argument for polygon segmentation. By default this value is 36
Examples
• geom_to_wkt( minimal_circle( geom_from_wkt( 'LINESTRING(0
5, 0 -5, 2 1)' ), 4 ) ) → ‚Polygon ((0 5, 5 -0, -0 -5, -5 0, 0 5))‘
• geom_to_wkt( minimal_circle( geom_from_wkt( 'MULTIPOINT(1
2, 3 4, 3 2)' ), 4 ) ) → ‚Polygon ((3 4, 3 2, 1 2, 1 4, 3 4))‘
Further reading: Minimum enclosing circles algorithm
nodes_to_points
Returns a multipoint geometry consisting of every node in the input geometry.
Syntax nodes_to_points(geometry, [ignore_closing_nodes=false])
[] marks optional arguments
Arguments
• geometry - geometry object
• ignore_closing_nodes - optional argument specifying whether to include duplicate nodes
which close lines or polygons rings. Defaults to false, set to true to avoid including these
duplicate nodes in the output collection.
Examples
• geom_to_wkt(nodes_to_points(geom_from_wkt('LINESTRING(0 0,
1 1, 2 2)'))) → ‚MultiPoint ((0 0),(1 1),(2 2))‘
• geom_to_wkt(nodes_to_points(geom_from_wkt('POLYGON((-1 -1,
4 0, 4 2, 0 2, -1 -1))'),true)) → ‚MultiPoint ((-1 -1),(4 0),(4 2),(0 2))‘
Further reading: Extract vertices algorithm
num_geometries
Returns the number of geometries in a geometry collection, or NULL if the input geometry is not a collection.
Syntax num_geometries(geometry)
Arguments
• geometry - geometry collection
Examples
• num_geometries(geom_from_wkt('GEOMETRYCOLLECTION(POINT(0
1), POINT(0 0), POINT(1 0), POINT(1 1))')) → 4
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num_interior_rings
Returns the number of interior rings in a polygon or geometry collection, or NULL if the input geometry is not
a polygon or collection.
Syntax num_interior_rings(geometry)
Arguments
• geometry - input geometry
Examples
• num_interior_rings(geom_from_wkt('POLYGON((-1 -1, 4 0, 4 2,
0 2, -1 -1),(-0.1 -0.1, 0.4 0, 0.4 0.2, 0 0.2, -0.1 -0.
1))')) → 1
num_points
Returns the number of vertices in a geometry.
Syntax num_points(geometry)
Arguments
• geometry - a geometry
Examples
• num_points($geometry) → number of vertices in the current feature’s geometry
num_rings
Returns the number of rings (including exterior rings) in a polygon or geometry collection, or NULL if the input
geometry is not a polygon or collection.
Syntax num_rings(geometry)
Arguments
• geometry - input geometry
Examples
• num_rings(geom_from_wkt('POLYGON((-1 -1, 4 0, 4 2, 0 2, -1
-1),(-0.1 -0.1, 0.4 0, 0.4 0.2, 0 0.2, -0.1 -0.1))')) → 2
offset_curve
Returns a geometry formed by offsetting a linestring geometry to the side. Distances are in the Spatial Reference
System of this geometry.
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Syntax offset_curve(geometry, distance, [segments=8], [join=1], [miter_limit=2.0])
[] marks optional arguments
Arguments
• geometry - a (multi)linestring geometry
• distance - offset distance. Positive values will be buffered to the left of lines, negative
values to the right
• segments - number of segments to use to represent a quarter circle when a round join
style is used. A larger number results in a smoother line with more nodes.
• join - join style for corners, where 1 = round, 2 = miter and 3 = bevel
• miter_limit - limit on the miter ratio used for very sharp corners (when using miter joins
only)
Examples
• offset_curve($geometry, 10.5) → line offset to the left by 10.5 units
• offset_curve($geometry, -10.5) → line offset to the right by 10.5 units
• offset_curve($geometry, 10.5, segments=16, join=1) → line offset
to the left by 10.5 units, using more segments to result in a smoother curve
• offset_curve($geometry, 10.5, join=3) → line offset to the left by 10.5
units, using a beveled join
Further reading: Offset lines algorithm
order_parts
Orders the parts of a MultiGeometry by a given criteria
Syntax order_parts(geometry, orderby, ascending)
Arguments
• geometry - a multi-type geometry
• orderby - an expression string defining the order criteria
• ascending - boolean, True for ascending, False for descending
Examples
• geom_to_wkt(order_parts(geom_from_wkt('MultiPolygon (((1
1, 5 1, 5 5, 1 5, 1 1)),((1 1, 9 1, 9 9, 1 9, 1 1)))'),
'area($geometry)', False)) → ‚MultiPolygon (((1 1, 9 1, 9 9, 1 9, 1 1)),((1 1,
5 1, 5 5, 1 5, 1 1)))‘
• geom_to_wkt(order_parts(geom_from_wkt('LineString(1 2, 3
2, 4 3)'), '1', True)) → ‚LineString(1 2, 3 2, 4 3)‘
oriented_bbox
Returns a geometry which represents the minimal oriented bounding box of an input geometry.
Syntax oriented_bbox(geometry)
Arguments
• geometry - a geometry
Examples
• geom_to_wkt( oriented_bbox( geom_from_wkt( 'MULTIPOINT(1 2,
3 4, 3 2)' ) ) ) → ‚Polygon ((3 2, 3 4, 1 4, 1 2, 3 2))‘
Further reading: Oriented minimum bounding box algorithm
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overlaps
Tests whether a geometry overlaps another. Returns true if the geometries share space, are of the same dimension,
but are not completely contained by each other.
Syntax overlaps(geometry1, geometry2)
Arguments
• geometry1 - a geometry
• geometry2 - a geometry
Examples
• overlaps( geom_from_wkt( 'LINESTRING(3 5, 4 4, 5 5, 5 3)'
), geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ) ) → true
• overlaps( geom_from_wkt( 'LINESTRING(0 0, 1 1)' ),
geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ) ) → false
overlay_contains
Returns whether the current feature spatially contains at least one feature from a target layer, or an array of expression-based
results for the features in the target layer contained in the current feature.
Read more on the underlying GEOS „Contains“ predicate, as described in PostGIS ST_Contains function.
Syntax overlay_contains(layer, [expression], [filter], [limit], [cache=false])
[] marks optional arguments
Arguments
• layer - the layer whose overlay is checked
• expression - an optional expression to evaluate on the features from the target layer. If not
set, the function will just return a boolean indicating whether there is at least one match.
• filter - an optional expression to filter the target features to check. If not set, all the features
will be checked.
• limit - an optional integer to limit the number of matching features. If not set, all the
matching features will be returned.
• cache - set this to true to build a local spatial index (most of the time, this is unwanted,
unless you are working with a particularly slow data provider)
Examples
• overlay_contains('regions') → true if the current feature spatially contains
a region
• overlay_contains('regions', filter:= population > 10000) →
true if the current feature spatially contains a region with a population greater than 10000
• overlay_contains('regions', name) → an array of names, for the regions
contained in the current feature
• array_to_string(overlay_contains('regions', name)) → a string
as a comma separated list of names, for the regions contained in the current feature
• array_length(overlay_contains('regions', name)) → the number of
regions contained in the current feature
• array_sort(overlay_contains(layer:='regions',
expression:="name", filter:= population > 10000)) → an
ordered array of names, for the regions contained in the current feature and with
a population greater than 10000
• overlay_contains(layer:='regions', expression:=
geom_to_wkt($geometry), limit:=2) → an array of geometries (in
WKT), for up to two regions contained in the current feature
Further reading: contains, array manipulation, Select by location algorithm
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overlay_crosses
Returns whether the current feature spatially crosses at least one feature from a target layer, or an array of expression-based
results for the features in the target layer crossed by the current feature.
Read more on the underlying GEOS „Crosses“ predicate, as described in PostGIS ST_Crosses function.
Syntax overlay_crosses(layer, [expression], [filter], [limit], [cache=false])
[] marks optional arguments
Arguments
• layer - the layer whose overlay is checked
• expression - an optional expression to evaluate on the features from the target layer. If not
set, the function will just return a boolean indicating whether there is at least one match.
• filter - an optional expression to filter the target features to check. If not set, all the features
will be checked.
• limit - an optional integer to limit the number of matching features. If not set, all the
matching features will be returned.
• cache - set this to true to build a local spatial index (most of the time, this is unwanted,
unless you are working with a particularly slow data provider)
Examples
• overlay_crosses('regions') → true if the current feature spatially crosses
a region
• overlay_crosses('regions', filter:= population > 10000) →
true if the current feature spatially crosses a region with a population greater than 10000
• overlay_crosses('regions', name) → an array of names, for the regions
crossed by the current feature
• array_to_string(overlay_crosses('regions', name)) → a string
as a comma separated list of names, for the regions crossed by the current feature
• array_sort(overlay_crosses(layer:='regions',
expression:="name", filter:= population > 10000)) → an
ordered array of names, for the regions crossed by the current feature and with
a population greater than 10000
• overlay_crosses(layer:='regions', expression:=
geom_to_wkt($geometry), limit:=2) → an array of geometries (in
WKT), for up to two regions crossed by the current feature
Further reading: crosses, array manipulation, Select by location algorithm
overlay_disjoint
Returns whether the current feature is spatially disjoint from all the features of a target layer, or an array of expression-based
results for the features in the target layer that are disjoint from the current feature.
Read more on the underlying GEOS „Disjoint“ predicate, as described in PostGIS ST_Disjoint function.
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Syntax overlay_disjoint(layer, [expression], [filter], [limit], [cache=false])
[] marks optional arguments
Arguments
• layer - the layer whose overlay is checked
• expression - an optional expression to evaluate on the features from the target layer. If not
set, the function will just return a boolean indicating whether there is at least one match.
• filter - an optional expression to filter the target features to check. If not set, all the features
will be checked.
• limit - an optional integer to limit the number of matching features. If not set, all the
matching features will be returned.
• cache - set this to true to build a local spatial index (most of the time, this is unwanted,
unless you are working with a particularly slow data provider)
Examples
• overlay_disjoint('regions') → true if the current feature is spatially disjoint
from all the regions
• overlay_disjoint('regions', filter:= population > 10000) →
true if the current feature is spatially disjoint from all the regions with a population greater
than 10000
• overlay_disjoint('regions', name) → an array of names, for the regions
spatially disjoint from the current feature
• array_to_string(overlay_disjoint('regions', name)) → a string
as a comma separated list of names, for the regions spatially disjoint from the current
feature
• array_sort(overlay_disjoint(layer:='regions',
expression:="name", filter:= population > 10000)) → an
ordered array of names, for the regions spatially disjoint from the current feature and
with a population greater than 10000
• overlay_disjoint(layer:='regions', expression:=
geom_to_wkt($geometry), limit:=2) → an array of geometries (in
WKT), for up to two regions spatially disjoint from the current feature
Further reading: disjoint, array manipulation, Select by location algorithm
overlay_equals
Returns whether the current feature spatially equals to at least one feature from a target layer, or an array of expression-based
results for the features in the target layer that are spatially equal to the current feature.
Read more on the underlying GEOS „Equals“ predicate, as described in PostGIS ST_Equals function.
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Syntax overlay_equals(layer, [expression], [filter], [limit], [cache=false])
[] marks optional arguments
Arguments
• layer - the layer whose overlay is checked
• expression - an optional expression to evaluate on the features from the target layer. If not
set, the function will just return a boolean indicating whether there is at least one match.
• filter - an optional expression to filter the target features to check. If not set, all the features
will be checked.
• limit - an optional integer to limit the number of matching features. If not set, all the
matching features will be returned.
• cache - set this to true to build a local spatial index (most of the time, this is unwanted,
unless you are working with a particularly slow data provider)
Examples
• overlay_equals('regions') → true if the current feature is spatially equal to
a region
• overlay_equals('regions', filter:= population > 10000) → true
if the current feature is spatially equal to a region with a population greater than 10000
• overlay_equals('regions', name) → an array of names, for the regions
spatially equal to the current feature
• array_to_string(overlay_equals('regions', name)) → a string
as a comma separated list of names, for the regions spatially equal to the current feature
• array_sort(overlay_equals(layer:='regions',
expression:="name", filter:= population > 10000)) → an
ordered array of names, for the regions spatially equal to the current feature and with
a population greater than 10000
• overlay_equals(layer:='regions', expression:=
geom_to_wkt($geometry), limit:=2) → an array of geometries (in
WKT), for up to two regions spatially equal to the current feature
Further reading: array manipulation, Select by location algorithm
overlay_intersects
Returns whether the current feature spatially intersects at least one feature from a target layer, or an array of
expression-based results for the features in the target layer intersected by the current feature.
Read more on the underlying GEOS „Intersects“ predicate, as described in PostGIS ST_Intersects function.
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Syntax overlay_intersects(layer, [expression], [filter], [limit], [cache=false])
[] marks optional arguments
Arguments
• layer - the layer whose overlay is checked
• expression - an optional expression to evaluate on the features from the target layer. If not
set, the function will just return a boolean indicating whether there is at least one match.
• filter - an optional expression to filter the target features to check. If not set, all the features
will be checked.
• limit - an optional integer to limit the number of matching features. If not set, all the
matching features will be returned.
• cache - set this to true to build a local spatial index (most of the time, this is unwanted,
unless you are working with a particularly slow data provider)
Examples
• overlay_intersects('regions') → true if the current feature spatially
intersects a region
• overlay_intersects('regions', filter:= population > 10000)
→ true if the current feature spatially intersects a region with a population greater than
10000
• overlay_intersects('regions', name) → an array of names, for the
regions intersected by the current feature
• array_to_string(overlay_intersects('regions', name)) →
a string as a comma separated list of names, for the regions intersected by the current
feature
• array_sort(overlay_intersects(layer:='regions',
expression:="name", filter:= population > 10000)) → an
ordered array of names, for the regions intersected by the current feature and with
a population greater than 10000
• overlay_intersects(layer:='regions', expression:=
geom_to_wkt($geometry), limit:=2) → an array of geometries (in
WKT), for up to two regions intersected by the current feature
Further reading: intersects, array manipulation, Select by location algorithm
overlay_nearest
Returns whether the current feature has feature(s) from a target layer within a given distance, or an array of expression-based
results for the features in the target layer within a distance from the current feature.
Note: This function can be slow and consume a lot of memory for large layers.
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Syntax overlay_nearest(layer, [expression], [filter], [limit=1], [max_distance], [cache=false])
[] marks optional arguments
Arguments
• layer - the target layer
• expression - an optional expression to evaluate on the features from the target layer. If not
set, the function will just return a boolean indicating whether there is at least one match.
• filter - an optional expression to filter the target features to check. If not set, all the features
in the target layer will be used.
• limit - an optional integer to limit the number of matching features. If not set, only the
nearest feature will be returned. If set to -1, returns all the matching features.
• max_distance - an optional distance to limit the search of matching features. If not set,
all the features in the target layer will be used.
• cache - set this to true to build a local spatial index (most of the time, this is unwanted,
unless you are working with a particularly slow data provider)
Examples
• overlay_nearest('airports') → true if the „airports“ layer has at least one
feature
• overlay_nearest('airports', max_distance:= 5000) → true if there
is an airport within a distance of 5000 map units from the current feature
• overlay_nearest('airports', name) → the name of the closest airport to
the current feature, as an array
• array_to_string(overlay_nearest('airports', name)) → the name
of the closest airport to the current feature, as a string
• overlay_nearest(layer:='airports', expression:= name,
max_distance:= 5000) → the name of the closest airport within a distance of
5000 map units from the current feature, as an array
• overlay_nearest(layer:='airports', expression:="name",
filter:= "Use"='Civilian', limit:=3) → an array of names, for up to
the three closest civilian airports ordered by distance
• overlay_nearest(layer:='airports', expression:="name",
limit:= -1, max_distance:= 5000) → an array of names, for all the airports
within a distance of 5000 map units from the current feature, ordered by distance
Further reading: array manipulation, Join attributes by nearest algorithm
overlay_touches
Returns whether the current feature spatially touches at least one feature from a target layer, or an array of expression-based
results for the features in the target layer touched by the current feature.
Read more on the underlying GEOS „Touches“ predicate, as described in PostGIS ST_Touches function.
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Syntax overlay_touches(layer, [expression], [filter], [limit], [cache=false])
[] marks optional arguments
Arguments
• layer - the layer whose overlay is checked
• expression - an optional expression to evaluate on the features from the target layer. If not
set, the function will just return a boolean indicating whether there is at least one match.
• filter - an optional expression to filter the target features to check. If not set, all the features
will be checked.
• limit - an optional integer to limit the number of matching features. If not set, all the
matching features will be returned.
• cache - set this to true to build a local spatial index (most of the time, this is unwanted,
unless you are working with a particularly slow data provider)
Examples
• overlay_touches('regions') → true if the current feature spatially touches
a region
• overlay_touches('regions', filter:= population > 10000) →
true if the current feature spatially touches a region with a population greater than 10000
• overlay_touches('regions', name) → an array of names, for the regions
touched by the current feature
• string_to_array(overlay_touches('regions', name)) → a string
as a comma separated list of names, for the regions touched by the current feature
• array_sort(overlay_touches(layer:='regions',
expression:="name", filter:= population > 10000)) → an
ordered array of names, for the regions touched by the current feature and with
a population greater than 10000
• overlay_touches(layer:='regions', expression:=
geom_to_wkt($geometry), limit:=2) → an array of geometries (in
WKT), for up to two regions touched by the current feature
Further reading: touches, array manipulation, Select by location algorithm
overlay_within
Returns whether the current feature is spatially within at least one feature from a target layer, or an array of expression-based
results for the features in the target layer that contain the current feature.
Read more on the underlying GEOS „Within“ predicate, as described in PostGIS ST_Within function.
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Syntax overlay_within(layer, [expression], [filter], [limit], [cache=false])
[] marks optional arguments
Arguments
• layer - the layer whose overlay is checked
• expression - an optional expression to evaluate on the features from the target layer. If not
set, the function will just return a boolean indicating whether there is at least one match.
• filter - an optional expression to filter the target features to check. If not set, all the features
will be checked.
• limit - an optional integer to limit the number of matching features. If not set, all the
matching features will be returned.
• cache - set this to true to build a local spatial index (most of the time, this is unwanted,
unless you are working with a particularly slow data provider)
Examples
• overlay_within('regions') → true if the current feature is spatially within
a region
• overlay_within('regions', filter:= population > 10000) → true
if the current feature is spatially within a region with a population greater than 10000
• overlay_within('regions', name) → an array of names, for the regions
containing the current feature
• array_to_string(overlay_within('regions', name)) → a string
as a comma separated list of names, for the regions containing the current feature
• array_sort(overlay_within(layer:='regions',
expression:="name", filter:= population > 10000)) → an
ordered array of names, for the regions containing the current feature and with
a population greater than 10000
• overlay_within(layer:='regions', expression:=
geom_to_wkt($geometry), limit:=2) → an array of geometries (in
WKT), for up to two regions containing the current feature
Further reading: within, array manipulation, Select by location algorithm
$perimeter
Returns the perimeter length of the current feature. The perimeter calculated by this function respects both the current
project’s ellipsoid setting and distance unit settings. For example, if an ellipsoid has been set for the project then the
calculated perimeter will be ellipsoidal, and if no ellipsoid is set then the calculated perimeter will be planimetric.
Syntax $perimeter
Examples
• $perimeter → 42
perimeter
Returns the perimeter of a geometry polygon object. Calculations are always planimetric in the Spatial Reference
System (SRS) of this geometry, and the units of the returned perimeter will match the units for the SRS. This differs
from the calculations performed by the $perimeter function, which will perform ellipsoidal calculations based on the
project’s ellipsoid and distance unit settings.
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Syntax perimeter(geometry)
Arguments
• geometry - polygon geometry object
Examples
• perimeter(geom_from_wkt('POLYGON((0 0, 4 0, 4 2, 0 2, 0
0))')) → 12.0
point_n
Returns a specific node from a geometry.
Syntax point_n(geometry, index)
Arguments
• geometry - geometry object
• index - index of node to return, where 1 is the first node; if the value is negative, the
selected vertex index will be its total count minus the absolute value
Examples
• geom_to_wkt(point_n(geom_from_wkt('POLYGON((0 0, 4 0, 4 2,
0 2, 0 0))'),2)) → ‚Point (4 0)‘
Further reading: Extract specific vertices algorithm
point_on_surface
Returns a point guaranteed to lie on the surface of a geometry.
Syntax point_on_surface(geometry)
Arguments
• geometry - a geometry
Examples
• point_on_surface($geometry) → a point geometry
Further reading: Point on Surface algorithm
pole_of_inaccessibility
Calculates the approximate pole of inaccessibility for a surface, which is the most distant internal point from the
boundary of the surface. This function uses the ‚polylabel‘ algorithm (Vladimir Agafonkin, 2016), which is an iterative
approach guaranteed to find the true pole of inaccessibility within a specified tolerance. More precise tolerances
require more iterations and will take longer to calculate.
Syntax pole_of_inaccessibility(geometry, tolerance)
Arguments
• geometry - a geometry
• tolerance - maximum distance between the returned point and the true pole location
Examples
• geom_to_wkt(pole_of_inaccessibility( geom_from_wkt('POLYGON((0
1, 0 9, 3 10, 3 3, 10 3, 10 1, 0 1))'), 0.1))' → ‚Point(1.546875
2.546875)‘
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Further reading: Pole of inaccessibility algorithm
project
Returns a point projected from a start point using a distance, a bearing (azimuth) and an elevation in radians.
Syntax project(point, distance, azimuth, [elevation])
[] marks optional arguments
Arguments
• point - start point
• distance - distance to project
• azimuth - azimuth in radians clockwise, where 0 corresponds to north
• elevation - angle of inclination in radians
Examples
• geom_to_wkt(project(make_point(1, 2), 3, radians(270))) →
‚Point(-2, 2)‘
Further reading: Project points (Cartesian) algorithm
relate
Tests the Dimensional Extended 9 Intersection Model (DE-9IM) representation of the relationship between two
geometries.
Relationship variant
Returns the Dimensional Extended 9 Intersection Model (DE-9IM) representation of the relationship between two
geometries.
Syntax relate(geometry, geometry)
Arguments
• geometry - a geometry
• geometry - a geometry
Examples
• relate( geom_from_wkt( 'LINESTRING(40 40,120 120)' ),
geom_from_wkt( 'LINESTRING(40 40,60 120)' ) ) → ‚FF1F00102‘
Pattern match variant
Tests whether the DE-9IM relationship between two geometries matches a specified pattern.
Syntax relate(geometry, geometry, pattern)
Arguments
• geometry - a geometry
• geometry - a geometry
• pattern - DE-9IM pattern to match
Examples
• relate( geom_from_wkt( 'LINESTRING(40 40,120 120)' ),
geom_from_wkt( 'LINESTRING(40 40,60 120)' ), '**1F001**'
) → True
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reverse
Reverses the direction of a line string by reversing the order of its vertices.
Syntax reverse(geometry)
Arguments
• geometry - a geometry
Examples
• geom_to_wkt(reverse(geom_from_wkt('LINESTRING(0 0, 1 1, 2
2)'))) → ‚LINESTRING(2 2, 1 1, 0 0)‘
Further reading: Reverse line direction algorithm
rotate
Returns a rotated version of a geometry. Calculations are in the Spatial Reference System of this geometry.
Syntax rotate(geometry, rotation, [center])
[] marks optional arguments
Arguments
• geometry - a geometry
• rotation - clockwise rotation in degrees
• center - rotation center point. If not specified, the center of the geometry’s bounding box
is used.
Examples
• rotate($geometry, 45, make_point(4, 5)) → geometry rotated 45
degrees clockwise around the (4, 5) point
• rotate($geometry, 45) → geometry rotated 45 degrees clockwise around the
center of its bounding box
segments_to_lines
Returns a multi line geometry consisting of a line for every segment in the input geometry.
Syntax segments_to_lines(geometry)
Arguments
• geometry - geometry object
Examples
• geom_to_wkt(segments_to_lines(geom_from_wkt('LINESTRING(0
0, 1 1, 2 2)'))) → ‚MultiLineString ((0 0, 1 1),(1 1, 2 2))‘
Further reading: Explode lines algorithm
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shortest_line
Returns the shortest line joining geometry1 to geometry2. The resultant line will start at geometry1 and end at
geometry2.
Syntax shortest_line(geometry1, geometry2)
Arguments
• geometry1 - geometry to find shortest line from
• geometry2 - geometry to find shortest line to
Examples
• geom_to_wkt(shortest_line(geom_from_wkt('LINESTRING (20
80, 98 190, 110 180, 50 75 )'),geom_from_wkt('POINT(100
100)'))) → ‚LineString(73.0769 115.384, 100 100)‘
simplify
Simplifies a geometry by removing nodes using a distance based threshold (ie, the Douglas Peucker algorithm). The
algorithm preserves large deviations in geometries and reduces the number of vertices in nearly straight segments.
Syntax simplify(geometry, tolerance)
Arguments
• geometry - a geometry
• tolerance - maximum deviation from straight segments for points to be removed
Examples
• geom_to_wkt(simplify(geometry:=geom_from_wkt('LineString(0
0, 5 0.1, 10 0)'),tolerance:=5)) → ‚LineString(0 0, 10 0)‘
Further reading: Simplify algorithm
simplify_vw
Simplifies a geometry by removing nodes using an area based threshold (ie, the Visvalingam-Whyatt algorithm). The
algorithm removes vertices which create small areas in geometries, e.g., narrow spikes or nearly straight segments.
Syntax simplify_vw(geometry, tolerance)
Arguments
• geometry - a geometry
• tolerance - a measure of the maximum area created by a node for the node to be removed
Examples
• geom_to_wkt(simplify_vw(geometry:=geom_from_wkt('LineString(0
0, 5 0, 5.01 10, 5.02 0, 10 0)'),tolerance:=5)) → ‚LineString(0
0, 10 0)‘
Further reading: Simplify algorithm
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single_sided_buffer
Returns a geometry formed by buffering out just one side of a linestring geometry. Distances are in the Spatial
Reference System of this geometry.
Syntax single_sided_buffer(geometry, distance, [segments=8], [join=1], [miter_limit=2.0])
[] marks optional arguments
Arguments
• geometry - a (multi)linestring geometry
• distance - buffer distance. Positive values will be buffered to the left of lines, negative
values to the right
• segments - number of segments to use to represent a quarter circle when a round join
style is used. A larger number results in a smoother buffer with more nodes.
• join - join style for corners, where 1 = round, 2 = miter and 3 = bevel
• miter_limit - limit on the miter ratio used for very sharp corners (when using miter joins
only)
Examples
• single_sided_buffer($geometry, 10.5) → line buffered to the left by 10.5
units
• single_sided_buffer($geometry, -10.5) → line buffered to the right by
10.5 units
• single_sided_buffer($geometry, 10.5, segments=16, join=1)
→ line buffered to the left by 10.5 units, using more segments to result in a smoother
buffer
• single_sided_buffer($geometry, 10.5, join=3) → line buffered to the
left by 10.5 units, using a beveled join
Further reading: Single sided buffer algorithm
smooth
Smooths a geometry by adding extra nodes which round off corners in the geometry. If input geometries contain
Z or M values, these will also be smoothed and the output geometry will retain the same dimensionality as the input
geometry.
Syntax smooth(geometry, [iterations=1], [offset=0.25], [min_length=-1], [max_angle=180])
[] marks optional arguments
Arguments
• geometry - a geometry
• iterations - number of smoothing iterations to apply. Larger numbers result in smoother
but more complex geometries.
• offset - value between 0 and 0.5 which controls how tightly the smoothed geometry follow
the original geometry. Smaller values result in a tighter smoothing, larger values result in
looser smoothing.
• min_length - minimum length of segments to apply smoothing to. This parameter can be
used to avoid placing excessive additional nodes in shorter segments of the geometry.
• max_angle - maximum angle at node for smoothing to be applied (0-180). By lowering
the maximum angle intentionally sharp corners in the geometry can be preserved. For
instance, a value of 80 degrees will retain right angles in the geometry.
Examples
• geom_to_wkt(smooth(geometry:=geom_from_wkt('LineString(0
0, 5 0, 5 5)'),iterations:=1,offset:=0.2,min_length:=-1,
max_angle:=180)) → ‚LineString (0 0, 4 0, 5 1, 5 5)‘
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Further reading: Smooth algorithm
start_point
Returns the first node from a geometry.
Syntax start_point(geometry)
Arguments
• geometry - geometry object
Examples
• geom_to_wkt(start_point(geom_from_wkt('LINESTRING(4 0, 4
2, 0 2)'))) → ‚Point (4 0)‘
Further reading: Extract specific vertices algorithm
sym_difference
Returns a geometry that represents the portions of two geometries that do not intersect.
Syntax sym_difference(geometry1, geometry2)
Arguments
• geometry1 - a geometry
• geometry2 - a geometry
Examples
• geom_to_wkt( sym_difference( geom_from_wkt( 'LINESTRING(3
3, 4 4, 5 5)' ), geom_from_wkt( 'LINESTRING(3 3, 8 8)' ) )
) → ‚LINESTRING(5 5, 8 8)‘
Further reading: Symmetrical difference algorithm
tapered_buffer
Creates a buffer along a line geometry where the buffer diameter varies evenly over the length of the line.
Syntax tapered_buffer(geometry, start_width, end_width, [segments=8])
[] marks optional arguments
Arguments
• geometry - input geometry. Must be a (multi)line geometry.
• start_width - width of buffer at start of line,
• end_width - width of buffer at end of line.
• segments - number of segments to approximate quarter-circle curves in the buffer.
Examples
• tapered_buffer(geometry:=geom_from_wkt('LINESTRING(1 2, 4
2)'),start_width:=1,end_width:=2,segments:=8) → A tapered buffer
starting with a diameter of 1 and ending with a diameter of 2 along the linestring geometry.
Further reading: Tapered buffers algorithm
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touches
Tests whether a geometry touches another. Returns true if the geometries have at least one point in common, but their
interiors do not intersect.
Syntax touches(geometry1, geometry2)
Arguments
• geometry1 - a geometry
• geometry2 - a geometry
Examples
• touches( geom_from_wkt( 'LINESTRING(5 3, 4 4)' ),
geom_from_wkt( 'LINESTRING(3 3, 4 4, 5 5)' ) ) → true
• touches( geom_from_wkt( 'POINT(4 4)' ), geom_from_wkt(
'POINT(5 5)' ) ) → false
Further reading: overlay_touches
transform
Returns the geometry transformed from a source CRS to a destination CRS.
Syntax transform(geometry, source_auth_id, dest_auth_id)
Arguments
• geometry - a geometry
• source_auth_id - the source auth CRS ID
• dest_auth_id - the destination auth CRS ID
Examples
• geom_to_wkt( transform( make_point(488995.53240249,
7104473.38600835), 'EPSG:2154', 'EPSG:4326' ) ) → ‚POINT(0
51)‘
Further reading: Reproject layer algorithm
translate
Returns a translated version of a geometry. Calculations are in the Spatial Reference System of this geometry.
Syntax translate(geometry, dx, dy)
Arguments
• geometry - a geometry
• dx - delta x
• dy - delta y
Examples
• translate($geometry, 5, 10) → a geometry of the same type like the original
one
Further reading: Translate algorithm
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union
Returns a geometry that represents the point set union of the geometries.
Syntax union(geometry1, geometry2)
Arguments
• geometry1 - a geometry
• geometry2 - a geometry
Examples
• geom_to_wkt( union( make_point(4, 4), make_point(5, 5) ) )
→ ‚MULTIPOINT(4 4, 5 5)‘
wedge_buffer
Returns a wedge shaped buffer originating from a point geometry.
Syntax wedge_buffer(center, azimuth, width, outer_radius, [inner_radius=0.0])
[] marks optional arguments
Arguments
• center - center point (origin) of buffer. Must be a point geometry.
• azimuth - angle (in degrees) for the middle of the wedge to point.
• width - buffer width (in degrees). Note that the wedge will extend to half of the angular
width either side of the azimuth direction.
• outer_radius - outer radius for buffers
• inner_radius - optional inner radius for buffers
Examples
• wedge_buffer(center:=geom_from_wkt('POINT(1 2)'),
azimuth:=90,width:=180,outer_radius:=1) → A wedge shaped buffer
centered on the point (1,2), facing to the East, with a width of 180 degrees and outer
radius of 1.
Further reading: Create wedge buffers algorithm
within
Tests whether a geometry is within another. Returns true if the geometry1 is completely within geometry2.
Syntax within(geometry1, geometry2)
Arguments
• geometry1 - a geometry
• geometry2 - a geometry
Examples
• within( geom_from_wkt( 'POINT( 0.5 0.5)' ), geom_from_wkt(
'POLYGON((0 0, 0 1, 1 1, 1 0, 0 0))' ) ) → true
• within( geom_from_wkt( 'POINT( 5 5 )' ), geom_from_wkt(
'POLYGON((0 0, 0 1, 1 1, 1 0, 0 0 ))' ) ) → false
Further reading: overlay_within
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$x
Returns the x coordinate of the current point feature. If the feature is a multipoint feature, then the x-coordinate of
the first point will be returned.
Syntax $x
Examples
• $x → 42
x
Returns the x coordinate of a point geometry, or the x coordinate of the centroid for a non-point geometry.
Syntax x(geometry)
Arguments
• geometry - a geometry
Examples
• x( geom_from_wkt( 'POINT(2 5)' ) ) → 2
• x( $geometry ) → x coordinate of the current feature’s centroid
$x_at
Retrieves a x coordinate of the current feature’s geometry.
Syntax $x_at(i)
Arguments
• i - index of point of a line (indices start at 0; negative values apply from the last index,
starting at -1)
Examples
• $x_at(1) → 5
x_max
Returns the maximum x coordinate of a geometry. Calculations are in the spatial reference system of this geometry.
Syntax x_max(geometry)
Arguments
• geometry - a geometry
Examples
• x_max( geom_from_wkt( 'LINESTRING(2 5, 3 6, 4 8)') ) → 4
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x_min
Returns the minimum x coordinate of a geometry. Calculations are in the spatial reference system of this geometry.
Syntax x_min(geometry)
Arguments
• geometry - a geometry
Examples
• x_min( geom_from_wkt( 'LINESTRING(2 5, 3 6, 4 8)') ) → 2
$y
Returns the y coordinate of the current point feature. If the feature is a multipoint feature, then the y-coordinate of
the first point will be returned.
Syntax $y
Examples
• $y → 42
y
Returns the y coordinate of a point geometry, or the y coordinate of the centroid for a non-point geometry.
Syntax y(geometry)
Arguments
• geometry - a geometry
Examples
• y( geom_from_wkt( 'POINT(2 5)' ) ) → 5
• y( $geometry ) → y coordinate of the current feature’s centroid
$y_at
Retrieves a y coordinate of the current feature’s geometry.
Syntax $y_at(i)
Arguments
• i - index of point of a line (indices start at 0; negative values apply from the last index,
starting at -1)
Examples
• $y_at(1) → 2
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y_max
Returns the maximum y coordinate of a geometry. Calculations are in the spatial reference system of this geometry.
Syntax y_max(geometry)
Arguments
• geometry - a geometry
Examples
• y_max( geom_from_wkt( 'LINESTRING(2 5, 3 6, 4 8)') ) → 8
y_min
Returns the minimum y coordinate of a geometry. Calculations are in the spatial reference system of this geometry.
Syntax y_min(geometry)
Arguments
• geometry - a geometry
Examples
• y_min( geom_from_wkt( 'LINESTRING(2 5, 3 6, 4 8)') ) → 5
z
Returns the z coordinate of a point geometry, or NULL if the geometry has no z value.
Syntax z(geometry)
Arguments
• geometry - a point geometry
Examples
• z( geom_from_wkt( 'POINTZ(2 5 7)' ) ) → 7
z_max
Returns the maximum z coordinate of a geometry, or NULL if the geometry has no z value.
Syntax z_max(geometry)
Arguments
• geometry - a geometry with z coordinate
Examples
• z_max( geom_from_wkt( 'POINT ( 0 0 1 )' ) ) → 1
• z_max( geom_from_wkt( 'MULTIPOINT ( 0 0 1 , 1 1 3 )' ) ) → 3
• z_max( make_line( make_point( 0,0,0 ), make_point( -1,-1,-2
) ) ) → 0
• z_max( geom_from_wkt( 'LINESTRING( 0 0 0, 1 0 2, 1 1 -1 )'
) ) → 2
• z_max( geom_from_wkt( 'POINT ( 0 0 )' ) ) → NULL
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z_min
Returns the minimum z coordinate of a geometry, or NULL if the geometry has no z value.
Syntax z_min(geometry)
Arguments
• geometry - a geometry with z coordinate
Examples
• z_min( geom_from_wkt( 'POINT ( 0 0 1 )' ) ) → 1
• z_min( geom_from_wkt( 'MULTIPOINT ( 0 0 1 , 1 1 3 )' ) ) → 1
• z_min( make_line( make_point( 0,0,0 ), make_point( -1,-1,-2
) ) ) → -2
• z_min( geom_from_wkt( 'LINESTRING( 0 0 0, 1 0 2, 1 1 -1 )'
) ) → -1
• z_min( geom_from_wkt( 'POINT ( 0 0 )' ) ) → NULL
14.3.14 Layout Functions
This group contains functions to manipulate print layout items properties.
• item_variables
item_variables
Returns a map of variables from a layout item inside this print layout.
Syntax item_variables(id)
Arguments
• id - layout item ID
Examples
• map_get( item_variables('Map 0'), 'map_scale') → scale of the item
‚Map 0‘ in the current print layout
Further reading: List of default variables
14.3.15 Map Layers
This group contains a list of the available layers in the current project. This offers a convenient way to write expressions
referring to multiple layers, such as when performing aggregates, attribute or spatial queries.
It also provides some convenient functions to manipulate layers.
• decode_uri
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decode_uri
Takes a layer and decodes the uri of the underlying data provider. It depends on the dataprovider, which data
is available.
Syntax decode_uri(layer, [part])
[] marks optional arguments
Arguments
• layer - The layer for which the uri should be decoded.
• part - The part of the uri to return. If unspecified, a map with all uri parts will be returned.
Examples
• decode_uri(@layer) → {‚layerId‘: ‚0‘, ‚layerName‘: ‚‘, ‚path‘:
‚/home/qgis/shapefile.shp‘}
• decode_uri(@layer) → {‚layerId‘: NULL, ‚layerName‘: ‚layer‘, ‚path‘:
‚/home/qgis/geopackage.gpkg‘}
• decode_uri(@layer, 'path') → ‚C:\my_data\qgis\shape.shp‘
14.3.16 Maps Functions
This group contains functions to create or manipulate keys and values of map data structures (also known as dictionary
objects, key-value pairs, or associative arrays). Unlike the list data structure where values order matters, the order of
the key-value pairs in the map object is not relevant and values are identified by their keys.
• from_json
• hstore_to_map
• json_to_map
• map
• map_akeys
• map_avals
• map_concat
• map_delete
• map_exist
• map_get
• map_insert
• map_to_hstore
• map_to_json
• to_json
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from_json
Loads a JSON formatted string.
Syntax from_json(string)
Arguments
• string - JSON string
Examples
• from_json('{"qgis":"rocks"}') → { ‚qgis‘: ‚rocks‘ }
• from_json('[1,2,3]') → [1,2,3]
hstore_to_map
Creates a map from a hstore-formatted string.
Syntax hstore_to_map(string)
Arguments
• string - the input string
Examples
• hstore_to_map('qgis=>rocks') → { ‚qgis‘: ‚rocks‘ }
json_to_map
Creates a map from a json-formatted string.
Syntax json_to_map(string)
Arguments
• string - the input string
Examples
• json_to_map('{"qgis":"rocks"}') → { ‚qgis‘: ‚rocks‘ }
map
Returns a map containing all the keys and values passed as pair of parameters.
Syntax map(key1, value1, key2, value2, …)
Arguments
• key - a key (string)
• value - a value
Examples
• map('1','one','2', 'two') → { ‚1‘: ‚one‘, ‚2‘: ‚two‘ }
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map_akeys
Returns all the keys of a map as an array.
Syntax map_akeys(map)
Arguments • map - a map
Examples
• map_akeys(map('1','one','2','two')) → [ ‚1‘, ‚2‘ ]
map_avals
Returns all the values of a map as an array.
Syntax map_avals(map)
Arguments • map - a map
Examples
• map_avals(map('1','one','2','two')) → [ ‚one‘, ‚two‘ ]
map_concat
Returns a map containing all the entries of the given maps. If two maps contain the same key, the value of the second
map is taken.
Syntax map_concat(map1, map2, …)
Arguments • map - a map
Examples
• map_concat(map('1','one', '2','overridden'),map('2','two',
'3','three')) → { ‚1‘: ‚one‘, ‚2‘: ‚two‘, ‚3‘: ‚three‘ }
map_delete
Returns a map with the given key and its corresponding value deleted.
Syntax map_delete(map, key)
Arguments • map - a map
• key - the key to delete
Examples
• map_delete(map('1','one','2','two'),'2') → { ‚1‘: ‚one‘ }
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map_exist
Returns true if the given key exists in the map.
Syntax map_exist(map, key)
Arguments • map - a map
• key - the key to lookup
Examples
• map_exist(map('1','one','2','two'),'3') → false
map_get
Returns the value of a map, given its key. Returns NULL if the key does not exist.
Syntax map_get(map, key)
Arguments • map - a map
• key - the key to lookup
Examples
• map_get(map('1','one','2','two'),'2') → ‚two‘
• map_get( item_variables('Map 0'), 'map_scale') → scale of the item
‚Map 0‘ (if it exists) in the current print layout
map_insert
Returns a map with an added key/value. If the key already exists, its value is overridden.
Syntax map_insert(map, key, value)
Arguments • map - a map
• key - the key to add
• value - the value to add
Examples
• map_insert(map('1','one'),'3','three') → { ‚1‘: ‚one‘, ‚3‘: ‚three‘ }
• map_insert(map('1','one','2','overridden'),'2','two') → {
‚1‘: ‚one‘, ‚2‘: ‚two‘ }
map_to_hstore
Merge map elements into a hstore-formatted string.
Syntax map_to_hstore(map)
Arguments
• map - the input map
Examples
• map_to_hstore(map('qgis','rocks')) → ‚„qgis“=>“rocks“‘
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map_to_json
Merge map elements into a json-formatted string.
Syntax map_to_json(map)
Arguments
• map - the input map
Examples
• map_to_json(map('qgis','rocks')) → {„qgis“:“rocks“}
to_json
Create a JSON formatted string from a map, array or other value.
Syntax to_json(value)
Arguments
• value - The input value
Examples
• to_json(map('qgis','rocks')) → {„qgis“:“rocks“}
• to_json(array(1,2,3)) → [1,2,3]
14.3.17 Matematické funkce
Tato skupina obsahuje matematické funkce (např. odmocnina, sin a cos).
• abs
• acos
• asin
• atan
• atan2
• azimuth
• ceil
• clamp
• cos
• degrees
• exp
• floor
• inclination
• ln
• log
• log10
• max
• min
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• pi
• radians
• rand
• randf
• round
• scale_exp
• scale_linear
• sin
• sqrt
• tan
abs
Returns the absolute value of a number.
Syntax abs(value)
Arguments
• value - a number
Examples
• abs(-2) → 2
acos
Returns the inverse cosine of a value in radians.
Syntax acos(value)
Arguments
• value - cosine of an angle in radians
Examples
• acos(0.5) → 1.0471975511966
asin
Returns the inverse sine of a value in radians.
Syntax asin(value)
Arguments
• value - sine of an angle in radians
Examples
• asin(1.0) → 1.5707963267949
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atan
Returns the inverse tangent of a value in radians.
Syntax atan(value)
Arguments
• value - tan of an angle in radians
Examples
• atan(0.5) → 0.463647609000806
atan2
Returns the inverse tangent of dy/dx by using the signs of the two arguments to determine the quadrant of the result.
Syntax atan2(dy, dx)
Arguments
• dy - y coordinate difference
• dx - x coordinate difference
Examples
• atan2(1.0, 1.732) → 0.523611477769969
azimuth
Returns the north-based azimuth as the angle in radians measured clockwise from the vertical on point_a to point_b.
Syntax azimuth(point_a, point_b)
Arguments
• point_a - point geometry
• point_b - point geometry
Examples
• degrees( azimuth( make_point(25, 45), make_point(75, 100)
) ) → 42.273689
• degrees( azimuth( make_point(75, 100), make_point(25,45) )
) → 222.273689
ceil
Rounds a number upwards.
Syntax ceil(value)
Arguments
• value - a number
Examples
• ceil(4.9) → 5
• ceil(-4.9) → -4
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clamp
Restricts an input value to a specified range.
Syntax clamp(minimum, input, maximum)
Arguments
• minimum - the smallest value input is allowed to take.
• input - a value which will be restricted to the range specified by minimum and maximum
• maximum - the largest value input is allowed to take
Examples
• clamp(1,5,10) → 5
input is between 1 and 10 so is returned unchanged
• clamp(1,0,10) → 1
input is less than minimum value of 1, so function returns 1
• clamp(1,11,10) → 10
input is greater than maximum value of 10, so function returns 10
cos
Returns cosine of an angle.
Syntax cos(angle)
Arguments
• angle - angle in radians
Examples
• cos(1.571) → 0.000796326710733263
degrees
Converts from radians to degrees.
Syntax degrees(radians)
Arguments
• radians - numeric value
Examples
• degrees(3.14159) → 180
• degrees(1) → 57.2958
exp
Returns exponential of an value.
Syntax exp(value)
Arguments
• value - number to return exponent of
Examples
• exp(1.0) → 2.71828182845905
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floor
Rounds a number downwards.
Syntax floor(value)
Arguments
• value - a number
Examples
• floor(4.9) → 4
• floor(-4.9) → -5
inclination
Returns the inclination measured from the zenith (0) to the nadir (180) on point_a to point_b.
Syntax inclination(point_a, point_b)
Arguments
• point_a - point geometry
• point_b - point geometry
Examples
• inclination( make_point( 5, 10, 0 ), make_point( 5, 10, 5
) ) → 0.0
• inclination( make_point( 5, 10, 0 ), make_point( 5, 10, 0
) ) → 90.0
• inclination( make_point( 5, 10, 0 ), make_point( 50, 100,
0 ) ) → 90.0
• inclination( make_point( 5, 10, 0 ), make_point( 5, 10, -5
) ) → 180.0
ln
Returns the natural logarithm of a value.
Syntax ln(value)
Arguments
• value - numeric value
Examples
• ln(1) → 0
• ln(2.7182818284590452354) → 1
log
Returns the value of the logarithm of the passed value and base.
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Syntax log(base, value)
Arguments
• base - any positive number
• value - any positive number
Examples
• log(2, 32) → 5
• log(0.5, 32) → -5
log10
Returns the value of the base 10 logarithm of the passed expression.
Syntax log10(value)
Arguments
• value - any positive number
Examples
• log10(1) → 0
• log10(100) → 2
max
Returns the largest value in a set of values.
Syntax max(value1, value2, …)
Arguments
• value - a number
Examples
• max(2,10.2,5.5) → 10.2
• max(20.5,NULL,6.2) → 20.5
min
Returns the smallest value in a set of values.
Syntax min(value1, value2, …)
Arguments
• value - a number
Examples
• min(20.5,10,6.2) → 6.2
• min(2,-10.3,NULL) → -10.3
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pi
Returns value of pi for calculations.
Syntax pi()
Examples
• pi() → 3.14159265358979
radians
Converts from degrees to radians.
Syntax radians(degrees)
Arguments
• degrees - numeric value
Examples
• radians(180) → 3.14159
• radians(57.2958) → 1
rand
Returns a random integer within the range specified by the minimum and maximum argument (inclusive). If a seed
is provided, the returned will always be the same, depending on the seed.
Syntax rand(min, max, [seed=NULL])
[] marks optional arguments
Arguments
• min - an integer representing the smallest possible random number desired
• max - an integer representing the largest possible random number desired
• seed - any value to use as seed
Examples
• rand(1, 10) → 8
randf
Returns a random float within the range specified by the minimum and maximum argument (inclusive). If a seed
is provided, the returned will always be the same, depending on the seed.
Syntax randf([min=0.0], [max=1.0], [seed=NULL])
[] marks optional arguments
Arguments
• min - an float representing the smallest possible random number desired
• max - an float representing the largest possible random number desired
• seed - any value to use as seed
Examples
• randf(1, 10) → 4.59258286403147
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round
Rounds a number to number of decimal places.
Syntax round(value, [places=0])
[] marks optional arguments
Arguments
• value - decimal number to be rounded
• places - Optional integer representing number of places to round decimals to. Can be
negative.
Examples
• round(1234.567, 2) → 1234.57
• round(1234.567) → 1235
scale_exp
Transforms a given value from an input domain to an output range using an exponential curve. This function can be
used to ease values in or out of the specified output range.
Syntax scale_exp(value, domain_min, domain_max, range_min, range_max, exponent)
Arguments
• value - A value in the input domain. The function will return a corresponding scaled value
in the output range.
• domain_min - Specifies the minimum value in the input domain, the smallest value the
input value should take.
• domain_max - Specifies the maximum value in the input domain, the largest value the
input value should take.
• range_min - Specifies the minimum value in the output range, the smallest value which
should be output by the function.
• range_max - Specifies the maximum value in the output range, the largest value which
should be output by the function.
• exponent - A positive value (greater than 0), which dictates the way input values are
mapped to the output range. Large exponents will cause the output values to ‚ease in‘,
starting slowly before accelerating as the input values approach the domain maximum.
Smaller exponents (less than 1) will cause output values to ‚ease out‘, where the mapping
starts quickly but slows as it approaches the domain maximum.
Examples
• scale_exp(5,0,10,0,100,2) → 25
easing in, using an exponent of 2
• scale_exp(3,0,10,0,100,0.5) → 54.772
easing out, using an exponent of 0.5
scale_linear
Transforms a given value from an input domain to an output range using linear interpolation.
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Syntax scale_linear(value, domain_min, domain_max, range_min, range_max)
Arguments
• value - A value in the input domain. The function will return a corresponding scaled value
in the output range.
• domain_min - Specifies the minimum value in the input domain, the smallest value the
input value should take.
• domain_max - Specifies the maximum value in the input domain, the largest value the
input value should take.
• range_min - Specifies the minimum value in the output range, the smallest value which
should be output by the function.
• range_max - Specifies the maximum value in the output range, the largest value which
should be output by the function.
Examples
• scale_linear(5,0,10,0,100) → 50
• scale_linear(0.2,0,1,0,360) → 72
scaling a value between 0 and 1 to an angle between 0 and 360
• scale_linear(1500,1000,10000,9,20) → 9.6111111
scaling a population which varies between 1000 and 10000 to a font size between 9 and
20
sin
Returns the sine of an angle.
Syntax sin(angle)
Arguments
• angle - angle in radians
Examples
• sin(1.571) → 0.999999682931835
sqrt
Returns square root of a value.
Syntax sqrt(value)
Arguments
• value - a number
Examples
• sqrt(9) → 3
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tan
Returns the tangent of an angle.
Syntax tan(angle)
Arguments
• angle - angle in radians
Examples
• tan(1.0) → 1.5574077246549
14.3.18 Operátory
This group contains operators (e.g., +, -, *). Note that for most of the mathematical functions below, if one of the
inputs is NULL then the result is NULL.
Function Popis
a + b Addition of two values (a plus b)
a - b Subtraction of two values (a minus b).
a * b Multiplication of two values (a multiplied by b)
a / b Division of two values (a divided by b)
a % b Remainder of division of a by b (eg, 7 % 2 = 1, or 2 fits into 7 three times with
remainder 1)
a ^ b Power of two values (for example, 2^2=4 or 2^3=8)
a < b Compares two values and evaluates to 1 if the left value is less than the right
value (a is smaller than b)
a <= b Compares two values and evaluates to 1 if the left value is less than or equal to
the right value
a <> b Compares two values and evaluates to 1 if they are not equal
a = b Compares two values and evaluates to 1 if they are equal
a != b a and b are not equal
a > b Compares two values and evaluates to 1 if the left value is greater than the right
value (a is larger than b)
a >= b Compares two values and evaluates to 1 if the left value is greater than or equal
to the right value
a ~ b a matches the regular expression b
|| Joins two values together into a string. If one of the values is NULL the result
will be NULL
‚\n‘ Inserts a new line in a string
LIKE Returns 1 if the first parameter matches the supplied pattern
ILIKE Returns 1 if the first parameter matches case-insensitive the supplied pattern
(ILIKE can be used instead of LIKE to make the match case-insensitive)
a IS b Tests whether two values are identical. Returns 1 if a is the same as b
a OR b Returns 1 when condition a or condition b is true
a AND b Returns 1 when conditions a and b are true
NOT Negates a condition
„Column_name“ Value of the field Column_name, take care to not be confused with simple quote,
see below
‚string‘ a string value, take care to not be confused with double quote, see above
NULL null value
a IS NULL a has no value
a IS NOT NULL a has a value
a IN (value[,value]) a is below the values listed
a NOT IN (value[,value]) a is not below the values listed
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Některé příklady:
• Připojí řetězec a hodnotu z názvu sloupce:
'My feature''s id is: ' || "gid"
• Test if the „description“ attribute field starts with the ‚Hello‘ string in the value (note the position of the %
character):
"description" LIKE 'Hello%'
14.3.19 Processing Functions
This group contains functions that operate on processing algorithms.
• parameter
parameter
Returns the value of a processing algorithm input parameter.
Syntax parameter(name)
Arguments
• name - name of the corresponding input parameter
Examples
• parameter('BUFFER_SIZE') → 5.6
14.3.20 Rasters Functions
This group contains functions to operate on raster layer.
• raster_statistic
• raster_value
raster_statistic
Returns statistics from a raster layer.
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Syntax raster_statistic(layer, band, property)
Arguments
• layer - a string, representing either a raster layer name or layer ID
• band - integer representing the band number from the raster layer, starting at 1
• property - a string corresponding to the property to return. Valid options are:
– min: minimum value
– max: maximum value
– avg: average (mean) value
– stdev: standard deviation of values
– range: range of values (max - min)
– sum: sum of all values from raster
Examples
• raster_statistic('lc',1,'avg') → Average value from band 1 from ‚lc‘
raster layer
• raster_statistic('ac2010',3,'min') → Minimum value from band 3 from
‚ac2010‘ raster layer
raster_value
Returns the raster value found at the provided point.
Syntax raster_value(layer, band, point)
Arguments
• layer - the name or id of a raster layer
• band - the band number to sample the value from.
• point - point geometry (for multipart geometries having more than one part, a NULL
value will be returned)
Examples
• raster_value('dem', 1, make_point(1,1)) → 25
14.3.21 Record and Attributes Functions
Tato skupina obsahuje funkce, které operují se záznamy identifikátorů.
• attribute
• attributes
• $currentfeature
• display_expression
• get_feature
• get_feature_by_id
• $id
• is_selected
• maptip
• num_selected
• represent_value
• sqlite_fetch_and_increment
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• uuid
attribute
Returns an attribute from a feature.
Variant 1
Returns the value of an attribute from the current feature.
Syntax attribute(attribute_name)
Arguments
• attribute_name - name of attribute to be returned
Examples
• attribute( 'name' ) → value stored in ‚name‘ attribute for the current feature
Variant 2
Allows the target feature and attribute name to be specified.
Syntax attribute(feature, attribute_name)
Arguments
• feature - a feature
• attribute_name - name of attribute to be returned
Examples
• attribute( @atlas_feature, 'name' ) → value stored in ‚name‘ attribute
for the current atlas feature
attributes
Returns a map containing all attributes from a feature, with field names as map keys.
Variant 1
Returns a map of all attributes from the current feature.
Syntax attributes()
Examples
• attributes()['name'] → value stored in ‚name‘ attribute for the current feature
Variant 2
Allows the target feature to be specified.
Syntax attributes(feature)
Arguments
• feature - a feature
Examples
• attributes( @atlas_feature )['name'] → value stored in ‚name‘ attribute
for the current atlas feature
Further reading: Maps Functions
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$currentfeature
Returns the current feature being evaluated. This can be used with the ‚attribute‘ function to evaluate attribute values
from the current feature.
Syntax $currentfeature
Examples
• attribute( $currentfeature, 'name' ) → value stored in ‚name‘ attribute
for the current feature
display_expression
Returns the display expression for a given feature in a layer. The expression is evaluated by default. Can be used with
zero, one or more arguments, see below for details.
No parameters
If called with no parameters, the function will evaluate the display expression of the current feature in the current
layer.
Syntax display_expression()
Examples
• display_expression() → The display expression of the current feature in the
current layer.
One ‚feature‘ parameter
If called with a ‚feature‘ parameter only, the function will evaluate the specified feature from the current layer.
Syntax display_expression(feature)
Arguments
• feature - The feature which should be evaluated.
Examples
• display_expression(@atlas_feature) → The display expression of the
current atlas feature.
Layer and feature parameters
If the function is called with both a layer and a feature, it will evaluate the specified feature from the specified layer.
Syntax display_expression(layer, feature, [evaluate=true])
[] marks optional arguments
Arguments
• layer - The layer (or its ID or name)
• feature - The feature which should be evaluated.
• evaluate - If the expression must be evaluated. If false, the expression will be returned
as a string literal only (which could potentially be later evaluated using the ‚eval‘ function).
Examples
• display_expression( 'streets', get_feature_by_id('streets',
1)) → The display expression of the feature with the ID 1 on the layer ‚streets‘.
• display_expression('a_layer_id', $currentfeature, 'False')
→ The display expression of the given feature not evaluated.
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get_feature
Returns the first feature of a layer matching a given attribute value.
Syntax get_feature(layer, attribute, value)
Arguments
• layer - layer name or ID
• attribute - attribute name
• value - attribute value to match
Examples
• get_feature('streets','name','main st') → first feature found in
„streets“ layer with „main st“ value in the „name“ field
get_feature_by_id
Returns the feature with an id on a layer.
Syntax get_feature_by_id(layer, feature_id)
Arguments
• layer - layer, layer name or layer id
• feature_id - the id of the feature which should be returned
Examples
• get_feature_by_id('streets', 1) → the feature with the id 1 on the layer
„streets“
Further reading: $id
$id
Returns the feature id of the current row.
Syntax $id
Examples
• $id → 42
is_selected
Returns True if a feature is selected. Can be used with zero, one or two arguments, see below for details.
No parameters
If called with no parameters, the function will return true if the current feature in the current layer is selected.
Syntax is_selected()
Examples
• is_selected() → True if the current feature in the current layer is selected.
One ‚feature‘ parameter
If called with a ‚feature‘ parameter only, the function returns true if the specified feature from the current layer
is selected.
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Syntax is_selected(feature)
Arguments
• feature - The feature which should be checked for selection.
Examples
• is_selected(@atlas_feature) → True if a selected feature on the current layer
is the active atlas feature.
• is_selected(get_feature(@layer, 'name', 'Main St.'))) → True
if the unique named „Main St.“ feature on the current layer is selected.
• is_selected(get_feature_by_id(@layer, 1)) → True if the feature with
the id 1 on the current layer is selected.
Two parameters
If the function is called with both a layer and a feature, it will return true if the specified feature from the specified
layer is selected.
Syntax is_selected(layer, feature)
Arguments
• layer - The layer (its ID or name) on which the selection will be checked.
• feature - The feature which should be checked for selection.
Examples
• is_selected( 'streets', get_feature('streets', 'name',
"street_name")) → True if the current building’s street is selected (assuming the
building layer has a field named ‚street_name‘ and the ‚streets‘ layer has a field called ‚name‘
with unique values).
• is_selected( 'streets', get_feature_by_id('streets', 1)) →
True if the feature with the id 1 on the „streets“ layer is selected.
maptip
Returns the maptip for a given feature in a layer. The expression is evaluated by default. Can be used with zero, one
or more arguments, see below for details.
No parameters
If called with no parameters, the function will evaluate the maptip of the current feature in the current layer.
Syntax maptip()
Examples
• maptip() → The maptip of the current feature in the current layer.
One ‚feature‘ parameter
If called with a ‚feature‘ parameter only, the function will evaluate the specified feature from the current layer.
Syntax maptip(feature)
Arguments
• feature - The feature which should be evaluated.
Examples
• maptip(@atlas_feature) → The maptip of the current atlas feature.
Layer and feature parameters
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If the function is called with both a layer and a feature, it will evaluate the specified feature from the specified layer.
Syntax maptip(layer, feature, [evaluate=true])
[] marks optional arguments
Arguments
• layer - The layer (or its ID or name)
• feature - The feature which should be evaluated.
• evaluate - If the expression must be evaluated. If false, the expression will be returned
as a string literal only (which could potentially be later evaluated using the ‚eval_template‘
function).
Examples
• maptip('streets', get_feature_by_id('streets', 1)) → The
maptip of the feature with the ID 1 on the layer ‚streets‘.
• maptip('a_layer_id', $currentfeature, 'False') → The maptip of
the given feature not evaluated.
num_selected
Returns the number of selected features on a given layer. By default works on the layer on which the expression
is evaluated.
Syntax num_selected([layer=current layer])
[] marks optional arguments
Arguments
• layer - The layer (or its id or name) on which the selection will be checked.
Examples
• num_selected() → The number of selected features on the current layer.
• num_selected('streets') → The number of selected features on the layer streets
represent_value
Returns the configured representation value for a field value. It depends on the configured widget type. Often, this
is useful for ‚Value Map‘ widgets.
Syntax represent_value(value, fieldName)
Arguments
• value - The value which should be resolved. Most likely a field.
• fieldName - The field name for which the widget configuration should be loaded.
(Optional)
Examples
• represent_value("field_with_value_map") → Description for value
• represent_value('static value', 'field_name') → Description for
static value
Further reading: widget types
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sqlite_fetch_and_increment
Manage autoincrementing values in sqlite databases.
SQlite default values can only be applied on insert and not prefetched.
This makes it impossible to acquire an incremented primary key via AUTO_INCREMENT before creating the row
in the database. Sidenote: with postgres, this works via the option evaluate default values.
When adding new features with relations, it is really nice to be able to already add children for a parent, while the
parents form is still open and hence the parent feature uncommitted.
To get around this limitation, this function can be used to manage sequence values in a separate table on sqlite based
formats like gpkg.
The sequence table will be filtered for a sequence id (filter_attribute and filter_value) and the current value of the
id_field will be incremented by 1 and the incremented value returned.
If additional columns require values to be specified, the default_values map can be used for this purpose.
Note
This function modifies the target sqlite table. It is intended for usage with default value configurations for attributes.
When the database parameter is a layer and the layer is in transaction mode, the value will only be retrieved once
during the lifetime of a transaction and cached and incremented. This makes it unsafe to work on the same database
from several processes in parallel.
Syntax sqlite_fetch_and_increment(database, table, id_field, filter_attribute, filter_value,
[default_values])
[] marks optional arguments
Arguments
• database - Path to the sqlite file or geopackage layer
• table - Name of the table that manages the sequences
• id_field - Name of the field that contains the current value
• filter_attribute - Name the field that contains a unique identifier for this sequence. Must
have a UNIQUE index.
• filter_value - Name of the sequence to use.
• default_values - Map with default values for additional columns on the table. The values
need to be fully quoted. Functions are allowed.
Examples
• sqlite_fetch_and_increment(@layer, 'sequence_table',
'last_unique_id', 'sequence_id', 'global',
map('last_change', 'date(''now'')', 'user', '''' ||
@user_account_name || '''')) → 0
• sqlite_fetch_and_increment(layer_property(@layer, 'path'),
'sequence_table', 'last_unique_id', 'sequence_id',
'global', map('last_change', 'date(''now'')', 'user',
'''' || @user_account_name || '''')) → 0
Further reading: Data Sources Properties, Creating one or many to many relations
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uuid
Generates a Universally Unique Identifier (UUID) for each row using the Qt QUuid::createUuid method. Each UUID
is 38 characters long.
Syntax uuid()
Examples
• uuid() → ‚{0bd2f60f-f157-4a6d-96af-d4ba4cb366a1}‘
14.3.22 Relations
This group contains the list of the relations available in the current project, with their description. It provides a quick
access to the relation ID for writing an expression (with e.g. the relation_aggregate function) or customizing a form.
14.3.23 Funkce řetězců
Tato skupina obsahuje funkce, které pracují s řetězci (např. které nahrazují, převádí na velká písmena).
• ascii
• char
• concat
• format
• format_date
• format_number
• left
• length
• lower
• lpad
• regexp_match
• regexp_replace
• regexp_substr
• replace
• right
• rpad
• strpos
• substr
• title
• to_string
• trim
• upper
• wordwrap
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ascii
Returns the unicode code associated with the first character of a string.
Syntax ascii(string)
Arguments
• string - the string to convert to unicode code
Examples
• ascii('Q') → 81
char
Returns the character associated with a unicode code.
Syntax char(code)
Arguments
• code - a unicode code number
Examples
• char(81) → ‚Q‘
concat
Concatenates several strings to one. NULL values are converted to empty strings. Other values (like numbers) are
converted to strings.
Syntax concat(string1, string2, …)
Arguments
• string - a string value
Examples
• concat('sun', 'set') → ‚sunset‘
• concat('a','b','c','d','e') → ‚abcde‘
• concat('Anno ', 1984) → ‚Anno 1984‘
• concat('The Wall', NULL) → ‚The Wall‘
About fields concatenation
You can also concatenate strings or field values using either || or + operators, with some special characteristics:
• The + operator also means sum up expression, so if you have an integer (field or numeric value) operand, this
can be error prone and you better use the others:
'My feature id is: ' + "gid" => triggers an error as gid returns an integer
• When any of the arguments is a NULL value, either || or + will return a NULL value. To return the other
arguments regardless the NULL value, you may want to use the concat function:
'My feature id is: ' + NULL ==> NULL
'My feature id is: ' || NULL => NULL
concat('My feature id is: ', NULL) => 'My feature id is: '
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format
Format a string using supplied arguments.
Syntax format(string, arg1, arg2, …)
Arguments
• string - A string with place holders for the arguments. Use %1, %2, etc for placeholders.
Placeholders can be repeated.
• arg - any type. Any number of arguments.
Examples
• format('This %1 a %2','is', 'test') → ‚This is a test‘
format_date
Formats a date type or string into a custom string format. Uses Qt date/time format strings. See QDateTime::toString.
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Syntax format_date(datetime, format, [language])
[] marks optional arguments
Arguments
• datetime - date, time or datetime value
• format - String template used to format the string.
Výraz Output
d the day as number without a leading zero (1 to 31)
dd the day as number with a leading zero (01 to 31)
ddd the abbreviated localized day name (e.g. ‚Mon‘ to ‚Sun‘)
dddd the long localized day name (e.g. ‚Monday‘ to ‚Sunday‘)
M the month as number without a leading zero (1-12)
MM the month as number with a leading zero (01-12)
MMM the abbreviated localized month name (e.g. ‚Jan‘ to ‚Dec‘)
MMMM the long localized month name (e.g. ‚January‘ to ‚December‘)
yy the year as two digit number (00-99)
yyyy the year as four digit number
These expressions may be used for the time part of the format string:
Výraz Output
h the hour without a leading zero (0 to 23 or 1 to 12 if AM/PM display)
hh the hour with a leading zero (00 to 23 or 01 to 12 if AM/PM display)
H the hour without a leading zero (0 to 23, even with AM/PM display)
HH the hour with a leading zero (00 to 23, even with AM/PM display)
m the minute without a leading zero (0 to 59)
mm the minute with a leading zero (00 to 59)
s the second without a leading zero (0 to 59)
ss the second with a leading zero (00 to 59)
z the milliseconds without trailing zeroes (0 to 999)
zzz the milliseconds with trailing zeroes (000 to 999)
AP or A interpret as an AM/PM time. AP must be either ‚AM‘ or ‚PM‘.
ap or a Interpret as an AM/PM time. ap must be either ‚am‘ or ‚pm‘.
• language - language (lowercase, two- or three-letter, ISO 639 language code) used to
format the date into a custom string
Examples
• format_date('2012-05-15','dd.MM.yyyy') → ‚15.05.2012‘
• format_date('2012-05-15','d MMMM yyyy','fr') → ‚15 mai 2012‘
• format_date('2012-05-15','dddd') → ‚Tuesday‘
• format_date('2012-05-15 13:54:20','dd.MM.yy') → ‚15.05.12‘
• format_date('13:54:20','hh:mm AP') → ‚01:54 PM‘
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format_number
Returns a number formatted with the locale separator for thousands. Also truncates the decimal places to the number
of supplied places.
Syntax format_number(number, places, [language])
[] marks optional arguments
Arguments
• number - number to be formatted
• places - integer representing the number of decimal places to truncate the string to.
• language - language (lowercase, two- or three-letter, ISO 639 language code) used to
format the number into a string
Examples
• format_number(10000000.332,2) → ‚10,000,000.33‘
• format_number(10000000.332,2,'fr') → ‚10 000 000,33‘
left
Returns a substring that contains the n leftmost characters of the string.
Syntax left(string, length)
Arguments
• string - a string
• length - integer. The number of characters from the left of the string to return.
Examples
• left('Hello World',5) → ‚Hello‘
length
Returns the number of characters in a string or the length of a geometry linestring.
String variant
Returns the number of characters in a string.
Syntax length(string)
Arguments
• string - string to count length of
Examples
• length('hello') → 5
Geometry variant
Calculate the length of a geometry line object. Calculations are always planimetric in the Spatial Reference System
(SRS) of this geometry, and the units of the returned length will match the units for the SRS. This differs from the
calculations performed by the $length function, which will perform ellipsoidal calculations based on the project’s
ellipsoid and distance unit settings.
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Syntax length(geometry)
Arguments
• geometry - line geometry object
Examples
• length(geom_from_wkt('LINESTRING(0 0, 4 0)')) → 4.0
lower
Converts a string to lower case letters.
Syntax lower(string)
Arguments
• string - the string to convert to lower case
Examples
• lower('HELLO World') → ‚hello world‘
lpad
Returns a string padded on the left to the specified width, using a fill character. If the target width is smaller than the
string’s length, the string is truncated.
Syntax lpad(string, width, fill)
Arguments
• string - string to pad
• width - length of new string
• fill - character to pad the remaining space with
Examples
• lpad('Hello', 10, 'x') → ‚xxxxxHello‘
• lpad('Hello', 3, 'x') → ‚Hel‘
regexp_match
Return the first matching position matching a regular expression within an unicode string, or 0 if the substring is not
found.
Syntax regexp_match(input_string, regex)
Arguments
• input_string - the string to test against the regular expression
• regex - The regular expression to test against. Backslash characters must be double escaped
(e.g., „\\s“ to match a white space character or „\\b“ to match a word boundary).
Examples
• regexp_match('QGIS ROCKS','\\sROCKS') → 5
• regexp_match('Budač','udač\\b') → 2
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regexp_replace
Returns a string with the supplied regular expression replaced.
Syntax regexp_replace(input_string, regex, replacement)
Arguments
• input_string - the string to replace matches in
• regex - The regular expression to replace. Backslash characters must be double escaped
(e.g., „\\s“ to match a white space character).
• replacement - The string that will replace any matching occurrences of the supplied
regular expression. Captured groups can be inserted into the replacement string using \\1,
\\2, etc.
Examples
• regexp_replace('QGIS SHOULD ROCK','\\sSHOULD\\s',' DOES ')
→ ‚QGIS DOES ROCK‘
• regexp_replace('ABC123','\\d+','') → ‚ABC‘
• regexp_replace('my name is John','(.*) is (.*)','\\2 is \\
1') → ‚John is my name‘
regexp_substr
Returns the portion of a string which matches a supplied regular expression.
Syntax regexp_substr(input_string, regex)
Arguments
• input_string - the string to find matches in
• regex - The regular expression to match against. Backslash characters must be double
escaped (e.g., „\\s“ to match a white space character).
Examples
• regexp_substr('abc123','(\\d+)') → ‚123‘
replace
Returns a string with the supplied string, array, or map of strings replaced.
String & array variant
Returns a string with the supplied string or array of strings replaced by a string or an array of strings.
Syntax replace(string, before, after)
Arguments
• string - the input string
• before - the string or array of strings to replace
• after - the string or array of strings to use as a replacement
Examples
• replace('QGIS SHOULD ROCK','SHOULD','DOES') → ‚QGIS DOES
ROCK‘
• replace('QGIS ABC',array('A','B','C'),array('X','Y','Z'))
→ ‚QGIS XYZ‘
• replace('QGIS',array('Q','S'),'') → ‚GI‘
Map variant
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Returns a string with the supplied map keys replaced by paired values.
Syntax replace(string, map)
Arguments
• string - the input string
• map - the map containing keys and values
Examples
• replace('APP SHOULD ROCK',map('APP','QGIS','SHOULD',
'DOES')) → ‚QGIS DOES ROCK‘
right
Returns a substring that contains the n rightmost characters of the string.
Syntax right(string, length)
Arguments
• string - a string
• length - integer. The number of characters from the right of the string to return.
Examples
• right('Hello World',5) → ‚World‘
rpad
Returns a string padded on the right to the specified width, using a fill character. If the target width is smaller than
the string’s length, the string is truncated.
Syntax rpad(string, width, fill)
Arguments
• string - string to pad
• width - length of new string
• fill - character to pad the remaining space with
Examples
• rpad('Hello', 10, 'x') → ‚Helloxxxxx‘
• rpad('Hello', 3, 'x') → ‚Hel‘
strpos
Return the first matching position of a substring within another string, or 0 if the substring is not found.
Syntax strpos(haystack, needle)
Arguments
• haystack - string that is to be searched
• needle - string to search for
Examples
• strpos('HELLO WORLD','WORLD') → 7
• strpos('HELLO WORLD','GOODBYE') → 0
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substr
Returns a part of a string.
Syntax substr(string, start, [length])
[] marks optional arguments
Arguments
• string - the full input string
• start - integer representing start position to extract beginning with 1; if start is negative,
the return string will begin at the end of the string minus the start value
• length - integer representing length of string to extract; if length is negative, the return
string will omit the given length of characters from the end of the string
Examples
• substr('HELLO WORLD',3,5) → ‚LLO W‘
• substr('HELLO WORLD',6) → ‚ WORLD‘
• substr('HELLO WORLD',-5) → ‚WORLD‘
• substr('HELLO',3,-1) → ‚LL‘
• substr('HELLO WORLD',-5,2) → ‚WO‘
• substr('HELLO WORLD',-5,-1) → ‚WORL‘
title
Converts all words of a string to title case (all words lower case with leading capital letter).
Syntax title(string)
Arguments
• string - the string to convert to title case
Examples
• title('hello WOrld') → ‚Hello World‘
to_string
Converts a number to string.
Syntax to_string(number)
Arguments
• number - Integer or real value. The number to convert to string.
Examples
• to_string(123) → ‚123‘
trim
Removes all leading and trailing whitespace (spaces, tabs, etc) from a string.
Syntax trim(string)
Arguments
• string - string to trim
Examples
• trim(' hello world ') → ‚hello world‘
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upper
Converts a string to upper case letters.
Syntax upper(string)
Arguments
• string - the string to convert to upper case
Examples
• upper('hello WOrld') → ‚HELLO WORLD‘
wordwrap
Returns a string wrapped to a maximum/minimum number of characters.
Syntax wordwrap(string, wrap_length, [delimiter_string])
[] marks optional arguments
Arguments
• string - the string to be wrapped
• wrap_length - an integer. If wrap_length is positive the number represents the ideal
maximum number of characters to wrap; if negative, the number represents the minimum
number of characters to wrap.
• delimiter_string - Optional delimiter string to wrap to a new line.
Examples
• wordwrap('UNIVERSITY OF QGIS',13) → ‚UNIVERSITY OF<br>QGIS‘
• wordwrap('UNIVERSITY OF QGIS',-3) → ‚UNIVERSITY<br>OF QGIS‘
14.3.24 User Expressions
This group contains the expressions saved as user expressions.
14.3.25 Variables
This group contains dynamic variables related to the application, the project file and other settings. The availability
of variables depends on the context:
• from the Select by expression
dialog
• from the Field calculator
dialog
• from the layer properties dialog
• from the print layout
To use these variables in an expression, they should be preceded by the @ character (e.g, @row_number).
Variable Popis
algorithm_id The unique ID of an algorithm
animation_end_time End of the animation’s overall temporal time range (as a datetime value)
animation_interval Duration of the animation’s overall temporal time range (as an interval value)
animation_start_time Start of the animation’s overall temporal time range (as a datetime value)
atlas_feature The current atlas feature (as feature object)
atlas_featureid The current atlas feature ID
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Variable Popis
atlas_featurenumber The current atlas feature number in the layout
atlas_filename The current atlas file name
atlas_geometry The current atlas feature geometry
atlas_layerid The current atlas coverage layer ID
atlas_layername The current atlas coverage layer name
atlas_pagename The current atlas page name
atlas_totalfeatures The total number of features in atlas
canvas_cursor_point The last cursor position on the canvas in the project’s geographical coordinates
cluster_color The color of symbols within a cluster, or NULL if symbols have mixed colors
cluster_size The number of symbols contained within a cluster
current_feature The feature currently being edited in the attribute form or table row
current_geometry The geometry of the feature currently being edited in the form or the table row
current_parent_feature represents the feature currently being edited in the parent form. Only usable in an
embedded form context.
current_parent_geometry represents the geometry of the feature currently being edited in the parent form.
Only usable in an embedded form context.
form_mode What the form is used for, like AddFeatureMode, SingleEditMode,
MultiEditMode, SearchMode, AggregateSearchMode or IdentifyMode as string.
frame_duration Temporal duration of each animation frame (as an interval value)
frame_number Current frame number during animation playback
frame_rate Number of frames per second during animation playback
fullextent_maxx Maximum x value from full canvas extent (including all layers)
fullextent_maxy Maximum y value from full canvas extent (including all layers)
fullextent_minx Minimum x value from full canvas extent (including all layers)
fullextent_miny Minimum y value from full canvas extent (including all layers)
geometry_part_count The number of parts in rendered feature’s geometry
geometry_part_num The current geometry part number for feature being rendered
geometry_point_count The number of points in the rendered geometry’s part
geometry_point_num The current point number in the rendered geometry’s part
grid_axis The current grid annotation axis (eg, ‚x‘ for longitude, ‚y‘ for latitude)
grid_number The current grid annotation value
item_id The layout item user ID (not necessarily unique)
item_uuid The layout item unique ID
layer The current layer
layer_id The ID of current layer
layer_ids The IDs of all the map layers in the current project as a list
layer_name The name of current layer
layers All the map layers in the current project as a list
layout_dpi The composition resolution (DPI)
layout_name The layout name
layout_numpages The number of pages in the layout
layout_page The page number of the current item in the layout
layout_pageheight The active page height in the layout (in mm)
layout_pagewidth The active page width in the layout (in mm)
legend_column_count The number of columns in the legend
legend_filter_by_map Indicates if the content of the legend is filtered by the map
legend_filter_out_atlas Indicates if the atlas is filtered out of the legend
legend_split_layers Indicates if layers can be split in the legend
legend_title The title of the legend
legend_wrap_string The character(s) used to wrap the legend text
map_crs The Coordinate reference system of the current map
map_crs_acronym The acronym of the Coordinate reference system of the current map
map_crs_definition The full definition of the Coordinate reference system of the current map
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Variable Popis
map_crs_description The name of the Coordinate reference system of the current map
map_crs_ellipsoid The acronym of the ellipsoid of the Coordinate reference system of the current map
map_crs_proj4 The Proj4 definition of the Coordinate reference system of the current map
map_crs_wkt The WKT definition of the Coordinate reference system of the current map
map_end_time The end of the map’s temporal time range (as a datetime value)
map_extent The geometry representing the current extent of the map
map_extent_center The point feature at the center of the map
map_extent_height The current height of the map
map_extent_width The current width of the map
map_id The ID of current map destination. This will be ‚canvas‘ for canvas renders, and the
item ID for layout map renders
map_interval The duration of the map’s temporal time range (as an interval value)
map_layer_ids The list of map layer IDs visible in the map
map_layers The list of map layers visible in the map
map_rotation The current rotation of the map
map_scale The current scale of the map
map_start_time The start of the map’s temporal time range (as a datetime value)
map_units The units of map measurements
model_path Full path (including file name) of current model (or project path if model
is embedded in a project).
model_folder Folder containing current model (or project folder if model is embedded in
a project).
model_name Name of current model
model_group Group for current model
notification_message Content of the notification message sent by the provider (available only for actions
triggered by provider notifications).
parent Refers to the current feature in the parent layer, providing access to its attributes
and geometry when filtering an aggregate function
project_abstract The project abstract, taken from project metadata
project_area_units The area unit for the current project, used when calculating areas of geometries
project_author The project author, taken from project metadata
project_basename The basename of current project’s filename (without path and extension)
project_creation_date The project creation date, taken from project metadata
project_crs The Coordinate reference system of the project
project_crs_arconym The acronym of the Coordinate reference system of the project
project_crs_definition The full definition of the Coordinate reference system of the project
project_crs_description The description of the Coordinate reference system of the project
project_crs_ellipsoid The ellipsoid of the Coordinate reference system of the project
project_crs_proj4 The Proj4 representation of the Coordinate reference system of the project
project_crs_wkt The WKT (well known text) representation of the coordinate reference system of
the project
project_distance_units The distance unit for the current project, used when calculating lengths of
geometries and distances
project_ellipsoid The name of the ellipsoid of the current project, used when calculating geodetic
areas or lengths of geometries
project_filename The filename of the current project
project_folder The folder of the current project
project_home The home path of the current project
project_identifier The project identifier, taken from the project’s metadata
project_keywords The project keywords, taken from the project’s metadata
project_last_saved Date/time when project was last saved.
project_path The full path (including file name) of the current project
project_title The title of current project
project_units The units of the project’s CRS
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Tabulka 14.2 – pokračujte na předchozí stránce
Variable Popis
qgis_locale The current language of QGIS
qgis_os_name The current Operating system name, eg ‚windows‘, ‚linux‘ or ‚osx‘
qgis_platform The QGIS platform, eg ‚desktop‘ or ‚server‘
qgis_release_name The current QGIS release name
qgis_short_version The current QGIS version short string
qgis_version The current QGIS version string
qgis_version_no The current QGIS version number
row_number Stores the number of the current row
snapping_results Gives access to snapping results while digitizing a feature (only available in add
feature)
scale_value The current scale bar distance value
symbol_angle The angle of the symbol used to render the feature (valid for marker symbols only)
symbol_color The color of the symbol used to render the feature
symbol_count The number of features represented by the symbol (in the layout legend)
symbol_id The Internal ID of the symbol (in the layout legend)
symbol_label The label for the symbol (either a user defined label or the default autogenerated
label - in the layout legend)
symbol_layer_count Total number of symbol layers in the symbol
symbol_layer_index Current symbol layer index
symbol_marker_column Column number for marker (valid for point pattern fills only).
symbol_marker_row Row number for marker (valid for point pattern fills only).
user_account_name The current user’s operating system account name
user_full_name The current user’s operating system user name
value The current value
with_variable Allows setting a variable for usage within an expression and avoid recalculating the
same value repeatedly
zoom_level Zoom level of the tile that is being rendered (derived from the current map scale).
Normally in interval [0, 20].
Některé příklady:
• Return the X coordinate of a map item center in layout:
x( map_get( item_variables( 'map1'), 'map_extent_center' ) )
• Return, for each feature in the current layer, the number of overlapping airport features:
aggregate( layer:='airport', aggregate:='count', expression:="code",
filter:=intersects( $geometry, geometry( @parent ) ) )
• Get the object_id of the first snapped point of a line:
with_variable(
'first_snapped_point',
array_first( @snapping_results ),
attribute(
get_feature_by_id(
map_get( @first_snapped_point, 'layer' ),
map_get( @first_snapped_point, 'feature_id' )
),
'object_id'
)
)
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14.3.26 Recent Functions
This group contains recently used functions. Depending on the context of its usage (feature selection, field calculator,
generic), recently applied expressions are added to the corresponding list (up to ten expressions), sorted from more
to less recent. This makes it easy to quickly retrieve and reapply previously used expressions.
14.4 Working with the Attribute Table
The attribute table displays information on features of a selected layer. Each row in the table represents a feature
(with or without geometry), and each column contains a particular piece of information about the feature. Features
in the table can be searched, selected, moved or even edited.
14.4.1 Foreword: Spatial and non-spatial tables
QGIS allows you to load spatial and non-spatial layers. This currently includes tables supported by OGR and delimited
text, as well as the PostgreSQL, MSSQL, SpatiaLite, DB2 and Oracle provider. All loaded layers are listed in the
Layers panel. Whether a layer is spatially enabled or not determines whether you can interact with it on the map.
Non-spatial tables can be browsed and edited using the attribute table view. Furthermore, they can be used for field
lookups. For example, you can use columns of a non-spatial table to define attribute values, or a range of values that
are allowed, to be added to a specific vector layer during digitizing. Have a closer look at the edit widget in section
Attributes Form Properties to find out more.
14.4.2 Introducing the attribute table interface
To open the attribute table for a vector layer, activate the layer by clicking on it in the Layers Panel. Then, from the
main Layer menu, choose Open Attribute Table. It is also possible to right-click on the layer and choose Open
Attribute Table from the drop-down menu, or to click on the Open Attribute Table button in the Attributes toolbar.
If you prefer shortcuts, F6 will open the attribute table. Shift+F6 will open the attribute table filtered to selected
features and Ctrl+F6 will open the attribute table filtered to visible features.
This will open a new window that displays the feature attributes for the layer (figure_attributes_table). According to
the setting in Settings ► Options ► Data sources menu, the attribute table will open in a docked window or a regular
window. The total number of features in the layer and the number of currently selected/filtered features are shown in
the attribute table title, as well as if the layer is spatially limited.
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Obr. 14.68: Attribute Table for regions layer
The buttons at the top of the attribute table window provide the following functionality:
Tabulka 14.3: Available Tools
Ikona Label Účel Default Shortcut
Toggle editing mode Enable editing functionalities Ctrl+E
Toggle multi edit mode Update multiple fields of many features
Save Edits Save current modifications
Reload the table
Add feature Add new geometryless feature
Delete selected features Remove selected features from the layer
Cut selected features to clipboard Ctrl+X
Copy selected features to clipboard Ctrl+C
Paste features from clipboard Insert new features from copied ones Ctrl+V
Select features using an Expression
Select All Select all features in the layer Ctrl+A
Invert selection Invert the current selection in the layer Ctrl+R
Deselect all Deselect all features in the current layer Ctrl+Shift+A
Filter/Select features using form Ctrl+F
Move selected to top Move selected rows to the top of the table
Pan map to the selected rows Ctrl+P
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Tabulka 14.3 – pokračujte na předchozí stránce
Ikona Label Účel Default Shortcut
Zoom map to the selected rows Ctrl+J
New field Add a new field to the data source Ctrl+W
Delete field Remove a field from the data source
Open field calculator Update field for many features in a row Ctrl+I
Conditional formatting Enable table formatting
Dock attribute table Allows to dock/undock the attribute table
Actions Lists the actions related to the layer
Poznámka: Depending on the format of the data and the OGR library built with your QGIS version, some tools
may not be available.
Below these buttons is the Quick Field Calculation bar (enabled only in edit mode), which allows to quickly apply
calculations to all or part of the features in the layer. This bar uses the same expressions as the Field Calculator
(see
Editing attribute values).
Table view vs Form view
QGIS provides two view modes to easily manipulate data in the attribute table:
• The Table view
, displays values of multiple features in a tabular mode, each row representing a feature and
each column a field.
• The Form view
shows feature identifiers in a first panel and displays only the attributes of the clicked identifier
in the second one. There is a pull-down menu at the top of the first panel where the „identifier“ can be specified
using an attribute (Column preview) or an Expression. The pull-down also includes the last 10 expressions for
re-use. Form view uses the layer fields configuration (see Attributes Form Properties). You can browse through
the feature identifiers with the arrows on the bottom of the first panel. Once you markered the feature in yellow
in the list it is selected in yellow on the canvas. Use the on top of the attribute table to zoom to the feature.
Clicking on an entry in the list (without using the rectangles) makes a feature flash in red color once so you can
see where it is situated.
You can switch from one mode to the other by clicking the corresponding icon at the bottom right of the dialog.
You can also specify the Default view mode at the opening of the attribute table in Settings ► Options ► Data Sources
menu. It can be ‚Remember last view‘, ‚Table view‘ or ‚Form view‘.
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Obr. 14.69: Attribute table in table view (top) vs form view (bottom)
Configuring the columns
Right-click in a column header when in table view to have access to tools that help you configure what can be displayed
in the attribute table and how.
Hiding and organizing columns and enabling actions
By right-clicking in a column header, you can choose to hide it from the attribute table. To change several columns
behavior at once, unhide a column or change the order of the columns, choose Organize columns …. In the new dialog,
you can:
• check/uncheck columns you want to show or hide
• drag-and-drop items to reorder the columns in the attribute table. Note that this change is for the table rendering
and does not alter the fields order in the layer datasource
• enable a new virtual Actions column that displays in each row a drop-down box or button list of actions for each
row, see Actions Properties for more information about actions.
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Resizing columns widths
Columns width can be set through a right-click on the column header and select either:
• Set width… to enter the desired value. By default, the current value is displayed in the widget
• Autosize to resize at the best fit the column.
It can also be changed by dragging the boundary on the right of the column heading. The new size of the column
is maintained for the layer, and restored at the next opening of the attribute table.
Sorting columns
The table can be sorted by any column, by clicking on the column header. A small arrow indicates the sort order
(downward pointing means descending values from the top row down, upward pointing means ascending values from
the top row down). You can also choose to sort the rows with the sort option of the column header context menu and
write an expression, e.g. to sort the row using multiple columns you can write concat(col0, col1).
In form view, features identifier can be sorted using the Sort by preview expression option.
Tip: Sorting based on columns of different types
Trying to sort an attribute table based on columns of string and numeric types may lead to unexpected result because
of the concat("USE", "ID") expression returning string values (ie, 'Borough105' < 'Borough6').
You can workaround this by using eg concat("USE", lpad("ID", 3, 0)) which returns 'Borough105'
> 'Borough006'.
Formatting of table cells using conditions
Conditional formatting settings can be used to highlight in the attribute table features you may want to put a particular
focus on, using custom conditions on feature’s:
• geometry (e.g., identifying multi-parts features, small area ones or in a defined map extent…);
• or field value (e.g., comparing values to a threshold, identifying empty cells…).
You can enable the conditional formatting panel clicking on at the top right of the attributes window in table view
(not available in form view).
The new panel allows user to add new rules to format rendering of Field or Full row. Adding new rule opens
a form to define:
• the name of the rule;
• a condition using any of the expression builder functions;
• the formatting: it can be choosen from a list of predefined formats or created based on properties like:
– background and text colors;
– use of icon;
– bold, italic, underline, or strikeout;
– font.
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Obr. 14.70: Conditional Formatting of an attribute table
14.4.3 Interacting with features in an attribute table
Selecting features
In table view, each row in the attribute table displays the attributes of a unique feature in the layer. Selecting a row
selects the feature and likewise, selecting a feature in the map canvas (in case of geometry enabled layer) selects the
row in the attribute table. If the set of features selected in the map canvas (or attribute table) is changed, then the
selection is also updated in the attribute table (or map canvas) accordingly.
Rows can be selected by clicking on the row number on the left side of the row. Multiple rows can be marked by
holding the Ctrl key. A continuous selection can be made by holding the Shift key and clicking on several row
headers on the left side of the rows. All rows between the current cursor position and the clicked row are selected.
Moving the cursor position in the attribute table, by clicking a cell in the table, does not change the row selection.
Changing the selection in the main canvas does not move the cursor position in the attribute table.
In form view of the attribute table, features are by default identified in the left panel by the value of their displayed
field (see Display Properties). This identifier can be replaced using the drop-down list at the top of the panel, either
by selecting an existing field or using a custom expression. You can also choose to sort the list of features from the
drop-down menu.
Click a value in the left panel to display the feature’s attributes in the right one. To select a feature, you need to click
inside the square symbol at the left of the identifier. By default, the symbol turns into yellow. Like in the table view,
you can perform multiple feature selection using the keyboard combinations previously exposed.
Beyond selecting features with the mouse, you can perform automatic selection based on feature’s attribute using tools
available in the attribute table toolbar, such as (see section Automatic selection and following one for more information
and use case):
• Select By Expression…
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• Select Features By Value…
• Deselect All Features from the Layer
• Select All Features
• Invert Feature Selection.
It is also possible to select features using the Filtering and selecting features using forms.
Filtering features
Once you have selected features in the attribute table, you may want to display only these records in the table. This
can be easily done using the Show Selected Features item from the drop-down list at the bottom left of the attribute
table dialog. This list offers the following filters:
• Show All Features
• Show Selected Features
• Show Features visible on map
• Show Edited and New Features
• Field Filter - allows the user to filter based on value of a field: choose a column from a list, type a value and
press Enter to filter. Then, only the matching features are shown in the attribute table.
• Advanced filter (Expression) - Opens the expression builder dialog. Within it, you can create complex expressions
to match table rows. For example, you can filter the table using more than one field. When applied, the filter
expression will show up at the bottom of the form.
It is also possible to filter features using forms.
Poznámka: Filtering records out of the attribute table does not filter features out of the layer; they are simply
momentaneously hidden from the table and can be accessed from the map canvas or by removing the filter. For filters
that do hide features from the layer, use the Query Builder.
Tip: Update datasource filtering with Show Features Visible on Map
When for performance reasons, features shown in attribute table are spatially limited to the canvas extent at its opening
(see Data Source Options for a how-to), selecting Show Features Visible on Map on a new canvas extent updates the
spatial restriction.
Filtering and selecting features using forms
Clicking the Filter/Select features using form
or pressing Ctrl+F will make the attribute table dialog switch to form view
and replace each widget with its search variant.
From this point onwards, this tool functionality is similar to the one described in Select Features By Value, where you
can find descriptions of all operators and selecting modes.
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Obr. 14.71: Attribute table filtered by the filter form
When selecting / filtering features from the attribute table, there is a Filter features button that allows defining and
refining filters. Its use triggers the Advanced filter (Expression) option and displays the corresponding filter expression
in an editable text widget at the bottom of the form.
If there are already filtered features, you can refine the filter using the drop-down list next to the Filter features button.
The options are:
• Filter within („AND“)
• Extend filter („OR“)
To clear the filter, either select the Show all features option from the bottom left pull-down menu, or clear the
expression and click Apply or press Enter.
14.4.4 Using action on features
Users have several possibilities to manipulate feature with the contextual menu like:
• Select all (Ctrl+A) the features;
• Copy the content of a cell in the clipboard with Copy cell content;
• Zoom to feature without having to select it beforehand;
• Pan to feature without having to select it beforehand;
• Flash feature, to highlight it in the map canvas;
• Open form: it toggles attribute table into form view with a focus on the clicked feature.
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Obr. 14.72: Copy cell content button
If you want to use attribute data in external programs (such as Excel, LibreOffice, QGIS or a custom web application),
select one or more row(s) and use the Copy selected rows to clipboard
button or press Ctrl+C.
In Settings ► Options ► Data Sources menu you can define the format to paste to with Copy features as dropdown list:
• Plain text, no geometry,
• Plain text, WKT geometry,
• GeoJSON
You can also display a list of actions in this contextual menu. This is enabled in the Layer properties ► Actions tab.
See Actions Properties for more information on actions.
Saving selected features as new layer
The selected features can be saved as any OGR-supported vector format and also transformed into another coordinate
reference system (CRS). In the contextual menu of the layer, from the Layers panel, click on Export ► Save selected
features as… to define the name of the output dataset, its format and CRS (see section Creating new layers from an
existing layer). You’ll notice that Save only selected features is checked. It is also possible to specify OGR creation
options within the dialog.
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14.4.5 Editing attribute values
Editing attribute values can be done by:
• typing the new value directly in the cell, whether the attribute table is in table or form view. Changes are hence
done cell by cell, feature by feature;
• using the field calculator: update in a row a field that may already exist or to be created but for multiple features.
It can be used to create virtual fields;
• using the quick field calculation bar: same as above but for only existing field;
• or using the multi edit mode: update in a row multiple fields for multiple features.
Using the Field Calculator
The Field Calculator
button in the attribute table allows you to perform calculations on the basis of existing attribute
values or defined functions, for instance, to calculate length or area of geometry features. The results can be used to
update an existing field, or written to a new field (that can be a virtual one).
The field calculator is available on any layer that supports edit. When you click on the field calculator icon the dialog
opens (see Obr. 14.73). If the layer is not in edit mode, a warning is displayed and using the field calculator will cause
the layer to be put in edit mode before the calculation is made.
Based on the Expression Builder dialog, the field calculator dialog offers a complete interface to define an expression
and apply it to an existing or a newly created field. To use the field calculator dialog, you must select whether you
want to:
1. apply calculation on the whole layer or on selected features only
2. create a new field for the calculation or update an existing one.
Obr. 14.73: Field Calculator
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If you choose to add a new field, you need to enter a field name, a field type (integer, real, date or string) and if needed,
the total field length and the field precision. For example, if you choose a field length of 10 and a field precision of 3,
it means you have 7 digits before the dot, and 3 digits for the decimal part.
A short example illustrates how field calculator works when using the Expression tab. We want to calculate the length
in km of the railroads layer from the QGIS sample dataset:
1. Load the shapefile railroads.shp in QGIS and press Open Attribute Table
.
2. Click on Toggle editing mode
and open the Field Calculator
dialog.
3. Select the Create a new field checkbox to save the calculations into a new field.
4. Set Output field name to length_km
5. Select Decimal number (real) as Output field type
6. Set the Output field length to 10 and the Precision to 3
7. Double click on $length in the Geometry group to add the length of the geometry into the Field calculator
expression box.
8. Complete the expression by typing / 1000 in the Field calculator expression box and click OK.
9. You can now find a new length_km field in the attribute table.
Creating a Virtual Field
A virtual field is a field based on an expression calculated on the fly, meaning that its value is automatically updated
as soon as an underlying parameter changes. The expression is set once; you no longer need to recalculate the field
each time underlying values change. For example, you may want to use a virtual field if you need area to be evaluated
as you digitize features or to automatically calculate a duration between dates that may change (e.g., using now()
function).
Poznámka: Use of Virtual Fields
• Virtual fields are not permanent in the layer attributes, meaning that they’re only saved and available in the
project file they’ve been created.
• A field can be set virtual only at its creation. Virtual fields are marked with a purple background in the fields
tab of the layer properties dialog to distinguish them from regular physical or joined fields. Their expression
can be edited later by pressing the expression button in the Comment column. An expression editor window
will be opened to adjust the expression of the virtual field.
Using the Quick Field Calculation Bar
While Field calculator is always available, the quick field calculation bar on top of the attribute table is only visible if
the layer is in edit mode. Thanks to the expression engine, it offers a quicker access to edit an already existing field:
1. Select the field to update in the drop-down list.
2. Fill the textbox with a value, an expression you directly write or build using the expression button.
3. Click on Update All, Update Selected or Update Filtered button according to your need.
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Obr. 14.74: Quick Field Calculation Bar
Editing multiple fields
Unlike the previous tools, multi edit mode allows multiple attributes of different features to be edited simultaneously.
When the layer is toggled to edit, multi edit capabilities are accessible:
• using the Toggle multi edit mode
button from the toolbar inside the attribute table dialog;
• or selecting Edit ► Modify attributes of selected features menu.
Poznámka: Unlike the tool from the attribute table, hitting the Edit ► Modify Attributes of Selected Features option
provides you with a modal dialog to fill attributes changes. Hence, features selection is required before execution.
In order to edit multiple fields in a row:
1. Select the features you want to edit.
2. From the attribute table toolbar, click the button. This will toggle the dialog to its form view. Feature
selection could also be made at this step.
3. At the right side of the attribute table, fields (and values) of selected features are shown. New widgets appear
next to each field allowing for display of the current multi edit state:
• The field contains different values for selected features. It’s shown empty and each feature will keep
its original value. You can reset the value of the field from the drop-down list of the widget.
• All selected features have the same value for this field and the value displayed in the form will be
kept.
• The field has been edited and the entered value will be applied to all the selected features. A message
appears at the top of the dialog, inviting you to either apply or reset your modification.
Clicking any of these widgets allows you to either set the current value for the field or reset to original value,
meaning that you can roll back changes on a field-by-field basis.
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Obr. 14.75: Editing fields of multiple features
4. Make the changes to the fields you want.
5. Click on Apply changes in the upper message text or any other feature in the left panel.
Changes will apply to all selected features. If no feature is selected, the whole table is updated with your changes.
Modifications are made as a single edit command. So pressing Undo
will rollback the attribute changes for all
selected features at once.
Poznámka: Multi edit mode is only available for auto generated and drag and drop forms (see Customizing a form
for your data); it is not supported by custom ui forms.
14.4.6 Creating one or many to many relations
Relations are a technique often used in databases. The concept is that features (rows) of different layers (tables) can
belong to each other.
Introducing 1-N relations
As an example you have a layer with all regions of alaska (polygon) which provides some attributes about its name
and region type and a unique id (which acts as primary key).
Then you get another point layer or table with information about airports that are located in the regions and you also
want to keep track of these. If you want to add them to the regions layer, you need to create a one to many relation
using foreign keys, because there are several airports in most regions.
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Obr. 14.76: Alaska region with airports
Layers in 1-N relations
QGIS makes no difference between a table and a vector layer. Basically, a vector layer is a table with a geometry.
So you can add your table as a vector layer. To demonstrate the 1-n relation, you can load the regions shapefile
and the airports shapefile which has a foreign key field (fk_region) to the layer regions. This means, that
each airport belongs to exactly one region while each region can have any number of airports (a typical one to many
relation).
Foreign keys in 1-N relations
In addition to the already existing attributes in the airports attribute table, you’ll need another field fk_region
which acts as a foreign key (if you have a database, you will probably want to define a constraint on it).
This field fk_region will always contain an id of a region. It can be seen like a pointer to the region it belongs to. And
you can design a custom edit form for editing and QGIS takes care of the setup. It works with different providers
(so you can also use it with shape and csv files) and all you have to do is to tell QGIS the relations between your tables.
Defining 1-N relations
The first thing we are going to do is to let QGIS know about the relations between the layers. This is done in Project
► Properties…. Open the Relations tab and click on Add Relation.
• Name is going to be used as a title. It should be a human readable string, describing, what the relation is used
for. We will just call say airport_relation in this case.
• Referenced Layer (Parent) also considered as parent layer, is the one with the primary key, pointed to, so here
it is the regions layer. You need to define the primary key of the referenced layer, so it is ID.
• Referencing Layer (Child) also considered as child layer, is the one with the foreign key field on it. In our
case, this is the airports layer. For this layer you need to add a referencing field which points to the other
layer, so this is fk_region.
Poznámka: Sometimes, you need more than a single field to uniquely identify features in a layer. Creating
a relation with such a layer requires a composite key, ie more than a single pair of matching fields. Use the
Add new field pair as part of a composite foreign key
button to add as many pairs as necessary.
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• Id will be used for internal purposes and has to be unique. You may need it to build custom forms. If you leave
it empty, one will be generated for you but you can assign one yourself to get one that is easier to handle
• Relationship strength sets the strength of the relation between the parent and the child layer. The default
Association type means that the parent layer is simply linked to the child one while the Composition type allows
you to duplicate also the child features when duplicating the parent ones.
Obr. 14.77: Adding a relation between regions and airports layers
From the Relations tab, you can also press the Discover Relation button to fetch the relations available from the
providers of the loaded layers. This is possible for layers stored in data providers like PostgreSQL or SpatiaLite.
Forms for 1-N relations
Now that QGIS knows about the relation, it will be used to improve the forms it generates. As we did not change the
default form method (autogenerated) it will just add a new widget in our form. So let’s select the layer region in the
legend and use the identify tool. Depending on your settings, the form might open directly or you will have to choose
to open it in the identification dialog under actions.
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Obr. 14.78: Identification dialog regions with relation to airports
As you can see, the airports assigned to this particular region are all shown in a table. And there are also some buttons
available. Let’s review them shortly:
• The button is for toggling the edit mode. Be aware that it toggles the edit mode of the airport layer, although
we are in the feature form of a feature from the region layer. But the table is representing features of the airport
layer.
• The button is for saving all the edits.
• The button will add a new record to the airport layer attribute table. And it will assign the new airport to
the current region by default.
• The is the same as but lets you digitize the airport geometry in the map canvas beforehand. Note that
the icon will change according to geometry type.
• The button allows you to copy one or more child features.
• The button will delete the selected airport permanently.
• The symbol will open a new dialog where you can select any existing airport which will then be assigned
to the current region. This may be handy if you created the airport on the wrong region by accident.
• The symbol will unlink the selected airport from the current region, leaving them unassigned (the foreign
key is set to NULL) effectively.
• With the button you can zoom the map to the selected child features.
• The two buttons and to the right switch between table view and form view where the later let’s you
view all the airports in their respective form.
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In the above example the referencing layer has geometries (so it isn’t just an alphanumeric table) so the above steps
will create an entry in the layer attribute table that has no corresponding geometric feature. To add the geometry:
1. Choose Open Attribute Table for the referencing layer.
2. Select the record that has been added previously within the feature form of the referenced layer.
3. Use the Add Part
digitizing tool to attach a geometry to the selected attributes table record.
If you work on the airport table, the widget Relation Reference is automatically set up for the fk_region field (the
one used to create the relation), see Relation Reference widget.
In the airport form you will see the button at the right side of the fk_region field: if you click on the button
the form of the region layer will be opened. This widget allows you to easily and quickly open the forms of the linked
parent features.
Obr. 14.79: Identification dialog airport with relation to regions
The Relation Reference widget has also an option to embed the form of the parent layer within the child one. It
is available in the Properties ► Attributes Form menu of the airport layer: select the fk_region field and check the
Show embedded form option.
If you look at the feature dialog now, you will see, that the form of the region is embedded inside the airports form
and will even have a combobox, which allows you to assign the current airport to another region.
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Moreover if you toggle the editing mode of the airport layer, the fk_region field has also an autocompleter
function: while typing you will see all the values of the id field of the region layer. Here it is possible to digitize
a polygon for the region layer using the button if you chose the option Allow adding new features in
the Properties ► Attributes Form menu of the airport layer.
The child layer can also be used in the Select Features By Value tool in order to select features of the parent layer
based on attributes of their children.
In Obr. 14.80, all the regions where the mean altitude of the airports is greater than 500 meters above sea level are
selected.
You will find that many different aggregation functions are available in the form.
Obr. 14.80: Select parent features with child values
Introducing many-to-many (N-M) relations
N-M relations are many-to-many relations between two tables. For instance, the airports and airlines layers:
an airport receives several airline companies and an airline company flies to several airports.
This SQL code creates the three tables we need for an N-M relationship in a PostgreSQL/PostGIS schema named
locations. You can run the code using the Database ► DB Manager… for PostGIS or external tools such as pgAdmin.
The airports table stores the airports layer and the airlines table stores the airlines layer. In both tables few
fields are used for clarity. The tricky part is the airports_airlines table. We need it to list all airlines for all
airports (or vice versa). This kind of table is known as a pivot table. The constraints in this table force that an airport
can be associated with an airline only if both already exist in their layers.
CREATE SCHEMA locations;
CREATE TABLE locations.airports
(
id serial NOT NULL,
geom geometry(Point, 4326) NOT NULL,
airport_name text NOT NULL,
CONSTRAINT airports_pkey PRIMARY KEY (id)
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);
CREATE INDEX airports_geom_idx ON locations.airports USING gist (geom);
CREATE TABLE locations.airlines
(
id serial NOT NULL,
geom geometry(Point, 4326) NOT NULL,
airline_name text NOT NULL,
CONSTRAINT airlines_pkey PRIMARY KEY (id)
);
CREATE INDEX airlines_geom_idx ON locations.airlines USING gist (geom);
CREATE TABLE locations.airports_airlines
(
id serial NOT NULL,
airport_fk integer NOT NULL,
airline_fk integer NOT NULL,
CONSTRAINT airports_airlines_pkey PRIMARY KEY (id),
CONSTRAINT airports_airlines_airport_fk_fkey FOREIGN KEY (airport_fk)
REFERENCES locations.airports (id)
ON DELETE CASCADE
ON UPDATE CASCADE
DEFERRABLE INITIALLY DEFERRED,
CONSTRAINT airports_airlines_airline_fk_fkey FOREIGN KEY (airline_fk)
REFERENCES locations.airlines (id)
ON DELETE CASCADE
ON UPDATE CASCADE
DEFERRABLE INITIALLY DEFERRED
);
Instead of PostgreSQL you can also use GeoPackage. In this case, the three tables can be created manually using the
Database ► DB Manager…. In GeoPackage there are no schemas so the locations prefix is not needed.
Foreign key constraints in airports_airlines table can´t be created using Table ► Create Table… or Table
► Edit Table… so they should be created using Database ► SQL Window…. GeoPackage doesn’t support ADD
CONSTRAINT statements so the airports_airlines table should be created in two steps:
1. Set up the table only with the id field using Table ► Create Table…
2. Using Database ► SQL Window…, type and execute this SQL code:
ALTER TABLE airports_airlines
ADD COLUMN airport_fk INTEGER
REFERENCES airports (id)
ON DELETE CASCADE
ON UPDATE CASCADE
DEFERRABLE INITIALLY DEFERRED;
ALTER TABLE airports_airlines
ADD COLUMN airline_fk INTEGER
REFERENCES airlines (id)
ON DELETE CASCADE
ON UPDATE CASCADE
DEFERRABLE INITIALLY DEFERRED;
Then in QGIS, you should set up two one-to-many relations as explained above:
• a relation between airlines table and the pivot table;
• and a second one between airports table and the pivot table.
An easier way to do it (only for PostgreSQL) is using the Discover Relations in Project ► Properties ► Relations.
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QGIS will automatically read all relations in your database and you only have to select the two you need. Remember
to load the three tables in the QGIS project first.
Obr. 14.81: Relations and autodiscover
In case you want to remove an airport or an airline, QGIS won’t remove the associated record(s) in
airports_airlines table. This task will be made by the database if we specify the right constraints in the
pivot table creation as in the current example.
Poznámka: Combining N-M relation with automatic transaction group
You should enable the transaction mode in Project Properties ► Data Sources ► when working on such context. QGIS
should be able to add or update row(s) in all tables (airlines, airports and the pivot tables).
Finally we have to select the right cardinalilty in the Layer Properties ► Attributes Form for the airports and
airlines layers. For the first one we should choose the airlines (id) option and for the second one the airports
(id) option.
Obr. 14.82: Set relationship cardinality
Now you can associate an airport with an airline (or an airline with an airport) using Add child feature or Link existing
child feature in the subforms. A record will automatically be inserted in the airports_airlines table.
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Obr. 14.83: N-M relationship between airports and airlines
Poznámka: Using Many to one relation cardinality
Sometimes hiding the pivot table in an N-M relationship is not desirable. Mainly because there are attributes in the
relationship that can only have values when a relationship is established. If your tables are layers (have a geometry field)
it could be interesting to activate the On map identification option (Layer Properties ► Attributes Form ► Available
widgets ► Fields) for the foreign key fields in the pivot table.
Poznámka: Pivot table primary key
Avoid using multiple fields in the primary key in a pivot table. QGIS assumes a single primary key so a constraint like
constraint airports_airlines_pkey primary key (airport_fk, airline_fk) will not
work.
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14.5 Editování
QGIS has various capabilities for editing OGR, SpatiaLite, PostGIS, MSSQL Spatial and Oracle Spatial vector layers
and tables.
Poznámka: The procedure for editing GRASS layers is different - see section Digitizing and editing a GRASS vector
layer for details.
Tip: Souběžné editace
This version of QGIS does not track if somebody else is editing the same feature at the same time as you are. The
last person to save the edits wins.
14.5.1 Nastavení přichytávací tolerance a vyhledání poloměru
For optimal and accurate editing of vector layer geometries, we need to set an appropriate value of snapping tolerance
and search radius for features vertices.
Přichytávací tolerance
When you add a new vertex or move an existing one, the snapping tolerance is the distance QGIS uses to search for
the closest vertex or segment you are trying to connect to. If you are not within the snapping tolerance, QGIS will
leave the vertex where you release the mouse button, instead of snapping it to an existing vertex or segment.
The snapping tolerance setting affects all tools that work with tolerance.
You can enable / disable snapping by using the Enable snapping
button on the Snapping Toolbar or pressing s. The
snapping mode, tolerance value, and units can also be configured in this toolbar.
The snapping configuration can also be set in Project ► Snapping Options….
There are three options to select the layer(s) to snap to:
• All layers: quick setting for all visible layers in the project so that the pointer snaps to all vertices and/or
segments. In most cases, it is sufficient to use this snapping mode, but beware when using it for projects with
many vector layers, as it may affect performance.
• Current layer: only the active layer is used, a convenient way to ensure topological consistency within the layer
being edited.
• Advanced Configuration: allows you to enable and adjust snapping mode and tolerance on a layer basis (see Obr.
14.84). If you need to edit a layer and snap its vertices to another, make sure that the target layer is checked
and increase the snapping tolerance to a higher value. Snapping will not occur to a layer that is not checked in
the snapping options dialog.
As for snapping mode, you can choose between To vertex, To segment, and To vertex and segment.
The tolerance values can be set either in the project’s map units or in pixels. The advantage of choosing
pixels is that it keeps the snapping constant at different map scales. 10 to 12 pixels is normally a good value, but it
depends on the DPI of your screen. Using map units allows the tolerance to be related to real ground distances. For
example, if you have a minimum distance between elements, this option can be useful to ensure that you don’t add
vertices too close to each other.
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Obr. 14.84: Snapping options (Advanced Configuration mode)
Poznámka: By default, only visible features (the features whose style is displayed, except for layers where the
symbology is „No symbols“) can be snapped. You can enable the snapping on invisible features by checking
Enable snapping on invisible features under the Settings ► Options ► Digitizing tab.
Tip: Enable snapping by default
You can set snapping to be enabled by default on all new projects in the Settings ► Options ► Digitizing tab. You can
also set the default snapping mode, tolerance value, and units, which will populate the Snapping Options dialog.
Enable snapping on intersections
Another available option is to use snapping on intersection, which allows you to snap to geometry intersections
of snapping enabled layers, even if there are no vertices at the intersections.
Snapping icons
QGIS will show different snap icons depending on the kind of snap:
Snapping to a vertex: box icon Snapping to a segment: hourglass
icon
Snapping to an intersection: cross
icon
Note that it is possible to change the color of these icons in the Digitizing part of your settings.
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Vyhledání poloměru
Search radius for vertex edits is the distance QGIS uses to search for the vertex to select when you click on the
map. If you are not within the search radius, QGIS will not find and select any vertex for editing. The search radius
for vertex edits can be defined under the Settings ► Options ► Digitizing tab (this is where you define the snapping
default values).
Snap tolerance and search radius are set in map units or pixels. You may need to experiment to get them right.
If you specify a too big tolerance, QGIS may snap to the wrong vertex, especially if you are dealing with a large
number of vertices in close proximity. The smaller the search radius, the more difficult it will be to hit what you want
to move.
Limit snapping to a scale range
In some cases snapping can become very slow. This is often caused by the amount of features in some layers that
require a heavy index to compute and maintain. Some parameters exist to enable snapping only when the map view
is inside a relevant scale range. This allows to only do the costly index computation related to snapping at a scale
where drawing is relevant.
Scale limit to snapping is configured in Project ► Snapping Options…. Limiting snapping to scale is only available in
Advanced Configuration mode.
To limit snapping to a scale range you have three modes available:
• Disabled: Snapping is enabled whatever the current map scale is. This is the default mode.
• Global: Snapping is limited and only enabled when the current scale of the map is between a global minimum
and a global maximum value. When selecting this mode two widgets become available to configure the range
of scales in which snapping is enabled.
• Per layer: The snapping scale range limit is defined for each layer. When selecting this mode two columns
become available to configure the minimum and maximum scales for each layer.
Please note that the minimum and maximum scales follow the QGIS convention: minimum scale is the most „zoomed
out“ scale while maximum scale is the most „zoomed in“. A minimum or maximum scale that is set to „0“ or „not
set“ is considered not limiting.
14.5.2 Topologická editace
In addition to these snapping options, the Snapping options… dialog (Project ► Snapping options) and the Snapping
toolbar allow you to enable / disable some other topological functionalities.
Povolení topologické editace
The Topological editing
button helps when editing and maintaining features with common boundaries. With this option
enabled, QGIS ‚detects‘ shared boundaries. When you move common vertices/segments, QGIS will also move them
in the geometries of the neighboring features.
Topological editing works with features from different layers, as long as the layers are visible and in editing mode.
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Avoid overlap of new polygons
When the snapping mode is set to Advanced configuration, for polygon layers, there’s an option called
Avoid overlap. This option prevents you from drawing new features that overlap existing ones in the selected layer,
speeding up digitizing of adjacent polygons.
With avoid overlap enabled, if you already have one polygon, you can digitize a second one such that they intersect.
QGIS will then cut the second polygon to the boundary of the existing one. The advantage is that you don’t have to
digitize all vertices of the common boundary.
Poznámka: If the new geometry is totally covered by existing ones, it gets cleared, and QGIS will show an error
message.
Varování: Use cautiously the Avoid overlap option
Since this option will cut new overlapping geometries of any polygon layer, you can get unexpected geometries if
you forget to uncheck it when no longer needed.
Geometry Checker
A core plugin can help the user to find the geometry invalidity. You can find more information on this plugin at
Geometry Checker Plugin.
Automatic Tracing
Usually, when using capturing map tools (add feature, add part, add ring, reshape and split), you need to click each
vertex of the feature. With the automatic tracing mode, you can speed up the digitization process as you no longer
need to manually place all the vertices during digitization:
1. Enable the Tracing
tool (in the Snapping toolbar) by pushing the icon or pressing T key.
2. Snap to a vertex or segment of a feature you want to trace along.
3. Move the mouse over another vertex or segment you’d like to snap and, instead of the usual straight line, the
digitizing rubber band represents a path from the last point you snapped to the current position. The tool also
works with curved geometries.
QGIS actually uses the underlying features topology to build the shortest path between the two points. Tracing
requires snapping to be activated in traceable layers to build the path. You should also snap to an existing
vertex or segment while digitizing and ensure that the two nodes are topologically connectable through existing
features edges, otherwise QGIS is unable to connect them and thus traces a single straight line.
4. Click and QGIS places the intermediate vertices following the displayed path.
Unfold the Enable Tracing
icon and set the Offset option to digitize a path parallel to the features instead of tracing
along them. A positive value shifts the new drawing to the left side of the tracing direction and a negative value does
the opposite.
Poznámka: Adjust map scale or snapping settings for an optimal tracing
If there are too many features in map display, tracing is disabled to avoid potentially long tracing structure preparation
and large memory overhead. After zooming in or disabling some layers the tracing is enabled again.
Poznámka: Does not add topological points
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This tool does not add points to existing polygon geometries even if Topological editing is enabled. If geometry
precision is activated on the edited layer, the resulting geometry might not exactly follow an existing geometry.
Tip: Quickly enable or disable automatic tracing by pressing the T key
By pressing the T key, tracing can be enabled/disabled anytime (even while digitizing a feature), so it is possible to
digitize parts of the feature with tracing enabled and other parts with tracing disabled. Tools behave as usual when
tracing is disabled.
Tip: Convert tracing to curved geometries
By using Settings ► Options ► Digitizing ► Tracing you can create curved geometries while digitizing. See digitizing
options.
14.5.3 Digitizing an existing layer
By default, QGIS loads layers read-only. This is a safeguard to avoid accidentally editing a layer if there is a slip of
the mouse. However, you can choose to edit any layer as long as the data provider supports it (see Exploring Data
Formats and Fields), and the underlying data source is writable (i.e., its files are not read-only).
Tip: Restrict edit permission on layers within a project
From the Project ► Properties… ► Data Sources ► Layers Capabilities table, you can choose to set any layer read-only
regardless the provider permission. This can be a handy way, in a multi-users environment to avoid unauthorized users
to mistakenly edit layers (e.g., Shapefile), hence potentially corrupt data. Note that this setting only applies inside the
current project.
In general, tools for editing vector layers are divided into a digitizing and an advanced digitizing toolbar, described
in section Advanced digitizing. You can select and unselect both under View ► Toolbars ►.
Using the basic digitizing tools, you can perform the following functions:
Ikona Účel Ikona Účel
Current edits Přepnout editaci
Save layer edits
Add new record Add Feature: Capture Point
Add Feature: Capture Line Add Feature: Capture Polygon
Vertex Tool (All Layers) Vertex Tool (Current Layer)
Modify the attributes of all selected features simultaneously
Vymazat vybrané Vyjmout prvky
Kopírovat prvky Vložit prvky
Zpět Znovu
Table Editing: Vector layer basic editing toolbar
Note that while using any of the digitizing tools, you can still zoom or pan in the map canvas without losing the focus
on the tool.
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All editing sessions start by choosing the Toggle editing
option found in the context menu of a given layer, from the
attribute table dialog, the digitizing toolbar or the Edit menu.
Once the layer is in edit mode, additional tool buttons on the editing toolbar will become available and markers will
appear at the vertices of all features unless Show markers only for selected features option under Settings ► Options…
► Digitizing menu is checked.
Tip: Save Regularly
Remember to Save Layer Edits
regularly. This will also check that your data source can accept all the changes.
Adding Features
Depending on the layer type, you can use the Add Record
, Add Point Feature
, Add Line Feature
or Add Polygon Feature
icons on the toolbar to add new features into the current layer.
To add a geometryless feature, click on the Add Record
button and you can enter attributes in the feature form that
opens. To create features with the spatially enabled tools, you first digitize the geometry then enter its attributes. To
digitize the geometry:
1. Left-click on the map area to create the first point of your new feature. For point features, this should be enough
and trigger, if required, the feature form to fill in their attributes. Having set the geometry precision in the layer
properties you can use snap to grid here to create features based on a regular distance.
2. For line or polygon geometries, keep on left-clicking for each additional point you wish to capture or use
automatic tracing capability to accelerate the digitization. This will create consecutive straight lines between
the vertices you place.
Poznámka: Pressing Delete or Backspace key reverts the last node you add.
3. When you have finished adding points, right-click anywhere on the map area to confirm you have finished
entering the geometry of that feature.
Poznámka: While digitizing line or polygon geometries, you can switch back and forth between the linear
Add feature tools and circular string tools to create compound curved geometries.
Tip: Customize the digitizing rubber band
While capturing polygon, the by-default red rubber band can hide underlying features or places you’d like to
capture a point. This can be fixed by setting a lower opacity (or alpha channel) to the rubber band’s Fill Color in
Settings ► Options ► Digitizing menu. You can also avoid the use of the rubber band by checking Don’t update
rubber band during node editing.
4. The attribute window will appear, allowing you to enter the information for the new feature. Obr. 14.85 shows
setting attributes for a fictitious new river in Alaska. However, in the Digitizing menu under the Settings ►
Options menu, you can also activate:
• Suppress attributes pop-up windows after each created feature to avoid the form opening;
• or Reuse last entered attribute values to have fields automatically filled at the opening of the form and
just have to type changing values.
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Obr. 14.85: Enter Attribute Values Dialog after digitizing a new vector feature
Vertex tool
Poznámka: QGIS 3 major changes
In QGIS 3, the node tool has been fully redesigned and renamed to vertex tool. It was previously working with „click
and drag“ ergonomy, and now uses a „click - click“ workflow. This allows major improvements like taking profit of
the advanced digitizing panel with the vertex tool while digitizing or editing objects of multiple layers at the same
time.
For any editable vector layer, the Vertex tool (Current Layer)
provides manipulation capabilities of feature vertices similar
to CAD programs. It is possible to simply select multiple vertices at once and to move, add or delete them altogether.
The vertex tool also supports the topological editing feature. This tool is selection persistent, so when some operation
is done, selection stays active for this feature and tool.
It is important to set the property Settings ► Options ► Digitizing ► Search Radius: to a number greater
than zero. Otherwise, QGIS will not be able to tell which vertex is being edited and will display a warning.
Tip: Vertex Markers
The current version of QGIS supports three kinds of vertex markers: ‚Semi-transparent circle‘, ‚Cross‘ and ‚None‘.
To change the marker style, choose Options from the Settings menu, click on the Digitizing tab and select the
appropriate entry.
Basic operations
Start by activating the Vertex Tool (Current Layer)
. Red circles will appear when hovering vertices.
• Selecting vertices: You can select vertices by clicking on them one at a time holding Shift key pressed, or
by clicking and dragging a rectangle around some vertices. When a vertex is selected, its color changes to blue.
To add more vertices to the current selection, hold down the Shift key while clicking. To remove vertices
from the selection, hold down Ctrl.
• Batch vertex selection mode: The batch selection mode can be activated by pressing Shift+R. Select a first
node with one single click, and then hover without clicking another vertex. This will dynamically select all the
nodes in between using the shortest path (for polygons).
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Obr. 14.86: Batch vertex selection using Shift+R
Press Ctrl will invert the selection, selecting the longest path along the feature boundary. Ending your node
selection with a second click, or pressing Esc will escape the batch mode.
• Adding vertices: To add a vertex, a virtual new node appears on the segment center. Simply grab it to add
a new vertex. A double-click on any location of the boundary also creates a new node. For lines, a virtual node
is also proposed at both extremities of a line to extend it.
Obr. 14.87: Virtual nodes for adding vertices
• Deleting vertices: Select the vertices and click the Delete key. Deleting all the vertices of a feature generates,
if compatible with the datasource, a geometryless feature. Note that this doesn’t delete the complete feature,
just the geometry part. To delete a complete feature use the Delete Selected
tool.
• Moving vertices: Select all the vertices you want to move, click on a selected vertex or edge, and click again on
the desired new location. All the selected vertices will move together. If snapping is enabled, the whole selection
can jump to the nearest vertex or line. You can use Advanced Digitizing Panel constraints for distance, angles,
exact X Y location before the second click.
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Here you can use the snap-to-grid feature. Having set a value for the geometry precision in the layer properties,
a grid appears on a zoom level according to the Geometry precision.
Obr. 14.88: Selecting a vertex and moving the vertices to grid
Each change made with the vertex is stored as a separate entry in the Undo dialog. Remember that all operations
support topological editing when this is turned on. On-the-fly projection is also supported, and the vertex tool provides
tooltips to identify a vertex by hovering the pointer over it.
The Vertex Editor Panel
When using the Vertex tool on a feature, it is possible to right click to open the Vertex Editor panel listing all the vertices
of the feature with their x, y (z, m if applicable) coordinates and r (for the radius, in case of circular geometry).
Simply select a row in the table does select the corresponding vertex in the map canvas, and vice versa. Simply
change a coordinate in the table and your vertex position is updated. You can also select multiple rows and delete
them altogether.
Poznámka: Changed behavior in QGIS 3.4
Right click on a feature will immediately show the vertex editor and lock this feature, thus disabling the editing of any
other features. While being locked, a feature is exclusive for editing: Selecting and moving of vertices and segments
by clicking or dragging is only possible for this feature. New vertices can only be added to the locked feature. Also,
the vertex editor panel now opens itself automatically upon activating the vertex tool, and its position/docked state
remembered across uses.
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Obr. 14.89: Vertex editor panel showing selected nodes
Cutting, Copying and Pasting Features
Selected features can be cut, copied and pasted between layers in the same QGIS project, as long as destination layers
are set to Toggle editing
beforehand.
Tip: Transform polygon into line and vice-versa using copy/paste
Copy a line feature and paste it in a polygon layer: QGIS pastes in the target layer a polygon whose boundary
corresponds to the closed geometry of the line feature. This is a quick way to generate different geometries of the
same data.
Features can also be pasted to external applications as text. That is, the features are represented in CSV format,
with the geometry data appearing in the OGC Well-Known Text (WKT) format. WKT and GeoJSON features from
outside QGIS can also be pasted to a layer within QGIS.
When would the copy and paste function come in handy? Well, it turns out that you can edit more than one layer
at a time and copy/paste features between layers. Why would we want to do this? Say we need to do some work on
a new layer but only need one or two lakes, not the 5,000 on our big_lakes layer. We can create a new layer and
use copy/paste to plop the needed lakes into it.
As an example, we will copy some lakes to a new layer:
1. Load the layer you want to copy from (source layer)
2. Load or create the layer you want to copy to (target layer)
3. Start editing for target layer
4. Make the source layer active by clicking on it in the legend
5. Use the Select Features by area or single click
tool to select the feature(s) on the source layer
6. Click on the Copy Features
tool
7. Make the destination layer active by clicking on it in the legend
8. Click on the Paste Features
tool
9. Stop editing and save the changes
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What happens if the source and target layers have different schemas (field names and types are not the same)? QGIS
populates what matches and ignores the rest. If you don’t care about the attributes being copied to the target layer,
it doesn’t matter how you design the fields and data types. If you want to make sure everything - the feature and its
attributes - gets copied, make sure the schemas match.
Poznámka: Congruency of Pasted Features
If your source and destination layers use the same projection, then the pasted features will have geometry identical to
the source layer. However, if the destination layer is a different projection, then QGIS cannot guarantee the geometry
is identical. This is simply because there are small rounding-off errors involved when converting between projections.
Tip: Copy string attribute into another
If you have created a new column in your attribute table with type ‚string‘ and want to paste values from another
attribute column that has a greater length the length of the column size will be extended to the same amount. This
is because the GDAL Shapefile driver starting with GDAL/OGR 1.10 knows to auto-extend string and integer fields
to dynamically accommodate for the length of the data to be inserted.
Deleting Selected Features
If we want to delete an entire feature (attribute and geometry), we can do that by first selecting the geometry using
the regular Select Features by area or single click
tool. Selection can also be done from the attribute table. Once you have
the selection set, press Delete or Backspace key or use the Delete Selected
tool to delete the features. Multiple
selected features can be deleted at once.
The Cut Features
tool on the digitizing toolbar can also be used to delete features. This effectively deletes the feature
but also places it on a „spatial clipboard“. So, we cut the feature to delete. We could then use the Paste Features
tool
to put it back, giving us a one-level undo capability. Cut, copy, and paste work on the currently selected features,
meaning we can operate on more than one at a time.
Zpět a znovu
The Undo
and Redo
tools allows you to undo or redo vector editing operations. There is also a dockable widget,
which shows all operations in the undo/redo history (see Obr. 14.90). This widget is not displayed by default; it can be
displayed by right-clicking on the toolbar and activating the Undo/Redo Panel checkbox. The Undo/Redo capability
is however active, even if the widget is not displayed.
Obr. 14.90: Redo and Undo digitizing steps
When Undo is hit or Ctrl+Z (or Cmd+Z) pressed, the state of all features and attributes are reverted to the state
before the reverted operation happened. Changes other than normal vector editing operations (for example, changes
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done by a plugin) may or may not be reverted, depending on how the changes were performed.
To use the undo/redo history widget, simply click to select an operation in the history list. All features will be reverted
to the state they were in after the selected operation.
Saving Edited Layers
When a layer is in editing mode, any changes remain in the memory of QGIS. Therefore, they are not committed/saved
immediately to the data source or disk. If you want to save edits to the current layer but want to continue editing
without leaving the editing mode, you can click the Save Layer Edits
button. When you turn editing mode off with
Toggle editing
(or quit QGIS for that matter), you are also asked if you want to save your changes or discard them.
If the changes cannot be saved (e.g., disk full, or the attributes have values that are out of range), the QGIS in-memory
state is preserved. This allows you to adjust your edits and try again.
Tip: Data Integrity
It is always a good idea to back up your data source before you start editing. While the authors of QGIS have made
every effort to preserve the integrity of your data, we offer no warranty in this regard.
Saving multiple layers at once
This feature allows the digitization of multiple layers. Choose Save for Selected Layers to save all changes you
made in multiple layers. You also have the opportunity to Rollback for Selected Layers, so that the digitization
may be withdrawn for all selected layers. If you want to stop editing the selected layers, Cancel for Selected
Layer(s) is an easy way.
The same functions are available for editing all layers of the project.
Tip: Use transaction group to edit, save or rollback multiple layers changes at once
When working with layers from the same PostGreSQL database, activate the Automatically create transaction groups
where possible option in Project ► Properties… ► Data Sources to sync their behavior (enter or exit the edit mode,
save or rollback changes at the same time).
14.5.4 Advanced digitizing
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Ikona Účel Ikona Účel
Enable Advanced Digitizing Tools Enable Tracing
Move Feature(s) Copy and Move Feature(s)
Rotovat prvek(prvky) Zjednodušit prvek
Přidat prstenec Přidat část
Fill Ring Swap direction
Smazat prstenec Smazat část
Odsazení křivky Změnit tvar prvků
Split Parts Rozdělit objekt
Sloučit atributy vybraných prvků Sloučit vybrané prvky
Rotovat symboly bodů Offset Point Symbols
Trim or Extend Feature
Table Advanced Editing: Vector layer advanced editing toolbar
Move Feature(s)
The Move Feature(s)
tool allows you to move existing features:
1. Select the feature(s) to move.
2. Click on the map canvas to indicate the origin point of the displacement; you can rely on snapping capabilities
to select an accurate point.
You can also take advantages of the advanced digitizing constraints to accurately set the origin point coordinates.
In that case:
1. First click on the button to enable the panel.
2. Type x and enter the corresponding value for the origin point you’d like to use. Then press the button
next to the option to lock the value.
3. Do the same for the y coordinate.
4. Click on the map canvas and your origin point is placed at the indicated coordinates.
3. Move over the map canvas to indicate the destination point of the displacement, still using snapping mode
or, as above, use the advanced digitizing panel which would provide complementary distance and angle
placement constraints to place the end point of the translation.
4. Click on the map canvas: the whole features are moved to new location.
Likewise, you can create a translated copy of the feature(s) using the Copy and Move Feature(s)
tool.
Poznámka: If no feature is selected when you first click on the map canvas with any of the Move Feature(s) or Copy
and Move Feature(s) tools, then only the feature under the mouse is affected by the action. So, if you want to move
several features, they should be selected first.
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Rotovat prvek(prvky)
Use the Rotate Feature(s)
tool to rotate one or multiple features in the map canvas:
1. Press the Rotate Feature(s)
icon
2. Then click on the feature to rotate. The feature’s centroid is referenced as rotation center, a preview of the
rotated feature is displayed and a widget opens showing the current Rotation angle.
3. Click on the map canvas when you are satisfied with the new placement or manually enter the rotation angle in
the text box. You can also use the Snap to ° box to constrain the rotation values.
4. If you want to rotate several features at once, they shall be selected first, and the rotation is by default around
the centroid of their combined geometries.
You can also use an anchor point different from the default feature centroid: press the Ctrl button, click on the map
canvas and that point will be used as the new rotation center.
If you hold Shift before clicking on the map, the rotation will be done in 45 degree steps, which can be modified
afterwards in the user input widget.
To abort feature rotation, press the ESC button or click on the Rotate Feature(s)
icon.
Zjednodušit prvek
The Simplify Feature
tool allows you to interactively reshape a line or polygon geometry by reducing or densifying
the number of vertices, as long as the geometry remains valid:
1. Select the Simplify Feature
tool.
2. Click on the feature or drag a rectangle over the features.
3. A dialog pops up allowing you to define the Method to apply, ie whether you would like to:
• simplify the geometry, meaning less vertices than the original. Available methods are Simplify by
distance, Simplify by snapping to grid or simplify by area (Visvalingam).
You’d then need to indicate the value of Tolerance in Layer units, Pixels or map units to use
for simplification. The higher the tolerance is the more vertices can be deleted.
• or densify the geometries with new vertices thanks to the Smooth option: for each existing vertex, two
vertices are placed on each of the segments originated from it, at an Offset distance representing the
percentage of the segment length. You can also set the number of Iterations the placement would be
processed: the more iterations, the more vertices and smoother is the feature.
Settings that you used will be saved when leaving a project or an edit session. So you can go back to the same
parameters the next time you simplify a feature.
4. A summary of the modifications that would apply is shown at the bottom of the dialog, listing number of
features and number of vertices (before and after the operation and the ratio the change represents). Also, in
the map canvas, the expected geometry is displayed over the existing one, using the rubberband color.
5. When the expected geometry fits your needs, click OK to apply the modification. Otherwise, to abort the
operation, you can either press Cancel or right-click in the map canvas.
Poznámka: Unlike the feature simplification option in Settings ► Options ► Rendering menu which simplifies the
geometry just for rendering, the Simplify Feature
tool permanently modifies feature’s geometry in data source.
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Přidat část
You can Add Part
to a selected feature generating a multipoint, multiline or multipolygon feature. The new part
must be digitized outside the existing one which should be selected beforehand.
The Add Part
can also be used to add a geometry to a geometryless feature. First, select the feature in the attribute
table and digitize the new geometry with the Add Part
tool.
Smazat část
The Delete Part
tool allows you to delete parts from multifeatures (e.g., to delete polygons from a multi-polygon
feature). This tool works with all multi-part geometries: point, line and polygon. Furthermore, it can be used to totally
remove the geometric component of a feature. To delete a part, simply click within the target part.
Přidat prstenec
You can create ring polygons using the Add Ring
icon in the toolbar. This means that inside an existing area, it
is possible to digitize further polygons that will occur as a ‚hole‘, so only the area between the boundaries of the outer
and inner polygons remains as a ring polygon.
Fill Ring
The Fill Ring
tool helps you create polygon feature that totally falls within another one without any overlapping
area; that is the new feature covers a hole within the existing one. To create such a feature:
1. Select the Fill Ring
tool.
2. Draw a new polygon over the existing feature: QGIS adds a ring to its geometry (like if you used the
Add Ring
tool) and creates a new feature whose geometry matches the ring (like if you traced over the interior
boundaries with the Add polygon feature
tool).
3. Or alternatively, if the ring already exists on the feature, place the mouse over the ring and left-click while
pressing Shift: a new feature filling the hole is drawn at that place.
The Feature Attributes form of the new feature opens, pre-filled with values of the „parent“ feature and/or fields
constraints.
Smazat prstenec
The Delete Ring
tool allows you to delete rings within an existing polygon, by clicking inside the hole. This tool
only works with polygon and multi-polygon features. It doesn’t change anything when it is used on the outer ring of
the polygon.
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Změnit tvar prvků
You can reshape line and polygon features using the Reshape Features
tool on the toolbar. For lines, it replaces the
line part from the first to the last intersection with the original line.
Obr. 14.91: Reshape line
Tip: Extend linestring geometries with reshape tool
Use the Reshape Features
tool to extend existing linestring geometries: snap to the first or last vertex of the line and
draw a new one. Validate and the feature’s geometry becomes the combination of the two lines.
For polygons, it will reshape the polygon’s boundary. For it to work, the reshape tool’s line must cross the polygon’s
boundary at least twice. To draw the line, click on the map canvas to add vertexes. To finish it, just right-click. Like
with the lines, only the segment between the first and the last intersections is considered. The reshape line’s segments
that are inside the polygon will result in cropping it, where the ones outside the polygon will extend it.
Obr. 14.92: Reshape polygon
With polygons, reshaping can sometimes lead to unintended results. It is mainly useful to replace smaller parts of
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a polygon, not for major overhauls, and the reshape line is not allowed to cross several polygon rings, as this would
generate an invalid polygon.
Poznámka: The reshape tool may alter the starting position of a polygon ring or a closed line. So, the point
that is represented ‚twice‘ will not be the same any more. This may not be a problem for most applications, but it
is something to consider.
Odsazení křivek
The Offset Curve
tool creates parallel shifts of line layers. The tool can be applied to the edited layer (the geometries
are modified) or also to background layers (in which case it creates copies of the lines / rings and adds them to the
edited layer). It is thus ideally suited for the creation of distance line layers. The User Input dialog pops-up, showing
the displacement distance.
To create a shift of a line layer, you must first go into editing mode and activate the Offset Curve
tool. Then click on
a feature to shift it. Move the mouse and click where wanted or enter the desired distance in the user input widget.
Your changes may then be saved with the Save Layer Edits
tool.
QGIS options dialog (Digitizing tab then Curve offset tools section) allows you to configure some parameters like
Join style, Quadrant segments, Miter limit.
Reverse Line
Changing the direction of a line geometry can be useful for cartographical purposes or when preparing for network
analysis.
To change a line direction:
1. Activate the reverse line tool by clicking Reverse line
.
2. Click on the line. The direction of the line is reversed.
Rozdělit objekt
Use the Split Features
tool to split a feature into two or more new and independent features, ie. each geometry
corresponding to a new row in the attribute table.
To split line or polygon features:
1. Select the Split Features
tool.
2. Draw a line across the feature(s) you want to split. If a selection is active, only selected features are split. When
set, default values or clauses are applied to corresponding fields and other attributes of the parent feature are
by default copied to the new features.
3. You can then as usually modify any of the attributes of any resulting feature.
Tip: Split a polyline into new features in one-click
Using the Split Features
tool, snap and click on an existing vertex of a polyline feature to split that feature into two
new features.
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Split parts
In QGIS it is possible to split the parts of a multi part feature so that the number of parts is increased. Just draw a line
across the part you want to split using the Split Parts
icon.
Tip: Split a polyline into new parts in one-click
Using the Split Parts
tool, snap and click on an existing vertex of a polyline feature to split the feature into two new
polylines belonging to the same feature.
Sloučit vybrané prvky
The Merge Selected Features
tool allows you to create a new feature by merging existing ones: their geometries are
merged to generate a new one. If features don’t have common boundaries, a multipolygon/multipolyline/multipoint
feature is created.
1. First, select the features you’d like to combine.
2. Then press the Merge Selected Features
button.
3. In the new dialog, the Merge line at the bottom of the table shows the attributes of the resulting feature. You
can alter any of these values either by:
• manually replacing the value in the corresponding cell;
• selecting a row in the table and pressing Take attributes from selected feature to use the values of this
initial feature;
• pressing Skip all fields to use empty attributes;
• or, expanding the drop down menu at the top of the table, select any of the above options to apply
to the corresponding field only. There, you can also choose to aggregate the initial features attributes
(Minimum, Maximum, Median, Sum, Count, Concatenation… depending on the type of the field. see
Statistical Summary Panel for the full list of functions).
Poznámka: If the layer has default values or clauses present on fields, these are used as the initial value for
the merged feature.
4. Press OK to apply the modifications. A single (multi)feature is created in the layer, replacing the previously
selected ones.
Sloučit atributy vybraných prvků
The Merge Attributes of Selected Features
tool allows you to apply same attributes to features without merging their
boundaries. The dialog is the same as the Merge Selected Features tool’s except that unlike that tool,
selected objects are kept with their geometry while some of their attributes are made identical.
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Rotovat symboly bodů
The Rotate Point Symbols
allows you to individually change the rotation of point symbols in the map canvas.
1. First, you need to indicate the field to store the rotation value in. This is made by assigning a field to the symbol
data-defined rotation property:
1. In the Layer Properties ► Symbology dialog, browse to the symbol editor dialog.
2. Click the Data-defined override widget near the Rotation option of the top Marker level (preferably)
of the symbol layers.
3. Choose a field in the Field Type combobox. Values of this field are hence used to rotate each feature’s
symbol accordingly.
You can also check the Store data in project
entry to generate an auxiliary data storage field to control the
rotation value.
Poznámka: Make sure that the same field is assigned to all the symbol layers
Setting the data-defined rotation field at the topmost level of the symbol tree automatically propagates it to
all the symbol layers, a prerequisite to perform graphical symbol rotation with the Rotate Point Symbols tool.
Indeed, if a symbol layer does not have the same field attached to its rotation property, the tool will not work.
Obr. 14.93: Rotating a point symbol
2. Then click on a point symbol in the map canvas with the Rotate Point Symbols
tool
3. Move the mouse around. A red arrow with the rotation value will be visualized (see Obr. 14.93). If you hold
the Ctrl key while moving, the rotation will be done in 15 degree steps.
4. When you get the expected angle value, click again. The symbol is rendered with this new rotation and the
associated field is updated accordingly.
You can right-click to abort symbol rotation.
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Offset Point Symbols
The Offset Point Symbols
allows you to interactively change the rendered position of point symbols in the map canvas.
This tool behaves like the Rotate Point Symbols
tool except that it requires you to connect a field to the data-defined
Offset (X,Y) property of each layer of the symbol. The field will then be populated with the offset coordinates for the
features whose symbol is moved in the map canvas.
1. Associate a field to the data-defined widget of the Offset (X,Y) property of the symbol. If the symbol is made
with many layers, you may want to assign the field to each of them
2. Select the Offset Point Symbols
tool
3. Click a point symbol
4. Move to a new location
5. Click again. The symbol is moved to the new place. Offset values from the original position are stored in the
linked field.
You can right-click to abort symbol offset.
Poznámka: The Offset Point Symbols
tool doesn’t move the point feature itself; you should use the
Vertex Tool (Current Layer)
or Move Feature
tool for this purpose.
Trim/Extend Feature
When a digitized line is too short or too long to snap to another line (missing or crossing the line), it is necessary to
be able to extend or shorten the segment.
The Trim/Extend
tool allows you to also modify (multi)lines AND (multi)polygons. Moreover, it is not necessarily
the end of the lines that is concerned; any segment of a geometry can be modified.
Poznámka: This can lead to invalid geometries.
Poznámka: You must activate segment snapping for this tool to work.
The tool asks you to select a limit (a segment) with respect to which another segment will be extended or trimmed.
Unlike the vertex tool, a check is performed to modify only the layer being edited.
When both segments are in 3D, the tool performs an interpolation on the limit segment to get the Z value.
In the case of a trim, you must select the part that will be shortened by clicking on it.
14.5.5 Shape digitizing
The Shape Digitizing toolbar offers a set of tools to draw regular shapes and curved geometries.
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Add Circular string
The Add circular string
or Add circular string by radius
buttons allow users to add line or polygon features with a circular
geometry.
Creating features with these tools follow the same rule as of other digitizing tools: left-click to place vertices and
right-click to finish the geometry. While drawing the geometry, you can switch from one tool to the other as well as to
the linear geometry tools, creating some coumpound geometries.
Poznámka: Curved geometries are stored as such only in compatible data provider
Although QGIS allows to digitize curved geometries within any editable data format, you need to be using a data
provider (e.g. PostGIS, memory layer, GML or WFS) that supports curves to have features stored as curved, otherwise
QGIS segmentizes the circular arcs.
Draw Circles
There is a set of tools for drawing circles. The tools are described below.
Circles are converted into circular strings. Therefore, as explained in Add Circular string, if allowed by the data
provider, it will be saved as a curved geometry, if not, QGIS will segmentize the circular arcs.
• Add circle from 2 points
: The two points define the diameter and the orientation of the circle. (Left-click, right-
-click)
• Add circle from 3 points
: Draws a circle from three known points on the circle. (Left-click, left-click, right-click)
• Add circle from center and a point
: Draws a circle with a given center and a point on the circle (Left-click, right-click).
When used with the The Advanced Digitizing panel this tool can become a „Add circle from center and
radius“ tool by setting and locking the distance value after first click.
• Add circle from 3 tangents
: Draws a circle that is tangential to three segments. Note that you must activate
snapping to segments (See Nastavení přichytávací tolerance a vyhledání poloměru). Click on a segment to
add a tangent. If two tangents are parallel, an error message appears and the input is cleared. (Left-click,
left-click, right-click)
• Add circle from 2 tangents and a point
: Similar to circle from 3 tangents, except that you have to select two tangents,
enter a radius and select the desired center.
Draw Ellipses
There is a set of tools for drawing ellipses. The tools are described below.
Ellipses cannot be converted as circular strings, so they will always be segmented.
• Add Ellipse from center and two points
: Draws an ellipse with a given center, major axis and minor axis. (Left-click,
left-click, right-click)
• Add Ellipse from center and a point
: Draws an ellipse into a bounding box with the center and a corner. (Left-click,
right-click)
• Add Ellipse from extent
: Draws an ellipse into a bounding box with two opposite corners. (Left-click, right-click)
• Add Ellipse from foci
: Draws an ellipse by 2 points for foci and a point on the ellipse. (Left-click, left-click,
right-click)
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Draw Rectangles
There is a set of tools for drawing rectangles. The tools are described below.
• Rectangle from center and a point
: Draws a rectangle from the center and a corner. (Left-click, right-click)
• Rectangle from extent
: Draws a rectangle from two opposite corners. (Left-click, right-click)
• Rectangle from 3 points (distance)
: Draws an oriented rectangle from three points. The first and second points
determine the length and angle of the first edge. The third point determines the length of the other edge.
One can use The Advanced Digitizing panel to set the length of the edges. (Left-click, left-click, right-click)
• Rectangle from 3 points (projected)
: Same as the preceding tool, but the length of the second edge is computed from
the projection of the third point on the first edge. (Left-click, left-click, right-click)
Obr. 14.94: Draw rectangle from 3 points using distance (right) and projected (left)
Draw Regular Polygons
There is a set of tools for drawing regular polygons. The tools are described below. Left-click to place the first point.
A dialog appears, where you can set the number of polygon edges. Right-click to finish the regular polygon.
• Regular polygon from two points
: Draws a regular polygon where the two points determine the length and angle of
the first edge.
• Regular polygon from center and a point
: Draws a regular polygon from the provided center point. The second point
determines the angle and distance to the middle of an edge.
• Regular polygon from center and a corner
: Same as the preceding tool, but the second point determines the angle and
distante to a vertex.
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14.5.6 The Advanced Digitizing panel
When capturing, reshaping, splitting new or existing geometries you also have the possibility to use the Advanced
Digitizing panel. You can digitize lines exactly parallel or perpendicular to a particular angle or lock lines to specific
angles. Furthermore, you can enter coordinates directly so that you can make a precise definition of your new
geometry.
Obr. 14.95: The Advanced Digitizing panel
The Advanced Digitizing panel can be open either with a right-click on the toolbar, from View ► Panels ► menu or
pressing Ctrl+4. Once the panel is visible, click the Enable advanced digitizing tools
button to activate the set of tools.
Poznámka: The tools are not enabled if the map view is in geographic coordinates.
Concepts
The aim of the Advanced Digitizing tool is to lock coordinates, lengths, and angles when moving the mouse during
the digitalizing in the map canvas.
You can also create constraints with relative or absolute reference. Relative reference means that the next vertex
constraints‘ values will be relative to the previous vertex or segment.
Snapping Settings
Click the button to set the Advanced Digitizing Tool snapping settings. You can make the tool snap to common
angles. The options are:
• Do not snap to common angles
• Snap to 30º angles
• Snap to 45º angles
• Snap to 90º angles
You can also control the snapping to features. The options are:
• Do not snap to vertices or segments
• Snap according to project configuration
• Snap to all layers
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Keyboard shortcuts
To speed up the use of Advanced Digitizing Panel, there are a couple of keyboard shortcuts available:
Key Simple Ctrl+ or Alt+ Shift+
D Set distance Lock distance
A Set angle Lock angle Toggle relative angle to last segment
X Set X coordinate Lock X coordinate Toggle relative X to last vertex
Y Set Y coordinate Lock Y coordinate Toggle relative Y to last vertex
C Toggle construction mode
P Toggle perpendicular and parallel modes
Absolute reference digitizing
When drawing a new geometry from scratch, it is very useful to have the possibility to start digitizing vertexes at
given coordinates.
For example, to add a new feature to a polygonal layer, click the button. You can choose the X and Y coordinates
where you want to start editing the feature, then:
• Click the x text box (or use the X keyboard shortcut).
• Type the X coordinate value you want and press Enter or click the button to their right to lock the mouse
to the X axis on the map canvas.
• Click the y text box (or use the Y keyboard shortcut).
• Type the Y coordinate value you want and press Enter or click the button to their right to lock the mouse
to the Y axis on the map canvas.
Two blue dotted lines and a green cross identify the exact coordinates you entered. Start digitizing by clicking on the
map canvas; the mouse position is locked at the green cross.
Obr. 14.96: Start drawing at given coordinates
You can continue digitizing by free hand, adding a new pair of coordinates, or you can type the segment’s length
(distance) and angle.
If you want to draw a segment of a given length, click the d (distance) text box (keyboard shortcut D), type the distance
value (in map units) and press Enter or click the button on the right to lock the mouse in the map canvas to
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the length of the segment. In the map canvas, the clicked point is surrounded by a circle whose radius is the value
entered in the distance text box.
Obr. 14.97: Fixed length segment
Finally, you can also choose the angle of the segment. As described before , click the a (angle) text box (keyboard
shortcut A), type the angle value (in degrees), and press Enter or click the buttons on the right to lock it. In this
way the segment will follow the desired angle:
Obr. 14.98: Fixed angle segment
Relative reference digitizing
Instead of using absolute values of angles or coordinates, you can also use values relative to the last digitized vertex
or segment.
For angles, you can click the button on the left of the a text box (or press Shift+A) to toggle relative angles to
the previous segment. With that option on, angles are measured between the last segment and the mouse pointer.
For coordinates, click the buttons to the left of the x or y text boxes (or press Shift+X or Shift+Y) to toggle
relative coordinates to the previous vertex. With these options on, coordinates measurement will consider the last
vertex to be the X and Y axes origin.
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Continuous lock
Both in absolute or relative reference digitizing, angle, distance, X and Y constraints can be locked continuously by
clicking the Continuous lock buttons. Using continuous lock allows you to digitize several points or vertexes using
the same constraints.
Parallel and perpendicular lines
All the tools described above can be combined with the Perpendicular
and Parallel
tools. These two tools allow
drawing segments perfectly perpendicular or parallel to another segment.
To draw a perpendicular segment, during the editing click the Perpendicular
icon (keyboard shortcut P) to activate it.
Before drawing the perpendicular line, click on the segment of an existing feature that you want to be perpendicular
to (the line of the existing feature will be colored in light orange); you should see a blue dotted line where your feature
will be snapped:
Obr. 14.99: Perpendicular digitizing
To draw a parallel feature, the steps are the same: click on the Parallel
icon (keyboard shortcut P twice), click on
the segment you want to use as reference and start drawing your feature:
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Obr. 14.100: Parallel digitizing
These two tools just find the right angle of the perpendicular and parallel angle and lock this parameter during your
editing.
Construction mode
You can enable and disable construction mode by clicking on the Construction
icon or with the C keyboard shortcut.
While in construction mode, clicking the map canvas won’t add new vertexes, but will capture the clicks‘ positions
so that you can use them as reference points to then lock distance, angle or X and Y relative values.
As an example, the construction mode can be used to draw some point at an exact distance from an existing point.
With an existing point in the map canvas and the snapping mode correctly activated, you can easily draw other points
at given distances and angles from it. In addition to the button, you have to activate also the construction mode
by clicking the Construction
icon or with the C keyboard shortcut.
Click next to the point from which you want to calculate the distance and click on the d box (D shortcut) type the
desired distance and press Enter to lock the mouse position in the map canvas:
Obr. 14.101: Distance from point
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Before adding the new point, press C to exit the construction mode. Now, you can click on the map canvas, and the
point will be placed at the distance entered.
You can also use the angle constraint to, for example, create another point at the same distance of the original one,
but at a particular angle from the newly added point. Click the Construction
icon or with the C keyboard shortcut
to enter construction mode. Click the recently added point, and then the other one to set a direction segment. Then,
click on the d text box (D shortcut) type the desired distance and press Enter. Click the a text box (A shortcut) type
the angle you want and press Enter. The mouse position will be locked both in distance and angle.
Obr. 14.102: Distance and angle from points
Before adding the new point, press C to exit the construction mode. Now, you can click on the map canvas, and the
point will be placed at the distance and angle entered. Repeating the process, several points can be added.
Obr. 14.103: Points at given distance and angle
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14.5.7 The Processing in-place layer modifier
The Processing menu provides access to a large set of tools to analyze and create new features based on the properties
of the input features or their relations with other features (within the same layer or not). While the common behavior
is to create new layers as outputs, some algorithms also allow modifications to the input layer. This is a handy way to
automate multiple features modification using advanced and complex operations.
To edit features in-place:
1. Select the layer to edit in the Layers panel.
2. Select the concerned features. You can skip this step, in which case the modification will apply to the whole
layer.
3. Press the Edit Features In-Place
button at the top of the Processing toolbox. The list of algorithms is filtered,
showing only those compatible with in-place modifications, i.e.:
• They work at the feature source and not at the layer level.
• They do not change the layer structure, e.g. adding or removing fields.
• They do not change the geometry type, e.g. from line to point layer.
Obr. 14.104: Processing algorithms: all (left) vs polygon in-place editors (right)
4. Find the algorithm you’d like to run and double-click it.
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Poznámka: If the algorithm does not need any additional user-set parameters (excluding the usual input and
output layer parameters), then the algorithm is run immediately without any dialog popup.
1. If parameters other than the usual input or output layers are needed, the algorithm dialog pops up. Fill in
the required information.
2. Click Modify Selected Features or Modify All Features depending on whether there’s an active selection.
Changes are applied to the layer and placed in the edit buffer: the layer is indeed toggled to editing mode with
unsaved modification as indicated by the icon next to the layer name.
5. As usual, press Save layer edits
to commit the changes in the layer. You can also press Undo
to rollback the
whole modification.
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KAPITOLA 15
Working with Raster Data
15.1 Raster Properties Dialog
To view and set the properties for a raster layer, double click on the layer name in the map legend, or right click on
the layer name and choose Properties from the context menu. This will open the Raster Layer Properties dialog.
There are several tabs in the dialog:
• Information
• Source
• Symbology
• Transparency
• Histogram
• Rendering
• Pyramids
• Metadata
• Legend
• QGIS Server
Tip: Live update rendering
The Layer Styling Panel provides you with some of the common features of the Layer properties dialog and is a good
modeless widget that you can use to speed up the configuration of the layer styles and view your changes on the map
canvas.
Poznámka: Because properties (symbology, label, actions, default values, forms…) of embedded layers (see
Vnořování projektů) are pulled from the original project file, and to avoid changes that may break this behavior,
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the layer properties dialog is made unavailable for these layers.
15.1.1 Information Properties
The Information tab is read-only and represents an interesting place to quickly grab summarized information and
metadata for the current layer. Provided information are:
• based on the provider of the layer (format of storage, path, data type, extent, width/height, compression, pixel
size, statistics on bands, number of columns, rows and no-data values of the raster…);
• picked from the provided metadata: access, links, contacts, history… as well as dataset information (CRS,
Extent, bands…).
15.1.2 Source Properties
The Source tab displays basic information about the selected raster, including:
• the Layer name to display in the Layers Panel;
• the Coordinate Reference System: Displays the layer’s Coordinate Reference System (CRS). You can change the
layer’s CRS, by selecting a recently used one in the drop-down list or clicking on the Select CRS
button (see
Coordinate Reference System Selector). Use this process only if the layer CRS is a wrong or not specified. If
you wish to reproject your data, use a reprojection algorithm from Processing or Save it as new dataset.
Obr. 15.1: Raster Layer Properties - Source Dialog
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15.1.3 Symbology Properties
Band rendering
QGIS offers many different Render types. The choice of renderer depends on the data type and the information you’d
like to highlight.
1. Multiband color - if the file comes with several bands (e.g. a satellite image with several bands).
2. Paletted/Unique values - for single band files that come with an indexed palette (e.g. a digital topographic map)
or for general use of palettes for rendering raster layers.
3. Singleband gray - (one band of) the image will be rendered as gray. QGIS will choose this renderer if the file
is neither multiband nor paletted (e.g. a shaded relief map).
4. Singleband pseudocolor - this renderer can be used for files with a continuous palette or color map (e.g. an
elevation map).
5. Hillshade - Creates hillshade from a band.
6. Contours - Generates contours on the fly for a source raster band.
Multiband color
With the multiband color renderer, three selected bands from the image will be used as the red, green or blue
component of the color image. QGIS automatically fetches Min and Max values for each band of the raster and
scales the coloring accordingly. You can control the value ranges in the Min/Max Value Settings section.
A Contrast enhancement method can be applied to the values: ‚No enhancement‘, ‚Stretch to MinMax‘, ‚Stretch and
clip to MinMax‘ and ‚Clip to min max‘.
Poznámka: Contrast enhancement
When adding GRASS rasters, the option Contrast enhancement will always be set automatically to stretch to min max,
even if this is set to another value in the QGIS general options.
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Obr. 15.2: Raster Symbology - Multiband color rendering
Tip: Viewing a Single Band of a Multiband Raster
If you want to view a single band of a multiband image (for example, Red), you might think you would set the Green
and Blue bands to Not Set. But the preferred way of doing this is to set the image type to Singleband gray, and then
select Red as the Gray band to use.
Paletted/Unique values
This is the standard render option for singleband files that include a color table, where a certain color is assigned to
each pixel value. In that case, the palette is rendered automatically.
It can be used for all kinds of raster bands, assigning a color to each unique raster value.
If you want to change a color, just double-click on the color and the Select color dialog appears.
It is also possible to assign labels to the colors. The label will then appear in the legend of the raster layer.
Right-clicking over selected rows in the color table shows a contextual menu to:
• Change Color… for the selection
• Change Opacity… for the selection
• Change Label… for the selection
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Obr. 15.3: Raster Symbology - Paletted unique value rendering
The pulldown menu, that opens when clicking the … (Advanced options) button below the color map to the right,
offers color map loading (Load Color Map from File…) and exporting (Export Color Map to File…), and loading of
classes (Load Classes from Layer).
Singleband gray
This renderer allows you to render a single band layer with a Color gradient: ‚Black to white‘ or ‚White to black‘. You
can change the range of values to color (Min and Max) in the Min/Max Value Settings.
A Contrast enhancement method can be applied to the values: ‚No enhancement‘, ‚Stretch to MinMax‘, ‚Stretch and
clip to MinMax‘ and ‚Clip to min max‘.
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Obr. 15.4: Raster Symbology - Singleband gray rendering
Singleband pseudocolor
This is a render option for single-band files that include a continuous palette. You can also create color maps for
a bands of a multiband raster.
Obr. 15.5: Raster Symbology - Singleband pseudocolor rendering
Using a Band of the layer and a values range, three types of color Interpolation are available:
• Discrete (a <= symbol appears in the header of the Value column)
• Linear
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• Exact (an = symbol appears in the header of the Value column)
The Color ramp drop down lists the available color ramps. You can create a new one and edit or save the currently
selected one. The name of the color ramp will be saved in the configuration and in the QML file.
The Label unit suffix is a label added after the value in the legend.
For classification Mode ‚Equal interval‘, you only need to select the number of classes and press the
button Classify. For Mode ‚Continuous‘, QGIS creates classes automatically depending on Min and Max.
The button Add values manually
adds a value to the table. The button Remove selected row
deletes a value from the
table. Double clicking in the Value column lets you insert a specific value. Double clicking in the Color column opens
the dialog Change color, where you can select a color to apply for that value. Further, you can also add labels for each
color, but this value won’t be displayed when you use the identify feature tool.
Right-clicking over selected rows in the color table shows a contextual menu to:
• Change Color… for the selection
• Change Opacity… for the selection
You can use the buttons Load color map from file
or Export color map to file
to load an existing color table or to save the
color table for later use.
The Clip out of range values allows QGIS to not render pixel greater than the Max value.
Hillshade
Render a band of the raster layer using hillshading.
Obr. 15.6: Raster Symbology - Hillshade rendering
Options:
• Band: The raster band to use.
• Altitude: The elevation angle of the light source (default is 45°).
• Azimuth: The azimuth of the light source (default is 315°).
• Z Factor: Scaling factor for the values of the raster band (default is 1).
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• Multidirectional: Specify if multidirectional hillshading is to be used (default is off).
Contours
This renderer draws contour lines that are calculated on the fly from the source raster band.
Obr. 15.7: Raster Symbology - Contours rendering
Options:
• Input band: the raster band to use.
• Contour interval: the distance between two consecutive contour lines
• Contour symbol: the symbol to apply to the common contour lines.
• Index contour interval: the distance between two consecutive index contours, that is the lines shown in
a distinctive manner for ease of identification, being commonly printed more heavily than other contour lines
and generally labeled with a value along its course.
• Index contour symbol: the symbol to apply to the index contour lines
• Input downscaling: Indicates by how much the renderer will scale down the request to the data provider (default
is 4.0).
For example, if you generate contour lines on input raster block with the same size as the output raster block, the
generated lines would contain too much detail. This detail can be reduced by the „downscale“ factor, requesting
lower resolution of the source raster. For a raster block 1000x500 with downscale 10, the renderer will request
raster 100x50 from provider. Higher downscale makes contour lines more simplified (at the expense of losing
some detail).
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Setting the min and max values
By default, QGIS reports the Min and Max values of the band(s) of the raster. A few very low and/or high values
can have a negative impact on the rendering of the raster. The Min/Max Value Settings frame helps you control the
rendering.
Obr. 15.8: Raster Symbology - Min and Max Value Settings
Available options are:
• User defined: The default Min and Max values of the band(s) can be overridden
• Cumulative count cut: Removes outliers. The standard range of values is 2% to 98%, but it can be adapted
manually.
• Min / max: Uses the whole range of values in the image band.
• Mean +/- standard deviation x: Creates a color table that only considers values within the standard deviation
or within multiple standard deviations. This is useful when you have one or two cells with abnormally high values
in a raster layer that impact the rendering of the raster negatively.
Calculations of the min and max values of the bands are made based on the:
• Statistics extent: it can be Whole raster, Current canvas or Updated canvas. Updated canvas means that min/max
values used for the rendering will change with the canvas extent (dynamic stretching).
• Accuracy, which can be either Estimate (faster) or Actual (slower).
Poznámka: For some settings, you may need to press the Apply button of the layer properties dialog in order to
display the actual min and max values in the widgets.
Color rendering
For all kinds of Band rendering, the Color rendering set.
You can achieve special rendering effects for your raster file(s) by using one of the blending modes (see Režim
míchání).
Further settings can be made by modifying the Brightness, Saturation, Gamma and Contrast. You can also use
a Grayscale option, where you can choose between ‚Off‘, ‚By lightness‘, ‚By luminosity‘ and ‚By average‘. For one
Hue in the color table, you can modify the ‚Strength‘.
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Resampling
The Resampling option has effect when you zoom in and out of an image. Resampling modes can optimize the
appearance of the map. They calculate a new gray value matrix through a geometric transformation.
Obr. 15.9: Raster Symbology - Color rendering and Resampling settings
When applying the ‚Nearest neighbour‘ method, the map can get a pixelated structure when zooming in. This
appearance can be improved by using the ‚Bilinear‘ or ‚Cubic‘ method, which cause sharp edges to be blurred. The
effect is a smoother image. This method can be applied to for instance digital topographic raster maps.
At the bottom of the Symbology tab, you can see a thumbnail of the layer, its legend symbol, and the palette.
15.1.4 Transparency Properties
QGIS has the ability to set the transparency level of a raster layer. Use the transparency slider
to set to what extent the underlying layers (if any) should be visible through the current raster layer. This is very useful
if you overlay raster layers (e.g., a shaded relief map overlayed by a classified raster map). This will make the look
of the map more three dimensional.
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Obr. 15.10: Raster Transparency
Additionally, you can enter a raster value that should be treated as an Additional no data value.
An even more flexible way to customize the transparency is available in the Custom transparency options section:
• Use Transparency band to apply transparency for an entire band.
• Provide a list of pixels to make transparent with corresponding levels of transparency:
1. Click the Add values manually
button. A new row will appear in the pixel list.
2. Enter the Red, Green and Blue values of the pixel and adjust the Percent Transparent to apply.
3. Alternatively, you can fetch the pixel values directly from the raster using the Add values from display
button.
Then enter the transparency value.
4. Repeat the steps to adjust more values with custom transparency.
5. Press the Apply button and have a look at the map.
As you can see, it is quite easy to set custom transparency, but it can be quite a lot of work. Therefore, you
can use the button Export to file
to save your transparency list to a file. The button Import from file
loads your
transparency settings and applies them to the current raster layer.
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15.1.5 Histogram Properties
The Histogram tab allows you to view the distribution of the values in your raster. The histogram is generated when
you press the Compute Histogram button. All existing bands will be displayed together. You can save the histogram
as an image with the button.
At the bottom of the histogram, you can select a raster band in the drop-down menu and Set min/max style for it. The
Prefs/Actions drop-down menu gives you advanced options to customize the histogram:
• With the Visibility option, you can display histograms for individual bands. You will need to select the option
Show selected band.
• The Min/max options allow you to ‚Always show min/max markers‘, to ‚Zoom to min/max‘ and to ‚Update style
to min/max‘.
• The Actions option allows you to ‚Reset‘ or ‚Recompute histogram‘ after you have changed the min or max
values of the band(s).
Obr. 15.11: Raster Histogram
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15.1.6 Rendering Properties
In the Rendering tab, it’s possible to:
• set Scale dependent visibility for the layer: You can set the Maximum (inclusive) and Minimum (exclusive)
scale, defining a range of scales in which the layer will be visible. It will be hidden outside this range. The
Set to current canvas scale
button helps you use the current map canvas scale as a boundary. See Vykreslování
v závislosti na měřítku for more information.
• Refresh layer at interval (seconds): set a timer to automatically refresh individual layers. Canvas updates are
deferred in order to avoid refreshing multiple times if more than one layer has an auto update interval set.
Obr. 15.12: Raster Rendering
15.1.7 Pyramids Properties
High resolution raster layers can slow navigation in QGIS. By creating lower resolution copies of the data (pyramids),
performance can be considerably improved, as QGIS selects the most suitable resolution to use depending on the
zoom level.
You must have write access in the directory where the original data is stored to build pyramids.
From the Resolutions list, select resolutions at which you want to create pyramid levels by clicking on them.
If you choose Internal (if possible) from the Overview format drop-down menu, QGIS tries to build pyramids
internally.
Poznámka: Please note that building pyramids may alter the original data file, and once created they cannot be
removed. If you wish to preserve a ‚non-pyramided‘ version of your raster, make a backup copy prior to pyramid
building.
If you choose External and External (Erdas Imagine) the pyramids will be created in a file next to the original
raster with the same name and a .ovr extension.
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Several Resampling methods can be used for pyramid calculation:
• Nearest Neighbour
• Average
• Gauss
• Cubic
• Cubic Spline
• Laczos
• Mode
• Žádná
Finally, click Build Pyramids to start the process.
Obr. 15.13: Raster Pyramids
15.1.8 Metadata Properties
The Metadata tab provides you with options to create and edit a metadata report on your layer. See vector layer
metadata properties for more information.
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Obr. 15.14: Raster Metadata
15.1.9 Legend Properties
The Legend tab provides you with a list of widgets you can embed within the layer tree in the Layers panel. The
idea is to have a way to quickly access some actions that are often used with the layer (setup transparency, filtering,
selection, style or other stuff…).
By default, QGIS provides a transparency widget but this can be extended by plugins that register their own widgets
and assign custom actions to layers they manage.
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Obr. 15.15: Raster Legend
15.1.10 QGIS Server Properties
From the QGIS Server tab, information can be provided for Description, Attribution, MetadataUrl and LegendUrl.
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Obr. 15.16: QGIS Server in Raster Properties
15.2 Raster Analysis
15.2.1 Raster Calculator
The Raster Calculator in the Raster menu allows you to perform calculations on the basis of existing raster pixel values
(see Obr. 15.17). The results are written to a new raster layer in a GDAL-supported format.
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Obr. 15.17: Raster Calculator
The Raster bands list contains all loaded raster layers that can be used. To add a raster to the raster calculator
expression field, double click its name in the Fields list. You can then use the operators to construct calculation
expressions, or you can just type them into the box.
In the Result layer section, you will need to define an output layer. You can then define the extent of the calculation
area based on an input raster layer, or based on X,Y coordinates and on columns and rows, to set the resolution of
the output layer. If the input layer has a different resolution, the values will be resampled with the nearest neighbor
algorithm.
The Operators section contains all available operators. To add an operator to the raster calculator expression box,
click the appropriate button. Mathematical calculations (+, -, *, … ) and trigonometric functions (sin, cos, tan,
… ) are available. Conditional expressions (=, !=, <, >=, … ) return either 0 for false or 1 for true, and therefore can
be used with other operators and functions.
With the Add result to project checkbox, the result layer will automatically be added to the legend area and can
be visualized.
Rada: See also the Raster calculator algorithm.
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Examples
Convert elevation values from meters to feet
Creating an elevation raster in feet from a raster in meters, you need to use the conversion factor for meters to feet:
3.28. The expression is:
"elevation@1" * 3.28
Using a mask
If you want to mask out parts of a raster – say, for instance, because you are only interested in elevations above 0
meters – you can use the following expression to create a mask and apply the result to a raster in one step.
("elevation@1" >= 0) * "elevation@1"
In other words, for every cell greater than or equal to 0 the conditional expression evaluates to 1, which keeps the
original value by multiplying it by 1. Otherwise the conditional expression evaluates to 0, which sets the raster value
to 0. This creates the mask on the fly.
If you want to classify a raster – say, for instance into two elevation classes, you can use the following expression to
create a raster with two values 1 and 2 in one step.
("elevation@1" < 50) * 1 + ("elevation@1" >= 50) * 2
In other words, for every cell less than 50 set its value to 1. For every cell greater than or equal 50 set its value to 2.
15.2.2 Raster Alignment
This tool is able to take several rasters as input and to align them perfectly, that means:
• reproject to the same CRS,
• resample to the same cell size and offset in the grid,
• clip to a region of interest,
• rescale values when required.
All rasters will be saved in another files.
First, open the tools from Raster ► Align Raster… and click on the Add new raster
button to choose one existing
raster in QGIS. Select an output file to save the raster after the alignment, the resampling method and if the tools
need to Rescale values according to the cell size. The resampling method can be (see Obr. 15.18):
• Nearest Neighbor
• Bilinear (2x2 kernel)
• Cubic (4x4 kernel): Cubic Convolution Approximation
• Cubic B-Spline (4x4 kernel): Cubic B-Spline Approximation
• Lanczos (6x6 kernel): Lanczos windowed sinc interpolation
• Average: computes the average of all non-NODATA contributing pixels
• Mode: selects the value which appears most often of all the sampled points
• Maximum, Minimum, Mediane, First Quartile (Q1) or Third Quartile (Q3) of all non-NODATA
contributing pixels
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Obr. 15.18: Select Raster Resampling Options
In the main Align raster dialog, you can still Edit file settings
or Remove an existing file
from the list of raster layers.
You can also choose one or more other options (see Obr. 15.19):
• Select the Reference Layer,
• Transform into a new CRS,
• Setup a different Cell size,
• Setup a different Grid Offset,
• Clip to Extent: it can be user-defined, bound to a layer or to the map canvas
• Output Size,
• Add aligned raster to the map canvas.
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Obr. 15.19: Raster Alignment
15.3 Georeferencer
The Georeferencer is a tool for generating world files for rasters. It allows you to reference rasters to geographic
or projected coordinate systems by creating a new GeoTiff or by adding a world file to the existing image. The
basic approach to georeferencing a raster is to locate points on the raster for which you can accurately determine
coordinates.
Features
Ikona Účel Ikona Účel
Open raster Start georeferencing
Generate GDAL Script Load GCP Points
Save GCP Points As Transformation settings
Add Point Delete Point
Move GCP Point Pan
Zoom In Zoom Out
Zoom To Layer Zoom Last
Zoom Next Link Georeferencer to QGIS
Link QGIS to Georeferencer Full histogram stretch
Local histogram stretch
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Table Georeferencer: Georeferencer Tools
15.3.1 Usual procedure
As X and Y coordinates (DMS (dd mm ss.ss), DD (dd.dd) or projected coordinates (mmmm.mm)), which correspond
with the selected point on the image, two alternative procedures can be used:
• The raster itself sometimes provides crosses with coordinates „written“ on the image. In this case, you can
enter the coordinates manually.
• Using already georeferenced layers. This can be either vector or raster data that contain the same
objects/features that you have on the image that you want to georeference and with the projection that you
want for your image. In this case, you can enter the coordinates by clicking on the reference dataset loaded in
the QGIS map canvas.
The usual procedure for georeferencing an image involves selecting multiple points on the raster, specifying their
coordinates, and choosing a relevant transformation type. Based on the input parameters and data, the Georeferencer
will compute the world file parameters. The more coordinates you provide, the better the result will be.
The first step is to start QGIS and click on Raster ► Georeferencer, which appears in the QGIS menu bar. The
Georeferencer dialog appears as shown in Obr. 15.20.
For this example, we are using a topo sheet of South Dakota from SDGS. It can later be visualized together with
the data from the GRASS spearfish60 location. You can download the topo sheet here: https://grass.osgeo.org/
sampledata/spearfish_toposheet.tar.gz.
Obr. 15.20: Georeferencer Dialog
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Entering ground control points (GCPs)
1. To start georeferencing an unreferenced raster, we must load it using the button. The raster will show up
in the main working area of the dialog. Once the raster is loaded, we can start to enter reference points.
2. Using the Add Point
button, add points to the main working area and enter their coordinates (see Figure Obr.
15.21). For this procedure you have three options:
• Click on a point in the raster image and enter the X and Y coordinates manually.
• Click on a point in the raster image and choose the From map canvas
button to add the X and Y coordinates
with the help of a georeferenced map already loaded in the QGIS map canvas.
• With the button, you can move the GCPs in both windows, if they are at the wrong place.
3. Continue entering points. You should have at least four points, and the more coordinates you can provide, the
better the result will be. There are additional tools for zooming and panning the working area in order to locate
a relevant set of GCP points.
Obr. 15.21: Add points to the raster image
The points that are added to the map will be stored in a separate text file ([filename].points) usually together
with the raster image. This allows us to reopen the Georeferencer at a later date and add new points or delete existing
ones to optimize the result. The points file contains values of the form: mapX, mapY, pixelX, pixelY. You
can use the Load GCP points
and Save GCP points as
buttons to manage the files.
Defining the transformation settings
After you have added your GCPs to the raster image, you need to define the transformation settings for the
georeferencing process.
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Obr. 15.22: Defining the georeferencer transformation settings
Available Transformation algorithms
A number of transformation algorithms are available, dependent on the type and quality of input data, the nature and
amount of geometric distortion that you are willing to introduce to the final result, and the number of ground control
points (GCPs).
Currently, the following Transformation types are available:
• The Linear algorithm is used to create a world file and is different from the other algorithms, as it does not
actually transform the raster pixels. It allows positioning (translating) the image and uniform scaling, but no
rotation or other transformations. It is the most suitable if your image is a good quality raster map, in a known
CRS, but is just missing georeferencing information. At least 2 GCPs are needed.
• The Helmert transformation also allows rotation. It is particularly useful if your raster is a good quality local
map or orthorectified aerial image, but not aligned with the grid bearing in your CRS. At least 2 GCPs are
needed.
• The Polynomial 1 algorithm allows a more general affine transformation, in particular also a uniform shear.
Straight lines remain straight (i.e., collinear points stay collinear) and parallel lines remain parallel. This
is particularly useful for georeferencing data cartograms, which may have been plotted (or data collected)
with different ground pixel sizes in different directions. At least 3 GCP’s are required.
• The Polynomial algorithms 2-3 use more general 2nd or 3rd degree polynomials instead of just affine
transformation. This allows them to account for curvature or other systematic warping of the image, for instance
photographed maps with curving edges. At least 6 (respectively 10) GCP’s are required. Angles and local scale
are not preserved or treated uniformly across the image. In particular, straight lines may become curved, and
there may be significant distortion introduced at the edges or far from any GCPs arising from extrapolating the
data-fitted polynomials too far.
• The Projective algorithm generalizes Polynomial 1 in a different way, allowing transformations representing
a central projection between 2 non-parallel planes, the image and the map canvas. Straight lines stay straight,
but parallelism is not preserved and scale across the image varies consistently with the change in perspective.
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This transformation type is most useful for georeferencing angled photographs (rather than flat scans) of good
quality maps, or oblique aerial images. A minimum of 4 GCPs is required.
• Finally, the Thin Plate Spline (TPS) algorithm „rubber sheets“ the raster using multiple local polynomials
to match the GCPs specified, with overall surface curvature minimized. Areas away from GCPs will be
moved around in the output to accommodate the GCP matching, but will otherwise be minimally locally
deformed. TPS is most useful for georeferencing damaged, deformed, or otherwise slightly inaccurate maps,
or poorly orthorectified aerials. It is also useful for approximately georeferencing and implicitly reprojecting
maps with unknown projection type or parameters, but where a regular grid or dense set of ad-hoc GCPs can
be matched with a reference map layer. It technically requires a minimum of 10 GCPs, but usually more to be
successful.
In all of the algorithms except TPS, if more than the minimum GCPs are specified, parameters will be fitted so that the
overall residual error is minimized. This is helpful to minimize the impact of registration errors, i.e. slight imprecisions
in pointer clicks or typed coordinates, or other small local image deformations. Absent other GCPs to compensate,
such errors or deformations could translate into significant distortions, especially near the edges of the georeferenced
image. However, if more than the minimum GCPs are specified, they will match only approximately in the output.
In contrast, TPS will precisely match all specified GCPs, but may introduce significant deformations between nearby
GCPs with registration errors.
Define the Resampling method
The type of resampling you choose will likely depend on your input data and the ultimate objective of the exercise.
If you don’t want to change statistics of the raster (other than as implied by nonuniform geometric scaling if using
other than the Linear, Helmert, or Polynomial 1 transformations), you might want to choose ‚Nearest neighbour‘. In
contrast, ‚cubic resampling‘, for instance, will usually generate a visually smoother result.
It is possible to choose between five different resampling methods:
1. Nearest neighbour
2. Linear
3. Cubic
4. Cubic Spline
5. Lanczos
Define the transformation settings
There are several options that need to be defined for the georeferenced output raster.
• The Create world file checkbox is only available if you decide to use the linear transformation type, because
this means that the raster image actually won’t be transformed. In this case, the Output raster field is not
activated, because only a new world file will be created.
• For all other transformation types, you have to define an Output raster. As default, a new file
([filename]_modified) will be created in the same folder together with the original raster image.
• As a next step, you have to define the Target SRS (Spatial Reference System) for the georeferenced raster (see
Práce s projekcemi).
• If you like, you can generate a pdf map and also a pdf report. The report includes information about the
used transformation parameters, an image of the residuals and a list with all GCPs and their RMS errors.
• Furthermore, you can activate the Set Target Resolution checkbox and define the pixel resolution of the
output raster. Default horizontal and vertical resolution is 1.
• The Use 0 for transparency when needed can be activated, if pixels with the value 0 shall be visualized
transparent. In our example toposheet, all white areas would be transparent.
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• Finally, Load in QGIS when done loads the output raster automatically into the QGIS map canvas when the
transformation is done.
Show and adapt raster properties
Clicking on the Raster properties option in the Settings menu opens the Layer properties dialog of the raster file that
you want to georeference.
Configure the georeferencer
• You can define whether you want to show GCP coordinates and/or IDs.
• As residual units, pixels and map units can be chosen.
• For the PDF report, a left and right margin can be defined and you can also set the paper size for the PDF map.
• Finally, you can activate to Show Georeferencer window docked.
Running the transformation
After all GCPs have been collected and all transformation settings are defined, just press the Start georeferencing
button to create the new georeferenced raster.
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Working with Mesh Data
16.1 What’s a mesh?
A mesh is an unstructured grid usually with temporal and other components. The spatial component contains
a collection of vertices, edges and faces in 2D or 3D space:
• vertices - XY(Z) points (in the layer’s coordinate reference system)
• edges - connect pairs of vertices
• faces - a face is a set of edges forming a closed shape - typically a triangle or a quadrilateral (quad), rarely
polygons with more vertices
Obr. 16.1: Different mesh types
QGIS can currently render mesh data using triangles or regular quads.
Mesh provides information about the spatial structure. In addition, the mesh can have datasets (groups) that assign
a value to every vertex. For example, having a triangular mesh with numbered vertices as shown in the image below:
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Obr. 16.2: Triangular grid with numbered vertices
Each vertex can store different datasets (typically multiple quantities), and those datasets can also have a temporal
dimension. Thus, a single file may contain multiple datasets.
The following table gives an idea about the information that can be stored in mesh datasets. Table columns represent
indices of mesh vertices, each row represents one dataset. Datasets can have different datatypes. In this case, it stores
wind velocity at 10m at a particular moments in time (t1, t2, t3).
In a similar way, the mesh dataset can also store vector values for each vertex. For example, wind direction vector at
the given time stamps:
10 metre wind 1 2 3 …
10 metre speed at time=t1 17251 24918 32858 …
10 metre speed at time=t2 19168 23001 36418 …
10 metre speed at time=t3 21085 30668 17251 …
… … … … …
10m wind direction time=t1 [20,2] [20,3] [20,4.5] …
10m wind direction time=t2 [21,3] [21,4] [21,5.5] …
10m wind direction time=t3 [22,4] [22,5] [22,6.5] …
… … … … …
We can visualize the data by assigning colors to values (similarly to how it is done with Singleband pseudocolor raster
rendering) and interpolating data between vertices according to the mesh topology. It is common that some quantities
are 2D vectors rather than being simple scalar values (e.g. wind direction). For such quantities it is desirable to display
arrows indicating the directions.
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Obr. 16.3: Possible visualisation of mesh data
16.2 Supported formats
QGIS accesses mesh data using the MDAL drivers. Hence, the natively supported formats are:
• NetCDF: Generic format for scientific data
• GRIB: Format commonly used in meteorology
• XMDF: As an example, hydraulic outputs from TUFLOW modelling package
• DAT: Outputs of various hydrodynamic modelling packages (e.g. BASEMENT, HYDRO_AS-2D, TUFLOW)
• 3Di: 3Di modelling package format based on Climate and Forecast Conventions (http://cfconventions.org/)
• Some examples of mesh datasets can be found at https://apps.ecmwf.int/datasets/data/interim-full-daily/
levtype=sfc/
To load a mesh dataset into QGIS, use the Mesh tab in the Data Source Manager dialog. Read Loading a mesh
layer for more details.
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16.3 Mesh Dataset Properties
16.3.1 Information Properties
Obr. 16.4: Mesh Layer Properties
The Information tab is read-only and represents an interesting place to quickly grab summarized information and
metadata on the current layer. Provided information are (based on the provider of the layer) uri, vertex count, face
count and dataset groups count.
16.3.2 Source Properties
The Source tab displays basic information about the selected mesh, including:
• the Layer name to display in the Layers panel
• setting the Coordinate Reference System: Displays the layer’s Coordinate Reference System (CRS). You can
change the layer’s CRS by selecting a recently used one in the drop-down list or clicking on Select CRS
button (see Coordinate Reference System Selector). Use this process only if the CRS applied to the layer is wrong
or if none was applied.
Use the Assign Extra Dataset to Mesh button to add more groups to the current mesh layer.
16.3.3 Symbology Properties
Click the Symbology button to activate the dialog as shown in the following image:
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Obr. 16.5: Mesh Layer Symbology
Symbology properties are divided in several tabs:
• General
• Contours Symbology
• Vectors Symbology
• Rendering
General
The tab presents the following items:
• groups available in the mesh dataset
• dataset in the selected group(s), for example, if the layer has a temporal dimension
• metadata if available
• blending mode available for the selected dataset.
The slider , the combo box and the |<, <, >, >| buttons allow to explore another dimension
of the data, if available. As the slider moves, the metadata is presented accordingly. See the figure Mesh groups below
as an example. The map canvas will display the selected dataset group as well.
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Obr. 16.6: Dataset in Selected Group(s)
You can apply symbology to each group using the tabs.
Contours Symbology
Under Groups, click on to show contours with default visualization parameters.
In the tab you can see and change the current visualization options of contours for the selected group, as shown
in Obr. 16.7 below:
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Obr. 16.7: Styling Contours in a Mesh Layer
Use the slide bar or combo box to set the opacity of the current group.
Use Load to adjust the min and max values of the current group.
The Interpolation list contains three options to render contours: Linear, Discrete and Exact.
The Color ramp widget opens the color ramp drop-down shortcut.
The Label unit suffix is a label added after the value in the legend.
By selecting Continuous in the classification Mode, QGIS creates classes automatically considering the Min and Max
values. With ‘Equal interval’, you only need to select the number of classes using the combo box Classes and press
the button Classify.
The button Add values manually
adds a value to the individual color table. The button Remove selected row
deletes
a value from the individual color table. Double clicking on the value column lets you insert a specific value. Double
clicking on the color column opens the dialog Change color, where you can select a color to apply on that value.
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Vectors Symbology
In the tab , click on to display vectors if available. The map canvas will display the vectors in the selected
group with default parameters. Click on the tab to change the visualization parameters for vectors as shown in
the image below:
Obr. 16.8: Styling Vectors in a Mesh Layer
The line width can be set using the combo box or typing the value. The color widget opens the dialog Change color,
where you can select a color to apply to vectors.
Enter values for Min and Max to filter vectors according to their magnitude.
Check on the box Display Vectors on User Grid and specify the X spacing and the Y spacing, QGIS will render
the vector considering the given spacing.
With the Head Options Head Options, QGIS allows the shape of the arrow head to be set by specifying width and
length (in percentage).
Vector’s Arrow length can be rendered in QGIS in three different ways:
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• Defined by Min and Max: You specify the minimum and maximum length for the vectors, QGIS will adjust
their visualization accordingly
• Scale to magnitude: You specify the (multiplying) factor to use
• Fixed: all the vectors are shown with the same length
Vykreslování
In the tab , QGIS offers two possibilities to display the grid, as shown in Obr. 16.9:
• Native Mesh Rendering that shows quadrants
• Triangular Mesh Rendering that display triangles
Obr. 16.9: Mesh Rendering
The line width and color can be changed in this dialog, and both the grid renderings can be turned off.
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Working with Vector Tiles
17.1 What are Vector Tiles?
Vector tiles are packets of geographic data, packaged into pre-defined roughly-square shaped „tiles“ for transfer over
the web. They combine pre-rendered raster map tiles and vector map tiles. The vector tile server returns vector
map data, which has been clipped to the boundaries of each tile, instead of a pre-rendered map image. The clipped
tiles represent the zoom-levels of the vector tile service, derived from a pyramid approach. Using this structure, the
data-transfer is reduced in comparison to un-tiled vector maps. Only data within the current map view, and at the
current zoom level need to be transferred. Also, compared to a tiled raster map, data transfer is also greatly reduced,
as vector data is typically much smaller than a rendered bitmap. Vector tiles do not have any styling information
assigned so QGIS needs to apply a cartographic style in order to display the data.
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Obr. 17.1: Pyramid structure of vector tiles with zoom-levels
17.2 Supported Formats
There is support for vector tiles through:
• remote sources (HTTP/S) - with XYZ template - type=xyz&url=http://example.com/{z}/{x}/
{y}.pbf
• local files - with XYZ template - e.g. type=xyz&url=file:///path/to/tiles/{z}/{x}/{y}.
pbf
• local MBTiles database - e.g. type=mbtiles&url=file:///path/to/file.mbtiles
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KAPITOLA 18
Laying out the maps
With Print Layouts and Reports you can create maps and atlases, and print them or save them as image, PDF or SVG
files.
18.1 Overview of the Print Layout
The print layout provides growing layout and printing capabilities. It allows you to add elements such as the QGIS
map canvas, text labels, images, legends, scale bars, basic shapes, arrows, attribute tables and HTML frames. You
can size, group, align, position and rotate each element and adjust their properties to create your layout. The layout
can be printed or exported to image formats, PostScript, PDF or to SVG. You can save the layout as a template and
load it again in another session. Finally, generating several maps based on a template can be done through the atlas
generator.
18.1.1 Sample Session for beginners
Before you start to work with the print layout, you need to load some raster or vector layers in the QGIS map canvas
and adapt their properties to suit your own convenience. After everything is rendered and symbolized to your liking,
click the New Print Layout
icon in the toolbar or choose File ► New Print Layout. You will be prompted to choose
a title for the new layout.
To demonstrate how to create a map please follow the next instructions.
1. On the left side, select the Add map
toolbar button and draw a rectangle on the canvas holding down the left
mouse button. Inside the drawn rectangle the QGIS map view to the canvas.
2. Select the Add scalebar
toolbar button and click with the left mouse button on the print layout canvas.
A scalebar will be added to the canvas.
3. Select the Add legend
toolbar button and draw a rectangle on the canvas holding down the left mouse button.
Inside the drawn rectangle the legend will be drawn.
4. Select the Select/Move item
icon to select the map on the canvas and move it a bit.
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5. While the map item is still selected you can also change the size of the map item. Click while holding down the
left mouse button, in a white little rectangle in one of the corners of the map item and drag it to a new location
to change its size.
6. Click the Item Properties panel on the left down side and find the setting for the orientation. Change the value
of the setting Map orientation to ‚15.00° ‚. You should see the orientation of the map item change.
7. Now, you can print or export your print layout to image formats, PDF or to SVG with the export tools in Layout
menu.
8. Finally, you can save your print layout within the project file with the Save Project
button.
You can add multiple elements to the print layout. It is also possible to have more than one map view or legend or
scale bar in the print layout canvas, on one or several pages. Each element has its own properties and, in the case of
the map, its own extent. If you want to remove any elements from the layout canvas you can do that with the Delete
or the Backspace key.
18.1.2 The Layout Manager
The Layout Manager is the main window to manage print layouts in the project. It gives you an overview of existing
print layouts and reports in the project and offers tools to:
• search for a layout;
• add new print layout or new report from scratch, template or duplicating an existing one;
• rename or delete any of them;
• open them in the project.
To open the layout manager dialog:
• from the main QGIS dialog, select Project ► Layout Manager… menu or click on the Layout Manager
button
in the Project Toolbar;
• from a print layout or report dialog, select Layout ► Layout Manager… menu or click on the Layout Manager
button in the Layout Toolbar.
Obr. 18.1: The Print Layout Manager
The layout manager lists in its upper part all the available print layouts or reports in the project with tools to:
• show the selection: you can select multiple reports and/or print layout(s) and open them in one-click. Double-click
a name also opens it;
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• duplicate the selected print layout or report (available only if one item is selected): it creates a new dialog using
the selected one as template. You’ll be prompted to choose a new title for the new layout;
• rename the report or layout (available only if one item is selected): you’ll be prompted to choose a new title for
the layout;
• remove the layout: the selected print layout(s) will be deleted from the project.
In the lower part, it’s possible to create new print layouts or reports from scratch or a template. By default, QGIS will
look for templates in the user profile and the application template directories (accessible with the two buttons at the
bottom of the frame) but also in any folder declared as Path(s) to search for extra print templates in Settings ► Options
► Layouts. Found templates are listed in the combobox. Select an item and press the Create button to generate a new
report or print layout.
You can also use layout templates from a custom folder; in that case, select specific in the templates drop-down list,
browse to the template and press Create.
Tip: Creating template-based print layouts from Browser panel
Drag-and-drop a print layout template .qpt file from any file browser onto the map canvas or double-click it in the
Browser panel generates a new print layout from the template.
18.1.3 Menus, tools and panels of the print layout
Opening the print layout provides you with a blank canvas that represents the paper surface when using the print
option. Initially you find buttons on the left beside the canvas to add print layout items: the current QGIS map canvas,
text labels, images, legends, scale bars, basic shapes, arrows, attribute tables and HTML frames. In this toolbar you
also find buttons to navigate, zoom in on an area and pan the view on the layout a well as buttons to select any layout
item and to move the contents of the map item.
Obr. 18.2 shows the initial view of the print layout before any elements are added.
Obr. 18.2: Print Layout
On the right beside the canvas you find two set of panels. The upper one holds the panels Items and Undo History and
the lower holds the panels Layout, Item properties and Atlas generation.
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• The Items panel provides a list of all the print layout items added to the canvas and ways to globally interact
with them (see The Items Panel for more information).
• The Undo History panel displays a history of all changes applied to the layout. With a mouse click, it is possible
to undo and redo layout steps back and forth to a certain status.
• The Layout panel allows you to set general parameters to apply to the layout when exporting or working within
(see The Layout Panel for more details);
• The Item Properties panel displays the properties for the selected item. Click the Select/Move item
icon to select
an item (e.g., legend, scale bar or label) on the canvas. Then click the Item Properties panel and customize the
settings for the selected item (see Layout Items for detailed information on each item settings).
• The Atlas panel allows you to enable the generation of an atlas for the current layout and gives access to its
parameters (see Generate an Atlas for detailed information on atlas generation usage).
In the bottom part of the print layout window, you can find a status bar with mouse position, current page number,
a combo box to set the zoom level, the number of selected items if applicable and, in the case of atlas generation, the
number of features.
In the upper part of the print layout window, you can find menus and other toolbars. All print layout tools are available
in menus and as icons in a toolbar.
The toolbars and the panels can be switched off and on using the right mouse button over any toolbar or through View
► Toolbars ► or View ► Panels ►.
Menus and Tools
Layout menu
The Layout provides action to manage the layout:
• Save the project file directly from the print layout window.
• Create a new and blank print layout with New Layout….
• Duplicate Layout… : Create a new print layout by duplicating the current one.
• Remove the current layout with Delete Layout….
• Open the Layout Manager….
• Layouts ► : Open an existing print layout.
Once the layout is designed, with Save as Template and Add Items from Template icons, you can save the
current state of a print layout session as a .qpt template file and load its items again in another session/print layout.
In the Layout menu, there are also powerful ways to share geographical information produced with QGIS that can be
included in reports or published. These tools are Export as Image…, Export as PDF…, Export as SVG…
and Print….
Below is a list of all the available tools in this menu with some convenient information.
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Tool Zkratka Panel nástrojů Reference
Save Project Ctrl+S Layout Introducing QGIS projects
New Layout Ctrl+N Layout The Layout Manager
Duplicate Layout Layout The Layout Manager
Delete Layout
Layout Manager… Layout The Layout Manager
Layouts ►
Layout Properties… The Layout Panel
Rename Layout…
Add Pages… Layout Working with the page properties
Add Items from Template Layout Creating a layout item
Save as Template… Layout The Layout Manager
Export as Image… Layout Export as Image
Export as SVG… Layout Export as SVG
Export as PDF… Layout Export as PDF
Page Setup… Ctrl+Shift+P
Print… Ctrl+P Layout Creating an Output
Close Ctrl+Q
Edit menu
The Edit menu offers tools to manipulate print layout items. It includes common actions like selection tools,
Copy/Cut/Paste and undo/redo (see The Undo History Panel: Revert and Restore actions) functionality for the items
in the layout.
When using the Paste action, the elements will be pasted according to the current mouse position. Using the Edit ►
Paste in Place action or pressing Ctrl+Shift+V will paste the items into the current page, at the same position
they were in their initial page. It ensures to copy/paste items at the same place, from page to page.
Below is a list of all the available tools in this menu with some convenient information.
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Tabulka 18.1: Available Tools
Tool Zkratka Panel
nástrojů
Reference
Undo (last change) Ctrl+Z Layout The Undo History Panel: Revert and
Restore actions
Redo (last reverted change) Ctrl+Y Layout The Undo History Panel: Revert and
Restore actions
Delete Del
Cut Ctrl+X
Copy Ctrl+C
Paste Ctrl+V
Paste in place Ctrl+Shift+V
Select All Ctrl+A
Deselect all Ctrl+Shift+A
Invert Selection
Select Next Item Below Ctrl+Alt+[
Select Next Item above Ctrl+Alt+]
Pan Layout P Toolbox
Zoom Z Toolbox
Select/Move Item V Toolbox Interacting with layout items
Move Content C Toolbox The Map Item
Edit Nodes Item Toolbox The Node-Based Shape Items
View menu
The View menu gives access to navigation tools and helps to configure general behavior of the print layout. Beside
the common zoom tools, you have means to:
• Refresh view
(if you find the view in an inconsistent state);
• enable a grid you could snap items to when moving or creating them. Grids setting is done in Settings ► Layout
Options… or in the Layout Panel;
• enable guides you could snap items to when moving or creating them. Guides are red lines that you can create
by clicking in the ruler (above or at the left side of the layout) and drag and drop to the desired location;
• Smart Guides: uses other layout items as guides to dynamically snap to as you move or reshape an item;
• Clear Guides to remove all current guides;
• Show Bounding box around the items to better identify your selection;
• Show Rules around the layout;
• Show Pages or set up pages to transparent. Often layout is used to create non-print layouts, e.g. for inclusion
in presentations or other documents, and it’s desirable to export the composition using a totally transparent
background. It’s sometimes referred to as „infinite canvas“ in other editing packages.
In the print layout, you can change the zoom level using the mouse wheel or the slider and combo box in the status
bar. If you need to switch to pan mode while working in the layout area, you can hold the Spacebar or the mouse
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wheel. With Ctrl+Spacebar, you can temporarily switch to Zoom In mode, and with Ctrl+Alt+Spacebar,
to Zoom Out mode.
Panels and toolbars can be enabled from the View ► menu. To maximise the space available to interact with
a composition you can check the View ► Toggle Panel Visibility option or press Ctrl+Tab; all panels are
hidden and only previously visible panels are restored when unchecked.
It’s also possible to switch to a full screen mode to have more space to interact with by pressing F11 or using View
► Toggle Full Screen.
Tool Zkratka Panel nástrojů Reference
Refresh F5 Navigation
Preview ►
Přiblížit Ctrl++ Navigation
Oddálit Ctrl+- Navigation
Zoom to 100% Ctrl+1 Navigation
Přiblížit na rozměry okna Ctrl+0 Navigation
Zoom to Width
Show Grid Ctrl+' Guides and Grid
Snap to Grid Ctrl+Shift+' Guides and Grid
Show Guides Ctrl+; Guides and Grid
Snap to Guides Ctrl+Shift+; Guides and Grid
Smart Guides Ctrl+Alt+;
Manage Guides… The Guides Panel
Clear Guides The Guides Panel
Show Rulers Ctrl+R
Show Bounding Boxes Ctrl+Shift+B
Show Pages
Nástrojové lišty ► Panely a nástrojové lišty
Panely ► Panely a nástrojové lišty
Toggle Full Screen F11 Zobrazit
Toggle Panel Visibility Ctrl+Tab Zobrazit
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Items menu
The Items helps you configure items‘ position in the layout and the relations between them (see Interacting with layout
items).
Tool Zkratka Panel nástrojů Reference
Group Ctrl+G Actions Grouping items
Ungroup Ctrl+Shift+G Actions Grouping items
Raise Ctrl+] Actions Alignment
Lower Ctrl+[ Actions Alignment
Bring to Front Ctrl+Shift+] Actions Alignment
Send to Back Ctrl+Shift+[ Actions Alignment
Lock Selected Items Ctrl+L Actions Locking items
Unlock All Ctrl+Shift+L Actions Locking items
Align Items ► Actions Alignment
Distribute Items ► Actions Moving and resizing items
Resize ► Actions Moving and resizing items
Add Item menu
These are tools to create layout items. Each of them is deeply described in Layout Items chapter.
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Tool Panel nástrojů Reference
Add Map Toolbox The Map Item
Add Picture Toolbox The Picture Item
Add Label Toolbox The Label Item
Add Legend Toolbox The Legend Item
Add Scale Bar Toolbox The Scale Bar Item
Add North Arrow Toolbox The North Arrow Item
Add Shape ► Toolbox The Regular Shape Item
► Add Rectangle Toolbox The Regular Shape Item
► Add Ellipse Toolbox The Regular Shape Item
► Add Triangle Toolbox The Regular Shape Item
Add Marker Toolbox
Add Arrow Toolbox The Arrow Item
Add Node Item ► Toolbox The Node-Based Shape Items
► Add Polygon Toolbox The Node-Based Shape Items
► Add Polyline Toolbox The Node-Based Shape Items
Add HTML Toolbox The HTML Frame Item
Add Attribute Table Toolbox Položka atributové tabulky
Add Fixed Table Toolbox The fixed table item
Add 3D Map Toolbox The 3D Map Item
Atlas menu
Tool Zkratka Panel nástrojů Reference
Preview Atlas Ctrl+ALt+/ Atlas Preview and generate an atlas
First Feature Ctrl+< Atlas Preview and generate an atlas
Previous Feature Ctrl+, Atlas Preview and generate an atlas
Next Feature Ctrl+. Atlas Preview and generate an atlas
Last feature Ctrl+> Atlas Preview and generate an atlas
Print Atlas… Atlas Preview and generate an atlas
Export Atlas as Images… Atlas Preview and generate an atlas
Export Atlas as SVG… Atlas Preview and generate an atlas
Export Atlas as PDF… Atlas Preview and generate an atlas
Atlas Settings Atlas Generate an Atlas
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Settings Menu
The Settings ► Layout Options… menu is a shortcut to Settings ► Options ► Layouts menu of QGIS main canvas.
Here, you can set some options that will be used as default on any new print layout:
• Layout defaults let you specify the default font to use;
• With Grid appearance, you can set the grid style and its color. There are three types of grid: Dots, Solid lines
and Crosses;
• Grid and guide defaults defines spacing, offset and tolerance of the grid (see Guides and Grid for more details);
• Layout Paths: to manage list of custom paths to search print templates.
Contextual menus
Depending on where you right-click in the print layout dialog, you open a contextual menu with various features:
• Right-click on the menu bar or any toolbar and you get the list of layout panels and toolbars you can enable or
disable in one-click.
• Right-click over a ruler and you can Show Guides, Snap to Guides, Manage Guides… opening the Guides
panel or Clear Guides. It’s also possible to hide the rulers.
• Right-click in the print layout canvas and:
– You’ll be able to Undo and Redo recent changes, or Paste any copied item (only available if no item
is selected).
– If you click over a page, you can additionally access the current Page Properties panel or Remove Page.
– If you click on a selected item then you can cut or copy it as well as open the Item Properties panel.
– If more than one item are selected, then you can either group them and/or ungroup if at least one group
is already in the selection.
• Right-click inside a text box or spinbox widget of any layout panel provides edit options to manipulate its
content.
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The Layout Panel
In the Layout panel, you can define the global settings of your print layout.
Obr. 18.3: Layout Settings in the Print Layout
General settings
In a print layout, you can use more than one map item. The Reference map represents the map item to use as the
layout’s master map. It’s assigned as long as there’s a map item in the layout. The layout will use this map in any
of their properties and variables calculating units or scale. This includes exporting the print layout to georeferenced
formats.
Moreover, new layout items such as scale bar, legend or north arrow have by default their settings (orientation,
displayed layers, scale, …) bound to the map item they are drawn over, and fall back to the reference map if no
overlapping map.
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Guides and Grid
You can put some reference marks on your paper sheet to help you accurately place some items. These marks can be:
• simple horizontal or vertical lines (called Guides) put at the position you want (see The Guides Panel for guides
creation).
• or regular Grid: a network of horizontal and vertical lines superimposed over the layout.
Settings like Grid spacing or Grid offset can be adjusted in this group as well as the Snap tolerance to use for items.
The tolerance is the maximum distance below which the mouse cursor is snapped to a grid or a guide, while moving,
resizing or creating an item.
Whether grid or guides should be shown is set in View menu. There, you can also decide if they might be used to
snap layout items. When both a grid line and a guide line are within tolerance of a point, guides will always take
precedence - since they have been manually set (hence, assumption that they have been explicitly placed at highly
desirable snapping locations, and should be selected over the general grid).
Poznámka: In the Settings ► Layout Options menu, you can also set the grid and guides parameters exposed above.
However, these options will only apply as defaults to new print layouts.
Export settings
You can define a resolution to use for all exported maps in Export resolution. This setting can then be overridden each
time you export a map.
Because of some advanced rendering options (blending mode, effects…), a layout item may need rasterization in order
to be exported correctly. QGIS will individually rasterize it without forcing every other item to also be rasterized.
This allows printing or saving as PostScript or PDF to keep items as much as possible as vectors, e.g. a map item
with layer opacity won’t force labels, scale bars, etc to be rasterized too. You can however:
• force all the items to be rasterized checking the Print as raster box;
• or use the opposite option, i.e. Always export as vectors, to force the export to keep items as vectors when
exported to a compatible format. Note that in some cases, this could cause the output to look different to
layout.
Where the format makes it possible (e.g., .TIF, .PDF) exporting a print layout results by default in a georeferenced
file (based on the Reference map item in the General settings group). For other formats, georeferenced output requires
you to generate a world file by checking Save world file. The world file is created beside the exported map(s), has
the name of the page output with the reference map item and contains information to georeference it easily.
Resize layout to content
Using the Resize page tool in this group, you create a unique page composition whose extent covers the current contents
of the print layout (with some optional margins around the cropped bounds).
Note that this behavior is different from the crop to content option in that all the items are placed on a real and unique
page in replacement of all the existing pages.
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Variables
The Variables lists all the variables available at the layout’s level (which includes all global and project’s variables).
It also allows the user to manage layout-level variables. Click the button to add a new custom layout-level variable.
Likewise, select a custom layout-level variable from the list and click the button to remove it.
More information on variables usage in the General Tools section.
Obr. 18.4: Variables Editor in the Print Layout
Working with the page properties
A layout can be composed of several pages. For instance, a first page can show a map canvas, and a second page can
show the attribute table associated with a layer, while a third one shows an HTML frame linking to your organization
website. Or you can add many types of items on each page.
Adding a new page
Futhermore, a layout can be made using different size and/or orientation of pages. To add a page, select the Add
Pages… tool from the Layout menu or Layout Toolbar. The Insert Pages dialog opens and you are asked to fill:
• the number of pages to insert;
• the position of the page(s): before or after a given page or at the end of the print layout;
• The Page size: it could be of a preset format page (A4, B0, Legal, Letter, ANSI A, Arch A and their
derivatives as well as a resolution type, such as 1920x1080 or 1024x768) with associated Orientation
(Portrait or Landscape).
The page size can also be of a custom format; In that case, you’d need to enter its Width and Height (with
locked size ratio if needed) and select the unit to use among mm, cm, px, pt, in, ft… Conversion of entered
values is automatically applied when switching from one unit to another.
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Obr. 18.5: Creating a new page in the Print Layout
Updating page properties
Any page can be later customized through the Page Item Properties panel. Right-click on a page and select Page
Properties…. The Item Properties panel opens with settings such as:
• the Page size frame described above. You can modify each property using the data defined override options
(see Explore Data-defined override buttons with atlas for a use case);
• the Exclude page from exports to control whether the current page with its content should be included in
the layout output;
• the Background of the current page using the color or symbol you want.
Obr. 18.6: Page properties dialog
The Guides Panel
Guides are vertical or horizontal line references you can place on a layout page to assist you on items placement, when
creating, moving or resizing them. To be active, guides require the View ► Show Guides and View ► Snap to Guides
options to be checked. To create a guide, there are two different methods:
• if the View ► Show Rulers option is set, drag out a ruler and release the mouse button within the page area, at
the desired position.
• for more precision, use the Guides panel from the View ► Toolbox ► or by selecting Manage guides for page…
from the page’s contextual menu.
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Obr. 18.7: The Guides panel
The Guides panel allows creation of snap lines at specific locations:
1. Select the Page you’d like to add the guides to
2. Click the Add new guide
button and enter the coordinates of the horizontal or vertical line. The origin is at the
top left corner. Different units are available for this.
The panel also allows adjusting the position of existing guides to exact coordinates: double-click and replace
the value.
3. The Guides panel lists only the items for the current page. It allows creation or removal of guides only in the
current page. However, you can use the Apply to All Pages button to replicate the guide configuration of the
current page to the other pages in the layout.
4. To delete a guide, select it and press the Remove selected guide
button. Use Clear All Guides to remove all the
guides in the current page.
Tip: Snapping to existing layout items
Other than guides and grids, you can use existing items as snapping references when moving, resizing or creating new
items; these are called smart guides and require View ► Smart Guides option to be checked. Anytime the mouse
pointer is close to an item’s bound, a snapping cross appears.
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The Items Panel
The Items panel offers some options to manage selection and visibility of items. All the items added to the print layout
canvas (including items group) are shown in a list and selecting an item makes the corresponding row selected in the
list as well as selecting a row does select the corresponding item in the print layout canvas. This is thus a handy way
to select an item placed behind another one. Note that a selected row is shown as bold.
For any selected item, you can :
• set it visible or not;
• lock or unlock its position;
• sort its Z position. You can move up and down each item in the list with a click and drag. The upper item in
the list will be brought to the foreground in the print layout canvas. By default, a newly created item is placed
in the foreground.
• change the item ID by double-clicking the text;
• right-click an item and copy or delete it or open its properties panel.
Once you have found the correct position for an item, you can lock it by ticking the box in column. Locked
items are not selectable on the canvas. Locked items can be unlocked by selecting the item in the Items panel and
unchecking the tickbox or you can use the icons on the toolbar.
The Undo History Panel: Revert and Restore actions
During the layout process, it is possible to revert and restore changes. This can be done with the revert and restore
tools available in the Edit menu, the Layout toolbar or the contextual menu any time you right-click in the print layout
area:
• Revert last change
• Restore last change
This can also be done by mouse click within the Undo history panel (see Obr. 18.8). The History panel lists the last
actions done within the print layout. Just select the point you want to revert to and once you do new action all the
actions done after the selected one will be removed.
Obr. 18.8: Undo History in the Print Layout
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18.2 Layout Items
18.2.1 Layout Items Common Options
QGIS provides a large set of items to layout a map. They can be of map, legend, scale bar, picture, table, north arrow,
image type… They however share some common options and behavior that are exposed below.
Creating a layout item
Items can be created using different tools, either from scratch or based on existing items.
To create a layout item from scratch:
1. Select the corresponding tool either from the Add Item menu or the Toolbox bar.
2. Then:
• Click on the page and fill the size and placement information requested in the New Item Properties dialog
that pops up (for details, see Position and Size);
Obr. 18.9: New Item properties dialog
• Or click-and-drag to define the initial size and placement of the item. You can rely on grids and guides
snapping for a better position.
Poznámka: Because they can have particular shapes, drawing node or arrow items does not work with one-click
nor click-and-drag methods; you need to click and place each node of the item. See The Node-Based Shape Items for
more details.
You can also:
1. Select an existing item with the Select/Move item
button from the Toolbox toolbar
2. Use the contextual menu or the Edit menu tools to copy/cut the item and paste it at the mouse position as a new
item.
You can also use the Paste in Place (Ctrl+Shift+V) command to duplicate an item from one page to another
and place it in the new page at the same coordinates as the original.
Moreover, you can create items using a print layout template (for details, see The Layout Manager) through the Layout
► Add Items from Template… command.
Tip: Add layout items using the file browser
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From your file browser or using the Browser panel, drag-and-drop a print layout template (.qpt file) onto a print
layout dialog and QGIS automatically adds all items from that template to the layout.
Interacting with layout items
Each item inside the print layout can be moved and resized to create a perfect layout. For both operations the first
step is to activate the Select/Move item
tool and click on the item.
You can select multiple items with the Select/Move item
button: click and drag over the items or hold the Shift
button and click on each of the items you want. To deselect an item, click on it holding the Shift button.
Each time there’s a selection, count of selected items is displayed on the status bar. Inside the Edit menu, you can find
actions to select all the items, clear all selections, invert the current selection and more…
Moving and resizing items
Unless View ► Show Bounding Boxes option is unchecked, a selected item will show squares on its boundaries ; moving
one of them with the mouse will resize the item in the corresponding direction. While resizing, holding Shift will
maintain the aspect ratio. Holding Alt will resize from the item center.
To move a layout item, select it with the mouse and move while holding the left button. If you need to constrain the
movements to the horizontal or vertical axis, just hold the Shift button on the keyboard while moving the mouse.
You can also move a selected item using the Arrow keys on the keyboard; if the movement is too slow, you
can speed it up by holding Shift. If you need better precision, use the Position and size properties, or grid/guides
snapping as explained above for item’s creation.
Resizing or moving several items at once is made the same way as for a single item. QGIS however provides some
advanced tools to automatically resize a selection of items following different rules:
• each item height matches the tallest or the shortest selected item;
• each item width matches the widest or the narrowest selected item;
• resizes items to squares: each item is enlarged to form a square.
Likewise, automated tools are available to organize multiple items position by distributing equidistantly:
• edges (left, right, top or bottom) of items;
• centers of items either horizontally or vertically.
Grouping items
Grouping items allows you to manipulate a set of items like a single one: you can easily resize, move, delete, copy the
items as a whole.
To create a group of items, select more than one and press the Group button on the View menu or the Actions
toolbar or from the right-click menu. A row named Group is added to the Items panel and can be locked or hidden
like any other Items panel’s object. Grouped items are not individually selectable on the canvas; use the Items panel
for direct selection and access the item’s properties panel.
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Locking items
Once you have found the correct position for an item, you can lock it by using the Lock selected items button in
the Items menu or the Actions toolbar or ticking the box next to the item in the Items panel. Locked items are not
selectable on the canvas.
Locked items can be unlocked by selecting the item in the Items panel and unchecking the tickbox or you can use the
icons on the toolbar.
Alignment
Raising or lowering the visual hierarchy for elements are inside the Raise selected items
pull-down menu. Choose
an element on the print layout canvas and select the matching functionality to raise or lower the selected element
compared to the other elements. This order is shown in the Items panel. You can also raise or lower objects in the
Items panel by clicking and dragging an object’s label in this list.
Obr. 18.10: Alignment helper lines in the print layout
There are several alignment options available within the Align selected items
pull-down menu (see Obr. 18.10). To use
an alignment function, you first select the elements and then click on one of the alignment icons:
• Align Left or Align Right;
• Align Top or Align Bottom;
• Align Center horizontally or Align Center Vertical.
All selected elements will then be aligned to their common bounding box. When moving items on the layout canvas,
alignment helper lines appear when borders, centers or corners are aligned.
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Items Common Properties
Layout items have a set of common properties you will find at the bottom of the Item Properties panel: Position and
size, Rotation, Frame, Background, Item ID, Variables and Rendering (See Obr. 18.11).
Obr. 18.11: Common Item Properties groups
Poznámka: The Data defined override
icon next to most of the options means that you can associate that property
with a layer, features attributes, geometry or with any other layout item’s property, using expressions or variables. For
more information see Data defined override setup.
• The Position and size group lets you define the size and position of the frame which contains the item (see
Position and Size for more information).
• The Rotation sets the rotation of the element (in degrees).
• The Frame shows or hides the frame around the item. Use the Color, Thickness and Join style widgets to
adjust those properties.
• Use the Background color menu for setting a background color. Click on the [Color…] button to display a dialog
where you can pick a color or choose from a custom setting. Transparency can be adjusted through altering the
alpha field settings.
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• Use the Item ID to create a relationship to other print layout items. This is used with QGIS server and other
potential web clients. You can set an ID on an item (for example, a map or a label), and then the web client
can send data to set a property (e.g., label text) for that specific item. The GetProjectSettings command will
list the items and IDs which are available in a layout.
• Rendering mode helps you set whether and how the item can be displayed: you can, for instance, apply blending
mode, adjust the opacity of the item or Exclude item from exports.
Position and Size
Extending the features of the New Item Properties dialog with data-defined capabilities, this group allows you to place
the items accurately.
Obr. 18.12: Position and size
• the actual number of the page to place the item on;
• the reference point of the item;
• the X and Y coordinates of the Reference point of the item on the chosen page. The ratio between these values
can be locked by clicking on the button. Changes made to a value using the widget or the Select/Move item
tool will be reflected in both of them;
• the Width and Height of the item bounding box. As for coordinates, the ratio between width and height can be
locked.
Rendering mode
QGIS allows advanced rendering for layout items just like vector and raster layers.
Obr. 18.13: Rendering mode
• Blending mode: With this tool you can achieve effects which would otherwise only be achieved using graphic
rendering software. The pixels of your overlaying and underlaying items can be mixed according to the mode
set (see Režim míchání for description of each effect).
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• Transparency : You can make the underlying item in the layout visible with this tool. Use
the slider to adapt the visibility of your item to your needs. You can also make a precise definition of the
percentage of visibility in the menu beside the slider.
• Exclude item from exports: You can decide to make an item invisible in all exports. After activating this
checkbox, the item will not be included in export to PDF, print etc..
Variables
The Variables lists all the variables available at the layout item’s level (which includes all global, project and
composition’s variables). Map items also include Map settings variables that provide easy access to values like the
map’s scale, extent, and so on.
In Variables, it’s also possible to manage item-level variables. Click the button to add a new custom variable.
Likewise, select any custom item-level variable from the list and click the button to remove it.
More information on variables usage in the Storing values in Variables section.
18.2.2 The Map Item
The map item is the main frame that displays the map you’ve designed in the map canvas. Use the Add Map tool
following items creation instructions to add a new map item that you can later manipulate the same way as exposed in
Interacting with layout items.
By default, a new map item shows the current status of the map canvas with its extent and visible layers. You can
customize it thanks to the Item Properties panel. Other than the items common properties, this feature has the following
functionalities:
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Obr. 18.14: Map Item Properties Panel
The Toolbar
The Map Item Properties panel embeds a toolbar with the following functionalities:
• Update map preview
• Set map canvas to match main canvas extent
• View current map extent in main canvas
• Set map scale to match main canvas scale
• Set main canvas to match current map scale
• Bookmarks
: set the map item extent to match an existing spatial bookmark
• Interactively edit map extent
: pan and zoom interactively within the map item
• Labeling settings
: control feature label behaviour (placement, visibility…) in the layout map item extent:
– set a Margin from map edges, a data definable distance from the map item’s limits inside which no label
should be displayed
– Allow truncated labels on edges of map: controls whether labels which fall partially outside of the map
item allowed extent should be rendered. If checked, these labels will be shown (when there’s no way to
place them fully within the visible area). If unchecked then partially visible labels will be skipped.
– Label blocking items: allows other layout items (such as scalebars, north arrows, inset maps, etc) to be
marked as a blockers for the map labels in the active map item. This prevents any map labels from being
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placed under those items - causing the labeling engine to either try alternative placement for these labels
or discard them altogether.
If a Margin from map edges is set, the map labels are not placed closer than the specified distance from
the checked layout items.
– Show unplaced labels: can be used to determine whether labels are missing from the layout map (e.g. due
to conflicts with other map labels or due to insufficient space to place the label) by highlighting them in
a predefined color.
• Clipping settings
: allows to clip the map item to the atlas feature and to shape and polygon items:
– Clip to atlas feature: you can determine that the layout map item will be clipped automatically to the
current atlas feature.
There are different clipping modes available:
∗ Clip During Render Only: applies a painter based clip, so that portions of vector features which sit
outside the atlas feature become invisible
∗ Clip Feature Before Render: applies the clip before rendering features, so borders of features which
fall partially outside the atlas feature will still be visible on the boundary of the atlas feature
∗ Render Intersecting Features Unchanged: renders all features which intersect the current atlas feature,
but without clipping their their geometry.
You can Force labels inside atlas feature. If you don’t want to Clip all layers to the atlas feature
you can use the Clip selected layers option.
– Clip to item: it is possible to change the shape of the map item by using a shape or polygon item from
the print layout. When you enable this option the map will be automatically clipped to the selected shape
in the combobox. Again, the above mentioned clipping modes are available and labels can be forced to
display only inside the clipping shape.
Main properties
In the Main properties group (see Obr. 18.14) of the map Item Properties panel, available options are:
• The Update Preview button to refresh the map item rendering if the view in map canvas has been modified.
Note that most of the time, the map item refresh is automatically triggered by the changes;
• The Scale to manually set the map item scale;
• The Map rotation allows you to rotate the map item content clockwise in degrees. The rotation of the map
canvas can be imitated here;
• The CRS allows you to display the map item content in any CRS. It defaults to Use project CRS;
• Draw map canvas items lets you show in the print layout annotations that are placed on the main map
canvas.
Layers
By default, map item appearance is synced with the map canvas rendering meaning that toggling visibility of the layers
or modifying their style in the Layers Panel is automatically applied to the map item. Because, like any other item,
you may want to add multiple map items to a print layout, there’s a need to break this synchronization in order to
allow showing different areas, layer combinations, at different scales… The Layers properties group (see Obr. 18.15)
helps you do that.
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Obr. 18.15: Map Layers group
If you want to keep the map item consistent with an existing map theme, check Follow map theme and select the
desired theme in the drop-down list. Any changes applied to the theme in QGIS‘ main window (using the replace
theme function) will automatically affect the map item. If a map theme is selected, the Lock styles for layers option
is disabled because Follow map theme also updates the style (symbology, labels, diagrams) of the layers.
To lock the layers shown in a map item to the current map canvas visibility, check Lock layers. When this
option is enabled, any changes on the layers‘ visibility in QGIS‘ main window will not affect the layout’s map item.
Nevertheless, style and labels of locked layers are still refreshed according to QGIS‘ main window. You can prevent
this by using Lock styles for layers.
Instead of using the current map canvas, you can also lock the layers of the map item to those of an existing map
theme: select a map theme from the Set layer list from a map theme
drop-down button, and the Lock layers is activated.
The set of visible layers in the map theme is from now on used for the map item until you select another map theme
or uncheck the Lock layers option. You then may need to refresh the view using the Refresh view
button of the
Navigation toolbar or the Update Preview button seen above.
Note that, unlike the Follow map theme option, if the Lock layers option is enabled and set to a map theme, the layers
in the map item will not be refreshed even if the map theme is updated (using the replace theme function) in QGIS‘
main window.
Locked layers in the map item can also be data-defined, using the icon beside the option. When used, this
overrides the selection set in the drop-down list. You need to pass a list of layers separated by | character. The
following example locks the map item to use only layers layer 1 and layer 2:
concat ('layer 1', '|', 'layer 2')
Extents
The Extents group of the map item properties panel provides the following functionalities (see Obr. 18.16):
Obr. 18.16: Map Extents group
The Extents area displays X and Y coordinates of the area shown in the map item. Each of these values can be
manually replaced, modifying the map canvas area displayed and/or map item size. Clicking the Set to Map Canvas
Extent button sets the extent of the layout map item to the extent of the main map canvas. The button View Extent in
Map Canvas does exactly the opposite; it updates the extent of the main map canvas to the extent of the layout map
item.
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You can also alter a map item extent using the Move item content
tool: click-and-drag within the map item to modify
its current view, keeping the same scale. With the tool enabled, use the mouse wheel to zoom in or out, modifying
the scale of the shown map. Combine the movement with Ctrl key pressed to have a smaller zoom.
Controlled by atlas
The Controlled by atlas group properties is available only if an atlas is active in the print layout. Check this
option if you want the map item being ruled by the atlas; when iterating over the coverage layer, the map item extent
is panned/zoomed to the atlas feature following:
• Margin around features: zooms to the feature at the best scale, keeping around each a margin representing
a percentage of the map item width or height. The margin can be the same for all features or set variable, e.g.,
depending on map scale;
• Predefined scale (best fit): zooms to the feature at the project predefined scale where the atlas feature best
fits;
• Fixed scale: atlas features are panned from one to another, keeping the same scale of the map item. Ideal
when working with features of same size (e.g., a grid) or willing to highlight size differences among atlas
features.
Grids
With grids, you can add, over your map, information relative to its extent or coordinates, either in the map item
projection or a different one. The Grids group provides the possibility to add several grids to a map item.
• With the and buttons you can add or remove a selected grid;
• With the and buttons you can move up and down a grid in the list, hence move it on top or bottom of
another one, over the map item.
Double-click the added grid to rename it.
Obr. 18.17: Map Grids Dialog
To modify a grid, select it and press the Modify Grid… button to open the Map Grid Properties panel and access its
configuration options.
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Grid Appearance
In the Map Grid Properties panel, check Grid enabled to show the grid on the map item.
As grid type, you can specify to use a:
• Solid: shows a line across the grid frame. The Line style can be customized using color and symbol selector
widget;
• Cross: displays segment at the grid lines intersection for which you can set the Line style and the Cross width;
• Markers: only displays customizable markers symbol at grid lines intersection;
• or Frame and annotations only.
Other than the grid type, you can define:
• the CRS of the grid. If not changed, it will follow the Map CRS. The Change button lets you set it to a different
CRS. Once set, it can be changed back to default by selecting any group heading (e.g Geographic Coordinate
System) under Predefined Coordinate Reference Systems in the CRS selection dialog.
• the Interval type to use for the grid references. Available options are Map Unit, Fit Segment Width,
Millimeter or Centimeter:
– choosing Fit Segment Width will dynamically select the grid interval based on the map extent to
a „pretty“ interval. When selected, the Minimum and Maximum intervals can be set.
– the other options allow you to set the distance between two consecutive grid references in the X and Y
directions.
• the Offset from the map item edges, in the X and/or the Y direction
• and the Blend mode of the grid (see Režim míchání) when compatible.
Obr. 18.18: Grid Appearance Dialog
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Grid Frame
There are different options to style the frame that holds the map. The following options are available: No Frame,
Zebra, Zebra (nautical), Interior ticks, Exterior ticks, Interior and Exterior
ticks, Line border and Line border (nautical).
When compatible, it’s possible to set the Frame size, a Frame margin, the Frame line thickness with associated color
and the Frame fill colors.
Using Latitude/Y only and Longitude/X only values in the divisions section you can prevent a mix of
latitude/Y and longitude/X coordinates showing on each side when working with rotated maps or reprojected grids.
Also you can choose to set visible or not each side of the grid frame.
Obr. 18.19: Grid Frame Dialog
Coordinates
The Draw coordinates checkbox allows you to add coordinates to the map frame. You can choose the annotation
numeric format, the options range from decimal to degrees, minute and seconds, with or without suffix, aligned or
not and a custom format using the expression dialog.
You can choose which annotation to show. The options are: show all, latitude only, longitude only, or disable(none).
This is useful when the map is rotated. The annotation can be drawn inside or outside the map frame. The annotation
direction can be defined as horizontal, vertical ascending or vertical descending.
Finally, you can define the annotation font, font color, distance from the map frame and the precision of the drawn
coordinates.
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Obr. 18.20: Grid Draw Coordinates dialog
Overviews
Sometimes you may have more than one map in the print layout and would like to locate the study area of one
map item on another one. This could be for example to help map readers identify the area in relation with its larger
geographic context shown in the second map.
The Overviews group of the map panel helps you create the link between two different maps extent and provides the
following functionalities:
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Obr. 18.21: Map Overviews group
To create an overview, select the map item on which you want to show the other map item’s extent and expand the
Overviews option in the Item Properties panel. Then press the button to add an overview.
Initially this overview is named ‚Overview 1‘ (see Obr. 18.21). You can:
• Rename it with a double-click
• With the and buttons, add or remove overviews
• With the and buttons, move an overview up and down in the list, placing it above or below other
overviews in the map item (when they are at the same stack position).
Then select the overview item in the list and check the Draw „<name_overview>“ overview to enable the drawing
of the overview on the selected map frame. You can customize it with:
• The Map frame selects the map item whose extents will be shown on the present map item.
• The Frame Style uses the symbol properties to render the overview frame.
• The Blending mode allows you to set different transparency blend modes.
• The Invert overview creates a mask around the extents when activated: the referenced map extents are
shown clearly, whereas the rest of the map item is blended with the frame fill color (if a fill color is used).
• The Center on overview pans the map item content so that the overview frame is displayed at the center of
the map. You can only use one overview item to center, when you have several overviews.
• The Position controls exactly where in the map item’s layer stack the overview will be placed, e.g. allowing an
overview extent to be drawn below some feature layers such as roads whilst drawing it above other background
layers. Available options are:
– Below map
– Below map layer and Above map layer: place the overview frame below and above the geometries of
a layer, respectively. The layer is selected in the Stacking layer option.
– Below map labels: given that labels are always rendered above all the feature geometries in a map item,
places the overview frame above all the geometries and below any label.
– Above map labels: places the overview frame above all the geometries and labels in the map item.
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18.2.3 The 3D Map Item
The 3D Map item is used to display a 3D map view. Use the Add 3D Map button, and follow items creation
instructions to add a new 3D Map item that you can later manipulate the same way as demonstrated in Interacting
with layout items.
By default, a new 3D Map item is empty. You can set the properties of the 3D view and customize it in the Item
Properties panel. In addition to the common properties, this feature has the following functionalities (Obr. 18.22):
Obr. 18.22: 3D Map Item Properties
Scene settings
Press Copy Settings from a 3D View… to choose the 3D map view to display.
The 3D map view is rendered with its current configuration (layers, terrain, lights, camera position and angle…).
Camera pose
• Center X sets the X coordinate of the point the camera is pointing at
• Center Y sets the Y coordinate of the point the camera is pointing at
• Center Z sets the Z coordinate of the point the camera is pointing at
• Distance sets the distance from the camera center to the point the camera is pointing at
• Pitch sets the rotation of the camera around the X-axis (vertical rotation). Values from 0 to 360 (degrees). 0°:
terrain seen straight from above; 90°: horizontal (from the side); 180°: straight from below; 270°: horizontal,
upside down; 360°: straight from above.
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• Heading sets the rotation of the camera around the Y-axis (horizontal rotation - 0 to 360 degrees). 0°/360°:
north; 90°: west; 180°: south; 270°: east.
The Set from a 3D View… pull-down menu lets you populate the items with the parameters of a 3D View.
18.2.4 The Label Item
The Label item is a tool that helps decorate your map with texts that would help to understand it; it can be the title,
author, data sources or any other information… You can add a label with the Add Label tool following items
creation instructions and manipulate it the same way as exposed in Interacting with layout items.
By default, the label item provides a default text that you can customize using its Item Properties panel. Other than
the items common properties, this feature has the following functionalities (see Obr. 18.23):
Obr. 18.23: Label Item Properties Panel
Main properties
The Main properties group is the place to provide the text (it can be in HTML) or the expression to build the label.
Expressions need to be surrounded by [% and %] in order to be interpreted as such.
• Labels can be interpreted as HTML code: check Render as HTML. You can now insert a URL, a clickable
image that links to a web page or something more complex.
• You can also use expressions: click on Insert or Edit an expression… button, write your formula as usual and
when the dialog is applied, QGIS automatically adds the surrounding characters.
Poznámka: Clicking the Insert or Edit an Expression… button when no selection is made in the textbox will append
the new expression to the existing text. If you want to update an existing text, you need to select it the part of interest
beforehand.
You can combine HTML rendering with expressions, leading to advanced labeling. The following code will output
Obr. 18.24:
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<html>
<head>
<style>
/* Define some custom styles, with attribute-based size */
name {color:red; font-size: [% ID %]px; font-family: Verdana; text-shadow:␣
→grey 1px 0 10px;}
use {color:blue;}
</style>
</head>
<body>
<!-- Information to display -->
<u>Feature Information</u>
<ul style="list-style-type:disc">
<li>Feature Id: [% ID %]</li>
<li>Airport: <name>[% NAME %]</name></li>
<li>Main use: <use>[% USE %]</use></li>
</ul>
Last check: [% concat( format_date( "control_date", 'yyyy-MM-dd'), ' by <b><i>',
→ @user_full_name, '</i></b>' ) %]
<!-- Insert an image -->
<p align=center><img src="path/to/logos/qgis-logo-made-with-color.svg" alt=
→"QGIS icon" style="width:80px;height:50px;"</p>
</body>
</html>
Obr. 18.24: Leveraging a label with HTML styling
Appearance
• Define Font by clicking on the Font… button or a Font color by pushing the color widget.
• You can specify different horizontal and vertical margins in mm. This is the margin from the edge of the layout
item. The label can be positioned outside the bounds of the label e.g. to align label items with other items. In
this case you have to use negative values for the margin.
• Using the text alignment is another way to position your label. It can be:
– Left, Center, Right or Justify for Horizontal alignment
– and Top, Middle, Bottom for Vertical alignment.
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Exploring expressions in a label item
Below some examples of expressions you can use to populate the label item with interesting information - remember
that the code, or at least the calculated part, should be surrounded by [% and %] in the Main properties frame:
• Display a title with the current atlas feature value in „field1“:
'This is the map for ' || "field1"
or, written in the Main properties section:
This is the map for [% "field1" %]
• Add a pagination for processed atlas features (eg, Page 1/10):
concat( 'Page ', @atlas_featurenumber, '/', @atlas_totalfeatures )
• Return the name of the airports of the current atlas region feature, based on their common attributes:
aggregate( layer := 'airports',
aggregate := 'concatenate',
expression := "NAME",
filter := fk_regionId = attribute( @atlas_feature, 'ID' ),
concatenator := ', '
)
Or, if an attributes relation is set:
relation_aggregate( relation := 'airports_in_region_relation',
aggregate := 'concatenate',
expression := "NAME",
concatenator := ', '
)
• Return the name of the airports contained in the current atlas region feature, based on their spatial relationship:
aggregate( layer := 'airports',
aggregate := 'concatenate',
expression := "NAME",
filter := contains( geometry( @parent ), $geometry ),
concatenator := ', '
)
OR:
array_to_string( array:= overlay_contains( layer := 'airports',
expression := "NAME" ),
delimiter:= ', '
)
• Return the lower X coordinate of the Map 1 item’s extent:
x_min( map_get( item_variables( 'Map 1' ), 'map_extent' ) )
• Retrieve the name of the layers in the current layout Map 1 item, and formats in one name by line:
array_to_string(
array_foreach(
map_get( item_variables( 'Map 1' ), 'map_layers' ), -- retrieve the layers␣
→list
layer_property( @element, 'name' ) -- retrieve each layer name
),
(continues on next page)
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(pokračujte na předchozí stránce)
'\n' -- converts the list to string separated by breaklines
)
18.2.5 The Legend Item
The Legend item is a box or a table that explains the meanings of the symbols used on the map. A legend is then
bound to a map item. You can add a legend item with the Add Legend tool following items creation instructions
and manipulate it the same way as exposed in Interacting with layout items.
By default, the legend item displays all available layers and can be refined using its Item Properties panel. Other than
the items common properties, this feature has the following functionalities (see Obr. 18.25):
Obr. 18.25: Legend Item Properties Panel
Main properties
The Main properties group of the legend Item Properties panel provides the following functionalities (see Obr. 18.26):
Obr. 18.26: Legend Main properties group
In Main properties you can:
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• Change the Title of the legend. It can be made dynamic using the data-defined override setting, useful for
example when generating an atlas;
• Choose which Map item the current legend will refer to. By default, the map over which the legend item is drawn
is picked. If none, then it falls back to the reference map.
Poznámka: Variables of the linked map item (@map_id, @map_scale, @map_extent…) are also accessible
from data-defined properties of the legend.
• Wrap the text of the legend on a given character: each time the character appears, it’s replaced with a line
break;
• Set the symbols and text placement in the legend: the Arrangement can be Symbols on left or Symbols on right.
The default value depends on the locale in use (right-to-left based or not).
• Use Resize to fit contents to control whether or not a legend should be automatically resized to fit its contents.
If unchecked, then the legend will never resize and instead just stick to whatever size the user has set. Any
content which doesn’t fit the size is cropped out.
Legend items
The Legend items group of the legend Item Properties panel provides the following functionalities (see Obr. 18.27):
Obr. 18.27: Legend Items group
• The legend will be updated automatically if Auto update is checked. When Auto update is unchecked this
will give you more control over the legend items. All the icons below the legend items list will be activated.
• The legend items window lists all legend items and allows you to change item order, group layers, remove and
restore items in the list, edit layer names and add a filter.
– The item order can be changed using the and buttons or with ‚drag-and-drop‘ functionality. The
order can not be changed for WMS legend graphics.
– Use the button to add a legend group.
– Use the button to add layers and button to remove groups, layers or symbol classes.
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– The button is used to edit the layer, group name or title. First you need to select the legend item.
Double-clicking the item also opens the text box to rename it.
– The button uses expressions to customize each symbol label of the selected layer (see Data-define
the legend labels)
– The button adds a feature count for each class of vector layer.
– The Filter legend by expression
helps you filter which of the legend items of a layer will be displayed, i.e.
using a layer that has different legend items (e.g., from a rule-based or categorized symbology), you
can specify a boolean expression to remove from the legend tree, styles that have no feature satisfying
a condition. Note that the features are nevertheless kept and shown in the layout map item.
While the default behavior of the legend item is to mimic the Layers panel tree, displaying the same groups,
layers and classes of symbology, right-click any item offers you options to hide layer’s name or raise it as a group
or subgroup. In case you have made some changes to a layer, you can revert them by choosing Reset to defaults
from the contextual menu of the legend entry.
After changing the symbology in the QGIS main window, you can click on Update All to adapt the changes in
the legend element of the print layout.
• With the Only show items inside linked map, only the legend items visible in the linked map will be listed
in the legend. This tool remains available when Auto-update is active
• While generating an atlas with polygon features, you can filter out legend items that lie outside the current atlas
feature. To do that, check the Only show items inside current atlas feature option.
Data-define the legend labels
allows you to add expressions to each symbol label of a given layer. New variables (@symbol_label,
@symbol_id and @symbol_count) help you interact with the legend entry.
For example, given a regions layer categorized by its type field, you can append to each class in the legend their
number of features and total area, e.g. Borough (3) - 850ha:
1. Select the layer entry in the legend tree
2. Press the button, opening the Expression String Builder dialog
3. Enter the following expression (assuming symbol labels have not been edited):
concat( @symbol_label,
' (', @symbol_count, ') - ',
round( aggregate(@layer, 'sum', $area, filter:= "type"=@symbol_label)/
→10000 ),
'ha'
)
4. Press OK
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Fonts
The Fonts group of the legend Item Properties panel provides the following functionalities:
Obr. 18.28: Legend Fonts properties
• You can change the font of the legend title, group, subgroup and item (feature) in the legend item using the
font selector widget
• For each of these levels you can set the text Alignment: it can be Left (default for left-to-right based locales),
Center or Right (default for right-to-left based locales).
• You set the Color of the labels using the color selector widget. The selected color will apply to all the font items
in the legend.
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Columns
Under the Columns group of the legend Item Properties panel, legend items can be arranged over several columns:
• Set the number of columns in the Count field. This value can be made dynamic e.g., following atlas
features, legend contents, the frame size…
• Equal column widths sets how legend columns should be adjusted.
• The Split layers option allows a categorized or a graduated layer legend to be divided between columns.
Obr. 18.29: Legend Columns settings
Symbol
The Symbol group of the legend Item Properties panel configures the size of symbols displayed next to the legend
labels. You can:
• Set the Symbol width and Symbol height
• Set the markers‘ Min symbol size and Max symbol size: 0.00mm means there is no value set.
• Draw stroke for raster symbols: this adds an outline to the symbol representing the band color of the raster
layer; you can set both the Stroke color and Tickness.
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Obr. 18.30: Legend Symbol configuration
WMS LegendGraphic and Spacing
The WMS LegendGraphic and Spacing groups of the legend Item Properties panel provide the following functionalities
(see Obr. 18.31):
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Obr. 18.31: WMS LegendGraphic and Spacing groups
When you have added a WMS layer and you insert a legend item, a request will be sent to the WMS server to provide
a WMS legend. This Legend will only be shown if the WMS server provides the GetLegendGraphic capability. The
WMS legend content will be provided as a raster image.
WMS LegendGraphic is used to be able to adjust the Legend width and the Legend height of the WMS legend raster
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image.
Spacing around title, groups, subgroups, symbols, labels, boxes, columns and lines can be customized through this
dialog.
18.2.6 The Scale Bar Item
Scale bars provide a visual indication of the size of features, and distance between features, on the map item. A scale
bar item requires a map item. Use the Add Scale Bar tool following items creation instructions to add a new scale
bar item that you can later manipulate the same way as exposed in Interacting with layout items.
By default, a new scale bar item shows the scale of the map item over which it is drawn. If there is no map item below,
the reference map is used. You can customize it in the Item Properties panel. Other than the items common properties,
this feature has the following functionalities (see Obr. 18.32):
Obr. 18.32: Scale Bar Item Properties Panel
Main properties
The Main properties group of the scale bar Item Properties panel provides the following functionalities (see Obr.
18.33):
Obr. 18.33: Scale Bar Main properties group
1. First, choose the map the scale bar will be attached to
2. Then, choose the style of the scale bar. Available styles are:
• Single box and Double box styles, which contain one or two lines of boxes alternating colors;
• Middle, Up or Down line ticks;
• Stepped line style that draws a stepped line representation of a scalebar
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• Hollow style that draws a single box with alternating color for the segments, with horizontal lines through
alternating segments
• Numeric, where the scale ratio is printed (e.g., 1:50000).
3. Set properties as appropriate
Units
The Units group of the scale bar Item Properties panel provides the functionalities to set the units of display and some
text formatting (see Obr. 18.34):
Obr. 18.34: Scale Bar Units group
• Select the units you want to use with Scalebar units. There are many possible choices: Map Units (the
default one), Meters, Feet, Miles or Nautical Miles… and some derivatives. Units conversion is handled
automatically.
• The Label unit multiplier specifies how many scale bar units per labeled unit. Eg, if your scale bar units are set
to „meters“, a multiplier of 1000 will result in the scale bar labels in „kilometers“.
• The Label for units field defines the text used to describe the units of the scale bar, eg m or km. This should be
matched to reflect the multiplier above.
• Press Customize next to Number format to have control over all the formatting properties for the numbers in
the scale bar, including thousand separators, decimal places, scientific notation, etc. (see Number Formatting
for more details). Very useful in the case of making maps for audiences outside of the current QGIS locale,
or when you would like to vary the style from the locale defaults (e.g. adding thousands separators when the
locale default is to hide them).
Segments
The Segments group of the scale bar Item Properties panel provides the functionalities to configure the number and
size of segments and subdivisions (see Obr. 18.35):
Obr. 18.35: Scale Bar Segments group
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• You can define the number of Segments that will be drawn at the left and right sides of the 0 of the scale bar:
– number of subdivisions of a unique segment on the Left side
– number of segments on the Right side
• You can set how long a segment will be (Fixed width), or limit the scale bar size in mm with Fit segment width
option. In the latter case, each time the map scale changes, the scale bar is resized (and its label updated) to fit
the range set.
• Height is used to define the height of the bar.
• Right segment subdivisions is used to define the number of sections the right-side segments of the scale bar can
have (for Line Ticks Down, Line Ticks Middle and Line Ticks Up scale bar styles) .
• Subdivision height is used to define the height of the subdivision segment.
Display
The Display group of the scale bar Item Properties panel provides the following functionalities:
Obr. 18.36: Scale Bar Display group
You can define how the scale bar will be displayed in its frame.
• Box margin : space between text and frame borders
• Label margin : space between text and scale bar drawing
• Vertical label placement: it can be above or below the scale bar segment
• Horizontal label placement: which would be centered at the scale bar segment’s edge or center
• Primary fill and Secondary fill of the scale bar drawing using fill symbols properties (color, opacity, patterns,
effects…) — for Single Box, Double Box and Hollow styles
• Line style of the scale bar drawing using line symbols properties (color, stroke, join, cap style, patterns, effects…)
— for all but Numeric style
• Division style and Subdivision style respectively for division and subdivision segments in Line Ticks Up, Line
Ticks Middle and Line Ticks Down scale bar styles using line symbols properties (color, stroke, join, cap style,
patterns, effects…)
• Alignment puts text on the left, center or right side of the frame (only for Numeric scale bar style)
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• Font to set the properties (size, font, color, letter spacing, shadow, background…) of the scale bar label.
Since most of the display properties of the scale bar rely on symbols whose properties can be data-defined, it’s possible
to render data-defined scale bars.
Example: The following code applied to the bold property of the scale labels will display numbers in bold when they
are a multiple of 500:
-- returns True (or 1) if the value displayed on the bar
-- is a multiple of 500
@scale_value % 500 = 0
18.2.7 Položky tabulky
Můžete použít položky tabulky pro ozdobení a vysvětlení Vaší mapy.
• Attribute table: shows a subset of the attributes of a layer, based on predefined rules
• Fixed table: inserts a manual text table where information can be independent from the layers.
Položka atributové tabulky
Atributy z jakékoliv vrstvy v projektu mohou být zobrazeny v náhledu pro tisk.
By default, a new attribute table item loads first rows of the first (alphabetically sorted) layer, with all the fields. You
can however customize the table thanks to its Item Properties panel. Other than the items common properties, this
feature has the following functionalities (see Obr. 18.37):
Obr. 18.37: Atributová tabulka Položka Panel nastavení
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Hlavní nastavení
The Main properties group of the attribute table provides the following functionalities (see Obr. 18.38):
Obr. 18.38: Attribute table Main properties Group
• For Source you can by default only select Layer features allowing you to select a Layer from the vector layers
loaded in the project.
The data-defined override
button near the layer list allows you to dynamically change the layer which is used to
populate the table, e.g. you could fill the attribute table with different layer attributes per atlas page. Note that
the table structure used (Obr. 18.41) is the one of the layer shown in the Layer drop-down list and it is left
intact, meaning that setting a data defined table to a layer with different field(s) will result in empty column(s)
in the table.
In case you activate the Generate an atlas option in the Atlas panel (see Generate an Atlas), there are two
additional Source possible:
– Current atlas feature (see Obr. 18.39): you won’t see any option to choose the layer, and the table item
will only show a row with the attributes from the current feature of the atlas coverage layer.
– and Relation children (see Obr. 18.40): an option with the relation names will show up. This feature can
only be used if you have defined a relation using your atlas coverage layer as parent, and the table will
show the children rows of the atlas coverage layer’s current feature.
• The button Refresh Table Data can be used to refresh the table when the actual contents of the table has
changed.
Obr. 18.39: Attribute table Main properties for ‚Current atlas feature‘
Obr. 18.40: Attribute table Main properties for ‚Relation children‘
• The button Attributes… starts the Select Attributes dialog, (see Obr. 18.41) that can be used to change the visible
contents of the table. The upper part of the window shows the list of the attributes to display and the lower part
helps you sort the data.
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Obr. 18.41: Attribute table Select attributes Dialog
In the Columns section you can:
– Move attributes up or down the list by selecting the rows and then using the and buttons to shift
the rows. Multiple rows can be selected and moved at any one time.
– Add an attribute with the button. This will add an empty row at the bottom of the table where you
can select a field to be the attribute value or create an attribute via a regular expression.
– Remove an attribute with the button. Multiple rows can be selected and removed at any one time.
– Reset the attribute table back to its default state with the Reset button.
– Clear the table using the Clear button. This is useful when you have a large table but only want to show
a small number of attributes. Instead of manually removing each row, it may be quicker to clear the table
and add the rows needed.
– Cell headings can be altered by adding the custom text in the Heading column.
– Cell alignment can be managed with the Alignment column which will dictate the texts position within
the table cell.
– Cell width can be manually managed by adding custom values to the width column.
In the Sorting section you can:
– Add an attribute to sort the table with: press the button and a new empty row is added. Insert a field
or an expression in the Attribute column and set the Sort order to Ascending or Descending.
– Select a row in the list and use the and buttons to change the sort priority on attribute level.
Selecting a cell in the Sort Order column helps you change the sorting order of the attribute field.
– Use the button to remove an attribute from the sorting list.
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Feature filtering
The Feature filtering group of the attribute table provides the following functionalities (see Obr. 18.42):
Obr. 18.42: Attribute table Feature filtering Group
You can:
• Define the Maximum rows to be displayed.
• Activate Remove duplicate rows from table to show unique records only.
• Activate Show only visible features within a map and select the corresponding Linked map whose visible
features attributes will be displayed.
• Activate Show only features intersecting Atlas feature is only available when Generate an atlas
is activated. When activated it will show a table with only the features which intersect the current atlas feature.
• Activate Filter with and provide a filter by typing in the input line or insert a regular expression using the
given expression button. A few examples of filtering statements you can use when you have loaded the
airports layer from the Sample dataset:
– ELEV > 500
– NAME = 'ANIAK'
– NAME NOT LIKE 'AN%'
– regexp_match( attribute( $currentfeature, 'USE' ) , '[i]')
The last regular expression will include only the airports that have a letter ‚i‘ in the attribute field ‚USE‘.
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Appearance
The Appearance group of the attribute table provides the following functionalities (see Obr. 18.43):
Obr. 18.43: Attribute table appearance Group
• Click Show empty rows to fill the attribute table with empty cells. This option can also be used to provide
additional empty cells when you have a result to show!
• With Cell margins you can define the margin around text in each cell of the table.
• With Display header you can select from a list one of ‚On first frame‘, ‚On all frames‘ default option, or ‚No
header‘.
• The option Empty table controls what will be displayed when the result selection is empty.
– Draw headers only, will only draw the header except if you have chosen ‚No header‘ for Display header.
– Hide entire table, will only draw the background of the table. You can activate Don’t draw
background if frame is empty in Frames to completely hide the table.
– Show set message, will draw the header and adds a cell spanning all columns and display a message like
‚No result‘ that can be provided in the option Message to display
• The option Message to display is only activated when you have selected Show set message for Empty table.
The message provided will be shown in the table in the first row, when the result is an empty table.
• With Background color you can set the background color of the table using the color selector widget. The
Advanced customization option helps you define different background colors for each cell (see Obr. 18.44)
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Obr. 18.44: Attribute table Advanced Background Dialog
• Apply layer conditional styling colors: the conditional table formatting present in the layer is applied
inside the layout attribute table (only background and foreground colors are currently supported). Conditional
formatting rules take precedence over other layout table formatting settings, e.g. they will override other cell
background color settings such as alternating row colors.
• With the Wrap text on option, you can define a character on which the cell content will be wraped each time it
is met
• With Oversized text you define the behavior when the width set for a column is smaller than its content’s length.
It can be Wrap text or Truncate text.
Poznámka: More properties of the attribute table item are described in the Tables common functionalities section.
The fixed table item
Additional information about the map can be inserted manually into a table by choosing Add Fixed Table and by
following items creation instructions to add a new table item that you can later manipulate the same way as exposed
in Interacting with layout items.
By default, an empty table with two minimized columns and rows appears in the map layout. You have to customize the
table in the Item Properties panel. Other than the items common properties, this feature has the following functionalities:
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Hlavní nastavení
Obr. 18.45: Fixed table Item Properties Panel with Table designer
In Main properties you can work with the Table designer when clicking the Edit table …:
• You can click into the table and insert texts manually.
• Through the menus on top it is possible to:
– Import Content From Clipboard by going to File (it overrides given inputs).
– work with selection functionalities for rows and columns by going to Edit.
– Insert rows, Insert columns, Delete Rows, Delete Columns as well as using the option to Include Header
Row.
• You can work with the Cell Contents section on the right and:
– Define the text format of selected cells in Formatting
∗ by clicking on the given expression button and using a regular expression for the input of the
cell
∗ by choosing the Text format
∗ by Format as number (several formats are available)
∗ by defining the Horizontal alignment and the Vertical alignment
∗ by choosing a Background color
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– Define the Cell Size with Row height and Column width.
Appearance
The Appearance group of the fixed table provides the following functionalities:
• Click Show empty rows to fill the attribute table with empty cells.
• With Cell margins you can define the margin around text in each cell of the table.
• With Display header you can select from a list one of ‚On first frame‘, ‚On all frames‘ default option, or ‚No
header‘.
• With Background color you can set the background color of the table using the color selector widget. The
Advanced customization option helps you define different background colors for each cell.
• With Oversized text you define the behavior when the width set for a column is smaller than its content’s length.
It can be Wrap text or Truncate text.
Poznámka: More properties of the fixed table item are described in the Tables common functionalities section.
Tables common functionalities
Show grid
The Show grid group of the table items provides the following functionalities (see Obr. 18.46):
Obr. 18.46: Attribute table Show grid Group
• Activate Show grid when you want to display the grid, the outlines of the table cells. You can also select to
either Draw horizontal lines or Draw vertical lines or both.
• With Line width you can set the thickness of the lines used in the grid.
• The Color of the grid can be set using the color selection widget.
Fonts and text styling
The Fonts and text styling group of the table items provides the following functionalities (see Obr. 18.47):
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Obr. 18.47: Attribute table Fonts and text styling Group
• You can define Font properties for Table heading and Table contents, using the advanced text settings widget
(with buffer, shadow, paint effects, transparence, background, coloring, …). Note that these changes do not
affect the cells that have custom font assigned, either from the Appearance section or the Table Designer dialog.
Only cells with the default rendering are overwritten.
• For Table heading you can additionally set the Alignment to Follow column alignment or override this
setting by choosing Left, Center or Right. The column alignment is set using the Select Attributes dialog
(see Obr. 18.41 ).
Frames
The Frames group of the table item properties provides the following functionalities (see Obr. 18.48):
Obr. 18.48: Attribute table Frames Group
• With Resize mode you can select how to render the attribute table contents:
– Use existing frames displays the result in the first frame and added frames only.
– Extend to next page will create as many frames (and corresponding pages) as necessary to display
the full selection of attribute table. Each frame can be moved around on the layout. If you resize a frame,
the resulting table will be divided up between the other frames. The last frame will be trimmed to fit the
table.
– Repeat until finished will also create as many frames as the Extend to next page option, except
all frames will have the same size.
• Use the Add Frame button to add another frame with the same size as selected frame. The result of the table that
will not fit in the first frame will continue in the next frame when you use the Resize mode Use existing
frames.
• Activate Don’t export page if frame is empty prevents the page to be exported when the table frame has no
contents. This means all other layout items, maps, scalebars, legends etc. will not be visible in the result.
• Activate Don’t draw background if frame is empty prevents the background to be drawn when the table
frame has no contents.
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18.2.8 The Picture and the North Arrow Items
The Picture item is a tool that helps decorate your map with pictures, logos… It can also be used to add north arrows,
despite the dedicated North arrow tool.
The Picture Item
You can add a picture by dragging it from your file manager onto the canvas, or by using the Add Picture
, following
items creation instructions. Then you can manipulate it, as explained in Interacting with layout items.
When using Add Picture
, the picture item will be a blank frame that you can customize using its Item Properties
panel. Other than the items common properties, this feature has the following functionalities (see Obr. 18.49):
Obr. 18.49: Picture Item Properties panel
There are several ways to set the Image source (to select the image you want to display):
1. In the Main properties group, use the … Browse
button of image source to select a file on your computer. The
browser will start in the SVG-libraries provided with QGIS. You can also select other image formats (like
.png or .jpg).
2. You can enter the source directly in the Image source text field. You can even provide a remote URL that points
to a picture.
3. From the Search directories area you can select an image from the loaded previews to set the image source.
These images are by default provided by folders set in Settings ► Options ► System ► SVG Paths.
4. Use the data defined override
button to set the image source from a feature attribute or using a regular expression.
Poznámka: In the Search directories group, you can use the Add and Remove buttons to customize the list of folders
to fetch and preview images from.
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With the Resize mode option, you can set how the image is displayed when the frame is resized:
• Zoom: enlarges/reduces the image to the frame while maintaining the aspect ratio of picture
• Stretch: stretches the image to fit inside the frame
• Clip: use this mode for raster images only, it sets the size of the image to the original image size without
scaling, and the frame is used to clip the image. So only the part of the image that is inside the frame will be
visible.
• Zoom and resize frame: enlarges the image to fit the frame, and then resizes frame to fit the resulting
image dimensions
• Resize frame to image size: sets the size of the frame to match the original size of the image (no
scaling)
Depending on the selected Resize mode, the Placement and Image rotation options may be disabled. Placement lets
you select the position of the image inside its frame.
The QGIS provided (default) .SVG files are customizable, meaning that you can easily apply other Fill color, Stroke
color (including opacity) and Stroke width than the original, using their corresponding feature in the SVG Parameters
group. These properties can also be data-defined.
If you add an .SVG file that does not enable these properties, you may need to add the following tags to the file in
order to add support e.g. for transparency:
• fill-opacity=“param(fill-opacity)“
• stroke-opacity=“param(outline-opacity)“
You can read this blog post to see an example.
Images can be rotated with the Image rotation field. Activating the Sync with map checkbox synchronizes the
rotation of the image with the rotation applied to a selected map item. This is a convenient feature for north arrows
that you can align with either:
• Grid north: the direction of a grid line which is parallel to the central meridian of the national/local grid
• True north: direction of a meridian of longitude.
You can also apply a declination Offset to the picture rotation.
The North Arrow Item
You can add a north arrow with the Add North Arrow
button, following items creation instructions and manipulate it
the same way as exposed in Interacting with layout items.
Since north arrows are images, the North Arrow item has the same properties as the picture item. The main differences
are:
• A default north arrow is used when adding the item, instead of a blank frame
• The north arrow item is synced with a map item by default: the Sync with map property is the map over which
the north arrow item is drawn. If none, it falls back to the reference map.
Poznámka: Many of the north arrows do not have an ‚N‘ added in the north arrow. This is done on purpose, since
there are languages that do not use an ‚N‘ for North.
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Obr. 18.50: North arrows available for selection in provided SVG library
18.2.9 The HTML Frame Item
It is possible to add a frame that displays the contents of a website or even create and style your own HTML page and
display it! You can add a picture with the Add HTML following items creation instructions and manipulate it the
same way as exposed in Interacting with layout items. Note that the HTML scale is controlled by the layout export
resolution at the time the HTML frame is created.
The HTML item can be customized using its Item Properties panel. Other than the items common properties, this
feature has the following functionalities (see Obr. 18.51):
Obr. 18.51: HTML Frame, the Item Properties Panel
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HTML Source
The HTML Source group of the HTML frame Item Properties panel provides the following functionalities (see Obr.
18.52):
Obr. 18.52: HTML frame, the HTML Source properties
• In URL you can enter the URL of a webpage you copied from your Internet browser or select an HTML file
using the … Browse
button. There is also the option to use the Data-defined override
button, to provide a URL
from the contents of an attribute field of a table or using a regular expression.
• In Source you can enter text in the textbox with some HTML tags or provide a full HTML page.
• The Insert or Edit an Expression… button can be used to add an expression like [%Year($now)%] in the
Source textbox to display the current year. This button is only activated when radiobutton Source is selected.
After inserting the expression click somewhere in the textbox before refreshing the HTML frame, otherwise
you will lose the expression.
• Activate Evaluate QGIS expressions in HTML code to see the result of the expression you have included,
otherwise you will see the expression instead.
• Use the Refresh HTML button to refresh the HTML frame(s) and see the result of changes.
Frames
The Frames group of the HTML frame Item Properties panel provides the following functionalities (see Obr. 18.53):
Obr. 18.53: HTML frame, the Frames properties
• With Resize mode you can select how to render the HTML contents:
– Use existing frames displays the result in the first frame and added frames only.
– Extend to next page will create as many frames (and corresponding pages) as necessary to render
the height of the web page. Each frame can be moved around on the layout. If you resize a frame, the
webpage will be divided up between the other frames. The last frame will be trimmed to fit the web page.
– Repeat on every page will repeat the upper left of the web page on every page in frames of the
same size.
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– Repeat until finished will also create as many frames as the Extend to next page
option, except all frames will have the same size.
• Use the Add Frame button to add another frame with the same size as selected frame. If the HTML page does
not fit in the first frame it will continue in the next frame when you use Resize mode or Use existing frames.
• Activate Don’t export page if frame is empty prevents the page from being exported when the frame has
no HTML contents. This means all other layout items, maps, scale bars, legends etc. will not be visible in the
result.
• Activate Don’t draw background if frame is empty prevents the HTML frame being drawn if the frame
is empty.
Use smart page breaks and User style sheet
The Use smart page breaks dialog and User style sheet dialog of the HTML frame Item Properties panel provides the
following functionalities (see Obr. 18.54):
Obr. 18.54: HTML frame, Use smart page breaks and User style sheet properties
• Activate Use smart page breaks to prevent the html frame contents from breaking mid-way a line of text
so it continues nice and smooth in the next frame.
• Set the Maximum distance allowed when calculating where to place page breaks in the html. This distance
is the maximum amount of empty space allowed at the bottom of a frame after calculating the optimum break
location. Setting a larger value will result in better choice of page break location, but more wasted space at the
bottom of frames. This is only used when Use smart page breaks is activated.
• Activate User style sheet to apply HTML styles that often is provided in cascading style sheets. An example
of style code is provided below to set the color of <h1> header tag to green and set the font and font size of
text included in paragraph tags <p>.
h1 {color: #00ff00;
}
p {font-family: "Times New Roman", Times, serif;
font-size: 20px;
}
• Use the Update HTML button to see the result of the style sheet settings.
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18.2.10 The Shape Items
QGIS provides a couple of tools to draw regular or more complex shapes over the print layout.
Poznámka: Unlike other print layout items, you can not style the frame nor the background color of the shapes
bounding frame (set to transparent by default).
The Regular Shape Item
The Shape item is a tool that helps to decorate your map with regular shapes like triangle, rectangle, ellipse… You can
add a regular shape using the Add Shape
tool which gives access to particular tools like Add Rectangle
, Add Ellipse
and Add Triangle
. Once you have selected the appropriate tool, you can draw the item following items creation
instructions. Like other layout items, a regular shape can be manipulated the same way as exposed in Interacting with
layout items.
Poznámka: Holding down the Shift key while drawing the basic shape with the click and drag method helps you
create a perfect square, circle or triangle.
The default shape item can be customized using its Item Properties panel. Other than the items common properties,
this feature has the following functionalities (see Obr. 18.55):
Obr. 18.55: Shape Item Properties Panel
The Main properties group shows and allows you to switch the type of the shape item (Ellipse, Rectangle or Triangle)
inside the given frame.
You can set the style of the shape using the advanced symbol and color selector widget…
For the rectangle shape, you can set in different units the value of the Corner radius to round of the corners.
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The Node-Based Shape Items
While the Add Shape tool provides way to create simple and predefined geometric item, the Add Node Item
tool helps you create a custom and more advanced geometric item. For polylines or polygons, you can draw as many
lines or sides as you want and vertices of the items can be independently and directly manipulated using the Edit
Nodes Item. The item itself can be manipulated as exposed in Interacting with layout items.
To add a node-based shape:
1. Click the Add Node Item
icon
2. Select either Add Polygon
or Add Polyline
tool
3. Perform consecutive left clicks to add nodes of your item. If you hold down the Shift key while drawing
a segment, it is constrained to follow an orientation multiple of 45°.
4. When you’re done, right-click to terminate the shape.
You can customize the appearance of the shape in the Item Properties panel.
Obr. 18.56: Polygon Node Shape Item Properties Panel
In the Main properties, you can set the style of the shape using the advanced symbol and color selector widget…
For polyline node items, you can also parameterize the Line markers i.e. add:
• start and/or end markers with options:
– None: draws a simple polyline.
– Arrow: adds a regular triangular arrow head that you can customize.
– SVG marker: uses an SVG file as arrow head of the item.
• customize the arrow head:
– Arrow stroke color: sets the stroke color of the arrow head.
– Arrow fill color: sets the fill color of the arrow head.
– Arrow stroke width: sets the stroke width of the arrow head.
– Arrow head width: sets the size of the arrow head.
SVG images are automatically rotated with the line. Stroke and fill colors of QGIS predefined SVG images can be
changed using the corresponding options. Custom SVG may require some tags following this instruction.
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Obr. 18.57: Polyline Node Shape Item Properties Panel
The Arrow Item
The Add Arrow
tool is a shortcut to create an arrow-enabled polyline by default and thus has the same properties
and behavior as a polyline node item.
Actually, the arrow item can be used to add a simple arrow, for example, to show the relation between two different
print layout items. However, to create a north arrow, the image item should be considered first as it gives access to
a set of north arrows in .SVG format that you can sync with a map item so that it rotates automatically with it.
Editing a node item geometry
A specific tool is provided to edit node-based shapes through Edit Nodes Item
. Within this mode, you can select a node
by clicking on it (a marker is displayed on the selected node). A selected node can be moved either by dragging it
or by using the arrow keys. Moreover, in this mode, you are able to add nodes to an existing shape: double-click on
a segment and a node is added at the place you click. Finally, you can remove the currently selected node by hitting
the Del key.
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18.3 Creating an Output
Obr. 18.58 shows an example print layout including all the types of layout items described in the previous section.
Obr. 18.58: Print Layout with map view, legend, image, scale bar, coordinates, text and HTML frame added
From the Layout menu or toolbar, you can output the print layout to different file formats, and it is possible to modify
the resolution (print quality) and paper size:
• The Print
icon allows you to print the layout to a connected printer or a PostScript file, depending on the
installed printer drivers.
• The Export as image
icon exports the print layout image formats such as PNG, BMP, TIF, JPG, and many
others…
• The Export as SVG
icon saves the print layout as an SVG (Scalable Vector Graphic).
• The Export as PDF
icon saves the defined print layout directly as a PDF (Portable Document Format) file.
18.3.1 Export settings
Whenever you export a print layout, there are a selection of export settings QGIS needs to check in order to produce
the most appropriate output. These configurations are:
• The Export settings of the Layout panel, such as Export resolution, Print as raster Always export as vectors or
Save world file
• Exclude page from exports in the page item properties panel
• Exclude item from exports in the item properties panel
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18.3.2 Export as Image
To export a layout as an image:
1. Click the Export as image
icon
2. Select the image format, the folder and filename (e.g. myill.png) to use. If the layout contains more than
one page, each page will be exported to a file with the given filename with the page number appended (e.g.
myill_2.png).
3. In the next (Image Export Options) dialog:
• You can override the print layout Export resolution and the exported page dimensions (as set in Layout
panel).
• Image rendering can also be improved with the Enable antialiasing option.
• If you want to export your layout as a georeferenced image (e.g., to share with other projects), check
the Generate world file option, and an ESRI World File with the same name as the exported image,
but a different extension (.tfw for TIFF, .pnw for PNG, jgw for JPEG, …) will be created when
exporting. This option can also be checked by default in the layout panel.
Poznámka: For multi-page output, only the page that contains the reference map will get a world file
(assuming that the Generate world file option is checked).
• By checking Crop to content option, the image output by the layout will include the minimal area
enclosing all the items (map, legend, scale bar, shapes, label, image…) of each page of the composition:
– If the composition includes a single page, then the output is resized to include EVERYTHING on
the composition. The page can then be reduced or extended to all items depending on their position
(on, above, below, left or right of the page).
– In case of a multi-page layout, each page will be resized to include items in its area (left and right sides
for all pages, plus top for the first page and bottom for the last page). Each resized page is exported
to a separate file.
The Crop to content dialog also lets you add margins around the cropped bounds.
Obr. 18.59: Image Export Options, output is resized to items extent
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Tip: Use image formats that support transparency when items extend beyond the paper extent
Layout items may be placed outside the paper extent. When exporting with the Crop to content option, the resulting
image may therefore extend beyond the paper extent. Since the background outside of the paper extent will be
transparent, for image formats that do not support transparency (e.g. BMP and JPG) the transparent background
will be rendered as full black, „corrupting“ the image. Use transparency-compatible formats (e.g. TIFF and PNG) in
such cases.
Poznámka: When supported by the format (e.g. PNG) and the underlying Qt library, the exported image may include
project metadata (author, title, date, description…)
18.3.3 Export as SVG
To export a layout as SVG:
1. Click the Export as SVG
icon
2. Fill in the path and filename (used as a base name for all the files in case of multi-page composition, as for
image export)
3. In the next SVG Export Options dialog, you can override the layout default export settings or configure new ones:
• Export map layers as SVG groups: exported items are grouped within layers whose name matches the
layer names from QGIS, making it much easier to understand the contents of the document.
• Always export as vectors: some rendering options require items to be rasterized for a better rendering.
Check this option to keep the objects as vectors with the risk that the appearance of the output file may
not match the print layout preview (for more details, see Export settings).
• Export RDF metadata of the document such as the title, author, date, description…
• Simplify geometries to reduce output file size: this avoids exporting ALL geometry vertices, which
can result in a ridiculously complex and large export file size that could fail to load in other applications.
Geometries will be simplified while exporting the layout in order to remove any redundant vertices which
are not discernably different at the export resolution (e.g. if the export resolution is 300 dpi, vertices
that are less than 1/600 inch apart will be removed).
• Set the Text export: controls whether text labels are exported as proper text objects (Always export texts
as text objects) or as paths only (Always export texts as paths). If they are exported as text objects, they can
be edited in external applications (e.g. Inkscape) as normal text. BUT the side effect is that the rendering
quality is reduced, AND there are issues with rendering when certain text settings like buffers are in place.
That’s why exporting as paths is recommended.
• Apply Crop to content option
• Disable tiled raster layer exports: When exporting files, QGIS uses a built-in raster layer tiled rendering
that saves memory. Sometimes, this can cause visible „seams“ in the rasters for generated files. Checking
this option would fix that, at the cost of a higher memory usage during exports.
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Obr. 18.60: SVG Export Options
Poznámka: Currently, the SVG output is very basic. This is not a QGIS problem, but a problem with the underlying
Qt library. This will hopefully be sorted out in future versions.
18.3.4 Export as PDF
To export a layout as PDF:
1. Click the Export as PDF
icon
2. Fill in the path and filename: unlike for image and SVG export, all the pages in the layout are exported to
a single PDF file.
3. In the next PDF Export Options dialog, you can override the layout default export settings or configure new ones:
• Always export as vectors: some rendering options require items to be rasterized for a better rendering.
Check this option to keep the objects as vectors with the risk that the appearance of the output file may
not match the print layout preview (for more details, see Export settings).
• Append georeference information: available only if the reference map, from which the information
is taken, is on the first page.
• Export RDF metadata of the document such as the title, author, date, description…
• Set the Text export: controls whether text labels are exported as proper text objects (Always export texts
as text objects) or as paths only (Always export texts as paths). If they are exported as text objects then
they can be edited in external applications (e.g. Inkscape) as normal text. BUT the side effect is that the
rendering quality is decreased, AND there are issues with rendering when certain text settings like buffers
are in place. That’s why exporting as paths is recommended.
• Control the PDF Image compression using:
– Lossy (JPEG), which is the default compression mode
– or Lossless, which creates bigger files in most cases, but is much more suitable for printing outputs
or for post-production in external applications (requires Qt 5.13 or later).
• Create Geospatial PDF (GeoPDF): Generate a georeferenced PDF file (requires GDAL version 3 or
later).
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• Disable tiled raster layer exports: When exporting files, QGIS uses tiled based rendering that saves
memory. Sometimes, this can cause visible „seams“ in the rasters for generated files. Checking this option
would fix that, at the cost of a higher memory usage during exports.
• Simplify geometries to reduce output file size: Geometries will be simplified while exporting the layout
by removing vertices that are not discernably different at the export resolution (e.g. if the export resolution
is 300 dpi, vertices that are less than 1/600 inch apart will be removed). This can reduce the size
and complexity of the export file (very large files can fail to load in other applications).
Obr. 18.61: PDF Export Options
Poznámka: Since QGIS 3.10, with GDAL 3, GeoPDF export is supported, and a number of GeoPDF specific
options are available:
• Format (GeoPDF format - there are some GeoPDF variations),
• Include multiple map themes (specify map themes to include),
• Include vector feature information (choose the layers and group them into logical PDF groups).
Poznámka: Exporting a print layout to formats that supports georeferencing (e.g. PDF and TIFF) creates
a georeferenced output by default.
18.3.5 Generate an Atlas
Atlas functions allow you to create map books in an automated way. Atlas uses the features of a table or vector layer
(Coverage layer) to create an output for each feature (atlas feature) in the table / layer. The most common usage
is to zoom a map item to the current atlas feature. Further use cases include:
• a map item showing, for another layer, only features that share the same attribute as the atlas feature or are
within its geometry.
• a label or HTML item whose text is replaced as features are iterated over
• a table item showing attributes of associated parent or children features of the current atlas feature…
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For each feature, the output is processed for all pages and items according to their exports settings.
Tip: Use variables for more flexibility
QGIS provides a large panel of functions and variables, including atlas related ones, that you can use to manipulate
the layout items, but also the symbology of the layers, according to atlas status. Combining these features gives you
a lot of flexibility and helps you easily produce advanced maps.
To enable the generation of an atlas and access atlas parameters, refer to the Atlas panel. This panel contains the
following (see Obr. 18.62):
Obr. 18.62: Atlas Panel
• Generate an atlas enables or disables atlas generation.
• Configuration
– A Coverage layer combo box that allows you to choose the table or vector layer containing the
features to iterate over.
– An optional Hidden coverage layer that, if checked, will hide the coverage layer (but not the other
layers) during the generation.
– An optional Page name combo box to specify the name for the feature page(s). You can select a field of
the coverage layer or set an expression. If this option is empty, QGIS will use an internal ID, according
to the filter and/or the sort order applied to the layer.
– An optional Filter with text area that allows you to specify an expression for filtering features from
the coverage layer. If the expression is not empty, only features that evaluate to True will be processed.
– An optional Sort by that allows you to sort features of the coverage layer (and the output), using
a field of the coverage layer or an expression. The sort order (either ascending or descending) is set by
the two-state Sort direction button that displays an up or a down arrow.
• Output - this is where the output of the atlas can be configured:
– An Output filename expression textbox that is used to generate a filename for each atlas feature. It is based
on expressions. is meaningful only for rendering to multiple files.
– A Single file export when possible that allows you to force the generation of a single file if this is possible
with the chosen output format (PDF, for instance). If this field is checked, the value of the Output filename
expression field is meaningless.
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– An Image export format drop-down list to select the output format when using the Export atlas as Images…
button.
Control map by atlas
The most common usage of atlas is with the map item, zooming to the current atlas feature, as iteration goes over
the coverage layer. This behavior is set in the Controlled by atlas group properties of the map item. See Controlled by
atlas for different settings you can apply on the map item.
Customize labels with expression
In order to adapt labels to the feature the atlas iterates over, you can include expressions. Make sure that you place the
expression part (including functions, fields or variables) between [% and %] (see The Label Item for more details).
For example, for a city layer with fields CITY_NAME and ZIPCODE, you could insert this:
The area of [% concat( upper(CITY_NAME), ',', ZIPCODE, ' is ',
format_number($area/1000000, 2) ) %] km2
or, another combination:
The area of [% upper(CITY_NAME)%],[%ZIPCODE%] is
[%format_number($area/1000000,2) %] km2
The information [% concat( upper(CITY_NAME), ',', ZIPCODE, ' is ',
format_number($area/1000000, 2) ) %] is an expression used inside the label. Both expressions would
result in the following type of label in the generated atlas:
The area of PARIS,75001 is 1.94 km2
Explore Data-defined override buttons with atlas
There are several places where you can use a Data defined override
button to override the selected setting. This
is particularly useful with atlas generation. See Data defined override setup for more details on this widget.
For the following examples the Regions layer of the QGIS sample dataset is used and selected as Coverage layer
for the atlas generation. We assume that it is a single page layout containing a map item and a label item.
When the height (north-south) of a region extent is greater than its width (east-west), you should use Portrait instead
of Landscape orientation to optimize the use of paper. With a Data Defined Override
button you can dynamically set
the paper orientation.
Right-click on the page and select Page Properties to open the panel. We want to set the orientation dynamically, using
an expression depending on the region geometry, so press the button of field Orientation, select Edit… to open
the Expression string builder dialog and enter the following expression:
CASE WHEN bounds_width(@atlas_geometry) > bounds_height(@atlas_geometry)
THEN 'Landscape' ELSE 'Portrait' END
Now if you preview the atlas, the paper orients itself automatically, but item placements may not be ideal. For each
Region you need to reposition the location of the layout items as well. For the map item you can use the button
of its Width property to set it dynamic using the following expression:
@layout_pagewidth - 20
Likewise, use the button of the Height property to provide the following expression to constrain map item size:
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@layout_pageheight - 20
To ensure the map item is centered in the page, set its Reference point to the upper left radio button and enter 10 for
its X and Y positions.
Let’s add a title above the map in the center of the page. Select the label item and set the horizontal alignment to
Center. Next move the label to the right position, choose the middle button for the Reference point, and provide the
following expression for field X:
@layout_pagewidth / 2
For all other layout items you can set the position in a similar way so they are correctly positioned both for portrait and
landscape. You can also do more tweaks such as customizing the title with feature attributes (see Customize labels with
expression example), changing images, resizing the number of legend columns number according to page orientation,
…
The information provided here is an update of the excellent blog (in English and Portuguese) on the Data Defined
Override options Multiple_format_map_series_using_QGIS_2.6 .
Another example for using data-defined override buttons is the usage of a dynamic picture. For the following examples
we use a geopackage layer containing a BLOB field called logo with the field type binary (see Creating a new
GeoPackage layer). For every feature there is defined a different picture so that the atlas can iterate over as described
in Preview and generate an atlas. All you need to do is add a picture in the print layout and go to its Item properties in
the atlas context. There you can find a data-defined override button in the Image source section of the Main Properties.
In the following window choose Edit so that the Expression String Builder opens. From the Fields and values section
you can find the BLOB field that was defined in the geopackage layer. Double-click the field name logo and click
OK.
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The atlas iterates over the entries in the BLOB field provided that you choose the geopackage layer as Coverage layer
(further instructions you can find in Preview and generate an atlas).
These are just two examples of how you can use some advanced settings with atlas.
Preview and generate an atlas
Obr. 18.63: Atlas Preview toolbar
Once the atlas settings have been configured, and layout items (map, table, image…) linked to it, you can create
a preview of all the pages by choosing Atlas ► Preview Atlas or clicking the Preview Atlas
icon. You can then use
the arrows to navigate through all the features:
• First feature
• Previous feature
• Next feature
• Last feature
You can also use the combo box to select and preview a specific feature. The combo box shows atlas feature names
according to the expression set in the atlas Page name option.
As for simple compositions, an atlas can be generated in different ways (see Creating an Output for more information
- just use tools from the Atlas menu or toolbar instead of the Layout menu.
This means that you can directly print your compositions with Atlas ► Print Atlas. You can also create a PDF using
Atlas ► Export Atlas as PDF…: You will be asked for a directory to save all the generated PDF files, except if the
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Single file export when possible has been selected. In that case, you’ll be prompted to give a filename.
With Atlas ► Export Atlas as Images… or Atlas ► Export Atlas as SVG… tool, you’re also prompted to select a folder.
Each page of each atlas feature composition is exported to the image file format set in Atlas panel or to SVG.
Poznámka: With multi-page output, an atlas behaves like a layout in that only the page that contains the General
settings will get a world file (for each feature output).
Tip: Print a specific atlas feature
If you want to print or export the composition of only one feature of the atlas, simply start the preview, select the
desired feature in the drop-down list and click on Layout ► Print (or Export… to any supported file format).
Use project defined relations for atlas creation
For users with HTML and Javascript knowledge it is possible to operate on GeoJSON objects and use project defined
relations from the QGIS project. The difference between this approach and using expressions directly inserted into the
HTML is that it gives you a full, unstructured GeoJSON feature to work with. This means that you can use existing
Javascript libraries and functions that operate on GeoJSON feature representations.
The following code includes all related child features from the defined relation. Using the JavaScript setFeature
function it allows you to make flexible HTML which represents relations in whatever format you like (lists, tables,
etc). In the code sample, we create a dynamic bullet list of the related child features.
// Declare the two HTML div elements we will use for the parent feature id
// and information about the children
<div id="parent"></div>
<div id="my_children"></div>
<script type="text/javascript">
function setFeature(feature)
{
// Show the parent feature's identifier (using its "ID" field)
document.getElementById('parent').innerHTML = feature.properties.ID;
//clear the existing relation contents
document.getElementById('my_children').innerHTML = '';
feature.properties.my_relation.forEach(function(child_feature) {
// for each related child feature, create a list element
// with the feature's name (using its "NAME" field)
var node = document.createElement("li");
node.appendChild(document.createTextNode(child_feature.NAME));
document.getElementById('my_children').appendChild(node);
});
}
</script>
During atlas creation there will be an iteration over the coverage layer containing the parent features. On each page,
you will see a bullet list of the related child features following the parent’s identifier.
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18.4 Creating a Report
This section will help you set up a report in QGIS.
18.4.1 What is it?
By definition, a GIS report is a document containing information organized in a narrative way, containing maps, text,
graphics, tables, etc. A report can be prepared ad hoc, periodic, recurring, regular, or as required. Reports may refer
to specific periods, events, occurrences, subjects or locations.
In QGIS, a Report is an extension of a Layouts.
Reports allow users to output their GIS projects in a simple, quick and structured way.
A report can be created with Project ► New Report or inside the Project ► Layout Manager.
Poznámka: The maps in QGIS reports behave in the same way as maps in print layouts and atlases. We will
concentrate on the specifics of QGIS reports. For details on map handling, see the sections on print layouts and
atlases.
18.4.2 Get started
In the Layout Manager dialog a report can be created through New from template by selecting the dropdown option
Empty Report and hitting the Create… button.
For this example, we use some administrative boundaries, populated places, ports and airports from the Natural Earth
dataset (1:10M).
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Using the Project ► New Report command, we create a blank report. Initially, there is not much to look at – the dialog
which is displayed looks much like the print layout designer, except for the Report Organizer panel to the left:
18.4.3 Layout Report Workspace
QGIS reports can consist of multiple, nested sections. In our new blank report we initially only have the main report
section. The only options for this report section is Include report header and Include report footer. If we enable these
options, a header will be included as the first page(s) (individual parts of reports can be multi-page if desired) in the
report, and a footer will constitute the last page(s). Enable the header (Include report header), and hit the Edit button
next to it:
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A few things happen as a result. Firstly, an edit pencil is shown next to Report in the Report Organizer, indicating
that the report section is currently being edited in the designer. We also see a new page with a small Report Header
title. The page has landscape orientation by default, but this (and other properties of the page) can be changed by
right-clicking on the page and choosing Page properties. This will bring up the Item properties tab for the page, and
page Size, Width, Height, and more can be specified.
In QGIS reports, every component of the report is made up of individual layouts. They can be created and modified
using the same tools as for standard print layouts – so you can use any desired combination of labels, pictures, maps,
tables, etc. Let us add some items to our report header to demonstrate:
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We will also create a simple footer for the report by checking the Include report footer option and hitting Edit.
Before proceeding further, let us export this report and see what we get. Exporting is done from the Report menu – in
this case we select Export Report as PDF… to render the whole report to a PDF file. Here is the not-very-impressive
result – a two page PDF consisting of our header and footer:
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Let us make things more interesting. By hitting the Add Section
button in the Report Organizer, we are given a choice
of new sections to add to our report.
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There are two options: Static Layout Section and Field Group Section.
The Add Static Layout Section is a single, static body layout. This can be used to embed static layouts mid-way through
a report.
The Field Group Section repeats its body layout for every feature of a layer. The features are sorted by the selected
grouping feature (with an option for ascending/descending sort). If a field group section has child sections (e.g. another
field group section with a different field), then only features with unique values for the group feature are iterated over.
This allows nested reports.
For now we will add a Field Group Section to our report. At its most basic level, you can think of a Field Group Section
as the equivalent of a print atlas: you select a layer to iterate over, and the report will insert a section for each feature
found. Selecting the new Field Group Section reveals a number of new related settings:
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In this case we’ve setup our Field Group so that we iterate over all the states from the Admin Level 1 layer, using
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the values from the adm1name field. The same options to include header and footer are present, together with a new
option to include a body for this section. We’ll do that, and edit the body:
Our body now consists of a map and a label showing the name of the state. To include the name of the state, we
selected Add Item ► Add Label and data defined the text under Main Properties with the help of Insert or Edit an
Expression….
The result was the following expression (name is the name of the attribute in the Admin Level 1 layer that contains
the name of the state):
[% "name" %]
The map is set to follow the current report feature (enabled by checking Controlled by Report – just like a map item
in an atlas will follow the current atlas feature when Controlled by Atlas is checked):
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If we went ahead and exported our report now, we’d get something like this:
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Obr. 18.64: The report header, a page for each state, and the report footer.
So more or less an atlas, but with a header and footer page.
Let us make things more interesting by adding a subsection to our state group. We do this by first selecting the Admin
Level 1 field group in the organizer, then hitting the Add Field
button and adding a new Field Group Section:
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When iterating over the features of a Field Group Section, the features will be filtered to match the defining field
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of its parent group (adm1name in this case). Here, the subsection we added will iterate over a Populated Places
layer, including a body section for each place encountered. The magic here is that the Populated Places layer has an
attribute with the same name as the defining field in the parent layer, adm1name, tagging each place with the state it
is contained within (if you’re lucky your data will already be structured like this – if not, run the Join Attributes by
Location Processing algorithm and create your own field). When we export this report, QGIS will grab the first state
from the Admin Level 1 layer, and then iterate over all the Populated Places with a matching adm1name value. Here’s
what we get:
Here we created a basic body for the Populated Places group, including a map of the place and a table of some place
attributes. So our report is now a report header, a page for the first state, followed by a page for every populated place
within that state, then the rest of the states with their populated places, and finally the report footer. If we were to add
a header for the Populated Places group, it would be included just before listing the populated places for each state,
as shown in the illustration below.
Similarly, a footer for the Populated Places group would be inserted after the final place for each state is included.
In addition to nested subsections, subsections in a report can also be included consecutively. If we add a second
subsection to the Admin Level 1 group for Airports, then (if the Airports layer has an attribute adm1name that can link
it to the parent group) our report will first list ALL the populated places for each state, followed by all the airports
within that state, before proceeding to the next state.
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The key point here is that our Airports group is a subsection of the Admin Level 1 group – not the Populated Places
group.
In this case our report would be structured like this (note that state flags have also been included - the procedure for
adding feature specific pictures in this way is described below):
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Including pictures in a report
Pictures can be quite useful in reports, and QGIS allows pictures in both the static and dynamic parts of a report.
Pictures are added in the same way as for standard print layouts, and for the static report parts (and static pictures in
dynamic parts) there is not more to it.
But if you want illustrations that are tailored to the report features, your layer must have an attribute that can be used
to define the picture to include.
QGIS depends on absolute file names for images in reports.
For dynamic pictures, you first add a picture to the body part of the group, as usual. In the Item properties of the
picture, you set the Image Source using the Data defined override
button, and either select an attribute that contains the
absolute path of the images or Edit… (to enter an expression that generates the absolute image path).
Below is an example expression that uses string concatenation to specify the absolute path to the pictures, using the
directory where the project file is located @project_path) and an attribute (adm1name) from which the file
name is generated (in this case by transforming the string in the adm1name attribute to uppercase, and appending
‚_flag.png‘):
concat(@project_folder, '/naturalearth/pictures/' ,
upper("adm1name"), '_flag.png')
This means that the pictures are located in the naturalearth/pictures subdirectory of the project file
directory.
Highlighting the current report feature in a map
In the above report, the report features are emphasized in the maps using highlighting (state) and circles (populated
places). To emphasize the report features in the maps (apart from placing them at the centre of the maps), you must
data define the style using a comparison between its @id and the @atlas_featureid, as for atlases.
For instance, if you would like to use a thicker line / border for the report feature than the other features you can data
define the line width:
if($id=@atlas_featureid, 2.0, 0.1)
The report feature will get a 2 units wide polygon outline, while all other features will get a 0.1 units wide line. It
is also possible to data define the colour (non-transparent dark magenta for the report feature and semi-transparent
light gray for the other features):
if($id=@atlas_featureid, '#FF880088', '#88CCCCCC')
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More level 1 groups
Combining nested and consecutive sections, together with section headers and footers allows for tons of flexibility.
For instance, in the below report we add another field group as a child of the main report for the :guilabel`Ports` layer.
Now, after listing the states together with their populated places and airports, we’ll get a summary list of all the ports
in the region:
This results in the last part of our report exporting as:
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18.4.4 Export settings
When you export a report (Report ► Export Report as Images… / SVG… / PDF…), you will be asked for a file name,
and then you get the opportunity to tune the export settings to get the most appropriate output.
As you see, reports in QGIS are extremely powerful and flexible!
Poznámka: The current information was adapted from a North Road blog, Exploring Reports in QGIS 3.0 - the
Ultimate Guide!
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KAPITOLA 19
Working with OGC / ISO protocols
The Open Geospatial Consortium (OGC) is an international organization with membership of more than 300
commercial, governmental, nonprofit and research organizations worldwide. Its members develop and implement
standards for geospatial content and services, GIS data processing and exchange.
Describing a basic data model for geographic features, an increasing number of specifications are developed by OGC
to serve specific needs for interoperable location and geospatial technology, including GIS. Further information can
be found at https://www.opengeospatial.org/.
Important OGC specifications supported by QGIS are:
• WMS — Web Map Service (WMS/WMTS Client)
• WMTS — Web Map Tile Service (WMS/WMTS Client)
• WFS — Web Feature Service (WFS and WFS-T Client)
• WFS-T — Web Feature Service - Transactional (WFS and WFS-T Client)
• WCS — Web Coverage Service (WCS Client)
• WPS — Web Processing Service
• CSW — Catalog Service for the Web
• SFS — Simple Features for SQL (PostGIS Layers)
• GML — Geography Markup Language
OGC services are increasingly being used to exchange geospatial data between different GIS implementations and
data stores. QGIS can deal with the above specifications as a client, being SFS (through support of the PostgreSQL /
PostGIS data provider, see section PostGIS Layers).
You can also share your maps and data through the WMS, WMTS, WFS, WFS-T and WCS protocols using
a webserver with QGIS Server, UMN MapServer or GeoServer installed.
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19.1 WMS/WMTS Client
19.1.1 Overview of WMS Support
QGIS currently can act as a WMS client that understands WMS 1.1, 1.1.1 and 1.3 servers. In particular, it has been
tested against publicly accessible servers such as DEMIS.
A WMS server acts upon requests by the client (e.g., QGIS) for a raster map with a given extent, set of layers,
symbolization style, and transparency. The WMS server then consults its local data sources, rasterizes the map, and
sends it back to the client in a raster format. For QGIS, this format would typically be JPEG or PNG.
WMS is generically a REST (Representational State Transfer) service rather than a full-blown Web service. As such,
you can actually take the URLs generated by QGIS and use them in a web browser to retrieve the same images that
QGIS uses internally. This can be useful for troubleshooting, as there are several brands of WMS server on the market
and they all have their own interpretation of the WMS standard.
WMS layers can be added quite simply, as long as you know the URL to access the WMS server, you have a serviceable
connection to that server, and the server understands HTTP as the data transport mechanism.
Additionally, QGIS will cache your WMS responses (i.e. images) for 24h as long as the GetCapabilities request is not
triggered. The GetCapabilities request is triggered everytime the Connect button in the Add Layer(s) from WMS(T)
Server dialog is used to retrieve the WMS server capabilities. This is an automatic feature meant to optimize project
loading time. If a project is saved with a WMS layer, the corresponding WMS tiles will be loaded from the cache the
next time the project is opened as long as they are no older than 24H.
19.1.2 Overview of WMTS Support
QGIS can also act as a WMTS client. WMTS is an OGC standard for distributing tile sets of geospatial data. This
is a faster and more efficient way of distributing data than WMS because with WMTS, the tile sets are pre-generated,
and the client only requests the transmission of the tiles, not their production. A WMS request typically involves
both the generation and transmission of the data. A well-known example of a non-OGC standard for viewing tiled
geospatial data is Google Maps.
In order to display the data at a variety of scales close to what the user might want, the WMTS tile sets are produced
at several different scale levels and are made available for the GIS client to request them.
This diagram illustrates the concept of tile sets:
Obr. 19.1: Concept of WMTS tile sets
The two types of WMTS interfaces that QGIS supports are via Key-Value-Pairs (KVP) and RESTful. These two
interfaces are different, and you need to specify them to QGIS differently.
1. In order to access a WMTS KVP service, a QGIS user must open the WMS/WMTS interface and add the
following string to the URL of the WMTS tile service:
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"?SERVICE=WMTS&REQUEST=GetCapabilities"
An example of this type of address is
https://opencache.statkart.no/gatekeeper/gk/gk.open_wmts?\
service=WMTS&request=GetCapabilities
For testing the topo2 layer in this WMTS works nicely. Adding this string indicates that a WMTS web service
is to be used instead of a WMS service.
2. The RESTful WMTS service takes a different form, a straightforward URL. The format recommended by
the OGC is:
{WMTSBaseURL}/1.0.0/WMTSCapabilities.xml
This format helps you to recognize that it is a RESTful address. A RESTful WMTS is accessed in QGIS by
simply adding its address in the WMS setup in the URL field of the form. An example of this type of address
for the case of an Austrian basemap is https://maps.wien.gv.at/basemap/1.0.0/WMTSCapabilities.xml.
Poznámka: You can still find some old services called WMS-C. These services are quite similar to WMTS (i.e.,
same purpose but working a little bit differently). You can manage them the same as you do WMTS services. Just add
?tiled=true at the end of the url. See https://wiki.osgeo.org/wiki/Tile_Map_Service_Specification for more
information about this specification.
When you read WMTS, you can often think WMS-C also.
19.1.3 Selecting WMS/WMTS Servers
The first time you use the WMS feature in QGIS, there are no servers defined.
You then need to create connections to the server you are targeting:
1. Go to the WMS/WMTS tab of the Data Source Manager dialog, either by:
• clicking the Open Data Source Manager
button (or pressing Ctrl+L) and enabling the tab
• clicking the Add WMS layer
button on the Manage Layers toolbar
• or selecting Layer ► Add Layer ► Add WMS/WMTS Layer… menu
2. Press New from the Layers tab. The Create a New WMS/WMTS Connection… dialog appears.
Tip: Right-click the WMS/WMTS entry from within the Browser panel and select New Connection… also
opens the Create a New WMS/WMTS Connection… dialog.
3. Then enter the parameters to connect to your desired WMS server, as listed below:
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Obr. 19.2: Creating a connection to a WMS server
• Name: A name for the connection. This name will be used in the Server Connections drop-down box
so that you can distinguish it from other WMS servers.
• URL: URL of the server providing the data. This must be a resolvable host name – the same format as you
would use to open a telnet connection or ping a host, i.e. the base URL only. For example, you shouldn’t
have fragments such as request=GetCapabilities or version=1.0.0 in your URL.
• Authentication (optional): using a stored configuration or a basic authentication with Username and
Password.
Varování: Entering username and password in the Authentication tab will keep unprotected
credentials in the connection configuration. Those credentials will be visible if, for instance,
you shared the project file with someone. Therefore, it’s advisable to save your credentials in
a Authentication configuration instead (configurations tab). See Ověřovací systém for more details.
• HTTP Referer
• DPI-Mode: Available options are all, off, QGIS, UMN and GeoServer
• Ignore GetMap/GetTile URI reported in capabilities: if checked, use given URI from the URL field
above.
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• Ignore GetFeatureInfo URI reported in capabilities: if checked, use given URI from the URL field
above.
• Ignore axis orientation (WMS 1.3/WMTS)
• Ignore reported layer extents: because the extent reported by raster layers may be smaller than the
actual area which can be rendered (notably for WMS servers with symbology which takes more space
than the data extent), check this option to avoid cropping raster layers to their reported extents, resulting
in truncated symbols on the borders of these layers.
• Invert axis orientation
• Smooth pixmap transformation
4. Press OK
Once the new WMS server connection has been created, it will be preserved for future QGIS sessions.
If you need to set up a proxy server to be able to receive WMS services from the internet, you can add your proxy
server in the options. Choose Settings ► Options and click on the Network tab. There, you can add your proxy settings
and enable them by setting Use proxy for web access. Make sure that you select the correct proxy type from the
Proxy type drop-down menu.
19.1.4 Loading WMS/WMTS Layers
Once you have successfully filled in your parameters, you can use the Connect button to retrieve the capabilities of
the selected server. This includes the image encoding, layers, layer styles and projections. Since this is a network
operation, the speed of the response depends on the quality of your network connection to the WMS server. While
downloading data from the WMS server, the download progress is visualized in the lower left corner of the main
QGIS dialog.
Your screen should now look a bit like Obr. 19.3, which shows the response provided by a WMS server.
Obr. 19.3: Dialog for adding a WMS server, with filter on available layers
The upper part of the Layers tab of the dialog shows a tree structure that can include layer groups embedding layers
with their associated image style(s) served by the server. Each item can be identified by:
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• an ID
• a Name
• a Title
• and an Abstract.
The list can be filtered using the widget in the top right corner.
Image Encoding
The Image encoding section lists the formats that are supported by both the client and server. Choose one depending
on your image accuracy requirements.
Tip: Image Encoding
You will typically find that a WMS server offers you the choice of JPEG or PNG image encoding. JPEG is a lossy
compression format, whereas PNG faithfully reproduces the raw raster data.
Use JPEG if you expect the WMS data to be photographic in nature and/or you don’t mind some loss in picture
quality. This trade-off typically reduces by five times the data transfer requirement compared with PNG.
Use PNG if you want precise representations of the original data and you don’t mind the increased data transfer
requirements.
Options
The Options area of the dialog provides means to configure the WMS requests. You can define:
• Tile size if you want to set tile sizes (e.g., 256x256) to split up the WMS request into multiple requests.
• The Request step size
• The Feature limit for GetFeatureInfo defines the maximum number of GetFeatureInfo results from the server.
• If you select a WMS from the list, a field with the default projection provided by the web server appears. Press
the Change… button to replace the default projection of the WMS with another CRS supported by the WMS
server.
• Finally you can activate Use contextual WMS Legend if the WMS Server supports this feature. Then only
the relevant legend for your current map view extent will be shown and thus will not include legend items for
items you can’t see in the current map.
At the bottom of the dialog, a Layer name text field displays the selected item’s Title. You can change the name at your
will. This name will appear in the Layers panel after you pressed the Add button and loaded the layer(s) in QGIS.
You can select several layers at once, but only one image style per layer. When several layers are selected, they will
be combined at the WMS server and transmitted to QGIS in one go, as a single layer. The default name is a slash (/)
separated list of their original title.
Layer Order
The Layer Order tab lists the selected layers available from the current connected WMS server.
WMS layers rendered by a server are overlaid in the order listed in the Layers tab, from top to bottom of the list. If
you want to change the overlay order, you can use the Up and Down buttons of the Layer Order tab.
Transparency
The Global transparency setting from the Layer Properties is hard coded to be always on, where available.
Tip: WMS Layer Transparency
The availability of WMS image transparency depends on the image encoding used: PNG and GIF support
transparency, whilst JPEG leaves it unsupported.
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Coordinate Reference System
A coordinate reference system (CRS) is the OGC terminology for a QGIS projection.
Each WMS layer can be presented in multiple CRSs, depending on the capability of the WMS server.
To choose a CRS, select Change… and a dialog similar to the one shown in Obr. 10.3 will appear. The main difference
with the WMS version of the dialog is that only those CRSs supported by the WMS server will be shown.
19.1.5 Sady dlaždic
When using WMTS (Cached WMS) services like
https://opencache.statkart.no/gatekeeper/gk/gk.open_wmts?\
service=WMTS&request=GetCapabilities
you are able to browse through the Tilesets tab given by the server. Additional information like tile size, formats and
supported CRS are listed in this table. In combination with this feature, you can use the tile scale slider by selecting
View ► Panels ( or Settings ► Panels), then choosing Tile Scale Panel. This gives you the available scales from
the tile server with a nice slider docked in.
19.1.6 Using the Identify Tool
Once you have added a WMS server, and if any layer from a WMS server is queryable, you can then use the
Identify
tool to select a pixel on the map canvas. A query is made to the WMS server for each selection made. The
results of the query are returned in plain text. The formatting of this text is dependent on the particular WMS server
used.
Format selection
If multiple output formats are supported by the server, a combo box with supported formats is automatically added
to the identify results dialog and the selected format may be stored in the project for the layer.
GML format support
The Identify
tool supports WMS server response (GetFeatureInfo) in GML format (it is called Feature in the QGIS
GUI in this context). If „Feature“ format is supported by the server and selected, results of the Identify tool are vector
features, as from a regular vector layer. When a single feature is selected in the tree, it is highlighted in the map and
it can be copied to the clipboard and pasted to another vector layer. See the example setup of the UMN Mapserver
below to support GetFeatureInfo in GML format.
# in layer METADATA add which fields should be included and define geometry␣
→(example):
"gml_include_items" "all"
"ows_geometries" "mygeom"
"ows_mygeom_type" "polygon"
# Then there are two possibilities/formats available, see a) and b):
# a) basic (output is generated by Mapserver and does not contain XSD)
# in WEB METADATA define formats (example):
"wms_getfeatureinfo_formatlist" "application/vnd.ogc.gml,text/html"
# b) using OGR (output is generated by OGR, it is send as multipart and contains␣
→XSD)
# in MAP define OUTPUTFORMAT (example):
OUTPUTFORMAT
NAME "OGRGML"
(continues on next page)
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(pokračujte na předchozí stránce)
MIMETYPE "ogr/gml"
DRIVER "OGR/GML"
FORMATOPTION "FORM=multipart"
END
# in WEB METADATA define formats (example):
"wms_getfeatureinfo_formatlist" "OGRGML,text/html"
Viewing Properties
Once you have added a WMS server, you can view its properties by right-clicking on it in the legend and selecting
Properties.
Metadata Tab
The tab Metadata displays a wealth of information about the WMS server, generally collected from the capabilities
statement returned from that server. Many definitions can be gleaned by reading the WMS standards (see OPEN-GEOSPATIAL-CONSORTIUM
in Literature and Web References), but here are a few handy definitions:
• Server Properties
– WMS Version — The WMS version supported by the server.
– Image Formats — The list of MIME-types the server can respond with when drawing the map. QGIS
supports whatever formats the underlying Qt libraries were built with, which is typically at least image/
png and image/jpeg.
– Identity Formats — The list of MIME-types the server can respond with when you use the Identify tool.
Currently, QGIS supports the text-plain type.
• Layer Properties
– Selected — Whether or not this layer was selected when its server was added to this project.
– Visible — Whether or not this layer is selected as visible in the legend (not yet used in this version of
QGIS).
– Can Identify — Whether or not this layer will return any results when the Identify tool is used on it.
– Can be Transparent — Whether or not this layer can be rendered with transparency. This version of
QGIS will always use transparency if this is Yes and the image encoding supports transparency.
– Can Zoom In — Whether or not this layer can be zoomed in by the server. This version of QGIS assumes
all WMS layers have this set to Yes. Deficient layers may be rendered strangely.
– Cascade Count — WMS servers can act as a proxy to other WMS servers to get the raster data for
a layer. This entry shows how many times the request for this layer is forwarded to peer WMS servers
for a result.
– Fixed Width, Fixed Height — Whether or not this layer has fixed source pixel dimensions. This version
of QGIS assumes all WMS layers have this set to nothing. Deficient layers may be rendered strangely.
– WGS 84 Bounding Box — The bounding box of the layer, in WGS 84 coordinates. Some WMS servers
do not set this correctly (e.g., UTM coordinates are used instead). If this is the case, then the initial view of
this layer may be rendered with a very ‚zoomed-out‘ appearance by QGIS. The WMS webmaster should
be informed of this error, which they may know as the WMS XML elements LatLonBoundingBox,
EX_GeographicBoundingBox or the CRS:84 BoundingBox.
– Available in CRS — The projections that this layer can be rendered in by the WMS server. These are
listed in the WMS-native format.
– Available in style — The image styles that this layer can be rendered in by the WMS server.
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19.1.7 Show WMS legend graphic in table of contents and layout
The QGIS WMS data provider is able to display a legend graphic in the table of contents‘ layer list and in the print
layout. The WMS legend will be shown only if the WMS server has GetLegendGraphic capability and the layer has
getCapability url specified, so you additionally have to select a styling for the layer.
If a legendGraphic is available, it is shown below the layer. It is little and you have to click on it to open it in real
dimension (due to QgsLegendInterface architectural limitation). Clicking on the layer’s legend will open a frame with
the legend at full resolution.
In the print layout, the legend will be integrated at it’s original (downloaded) dimension. Resolution of the legend
graphic can be set in the item properties under Legend ► WMS LegendGraphic to match your printing requirements.
The legend will display contextual information based on your current scale. The WMS legend will be shown only if
the WMS server has GetLegendGraphic capability and the layer has getCapability url specified, so you have to select
a styling.
19.1.8 WMS Client Limitations
Not all possible WMS client functionality had been included in this version of QGIS. Some of the more noteworthy
exceptions follow.
Editing WMS Layer Settings
Once you’ve completed the Add WMS layer
procedure, there is no way to change the settings. A work-around is to
delete the layer completely and start again.
WMS Servers Requiring Authentication
Currently, publicly accessible and secured WMS services are supported. The secured WMS servers can be accessed
by public authentication. You can add the (optional) credentials when you add a WMS server. See section Selecting
WMS/WMTS Servers for details.
Tip: Accessing secured OGC-layers
If you need to access secured layers with secured methods other than basic authentication, you can use InteProxy
as a transparent proxy, which does support several authentication methods. More information can be found in the
InteProxy manual at https://inteproxy.wald.intevation.org.
Tip: QGIS WMS Mapserver
Since Version 1.7.0, QGIS has its own implementation of a WMS 1.3.0 Mapserver. Read more about this in QGIS-
-Server-manual.
19.2 WCS Client
A Web Coverage Service (WCS) provides access to raster data in forms that are useful for client-side rendering,
as input into scientific models, and for other clients. The WCS may be compared to the WFS and the WMS. As WMS
and WFS service instances, a WCS allows clients to choose portions of a server’s information holdings based on spatial
constraints and other query criteria.
QGIS has a native WCS provider and supports both version 1.0 and 1.1 (which are significantly different), but
currently it prefers 1.0, because 1.1 has many issues (i.e., each server implements it in a different way with various
particularities).
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The native WCS provider handles all network requests and uses all standard QGIS network settings (especially proxy).
It is also possible to select cache mode (‚always cache‘, ‚prefer cache‘, ‚prefer network‘, ‚always network‘), and the
provider also supports selection of time position, if temporal domain is offered by the server.
Varování: Entering username and password in the Authentication tab will keep unprotected credentials in
the connection configuration. Those credentials will be visible if, for instance, you shared the project file with
someone. Therefore, it’s advisable to save your credentials in a Authentication configuration instead (configurations
tab). See Ověřovací systém for more details.
19.3 WFS and WFS-T Client
In QGIS, a WFS layer behaves pretty much like any other vector layer. You can identify and select features, and
view the attribute table. QGIS supports WFS 1.0.0, 1.1.0, 2.0 and WFS3 (OGC API - Features), including editing
(through WFS-T).
In general, adding a WFS layer is very similar to the procedure used with WMS. There are no default servers defined,
so you have to add your own. You can find WFS servers by using the MetaSearch plugin or your favourite web search
engine. There are a number of lists with public URLs, some of them maintained and some not.
Loading a WFS Layer
As an example, we use the Gateway Geomatics WFS server and display a layer. https://demo.gatewaygeomatics.com/
cgi-bin/wfs_gateway?REQUEST=GetCapabilities&VERSION=1.0.0&SERVICE=WFS
To be able to load a WFS Layer, first create a connection to the WFS server:
1. Open the Data Source Manager dialog by pressing the Open Data Source Manager
button
2. Enable the WFS/OGC API-Features tab
3. Click on New… to open the Create a New WFS Connection dialog
4. Enter Gateway Geomatics as name
5. Enter the URL (see above)
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Obr. 19.4: Creating a connection to a WFS server
Poznámka: In case of an OGC API - Features (WFS3), the URL to provide should be the landing page, ie
the main page from which it is possible to navigate to all the available service endpoints.
6. In the WFS settings dialog, you can:
• Indicate the WFS version of the server. If unknown, press the Detect button to automatically retrieve it.
• Define the maximum number of features retrieved in a single GetFetFeature request. If empty, no limit
is set.
• Invert axis orientation.
• And depending on the WFS version:
– Force to Ignore axis orientation (WFS 1.1/WFS 2.0)
– Enable feature paging and specify the maximum number of features to retrieve with Page size. If no
limit is defined, then the server default is applied.
Varování: Entering username and password in the Authentication tab will keep unprotected credentials
in the connection configuration. Those credentials will be visible if, for instance, you shared the project file
with someone. Therefore, it’s advisable to save your credentials in an Authentication configuration instead
(Configurations tab). See Ověřovací systém for more details.
7. Press OK to create the connection.
Note that any proxy settings you may have set in your preferences are also recognized.
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Now we are ready to load WFS layers from the above connection.
1. Choose ‚Gateway Geomatics‘ from the Server Connections drop-down list.
2. Click Connect
3. Select the Parks layer in the list
4. You can also choose whether to:
• Use title for layer name, showing the layer’s title as defined on the server in the Layers panel instead
of its Name
• Only request features overlapping the view extent
• Change the layer’s CRS
• or Build query to specify particular features to retrieve, by either using the corresponding button or double-clicking
the target layer.
5. Click Add to add the layer to the map.
Obr. 19.5: Adding a WFS layer
You’ll notice the download progress is visualized in the lower left of the QGIS main window. Once the layer is loaded,
you can identify and select a couple of features and view the attribute table.
Poznámka: QGIS supports different versions of the WFS protocol, with background download and progressive
rendering, on-disk caching of downloaded features and version autodetection.
662 Kapitola 19. Working with OGC / ISO protocols
KAPITOLA 20
Working with GPS Data
20.1 GPS Plugin
20.1.1 What is GPS?
GPS, the Global Positioning System, is a satellite-based system that allows anyone with a GPS receiver to find their
exact position anywhere in the world. GPS is used as an aid in navigation, for example in airplanes, in boats and
by hikers. The GPS receiver uses the signals from the satellites to calculate its latitude, longitude and (sometimes)
elevation. Most receivers also have the capability to store locations (known as waypoints), sequences of locations
that make up a planned route and a tracklog or track of the receiver’s movement over time. Waypoints, routes and
tracks are the three basic feature types in GPS data. QGIS displays waypoints in point layers, while routes and tracks
are displayed in linestring layers.
Poznámka: QGIS supports also GNSS receivers. But we keep using the term GPS in this documentation.
20.1.2 Loading GPS data from a file
There are dozens of different file formats for storing GPS data. The format that QGIS uses is called GPX (GPS
eXchange format), which is a standard interchange format that can contain any number of waypoints, routes and
tracks in the same file.
To load a GPX file, you first need to load the plugin. Plugins ► Plugin Manager… opens the Plugin Manager
Dialog. Activate the GPS Tools checkbox. When this plugin is loaded, a button with a small handheld GPS device
will show up in the toolbar and in Layer ► Create Layer ► :
• GPS Tools
• Create new GPX Layer
For working with GPS data, we provide an example GPX file available in the QGIS sample dataset:
qgis_sample_data/gps/national_monuments.gpx. See section Downloading sample data for more
information about the sample data.
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1. Select Vector ► GPS Tools or click the GPS Tools
icon in the toolbar and open the Load GPX file tab (see
Obr. 20.1).
2. Browse to the folder qgis_sample_data/gps/, select the GPX file national_monuments.gpx
and click Open.
Obr. 20.1: The GPS Tools dialog window
Use the Browse… button to select the GPX file, then use the checkboxes to select the feature types you want
to load from that GPX file. Each feature type will be loaded in a separate layer when you click OK. The file
national_monuments.gpx only includes waypoints.
Poznámka: GPS units allow you to store data in different coordinate systems. When downloading a GPX file (from
your GPS unit or a web site) and then loading it in QGIS, be sure that the data stored in the GPX file uses WGS
84 (latitude/longitude). QGIS expects this, and it is the official GPX specification. See https://www.topografix.com/
GPX/1/1/.
20.1.3 GPSBabel
Since QGIS uses GPX files, you need a way to convert other GPS file formats to GPX. This can be done for
many formats using the free program GPSBabel, which is available at https://www.gpsbabel.org. This program can
also transfer GPS data between your computer and a GPS device. QGIS uses GPSBabel to do these things, so it
is recommended that you install it. However, if you just want to load GPS data from GPX files you will not need it.
Version 1.2.3 of GPSBabel is known to work with QGIS, but you should be able to use later versions without any
problems.
20.1.4 Importing GPS data
To import GPS data from a file that is not a GPX file, you use the tool Import other file in the GPS Tools dialog. Here,
you select the file that you want to import (and the file type), which feature type you want to import from it, where
you want to store the converted GPX file and what the name of the new layer should be. Note that not all GPS data
formats will support all three feature types, so for many formats you will only be able to choose between one or two
types.
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20.1.5 Downloading GPS data from a device
QGIS can use GPSBabel to download data from a GPS device directly as new vector layers. For this we use the
Download from GPS tab of the GPS Tools dialog (see Obr. 20.2). Here, we select the type of GPS device, the port
that it is connected to (or USB if your GPS supports this), the feature type that you want to download, the GPX file
where the data should be stored, and the name of the new layer.
Obr. 20.2: The download tool
The device type you select in the GPS device menu determines how GPSBabel tries to communicate with your GPS
device. If none of the available types work with your GPS device, you can create a new type (see section Defining
new device types).
The port may be a file name or some other name that your operating system uses as a reference to the physical port
in your computer that the GPS device is connected to. It may also be simply USB, for USB-enabled GPS units.
• On Linux, this is something like /dev/ttyS0 or /dev/ttyS1.
• On Windows, it is COM1 or COM2.
When you click OK, the data will be downloaded from the device and appear as a layer in QGIS.
20.1.6 Uploading GPS data to a device
You can also upload data directly from a vector layer in QGIS to a GPS device using the Upload to GPS tab of the
GPS Tools dialog. To do this, you simply select the layer that you want to upload (which must be a GPX layer), your
GPS device type, and the port (or USB) that it is connected to. Just as with the download tool, you can specify new
device types if your device isn’t in the list.
This tool is very useful in combination with the vector-editing capabilities of QGIS. It allows you to load a map,
create waypoints and routes, and then upload them and use them on your GPS device.
20.1.7 Defining new device types
There are lots of different types of GPS devices. The QGIS developers can’t test all of them, so if you have one that
does not work with any of the device types listed in the Download from GPS and Upload to GPS tools, you can define
your own device type for it. You do this by using the GPS device editor, which you start by clicking the Edit Devices
button in the download or the upload tab.
To define a new device, you simply click the New Device button, enter a name, enter download and upload commands
for your device, and click the Update Device button. The name will be listed in the device menus in the upload and
download windows – it can be any string. The download command is the command that is used to download data
from the device to a GPX file. This will probably be a GPSBabel command, but you can use any other command
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line program that can create a GPX file. QGIS will replace the keywords %type, %in, and %out when it runs the
command.
%type will be replaced by -w if you are downloading waypoints, -r if you are downloading routes and -t if you
are downloading tracks. These are command-line options that tell GPSBabel which feature type to download.
%in will be replaced by the port name that you choose in the download window and %out will be replaced by the
name you choose for the GPX file that the downloaded data should be stored in. So, if you create a device type
with the download command gpsbabel %type -i garmin -o gpx %in %out (this is actually the
download command for the predefined device type ‚Garmin serial‘) and then use it to download waypoints from port
/dev/ttyS0 to the file output.gpx, QGIS will replace the keywords and run the command gpsbabel -w
-i garmin -o gpx /dev/ttyS0 output.gpx.
The upload command is the command that is used to upload data to the device. The same keywords are used, but
%in is now replaced by the name of the GPX file for the layer that is being uploaded, and %out is replaced by the
port name.
You can learn more about GPSBabel and its available command line options at https://www.gpsbabel.org.
Once you have created a new device type, it will appear in the device lists for the download and upload tools.
20.1.8 Download of points/tracks from GPS units
As described in previous sections QGIS uses GPSBabel to download points/tracks directly in the project. QGIS comes
out of the box with a pre-defined profile to download from Garmin devices. Unfortunately there is a bug #6318 that
does not allow create other profiles, so downloading directly in QGIS using the GPS Tools is at the moment limited
to Garmin USB units.
Garmin GPSMAP 60cs
MS Windows
Install the Garmin USB drivers from https://www8.garmin.com/support/download_details.jsp?id=591
Connect the unit. Open GPS Tools and use type=garmin serial and port=usb: Fill the fields Layer name
and Output file. Sometimes it seems to have problems saving in a certain folder, using something like c:\temp
usually works.
Ubuntu/Mint GNU/Linux
It is first needed an issue about the permissions of the device, as described at https://wiki.openstreetmap.org/
wiki/USB_Garmin_on_GNU/Linux. You can try to create a file /etc/udev/rules.d/51-garmin.rules
containing this rule
ATTRS{idVendor}=="091e", ATTRS{idProduct}=="0003", MODE="666"
After that is necessary to be sure that the garmin_gps kernel module is not loaded
rmmod garmin_gps
and then you can use the GPS Tools. Unfortunately there seems to be a bug #7182 and usually QGIS freezes several
times before the operation work fine.
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BTGP-38KM datalogger (only Bluetooth)
MS Windows
The already referred bug does not allow to download the data from within QGIS, so it is needed to use GPSBabel
from the command line or using its interface. The working command is
gpsbabel -t -i skytraq,baud=9600,initbaud=9600 -f COM9 -o gpx -F C:/GPX/aaa.gpx
Ubuntu/Mint GNU/Linux
Use same command (or settings if you use GPSBabel GUI) as in Windows. On Linux it maybe somehow common
to get a message like
skytraq: Too many read errors on serial port
it is just a matter to turn off and on the datalogger and try again.
BlueMax GPS-4044 datalogger (both BT and USB)
MS Windows
Poznámka: It needs to install its drivers before using it on Windows 7. See in the manufacturer site for the proper
download.
Downloading with GPSBabel, both with USB and BT returns always an error like
gpsbabel -t -i mtk -f COM12 -o gpx -F C:/temp/test.gpx
mtk_logger: Can't create temporary file data.bin
Error running gpsbabel: Process exited unsuccessfully with code 1
Ubuntu/Mint GNU/Linux
With USB
After having connected the cable use the dmesg command to understand what port is being used, for example
/dev/ttyACM3. Then as usual use GPSBabel from the CLI or GUI
gpsbabel -t -i mtk -f /dev/ttyACM3 -o gpx -F /home/user/bluemax.gpx
With Bluetooth
Use Blueman Device Manager to pair the device and make it available through a system port, then run GPSBabel
gpsbabel -t -i mtk -f /dev/rfcomm0 -o gpx -F /home/user/bluemax_bt.gpx
20.2 Live GPS tracking
To activate live GPS tracking in QGIS, you need to select View ► Panels GPS Information Panel or press Ctrl+0.
You will get a new docked window on the left side of the canvas.
There are four possible screens in this GPS tracking window:
• GPS position coordinates and an interface for manually entering vertices and features
• GPS signal strength of satellite connections
• GPS options screen (see Obr. 20.5)
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With a plugged-in GPS receiver (has to be supported by your operating system), a simple click on Connect connects
the GPS to QGIS. A second click (now on Disconnect) disconnects the GPS receiver from your computer. For
GNU/Linux, gpsd support is integrated to support connection to most GPS receivers. Therefore, you first have to
configure gpsd properly to connect QGIS to it.
Varování: If you want to record your position to the canvas, you have to create a new vector layer first and switch
it to editable status to be able to record your track.
20.2.1 Position and additional attributes
If the GPS is receiving signals from satellites, you will see your position in latitude, longitude and altitude together
with additional attributes.
Obr. 20.3: GPS tracking position and additional attributes
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20.2.2 GPS signal strength
Here, you can see the signal strength of the satellites you are receiving signals from.
Obr. 20.4: GPS tracking signal strength
20.2.3 GPS options
In case of connection problems, you can switch between:
• Autodetect
• Internal
• Serial device
• gpsd (selecting the Host, Port and Device your GPS is connected to)
A click on Connect again initiates the connection to the GPS receiver.
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Obr. 20.5: GPS tracking options window
You can activate Automatically save added features when you are in editing mode. Or you can activate
Automatically add points to the map canvas with a certain width and color.
Activating Cursor, you can use a slider to shrink and grow the position cursor on the canvas.
You can also set an Acquisition interval (seconds) and a Distance threshold (meters) parameters to keep the cursor still
active when the receiver is in static conditions.
Activating Map centering allows you to decide in which way the canvas will be updated. This includes ‚always‘,
‚when leaving‘, if your recorded coordinates start to move out of the canvas, or ‚never‘, to keep map extent.
Finally, you can activate Log file and define a path and a file where log messages about the GPS tracking are
logged.
If you want to set a feature manually, you have to go back to Position
and click on Add Point or Add Track Point.
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20.2.4 Connect to a Bluetooth GPS for live tracking
With QGIS you can connect a Bluetooth GPS for field data collection. To perform this task you need a GPS Bluetooth
device and a Bluetooth receiver on your computer.
At first you must let your GPS device be recognized and paired to the computer. Turn on the GPS, go to the Bluetooth
icon on your notification area and search for a New Device.
On the right side of the Device selection mask make sure that all devices are selected so your GPS unit will probably
appear among those available. In the next step a serial connection service should be available, select it and click on
Configure button.
Remember the number of the COM port assigned to the GPS connection as resulting by the Bluetooth properties.
After the GPS has been recognized, make the pairing for the connection. Usually the authorization code is 0000.
Now open GPS information panel and switch to GPS options screen. Select the COM port assigned to the GPS
connection and click the Connect. After a while a cursor indicating your position should appear.
If QGIS can’t receive GPS data, then you should restart your GPS device, wait 5-10 seconds then try to connect
again. Usually this solution work. If you receive again a connection error make sure you don’t have another Bluetooth
receiver near you, paired with the same GPS unit.
20.2.5 Using GPSMAP 60cs
MS Windows
Easiest way to make it work is to use a middleware (freeware, not open) called GPSGate.
Launch the program, make it scan for GPS devices (works for both USB and BT ones) and then in QGIS just click
Connect in the Live tracking panel using the Autodetect mode.
Ubuntu/Mint GNU/Linux
As for Windows the easiest way is to use a server in the middle, in this case GPSD, so
sudo apt install gpsd
Then load the garmin_gps kernel module
sudo modprobe garmin_gps
And then connect the unit. Then check with dmesg the actual device being used bu the unit, for example /dev/
ttyUSB0. Now you can launch gpsd
gpsd /dev/ttyUSB0
And finally connect with the QGIS live tracking tool.
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20.2.6 Using BTGP-38KM datalogger (only Bluetooth)
Using GPSD (under Linux) or GPSGate (under Windows) is effortless.
20.2.7 Using BlueMax GPS-4044 datalogger (both BT and USB)
MS Windows
The live tracking works for both USB and BT modes, by using GPSGate or even without it, just use the Autodetect
mode, or point the tool the right port.
Ubuntu/Mint GNU/Linux
For USB
The live tracking works both with GPSD
gpsd /dev/ttyACM3
or without it, by connecting the QGIS live tracking tool directly to the device (for example /dev/ttyACM3).
For Bluetooth
The live tracking works both with GPSD
gpsd /dev/rfcomm0
or without it, by connecting the QGIS live tracking tool directly to the device (for example /dev/rfcomm0).
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Ověřovací systém
21.1 Authentication System Overview
Obr. 21.1: Anatomy of authentication system
21.1.1 Authentication database
The new authentication system stores authentication configurations in an SQLite database file located, by default, at
<profile directory>/qgis-auth.db.
This authentication database can be moved between QGIS installations without affecting other current QGIS
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user preferences, as it is completely separate from normal QGIS settings. A configuration ID (a random 7-character
alphanumeric string) is generated when initially storing a configuration to the database. This represents
the configuration, thereby allowing the ID to be stored in plain text application components, (such as project, plugin,
or settings files) without disclosure of its associated credentials.
Poznámka: The parent directory of the qgis-auth.db can be set using the following environment variable,
QGIS_AUTH_DB_DIR_PATH, or set on the command line during launch with the --authdbdirectory option.
21.1.2 Master password
To store or access sensitive information within the database, a user must define a master password. A new master
password is requested and verified when initially storing any encrypted data to the database. When sensitive
information is accessed, the user is prompted for the master password. The password is then cached for the remainder
of the session (until application is quit), unless the user manually chooses an action to clear its cached value. Some
instances of using the authentication system do not require input of the master password, such as when selecting
an existing authentication configuration, or applying a configuration to a server configuration (such as when adding
a WMS layer).
You can choose to save the password in the Wallet/Keyring of your computer.
Obr. 21.2: Input new master password
Poznámka: A path to a file containing the master password can be set using the following environment variable,
QGIS_AUTH_PASSWORD_FILE.
Managing the master password
Once set, the master password can be reset; the current master password will be needed prior to resetting. During
this process, there is an option to generate a complete backup of the current database.
Obr. 21.3: Resetting master password
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If the user forgets the master password, there is no way to retrieve or override it. There is also no means of retrieving
encrypted information without knowing the master password.
If a user inputs their existing password incorrectly three times, the dialog will offer to erase the database.
Obr. 21.4: Password prompt after three invalid attempts
21.1.3 Authentication Configurations
You can manage authentication configurations from Configurations in the Authentication tab of the QGIS Options
dialog (Settings ► Options).
Obr. 21.5: Configurations editor
Use the button to add a new configuration, the button to remove configurations, and the button to modify
existing ones.
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Obr. 21.6: Adding config from within Configuration editor
The same type of operations for authentication configuration management (Add, Edit and Remove) can be done
when configuring a given service connection, such as configuring an OWS service connection. For that, there are
action buttons within the configuration selector for fully managing configurations found within the authentication
database. In this case, there is no need to go to the configurations in Authentication tab of QGIS options unless you
need to do more comprehensive configuration management.
Obr. 21.7: WMS connection dialog showing Add, Edit, and Remove authentication configuration buttons
When creating or editing an authentication configuration, the info required is a name, an authentication method
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and any other info that the authentication method requires (see more about the available authentication types in
Authentication Methods).
21.1.4 Authentication Methods
Available authentications are provided by C++ plugins much in the same way data provider plugins are supported by
QGIS. The method of authentication that can be selected is relative to the access needed for the resource/provider,
e.g. HTTP(S) or database, and whether there is support in both QGIS code and a plugin. As such, some authentication
method plugins may not be applicable everywhere an authentication configuration selector is shown. A list of available
authentication method plugins and their compatible resource/providers can be accessed going to Settings ► Options
and, in the Authentication tab, click the Installed Plugins button.
Obr. 21.8: Available method plugins list
Plugins can be created for new authentication methods that do not require QGIS to be recompiled. Since the support
for plugins is currently C++-only, QGIS will need to be restarted for the new dropped-in plugin to become available
to the user. Ensure your plugin is compiled against the same target version of QGIS if you intend to add it to an
existing target install.
Obr. 21.9: Basic HTTP authentication configs
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Obr. 21.10: ESRI Token authentication configs
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Obr. 21.11: OAuth2 authentication configs
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Obr. 21.12: PKI paths authentication configs
Obr. 21.13: PKI PKCS#12 file paths authentication configs
Obr. 21.14: Stored Identity authentication configs
Poznámka: The Resource URL is currently an unimplemented feature that will eventually allow a particular
configuration to be auto-chosen when connecting to resources at a given URL.
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21.1.5 Master Password and Auth Config Utilities
Under the Options menu (Settings ► Options) in the Authentication tab, there are several utility actions to manage the
authentication database and configurations:
Obr. 21.15: Utilities menu
• Input master password: opens the master password input dialog, independent of performing any
authentication database command
• Clear cached master password: unsets the master password if it has been set
• Reset master password: opens a dialog to change the master password (the current password must be known)
and optionally back up the current database
• Clear network authentication access cache: clears the authentication cache of all connections
• Automatically clear network authentication access cache on SSL errors: the connection cache stores all
authentication data for connections, also when the connection fails. If you change authentication configurations
or certification authorities, you should clear the authentication cache or restart QGIS. When this option
is checked, the authentication cache will be automatically cleared every time an SSL error occurs and you
choose to abort the connection
• Integrate master password with your Wallet/Keyring: adds the master password to your personal
Wallet/Keyring
• Store/update the master password in your Wallet/Keyring: updates the changed master password in your
Wallet/Keyring
• Clear the master password from your Wallet/Keyring: deletes the master password from your
Wallet/Keyring
• Enable password helper debug log: enables a debug tool that will contain all the log information of the
authentication methods
• Clear cached authentication configurations: clears the internal lookup cache for configurations, used to
speed up network connections. This does not clear QGIS’s core network access manager’s cache, which requires
a relaunch of QGIS.
• Remove all authentication configurations: clears the database of all configuration records, without removing
other stored records.
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• Erase authentication database: schedules a backup of the current database and complete rebuild of the
database table structure. The actions are scheduled for a later time, to ensure that other operations, like project
loading, do not interrupt the operation or cause errors due to a temporarily missing database.
Obr. 21.16: DB erase verification menu
21.1.6 Using authentication configurations
Typically, an authentication configuration is selected in a configuration dialog for a network services (such as WMS).
However, the selector widget can be embedded anywhere authentication is needed or in non-core functionality, like
in third-party PyQGIS or C++ plugins.
When using the selector, No authentication is displayed in the pop-up menu control when nothing is selected, when
there are no configurations to choose from, or when a previously assigned configuration can no longer be found in the
database. The Type and Id fields are read-only and provide a description of the authentication method and the config’s
ID respectively.
Obr. 21.17: Authentication configuration selector with no authentication
Obr. 21.18: Authentication configuration selector with selected config
21.1.7 Python bindings
All classes and public functions have sip bindings, except QgsAuthCrypto, since management of the master
password hashing and auth database encryption should be handled by the main app, and not via Python. See Security
Considerations concerning Python access.
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21.2 User Authentication Workflows
Obr. 21.19: Generic user workflow
21.2.1 HTTP(S) authentication
One of the most common resource connections is via HTTP(S), e.g. web mapping servers, and authentication method
plugins often work for these types of connections. Method plugins have access to the HTTP request object and can
manipulate both the request as well as its headers. This allows for many forms of internet-based authentication. When
connecting via HTTP(S) using the standard username/password authentication method will attempt HTTP BASIC
authentication upon connection.
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Obr. 21.20: Configuring a WMS connection for HTTP BASIC
21.2.2 Database authentication
Connections to database resources are generally stored as key=value pairs, which will expose usernames and
(optionally) passwords, if not using an authentication configuration. When configuring with the auth system, the
key=value will be an abstracted representation of the credentials, e.g. authfg=81t21b9.
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Obr. 21.21: Configuring a Postgres SSL-with-PKI connection
21.2.3 PKI authentication
When configuring PKI components within the authentication system, you have the option of importing components
into the database or referencing component files stored on your filesystem. The latter may be useful if such components
change frequently, or where the components will be replaced by a system administrator. In either instance you will
need to store any passphrase needed to access private keys within the database.
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Obr. 21.22: PKI configuration workflow
All PKI components can be managed in separate editors within the Certificate Manager, which can be accessed in
the Authentication tab in QGIS Options dialog (Settings ► Options) by clicking the Manage Certificates button.
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Obr. 21.23: Opening the Certificate Manager
In the Certificate Manager, there are editors for Identities, Servers and Authorities. Each of these are contained in
their own tabs, and are described below in the order they are encountered in the workflow chart above. The tab order
is relative to frequently accessed editors once you are accustomed to the workflow.
Poznámka: Because all authentication system edits write immediately to the authentication database, there is no
need to click the Options dialog OK button for any changes to be saved. This is unlike other settings in the Options
dialog.
Authorities
You can manage available Certificate Authorities (CAs) from the Authorities tab in the Certificate manager from
the Authentication tab of the QGIS Options dialog.
As referenced in the workflow chart above, the first step is to import or reference a file of CAs. This step is optional,
and may be unnecessary if your PKI trust chain originates from root CAs already installed in your operating system
(OS), such as a certificate from a commercial certificate vendor. If your authenticating root CA is not in the OS’s
trusted root CAs, it will need to be imported or have its file system path referenced. (Contact your system administrator
if unsure.)
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Obr. 21.24: Authorities editor
By default, the root CAs from your OS are available; however, their trust settings are not inherited. You should review
the certificate trust policy settings, especially if your OS root CAs have had their policies adjusted. Any certificate
that is expired will be set to untrusted and will not be used in secure server connections, unless you specifically
override its trust policy. To see the QGIS-discoverable trust chain for any certificate, select it and click the
Show information for certificate
.
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Obr. 21.25: Certificate info dialog
You can edit the Trust policy for any selected certificate within the chain. Any change in trust policy to a selected
certificate will not be saved to the database unless the Save certificate trust policy change to database
button is clicked per
selected certification. Closing the dialog will not apply the policy changes.
Obr. 21.26: Saving the trust policy changes
You can review the filtered CAs, both intermediate and root certificates, that will be trusted for secure connections
or change the default trust policy by clicking the Options button.
Varování: Changing the default trust policy may result in problems with secure connections.
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Obr. 21.27: Authorities options menu
You can import CAs or save a file system path from a file that contains multiple CAs, or import individual CAs. The
standard PEM format for files that contain multiple CA chain certifications has the root cert at the bottom of the file
and all subsequently signed child certificates above, towards the beginning of the file.
The CA certificate import dialog will find all CA certificates within the file, regardless of order, and also offers the
option to import certificates that are considered invalid (in case you want to override their trust policy). You can
override the trust policy upon import, or do so later within the Authorities editor.
Obr. 21.28: Import certificates dialog
Poznámka: If you are pasting certificate information into the PEM text field, note that encrypted certificates are not
supported.
Identities
You can manage available client identity bundles from the Identities tab in the Certificate manager from the
Authentication tab of the QGIS Options dialog. An identity is what authenticates you against a PKI-enabled service
and usually consists of a client certificate and private key, either as separate files or combined into a single „bundled“
file. The bundle or private key is often passphrase-protected.
Once you have any Certificate Authorities (CAs) imported you can optionally import any identity bundles into the
authentication database. If you do not wish to store the identities, you can reference their component file system paths
within an individual authentication configuration.
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Obr. 21.29: Identities editor
When importing an identity bundle, it can be passphrase-protected or unprotected, and can contain CA certificates
forming a trust chain. Trust chain certifications will not be imported here; they can be added separately under the
Authorities tab.
Upon import the bundle’s certificate and private key will be stored in the database, with the key’s storage encrypted
using the QGIS master password. Subsequent usage of the stored bundle from the database will only require input of
the master password.
Personal identity bundles consisting of PEM/DER (.pem/.der) and PKCS#12 (.p12/.pfx) components are supported.
If a key or bundle is passphrase-protected, the password will be required to validate the component prior to import.
Likewise, if the client certificate in the bundle is invalid (for example, its effective date has not yet started or has
elapsed) the bundle can not be imported.
Obr. 21.30: PEM/DER identity import
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Obr. 21.31: PKCS#12 identity import
21.2.4 Handling bad layers
Occasionally, the authentication configuration ID that is saved with a project file is no longer valid, possibly because
the current authentication database is different than when the project was last saved, or due to a credentials mismatch.
In such cases the Handle bad layers dialog will be presented upon QGIS launch.
Obr. 21.32: Handle bad layers with authentication
If a data source is found to have an authentication configuration ID associated with it, you will be able to edit it. Doing
so will automatically edit the data source string, much in the same way as opening the project file in a text editor and
editing the string.
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Obr. 21.33: Edit bad layer’s authentication config ID
21.2.5 Changing authentication config ID
Occasionally, you will need to change the authentication configuration ID that is associated with accessing a resource.
There are instances where this is useful:
• Resource auth config ID is no longer valid: This can occur when you have switched auth databases add need
to align a new configuration to the ID already associated with a resource.
• Shared project files: If you intended to share projects between users, e.g. via a shared file server, you can
predefine a 7-character (containing a-z and/or 0-9) that is associated with the resource. Then, individual users
change the ID of an authentication configuration that is specific to their credentials of the resource. When the
project is opened, the ID is found in the authentication database, but the credentials are different per user.
Obr. 21.34: Changing a layer’s authentication config ID (unlocked yellow text field)
Varování: Changing the auth config ID is considered an advanced operation and should only be done with full
knowledge as to why it is necessary. This is why there is a lock button that needs clicked, to unlock the ID’s text
field prior to editing the ID.
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21.2.6 QGIS Server support
When using a project file, with layers that have authentication configurations, as a basis for a map in QGIS Server,
there are a couple of additional setup steps necessary for QGIS to load the resources:
• Authentication database needs to be available
• Authentication database’s master password needs to be available
When instantiating the authentication system, Server will create or use qgis-auth.db file in the active user profile,
or the directory defined by the QGIS_AUTH_DB_DIR_PATH environment variable. It may be that the Server’s user
has no HOME directory, in which case, use the environment variable to define a directory that the Server’s user has
read/write permissions and is not located within the web-accessible directories.
To pass the master password to Server, write it to the first line of file at a path on the file system readable by the Server
processes user and defined using the QGIS_AUTH_PASSWORD_FILE environment variable. Ensure to limit the file
as only readable by the Server’s process user and to not store the file within web-accessible directories.
Poznámka: QGIS_AUTH_PASSWORD_FILE variable will be removed from the Server environment immediately
after accessing.
21.2.7 SSL server exceptions
Obr. 21.35: SSL server exception
You can manage SSL server configurations and exceptions from the Servers tab in the Authentication section of the
QGIS Options dialog.
Sometimes, when connecting to an SSL server, there are errors with the SSL „handshake“ or the server’s certificate.
You can ignore those errors or create an SSL server configuration as an exception. This is similar to how web browsers
allow you to override SSL errors, but with more granular control.
Varování: You should not create an SSL server configuration unless you have complete knowledge of the entire
SSL setup between the server and client. Instead, report the issue to the server administrator.
Poznámka: Some PKI setups use a completely different CA trust chain to validate client identities than the chain
used to validate the SSL server certificate. In such circumstances, any configuration created for the connecting server
will not necessarily fix an issue with the validation of your client identity, and only your client identity’s issuer or
server administrator can fix the issue.
You can pre-configure an SSL server configuration by clicking the button. Alternatively, you can add
a configuration when an SSL error occurs during a connection and you are presented with an SSL Error dialog
(where the error can be ignored temporarily or saved to the database and ignored):
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Obr. 21.36: Manually adding configuration
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Obr. 21.37: Adding configuration during SSL error
Once an SSL configuration is saved to the database, it can be edited or deleted.
Obr. 21.38: Existing SSL configuration
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Obr. 21.39: Editing an existing SSL configuration
If you want to pre-configure an SSL configuration and the import dialog is not working for your server’s connection,
you can manually trigger a connection via the Python Console by running the following code (replace https://
bugreports.qt-project.org with the URL of your server):
from qgis.PyQt.QtNetwork import QNetworkRequest
from qgis.PyQt.QtCore import QUrl
from qgis.core import QgsNetworkAccessManager
req = QNetworkRequest(QUrl('https://bugreports.qt-project.org'))
reply = QgsNetworkAccessManager.instance().get(req)
This will open an SSL error dialog if any errors occur, where you can choose to save the configuration to the database.
21.3 Security Considerations
Once the master password is entered, the API is open to access authentication configs in the authentication database,
similar to how Firefox works. However, in the initial implementation, no wall against PyQGIS access has been defined.
This may lead to issues where a user downloads/installs a malicious PyQGIS plugin or standalone app that gains access
to authentication credentials.
The quick solution for initial release of feature is to just not include most PyQGIS bindings for the authentication
system.
Another simple, though not robust, fix is to add a combobox in Settings ► Options ► Authentication (defaults to
„never“):
"Allow Python access to authentication system"
Choices: [ confirm once per session | always confirm | always allow | never]
Such an option’s setting would need to be saved in a location non-accessible to Python, e.g. the authentication database,
and encrypted with the master password.
• Another option may be to track which plugins the user has specifically
• allowed to access the authentication system, though it may be tricky to deduce which plugin is actually making
the call.
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• Sandboxing plugins, possibly in their own virtual environments, would reduce ‚cross-plugin‘ hacking of
authentication configs from another plugin that is authorized. This might mean limiting cross-plugin
communication as well, but maybe only between third-party plugins.
• Another good solution is to issue code-signing certificates to vetted plugin authors. Then validate the plugin’s
certificate upon loading. If need be the user can also directly set an untrusted policy for the certificate associated
with the plugin using existing certificate management dialogs.
• Alternatively, access to sensitive authentication system data from Python
• could never be allowed, and only the use of QGIS core widgets, or duplicating authentication system
integrations, would allow the plugin to work with resources that have an authentication configuration, while
keeping master password and authentication config loading in the realm of the main app.
The same security concerns apply to C++ plugins, though it will be harder to restrict access, since there is no function
binding to simply be removed as with Python.
21.3.1 Restrictions
The confusing licensing and exporting issues associated with OpenSSL apply. In order for Qt to work with SSL
certificates, it needs access to the OpenSSL libraries. Depending upon how Qt was compiled, the default is to
dynamically link to the OpenSSL libs at run-time (to avoid the export limitations).
QCA follows a similar tactic, whereby linking to QCA incurs no restrictions, because the qca-ossl (OpenSSL) plugin
is loaded at run-time. The qca-ossl plugin is directly linked to the OpenSSL libs. Packagers would be the ones needing
to ensure any OpenSSL-linking restrictions are met, if they ship the plugin. Maybe. I don’t really know. I’m not
a lawyer.
The authentication system safely disables itself when qca-ossl is not found at run-time.
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KAPITOLA 22
GRASS GIS Integration
GRASS integration provides access to GRASS GIS databases and functionalities (see GRASS-PROJECT in Literature
and Web References). The integration consists of two parts: provider and plugin. The provider allows to browse,
manage and visualize GRASS raster and vector layers. The plugin can be used to create new GRASS locations and
mapsets, change GRASS region, create and edit vector layers and analyze GRASS 2-D and 3-D data with more than
400 GRASS modules. In this section, we’ll introduce the provider and plugin functionalities and give some examples
of managing and working with GRASS data.
The provider supports GRASS version 6 and 7, the plugin supports GRASS 6 and 7 (starting from QGIS 2.12). QGIS
distribution may contain provider/plugin for either GRASS 6 or GRASS 7 or for both versions at the same time
(binaries have different file names). Only one version of the provider/plugin may be loaded on runtime however.
22.1 Demo dataset
As an example, we will use the QGIS Alaska dataset (see section Downloading sample data). It includes a small sample
GRASS LOCATION with three vector layers and one raster elevation map. Create a new folder called grassdata,
download the QGIS ‚Alaska‘ dataset qgis_sample_data.zip from https://qgis.org/downloads/data/ and unzip
the file into grassdata.
More sample GRASS LOCATIONs are available at the GRASS website at https://grass.osgeo.org/download/
sample-data/.
22.2 Loading GRASS raster and vector layers
If the provider is loaded in QGIS, the location item with GRASS icon is added in the browser tree under each
folder item which contains GRASS location. Go to the folder grassdata and expand location alaska and mapset
demo.
You can load GRASS raster and vector layers like any other layer from the browser either by double click on layer
item or by dragging and dropping to map canvas or legend.
Tip: GRASS Data Loading
If you don’t see GRASS location item, verify in Help ► About ► Providers if GRASS vector provider is loaded.
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22.3 Importing data into a GRASS LOCATION via drag and drop
This section gives an example of how to import raster and vector data into a GRASS mapset.
1. In QGIS browser navigate to the mapset you want to import data into.
2. In QGIS browser find a layer you want to import to GRASS, note that you can open another instance of the
browser (Browser Panel (2)) if source data are too far from the mapset in the tree.
3. Drag a layer and drop it on the target mapset. The import may take some time for larger layers, you will see
animated icon in front of new layer item until the import finishes.
When raster data are in different CRS, they can be reprojected using an Approximate (fast) or Exact (precise)
transformation. If a link to the source raster is created (using r.external), the source data are in the same CRS
and the format is known to GDAL, the source data CRS will be used. You can set these options in the Browser tab
in GRASS Options.
If a source raster has more bands, a new GRASS map is created for each layer with .<band number> suffix and
group of all maps with icon is created. External rasters have a different icon .
22.4 Managing GRASS data in QGIS Browser
• Copying maps: GRASS maps may be copied between mapsets within the same location using drag and drop.
• Deleting maps: Right click on a GRASS map and select Delete from context menu.
• Renaming maps: Right click on a GRASS map and select Rename from context menu.
22.5 GRASS Options
GRASS options may be set in GRASS Options dialog, which can be opened by right clicking on the location or mapset
item in the browser and then choosing GRASS Options.
22.6 Starting the GRASS plugin
To use GRASS functionalities in QGIS, you must select and load the GRASS plugin using the Plugin Manager. To
do this, go to the menu Plugins ► Manage and Install Plugins…, select GRASS and click OK.
The following main features are provided with the GRASS menu (Plugins ► GRASS) when you start the GRASS
plugin:
• Open Mapset
• New Mapset
• Close Mapset
• Open GRASS Tools
• Display Current GRASS Region
• GRASS Options
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22.7 Opening GRASS mapset
A GRASS mapset must be opened to get access to GRASS Tools in the plugin (the tools are disabled if no mapset
is open). You can open a mapset from the browser: right click on mapset item and then choose Open mapset from
context menu.
22.8 GRASS LOCATION and MAPSET
GRASS data are stored in a directory referred to as GISDBASE. This directory, often called grassdata, must
be created before you start working with the GRASS plugin in QGIS. Within this directory, the GRASS GIS data
are organized by projects stored in subdirectories called LOCATIONs. Each LOCATION is defined by its coordinate
system, map projection and geographical boundaries. Each LOCATION can have several MAPSETs (subdirectories
of the LOCATION) that are used to subdivide the project into different topics or subregions, or as workspaces for
individual team members (see Neteler & Mitasova 2008 in Literature and Web References). In order to analyse
vector and raster layers with GRASS modules, you generally have to import them into a GRASS LOCATION. (This
is not strictly true – with the GRASS modules r.external and v.external you can create read-only links to
external GDAL/OGR-supported datasets without importing them. This is not the usual way for beginners to work
with GRASS, therefore this functionality will not be described here.)
Obr. 22.1: GRASS data in the alaska LOCATION
22.9 Importing data into a GRASS LOCATION
See section Importing data into a GRASS LOCATION via drag and drop to find how data can be easily imported by
dragging and dropping in the browser.
This section gives an example of how to import raster and vector data into the ‚alaska‘ GRASS LOCATION provided by
the QGIS ‚Alaska‘ dataset in traditional way, using standard GRASS modules. Therefore, we use the landcover raster
map landcover.img and the vector GML file lakes.gml from the QGIS ‚Alaska‘ dataset (see Downloading
sample data).
1. Start QGIS and make sure the GRASS plugin is loaded.
2. In the GRASS toolbar, click the Open MAPSET
icon to bring up the MAPSET wizard.
3. Select as GRASS database the folder grassdata in the QGIS Alaska dataset, as LOCATION ‚alaska‘,
as MAPSET ‚demo‘ and click OK.
4. Now click the Open GRASS tools
icon. The GRASS Toolbox (see section The GRASS Toolbox) dialog appears.
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5. To import the raster map landcover.img, click the module r.in.gdal in the Modules Tree tab. This
GRASS module allows you to import GDAL-supported raster files into a GRASS LOCATION. The module
dialog for r.in.gdal appears.
6. Browse to the folder raster in the QGIS ‚Alaska‘ dataset and select the file landcover.img.
7. As raster output name, define landcover_grass and click Run. In the Output tab, you see
the currently running GRASS command r.in.gdal -o input=/path/to/landcover.img
output=landcover_grass.
8. When it says Successfully finished, click View Output. The landcover_grass raster layer is now imported
into GRASS and will be visualized in the QGIS canvas.
9. To import the vector GML file lakes.gml, click the module v.in.ogr in the Modules Tree tab. This
GRASS module allows you to import OGR-supported vector files into a GRASS LOCATION. The module
dialog for v.in.ogr appears.
10. Browse to the folder gml in the QGIS ‚Alaska‘ dataset and select the file lakes.gml as OGR file.
11. As vector output name, define lakes_grass and click Run. You don’t have to care about the other options
in this example. In the Output tab you see the currently running GRASS command v.in.ogr -o dsn=/
path/to/lakes.gml output=lakes\_grass.
12. When it says Succesfully finished, click View Output. The lakes_grass vector layer is now imported into
GRASS and will be visualized in the QGIS canvas.
22.9.1 Creating a new GRASS LOCATION
As an example, here is the sample GRASS LOCATION alaska, which is projected in the Albers Equal Area
projection using feet as units. This sample GRASS LOCATION alaska will be used for all examples and exercises
in the following GRASS-related sections. It is useful to download and install the dataset on your computer (see
Downloading sample data).
1. Start QGIS and make sure the GRASS plugin is loaded.
2. Visualize the alaska.shp shapefile (see section Loading a layer from a file) from the QGIS Alaska dataset
(see Downloading sample data).
3. In the GRASS toolbar, click on the New mapset
icon to bring up the MAPSET wizard.
4. Select an existing GRASS database (GISDBASE) folder grassdata, or create one for the new LOCATION
using a file manager on your computer. Then click Next.
5. We can use this wizard to create a new MAPSET within an existing LOCATION (see section Adding a new
MAPSET) or to create a new LOCATION altogether. Select Create new location (see Obr. 22.2).
6. Enter a name for the LOCATION – we used ‚alaska‘ – and click Next.
7. Define the projection by clicking on the radio button Projection to enable the projection list.
8. We are using Albers Equal Area Alaska (feet) projection. Since we happen to know that it is represented by the
EPSG ID 2964, we enter it in the search box. (Note: If you want to repeat this process for another LOCATION
and projection and haven’t memorized the EPSG ID, click on the CRS Status
icon in the lower right-hand
corner of the status bar (see section Práce s projekcemi)).
9. In Filter, insert 2964 to select the projection.
10. Click Next.
11. To define the default region, we have to enter the LOCATION bounds in the north, south, east, and west
directions. Here, we simply click on the button Set Current QGIS Extent, to apply the extent of the loaded layer
alaska.shp as the GRASS default region extent.
12. Click Next.
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13. We also need to define a MAPSET within our new LOCATION (this is necessary when creating a new
LOCATION). You can name it whatever you like - we used ‚demo‘. GRASS automatically creates a special
MAPSET called PERMANENT, designed to store the core data for the project, its default spatial extent and
coordinate system definitions (see Neteler & Mitasova 2008 in Literature and Web References).
14. Check out the summary to make sure it’s correct and click Finish.
15. The new LOCATION, ‚alaska‘, and two MAPSETs, ‚demo‘ and ‚PERMANENT‘, are created. The currently
opened working set is ‚demo‘, as you defined.
16. Notice that some of the tools in the GRASS toolbar that were disabled are now enabled.
Obr. 22.2: Creating a new GRASS LOCATION or a new MAPSET in QGIS
If that seemed like a lot of steps, it’s really not all that bad and a very quick way to create a LOCATION. The
LOCATION ‚alaska‘ is now ready for data import (see section Importing data into a GRASS LOCATION). You can
also use the already-existing vector and raster data in the sample GRASS LOCATION ‚alaska‘, included in the QGIS
‚Alaska‘ dataset Downloading sample data, and move on to section The GRASS vector data model.
22.9.2 Adding a new MAPSET
A user has write access only to a GRASS MAPSET which he or she created. This means that besides access to your
own MAPSET, you can read maps in other users‘ MAPSETs (and they can read yours), but you can modify or remove
only the maps in your own MAPSET.
All MAPSETs include a WIND file that stores the current boundary coordinate values and the currently selected raster
resolution (see Neteler & Mitasova 2008 in Literature and Web References, and section The GRASS region tool).
1. Start QGIS and make sure the GRASS plugin is loaded.
2. In the GRASS toolbar, click on the New mapset
icon to bring up the MAPSET wizard.
3. Select the GRASS database (GISDBASE) folder grassdata with the LOCATION ‚alaska‘, where we want
to add a further MAPSET called ‚test‘.
4. Click Next.
5. We can use this wizard to create a new MAPSET within an existing LOCATION or to create a new LOCATION
altogether. Click on the radio button Select location (see Obr. 22.2) and click Next.
6. Enter the name test for the new MAPSET. Below in the wizard, you see a list of existing MAPSETs and
corresponding owners.
7. Click Next, check out the summary to make sure it’s all correct and click Finish.
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22.10 The GRASS vector data model
It is important to understand the GRASS vector data model prior to digitizing. In general, GRASS uses a topological
vector model. This means that areas are not represented as closed polygons, but by one or more boundaries.
A boundary between two adjacent areas is digitized only once, and it is shared by both areas. Boundaries must be
connected and closed without gaps. An area is identified (and labelled) by the centroid of the area.
Besides boundaries and centroids, a vector map can also contain points and lines. All these geometry elements can
be mixed in one vector and will be represented in different so-called ‚layers‘ inside one GRASS vector map. So in
GRASS, a layer is not a vector or raster map but a level inside a vector layer. This is important to distinguish carefully.
(Although it is possible to mix geometry elements, it is unusual and, even in GRASS, only used in special cases such
as vector network analysis. Normally, you should prefer to store different geometry elements in different layers.)
It is possible to store several ‚layers‘ in one vector dataset. For example, fields, forests and lakes can be stored in one
vector. An adjacent forest and lake can share the same boundary, but they have separate attribute tables. It is also
possible to attach attributes to boundaries. An example might be the case where the boundary between a lake and
a forest is a road, so it can have a different attribute table.
The ‚layer‘ of the feature is defined by the ‚layer‘ inside GRASS. ‚Layer‘ is the number which defines if there is more
than one layer inside the dataset (e.g., if the geometry is forest or lake). For now, it can be only a number. In the
future, GRASS will also support names as fields in the user interface.
Attributes can be stored inside the GRASS LOCATION as dBase, SQLite3 or in external database tables, for example,
PostgreSQL, MySQL, Oracle, etc.
Attributes in database tables are linked to geometry elements using a ‚category‘ value.
‚Category‘ (key, ID) is an integer attached to geometry primitives, and it is used as the link to one key column in the
database table.
Tip: Learning the GRASS Vector Model
The best way to learn the GRASS vector model and its capabilities is to download one of the many GRASS tutorials
where the vector model is described more deeply. See https://grass.osgeo.org/documentation/manuals/ for more
information, books and tutorials in several languages.
22.11 Creating a new GRASS vector layer
To create a new GRASS vector layer, select one of following items from mapset context menu in the browser:
• New Point Layer
• New Line Layer
• New Polygon Layer
and enter a name in the dialog. A new vector map will be created and layer will be added to canvas and editing started.
Selecting type of the layer does not restrict geometry types which can be digitized in the vector map. In GRASS, it
is possible to organize all sorts of geometry types (point, line and polygon) in one vector map. The type is only used
to add the layer to the canvas, because QGIS requires a layer to have a specific type.
It is also possible to add layers to existing vector maps selecting one of the items described above from context menu
of existing vector map.
In GRASS, it is possible to organize all sorts of geometry types (point, line and area) in one layer, because GRASS
uses a topological vector model, so you don’t need to select the geometry type when creating a new GRASS vector.
This is different from shapefile creation with QGIS, because shapefiles use the Simple Feature vector model (see
section Creating new vector layers).
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22.12 Digitizing and editing a GRASS vector layer
GRASS vector layers can be digitized using the standard QGIS digitizing tools. There are however some
particularities, which you should know about, due to
• GRASS topological model versus QGIS simple feature
• complexity of GRASS model
– multiple layers in single maps
– multiple geometry types in single map
– geometry sharing by multiple features from multiple layers
The particularities are discussed in the following sections.
Save, discard changes, undo, redo
Varování: All the changes done during editing are immediately written to vector map and related attribute tables.
Changes are written after each operation, it is however, possible to do undo/redo or discard all changes when closing
editing. If undo or discard changes is used, original state is rewritten in vector map and attribute tables.
There are two main reasons for this behaviour:
• It is the nature of GRASS vectors coming from conviction that user wants to do what he is doing and it is better
to have data saved when the work is suddenly interrupted (for example, blackout)
• Necessity for effective editing of topological data is visualized information about topological correctness, such
information can only be acquired from GRASS vector map if changes are written to the map.
Toolbar
The ‚Digitizing Toolbar‘ has some specific tools when a GRASS layer is edited:
Ikona Tool Účel
New Point Digitize new point
New Line Digitize new line
New Boundary Digitize new boundary
New Centroid Digitize new centroid (label existing area)
New Closed Boundary Digitize new closed boundary
Table GRASS Digitizing: GRASS Digitizing Tools
Tip: Digitizing polygons in GRASS
If you want to create a polygon in GRASS, you first digitize the boundary of the polygon. Then you add a centroid (label
point) into the closed boundary. The reason for this is that a topological vector model links the attribute information
of a polygon always to the centroid and not to the boundary.
Category
Category, often called cat, is sort of ID. The name comes from times when GRASS vectors had only singly attribute
„category“. Category is used as a link between geometry and attributes. A single geometry may have multiple
categories and thus represent multiple features in different layers. Currently it is possible to assign only one category
per layer using QGIS editing tools. New features have automatically assigned new unique category, except boundaries.
Boundaries usually only form areas and do not represent linear features, it is however possible to define attributes for
a boundary later, for example in different layer.
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New categories are always created only in currently being edited layer.
It is not possible to assign more categories to geometry using QGIS editing, such data are properly represented
as multiple features, and individual features, even from different layers, may be deleted.
Attributes
Attributes of currently edited layer can only be modified. If the vector map contains more layers, features of other
layers will have all attributes set to ‚<not editable (layer #)>‘ to warn you that such attribute is not editable. The reason
is, that other layers may have and usually have different set of fields while QGIS only supports one fixed set of fields
per layer.
If a geometry primitive does not have a category assigned, a new unique category is automatically assigned and new
record in attribute table is created when an attribute of that geometry is changed.
Tip: If you want to do bulk update of attributes in table, for example using ‚Field Calculator‘ (Using the Field
Calculator), and there are features without category which you don’t want to update (typically boundaries), you can
filter them out by setting ‚Advanced Filter‘ to cat is not null.
Editing style
The topological symbology is essential for effective editing of topological data. When editing starts, a specialized
‚GRASS Edit‘ renderer is set on the layer automatically and original renderer is restored when editing is closed. The
style may be customized in layer properties ‚Style‘ tab. The style can also be stored in project file or in separate file
as any other style. If you customize the style, do not change its name, because it is used to reset the style when editing
is started again.
Tip: Do not save project file when the layer is edited, the layer would be stored with ‚Edit Style‘ which has no meaning
if layer is not edited.
The style is based on topological information which is temporarily added to attribute table as field ‚topo_symbol‘. The
field is automatically removed when editing is closed.
Tip: Do not remove ‚topo_symbol‘ field from attribute table, that would make features invisible because the renderer
is based on that column.
Uchycení
To form an area, vertices of connected boundaries must have exactly the same coordinates. This can be achieved using
snapping tool only if canvas and vector map have the same CRS. Otherwise, due conversion from map coordinates to
canvas and back, the coordinate may become slightly different due to representation error and CRS transformations.
Tip: Use layer’s CRS also for canvas when editing.
Limitations
Simultaneous editing of multiple layers within the same vector at the same time is not supported. This is mainly due
to the impossibility of handling multiple undo stacks for a single data source.
On Linux and macOS only one GRASS layer can be edited at time. This is due to a bug in GRASS which does
not allow to close database drivers in random order. This is being solved with GRASS developers.
Tip: GRASS Edit Permissions
You must be the owner of the GRASS MAPSET you want to edit. It is impossible to edit data layers in a MAPSET
that is not yours, even if you have write permission.
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22.13 The GRASS region tool
The region definition (setting a spatial working window) in GRASS is important for working with raster layers. Vector
analysis is by default not limited to any defined region definitions. But all newly created rasters will have the spatial
extension and resolution of the currently defined GRASS region, regardless of their original extension and resolution.
The current GRASS region is stored in the $LOCATION/$MAPSET/WIND file, and it defines north, south, east and
west bounds, number of columns and rows, horizontal and vertical spatial resolution.
It is possible to switch on and off the visualization of the GRASS region in the QGIS canvas using the
Display current GRASS region
button.
The region can be modified in ‚Region‘ tab in ‚GRASS Tolls‘ dock widget. Type in the new region bounds and
resolution, and click Apply. If you click on Select the extent by dragging on canvas you can select a new region
interactively with your mouse on the QGIS canvas dragging a rectangle.
The GRASS module g.region provides a lot more parameters to define an appropriate region extent and resolution
for your raster analysis. You can use these parameters with the GRASS Toolbox, described in section The GRASS
Toolbox.
22.14 The GRASS Toolbox
The Open GRASS Tools
box provides GRASS module functionalities to work with data inside a selected GRASS
LOCATION and MAPSET. To use the GRASS Toolbox you need to open a LOCATION and MAPSET that you have
write permission for (usually granted, if you created the MAPSET). This is necessary, because new raster or vector
layers created during analysis need to be written to the currently selected LOCATION and MAPSET.
Obr. 22.3: GRASS Toolbox and Module Tree
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22.14.1 Working with GRASS modules
The GRASS shell inside the GRASS Toolbox provides access to almost all (more than 300) GRASS modules in
a command line interface. To offer a more user-friendly working environment, about 200 of the available GRASS
modules and functionalities are also provided by graphical dialogs within the GRASS plugin Toolbox.
A complete list of GRASS modules available in the graphical Toolbox in QGIS version 3.16 is available in the GRASS
wiki at https://grasswiki.osgeo.org/wiki/GRASS-QGIS_relevant_module_list.
It is also possible to customize the GRASS Toolbox content. This procedure is described in section Customizing the
GRASS Toolbox.
As shown in Obr. 22.3, you can look for the appropriate GRASS module using the thematically grouped Modules
Tree or the searchable Modules List tab.
By clicking on a graphical module icon, a new tab will be added to the Toolbox dialog, providing three new sub-tabs:
Options, Output and Manual.
Options
The Options tab provides a simplified module dialog where you can usually select a raster or vector layer visualized
in the QGIS canvas and enter further module-specific parameters to run the module.
Obr. 22.4: GRASS Toolbox Module Options
The provided module parameters are often not complete to keep the dialog simple. If you want to use further module
parameters and flags, you need to start the GRASS shell and run the module in the command line.
A new feature since QGIS 1.8 is the support for a Show Advanced Options button below the simplified module dialog
in the Options tab. At the moment, it is only added to the module v.in.ascii as an example of use, but it will
probably be part of more or all modules in the GRASS Toolbox in future versions of QGIS. This allows you to use
the complete GRASS module options without the need to switch to the GRASS shell.
Output
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Obr. 22.5: GRASS Toolbox Module Output
The Output tab provides information about the output status of the module. When you click the Run button, the
module switches to the Output tab and you see information about the analysis process. If all works well, you will
finally see a Successfully finished message.
Manual
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Obr. 22.6: GRASS Toolbox Module Manual
The Manual tab shows the HTML help page of the GRASS module. You can use it to check further module parameters
and flags or to get a deeper knowledge about the purpose of the module. At the end of each module manual page,
you see further links to the Main Help index, the Thematic index and the Full index. These links
provide the same information as the module g.manual.
Tip: Display results immediately
If you want to display your calculation results immediately in your map canvas, you can use the ‚View Output‘ button
at the bottom of the module tab.
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22.14.2 GRASS module examples
The following examples will demonstrate the power of some of the GRASS modules.
Creating contour lines
The first example creates a vector contour map from an elevation raster (DEM). Here, it is assumed that you have the
Alaska LOCATION set up as explained in section Importing data into a GRASS LOCATION.
• First, open the location by clicking the Open mapset
button and choosing the Alaska location.
• Now open the Toolbox with the Open GRASS tools
button.
• In the list of tool categories, double-click Raster ► Surface Management ► Generate vector contour lines.
• Now a single click on the tool r.contour will open the tool dialog as explained above (see Working with GRASS
modules).
• In the Name of input raster map enter gtopo30.
• Type into the Increment between Contour levels the value 100. (This will create contour lines at intervals
of 100 meters.)
• Type into the Name for output vector map the name ctour_100.
• Click Run to start the process. Wait for several moments until the message Successfully finished
appears in the output window. Then click View Output and Close.
Since this is a large region, it will take a while to display. After it finishes rendering, you can open the layer properties
window to change the line color so that the contours appear clearly over the elevation raster, as in The Vector Properties
Dialog.
Next, zoom in to a small, mountainous area in the center of Alaska. Zooming in close, you will notice that the contours
have sharp corners. GRASS offers the v.generalize tool to slightly alter vector maps while keeping their overall shape.
The tool uses several different algorithms with different purposes. Some of the algorithms (i.e., Douglas Peuker and
Vertex Reduction) simplify the line by removing some of the vertices. The resulting vector will load faster. This
process is useful when you have a highly detailed vector, but you are creating a very small-scale map, so the detail
is unnecessary.
Tip: The simplify tool
Note that QGIS has a Vector ► Geometry Tools ► Simplify geometries tool that works just like the GRASS
v.generalize Douglas-Peuker algorithm.
However, the purpose of this example is different. The contour lines created by r.contour have sharp angles
that should be smoothed. Among the v.generalize algorithms, there is Chaiken’s, which does just that (also Hermite
splines). Be aware that these algorithms can add additional vertices to the vector, causing it to load even more slowly.
• Open the GRASS Toolbox and double-click the categories Vector ► Develop map ► Generalization, then click
on the v.generalize module to open its options window.
• Check that the ‚ctour_100‘ vector appears as the Name of input vector.
• From the list of algorithms, choose Chaiken’s. Leave all other options at their default, and scroll down to the
last row to enter in the field Name for output vector map ‚ctour_100_smooth‘, and click Run.
• The process takes several moments. Once Successfully finished appears in the output windows,
click View Output and then Close.
• You may change the color of the vector to display it clearly on the raster background and to contrast with the
original contour lines. You will notice that the new contour lines have smoother corners than the original while
staying faithful to the original overall shape.
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Obr. 22.7: GRASS module v.generalize to smooth a vector map
Tip: Other uses for r.contour
The procedure described above can be used in other equivalent situations. If you have a raster map of precipitation
data, for example, then the same method will be used to create a vector map of isohyetal (constant rainfall) lines.
Creating a Hillshade 3-D effect
Several methods are used to display elevation layers and give a 3-D effect to maps. The use of contour lines, as shown
above, is one popular method often chosen to produce topographic maps. Another way to display a 3-D effect is by
hillshading. The hillshade effect is created from a DEM (elevation) raster by first calculating the slope and aspect
of each cell, then simulating the sun’s position in the sky and giving a reflectance value to each cell. Thus, you get
sun-facing slopes lighted; the slopes facing away from the sun (in shadow) are darkened.
• Begin this example by loading the gtopo30 elevation raster. Start the GRASS Toolbox, and under the Raster
category, double-click to open Spatial analysis ► Terrain analysis.
• Then click r.shaded.relief to open the module.
• Change the azimuth angle 270 to 315.
• Enter gtopo30_shade for the new hillshade raster, and click Run.
• When the process completes, add the hillshade raster to the map. You should see it displayed in grayscale.
• To view both the hillshading and the colors of the gtopo30 together, move the hillshade map below
the gtopo30 map in the table of contents, then open the Properties window of gtopo30, switch to the
Transparency tab and set its transparency level to about 25%.
You should now have the gtopo30 elevation with its colormap and transparency setting displayed above the
grayscale hillshade map. In order to see the visual effects of the hillshading, turn off the gtopo30_shade map,
then turn it back on.
Using the GRASS shell
The GRASS plugin in QGIS is designed for users who are new to GRASS and not familiar with all the modules and
options. As such, some modules in the Toolbox do not show all the options available, and some modules do not appear
at all. The GRASS shell (or console) gives the user access to those additional GRASS modules that do not appear in
the Toolbox tree, and also to some additional options to the modules that are in the Toolbox with the simplest default
parameters. This example demonstrates the use of an additional option in the r.shaded.relief module that was shown
above.
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Obr. 22.8: The GRASS shell, r.shaded.relief module
The module r.shaded.relief can take a parameter zmult, which multiplies the elevation values relative to the X-Y
coordinate units so that the hillshade effect is even more pronounced.
• Load the gtopo30 elevation raster as above, then start the GRASS Toolbox and click on the GRASS shell. In
the shell window, type the command r.shaded.relief map=gtopo30 shade=gtopo30_shade2
azimuth=315 zmult=3 and press Enter.
• After the process finishes, shift to the Browse tab and double-click on the new gtopo30_shade2 raster to
display it in QGIS.
• As explained above, move the shaded relief raster below the gtopo30 raster in the table of contents, then
check the transparency of the colored gtopo30 layer. You should see that the 3-D effect stands out more
strongly compared with the first shaded relief map.
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Obr. 22.9: Displaying shaded relief created with the GRASS module r.shaded.relief
Raster statistics in a vector map
The next example shows how a GRASS module can aggregate raster data and add columns of statistics for each
polygon in a vector map.
• Again using the Alaska data, refer to Importing data into a GRASS LOCATION to import the shapefiles/
trees.shp file into GRASS.
• Now an intermediate step is required: centroids must be added to the imported trees map to make it a complete
GRASS area vector (including both boundaries and centroids).
• From the Toolbox, choose Vector ► Manage features, and open the module v.centroids.
• Enter as the output vector map ‚forest_areas‘ and run the module.
• Now load the forest_areas vector and display the types of forests - deciduous, evergreen, mixed - in
different colors: In the layer Properties window, Symbology tab, choose from Legend type ‚Unique value‘
and set the Classification field to ‚VEGDESC‘. (Refer to the explanation of the symbology tab in Symbology
Properties of the vector section.)
• Next, reopen the GRASS Toolbox and open Vector ► Vector update by other maps.
• Click on the v.rast.stats module. Enter gtopo30 and forest_areas.
• Only one additional parameter is needed: Enter column prefix elev, and click Run. This is a computationally
heavy operation, which will run for a long time (probably up to two hours).
• Finally, open the forest_areas attribute table, and verify that several new columns have been added,
including elev_min, elev_max, elev_mean, etc., for each forest polygon.
22.14.3 Customizing the GRASS Toolbox
Nearly all GRASS modules can be added to the GRASS Toolbox. An XML interface is provided to parse the pretty
simple XML files that configure the modules‘ appearance and parameters inside the Toolbox.
A sample XML file for generating the module v.buffer (v.buffer.qgm) looks like this:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE qgisgrassmodule SYSTEM "http://mrcc.com/qgisgrassmodule.dtd">
<qgisgrassmodule label="Vector buffer" module="v.buffer">
<option key="input" typeoption="type" layeroption="layer" />
(continues on next page)
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(pokračujte na předchozí stránce)
<option key="buffer"/>
<option key="output" />
</qgisgrassmodule>
The parser reads this definition and creates a new tab inside the Toolbox when you select the module. A more
detailed description for adding new modules, changing a module’s group, etc., can be found at https://qgis.org/en/
site/getinvolved/development/addinggrasstools.html.
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KAPITOLA 23
QGIS processing framework
23.1 Úvod
This chapter introduces the QGIS processing framework, a geoprocessing environment that can be used to call native
and third-party algorithms from QGIS, making your spatial analysis tasks more productive and easy to accomplish.
As a Core plugin, Processing is installed by default but you need to activate it:
1. Go to Plugins ► Manage and install plugins…
2. Click on the Installed tab at the left
3. Check the box next to the Processing entry
4. Close the dialog.
A Processing menu is now available in the top menu bar. From there you can reach the main components of
this framework.
In the following sections, we will review how to use the graphical elements of this framework and make the most out
of each one of them.
There are four basic elements in the framework GUI, which are used to run algorithms for different purposes.
Choosing one tool or another will depend on the kind of analysis that is to be performed and the particular
characteristics of each user and project. All of them (except for the batch processing interface, which is called from
the toolbox or the algorithm execution dialog, as we will see) can be accessed from the Processing menu item (you will
see more entries; the remaining ones are not used to execute algorithms and will be explained later in this chapter).
• The Toolbox: The main element of the GUI, it is used to execute a single algorithm or run a batch process
based on that algorithm.
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Obr. 23.1: Nástroje zpracování
• The Graphical Modeler: Several algorithms can be combined graphically using the modeler to define a workflow,
creating a single process that involves several subprocesses.
Obr. 23.2: Modelář zpracování
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• The History manager: All actions performed using any of the aforementioned elements are stored in a history
file and can be later easily reproduced using the history manager.
Obr. 23.3: Processing History
• The Batch Processing interface: This interface allows you to execute batch processes and automate the execution
of a single algorithm on multiple datasets.
Obr. 23.4: Batch Processing interface
In the following sections, we will review each one of these elements in detail.
23.2 Configuring the Processing Framework
The Processing Options menu (Settings► Options ► Processing tab) allows you to configure how algorithms work.
Configuration parameters are structured in separate blocks that you can select on the left-hand side of the dialog.
The General block contains a number of interesting parameters.
• Default output raster layer extension is by default tif
• Default output vector layer extension is by default gpkg
• Invalid features filtering
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• Keep dialog open after running algorithm. Once an algorithm has finished execution and its output layers are
loaded into the QGIS project, the algorithm dialog is closed. If you want to keep it open (to run the algorithm
again with different parameters, or to better check the output that is written to the log tab), check this option.
• Max Threads
• Output folder
• Pre-execution script and Post-execution script. These parameters point to files that contain scripts written using
the processing scripting functionality, explained in the section covering scripting and the console.
• Prefer output filename for layer names. The name of each resulting layer created by an algorithm is defined
by the algorithm itself. In some cases, a fixed name might be used, meaning that the same output name will
be used, no matter which input layer is used. In other cases, the name might depend on the name of the input
layer or some of the parameters used to run the algorithm. If this checkbox is checked, the name will be taken
from the output filename instead. Notice that, if the output is saved to a temporary file, the filename of this
temporary file is usually a long and meaningless one intended to avoid collision with other already existing
filenames.
• Results group name. If you want to obtain all processing result layers in a group in the Layers panel, set a group
name for this parameter. The group may exist already or not. QGIS will add all output layers to such a group. By
default, this parameter is empty, so all output layers are added to different places in the Layers panel, depending
on the item that is active when running an algorithm. Note that output layers will be loaded to the Layers panel
only if Open output file after running algorithm is checked in the algorithm dialog.
• Show algorithms with known issues
• Show layer CRS definition in selection boxes
• Show tooltip when there are disabled providers
• Style for line layers, Style for point layers, Style for polygons layers and Style for raster layers are used for setting
the default rendering style for output layers (that is, layers generated by processing algorithms). Just create the
style you want using QGIS, save it to a file, and then enter the path to that file in the settings so the algorithms
can use it. Whenever a layer is loaded by Processing and added to the QGIS canvas, it will be rendered with
that style.
Rendering styles can be configured individually for each algorithm and each one of its outputs. Just right-click
on the name of the algorithm in the toolbox and select Edit rendering styles for outputs. You will see a dialog
like the one shown next.
Obr. 23.5: Rendering Styles
Select the style file (.qml) that you want for each output and press OK.
• Temporary output folder path
• Warn before executing if parameter CRS’s do not match
You will also find a block for algorithm Providers. Each entry in this block contains an Activate item that you can use
to make algorithms appear or not in the toolbox. Some algorithm providers have their own configuration items, which
will be explained when covering particular algorithm providers.
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23.3 The Toolbox
The Processing Toolbox is the main element of the processing GUI, and the one that you are more likely to use in
your daily work. It shows the list of all available algorithms grouped in different blocks called Providers, and custom
models and scripts you can add to extend the set of tools. Hence the toolbox is the access point to run them, whether
as a single process or as a batch process involving several executions of the same algorithm on different sets of inputs.
Obr. 23.6: Nástroje zpracování
Providers can be (de)activated in the Processing settings dialog. By default, only providers that do not rely on third-party
applications (that is, those that only require QGIS elements to be run) are active. Algorithms requiring external
applications might need additional configuration. Configuring providers is explained in a later chapter in this manual.
In the upper part of the toolbox dialog, you will find a set of tools to:
• work with Models
: Create New Model…, Open Existing Model… and Add Model to Toolbox…;
• work with Scripts
: Create New Script…, Create New Script from Template…, Open Existing Script… and Add
Script to Toolbox…;
• open the History
panel;
• open the Results Viewer
panel;
• toggle the toolbox to the in-place modification mode using the Edit Features In-Place
button: only the algorithms
that are suitable to be executed on the active layer without outputting a new layer are displayed;
• open the Options
dialog.
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Below this toolbar is a Search… box to help you easily find the tools you need. You can enter any word or phrase
on the text box. Notice that, as you type, the number of algorithms, models or scripts in the toolbox is reduced to just
those that contain the text you have entered in their names or keywords.
Poznámka: At the top of the list of algorithms are displayed the most recent used tools; handy if you want to
reexecute any.
Obr. 23.7: Processing Toolbox showing search results
To execute a tool, just double-click on its name in the toolbox.
23.3.1 The algorithm dialog
Once you double-click on the name of the algorithm that you want to execute, a dialog similar to that in the Obr. 23.8
below is shown (in this case, the dialog corresponds to the Centroids algorithm).
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Obr. 23.8: Algorithm Dialog - Parameters
The dialog shows two tabs (Parameters and Log) on the left part, the algorithm description on the right, and a set of
buttons at the bottom.
The Parameters tab is used to set the input values that the algorithm needs to be executed. It shows a list of input
values and configuration parameters to be set. It of course has a different content, depending on the requirements of
the algorithm to be executed, and is created automatically based on those requirements.
Although the number and type of parameters depend on the characteristics of the algorithm, the structure is similar
for all of them. The parameters found in the table can be of one of the following types.
• A raster layer, to select from a list of all such layers available (currently opened) in QGIS. The selector contains
as well a button on its right-hand side, to let you select filenames that represent layers currently not loaded in
QGIS.
• A vector layer, to select from a list of all vector layers available in QGIS. Layers not loaded in QGIS can be
selected as well, as in the case of raster layers, but only if the algorithm does not require a table field selected
from the attributes table of the layer. In that case, only opened layers can be selected, since they need to be
open so as to retrieve the list of field names available.
You will see an iterator button by each vector layer selector, as shown in the figure below.
Obr. 23.9: Vector iterator button
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If the algorithm contains several of them, you will be able to toggle just one of them. If the button corresponding
to a vector input is toggled, the algorithm will be executed iteratively on each one of its features, instead of
just once for the whole layer, producing as many outputs as times the algorithm is executed. This allows for
automating the process when all features in a layer have to be processed separately.
Poznámka: By default, the parameters dialog will show a description of the CRS of each layer along with its name.
If you do not want to see this additional information, you can disable this functionality in the Processing Settings
dialog, unchecking the General ► Show layer CRS definition in selection boxes option.
• A table, to select from a list of all available in QGIS. Non-spatial tables are loaded into QGIS like vector layers,
and in fact they are treated as such by the program. Currently, the list of available tables that you will see when
executing an algorithm that needs one of them is restricted to tables coming from files in dBase (.dbf) or
Comma-Separated Values (.csv) formats.
• An option, to choose from a selection list of possible options.
• A numerical value, to be introduced in a spin box. In some contexts (when the parameter applies at the
feature level and not at the layer’s), you will find a Data-defined override
button by its side, allowing you to open
the expression builder and enter a mathematical expression to generate variable values for the parameter. Some
useful variables related to data loaded into QGIS can be added to your expression, so you can select a value
derived from any of these variables, such as the cell size of a layer or the northernmost coordinate of another
one.
Obr. 23.10: Vstup založený na výrazu
• A range, with min and max values to be introduced in two text boxes.
• A text string, to be introduced in a text box.
• A field, to choose from the attributes table of a vector layer or a single table selected in another parameter.
• A coordinate reference system. You can select it among the recently used ones from the drop-down list or
from the CRS selection dialog that appears when you click on the button on the right-hand side.
• An extent, a text box defining a rectangle through its corners coordinate in the format xmin, xmax, ymin,
ymax. Clicking on the button on the right-hand side of the value selector, a pop-up menu will appear, giving
you options to:
– Calculate from layer: fills the text box with the coordinates of the bounding box of a layer to select among
the loaded ones
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– Use map canvas extent
– Draw on canvas: the parameters window will hide itself, so you can click and drag onto the canvas. Once
you have defined the extent rectangle, the dialog will reappear, containing the values in the extent text
box.
Obr. 23.11: Extent selector
• A list of elements (whether raster or vector layers, tables, fields) to select from. Click on the … button at
the left of the option to see a dialog like the following one. Multiple selection is allowed and when the dialog
is closed, number of selected items is displayed in the parameter text box widget.
Obr. 23.12: Multiple Selection
• A small table to be edited by the user. These are used to define parameters like lookup tables or convolution
kernels, among others.
Click on the button on the right side to see the table and edit its values.
Obr. 23.13: Pevná tabulka
Depending on the algorithm, the number of rows can be modified or not by using the buttons on the right side
of the window.
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Poznámka: Some algorithms require many parameters to run, e.g. in the Raster calculator you have to specify
manually the cell size, the extent and the CRS. You can avoid to choose all the parameters manually when the
algorithm has the Reference layers parameter. With this parameter you can choose the reference layer and
all its properties (cell size, extent, CRS) will be used.
Along with the Parameters tab, there is another tab named Log (see Obr. 23.14 below). Information provided by the
algorithm during its execution is written in this tab, and allow you to track the execution and be aware and have more
details about the algorithm as it runs. Information on algorithm execution is also output in the View ► Panels ► Log
Messages Panel.
Notice that not all algorithms write information to the Log tab, and many of them might run silently without producing
any output other than the final files. Check the Log Messages Panel in that case.
Obr. 23.14: Algorithm Dialog - Log
At the bottom of the Log tab you will find buttons to Save Log to File, Copy Log to Clipboard and Clear
Log. These are particularly handy when you have checked the Keep dialog open after running algorithm in the General
part of the Processing options.
On the right hand side of the dialog you will find a short description of the algorithm, which will help you understand
its purpose and its basic ideas. If such a description is not available, the description panel will not be shown.
For a more detailed help file, which might include description of every parameter it uses, or examples, you will find
a Help button at the bottom of the dialog bringing you to the Processing algorithms documentation or to the provider
documentation (for some third-party providers).
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The Run as batch process button triggers the batch processing mode allowing to configure and run multiple instances
of the algorithm with a variety of parameters.
A note on projections
Processing algorithm execution are always performed in the input layer coordinate reference system (CRS). Due to
QGIS’s on-the-fly reprojecting capabilities, although two layers might seem to overlap and match, that might not be
true if their original coordinates are used without reprojecting them onto a common coordinate system. Whenever you
use more than one layer as input to a QGIS native algorithm, whether vector or raster, the layers will all be reprojected
to match the coordinate reference system of the first input layer.
This is however less true for most of the external applications whose algorithms are exposed through the processing
framework as they assume that all of the layers are already in a common coordinate system and ready to be analyzed.
By default, the parameters dialog will show a description of the CRS of each layer along with its name, making it
easy to select layers that share the same CRS to be used as input layers. If you do not want to see this additional
information, you can disable this functionality in the Processing settings dialog, unchecking the Show layer CRS
definition in selection boxes option.
If you try to execute an algorithm using as input two or more layers with unmatching CRSs, a warning dialog will be
shown. This occurs thanks to the Warn before executing if layer CRS’s do not match option.
You still can execute the algorithm, but be aware that in most cases that will produce wrong results, such as empty
layers due to input layers not overlapping.
Tip: Use Processing algorithms to do intermediate reprojection
When an algorithm can not successfully perform on multiple input layers due to unmatching CRSs, use QGIS internal
algorithm such as Reproject layer to perform layers‘ reprojection to the same CRS before executing the algorithm using
these outputs.
23.3.2 Data objects generated by algorithms
Data objects generated by an algorithm can be of any of the following types:
• A raster layer
• A vector layer
• A table
• An HTML file (used for text and graphical outputs)
These are all saved to disk, and the parameters table will contain a text box corresponding to each one of these outputs,
where you can type the output channel to use for saving it. An output channel contains the information needed to
save the resulting object somewhere. In the most usual case, you will save it to a file, but in the case of vector layers,
and when they are generated by native algorithms (algorithms not using external applications) you can also save to
a PostGIS, GeoPackage or SpatiaLite database, or a memory layer.
To select an output channel, just click on the button on the right side of the text box, and you will see a small context
menu with the available options.
In the most usual case, you will select saving to a file. If you select that option, you will be prompted with a save file
dialog, where you can select the desired file path. Supported file extensions are shown in the file format selector of
the dialog, depending on the kind of output and the algorithm.
The format of the output is defined by the filename extension. The supported formats depend on what is supported
by the algorithm itself. To select a format, just select the corresponding file extension (or add it, if you are directly
typing the file path instead). If the extension of the file path you entered does not match any of the supported formats,
a default extension will be appended to the file path, and the file format corresponding to that extension will be used
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to save the layer or table. Default extensions are .dbf for tables, .tif for raster layers and .gpkg for vector layers.
These can be modified in the setting dialog, selecting any other of the formats supported by QGIS.
If you do not enter any filename in the output text box (or select the corresponding option in the context menu), the
result will be saved as a temporary file in the corresponding default file format, and it will be deleted once you exit
QGIS (take care with that, in case you save your project and it contains temporary layers).
You can set a default folder for output data objects. Go to the settings dialog (you can open it from the Settings ►
Options ► Processing menu), and in the General group, you will find a parameter named Output folder. This output
folder is used as the default path in case you type just a filename with no path (i.e., myfile.shp) when executing
an algorithm.
When running an algorithm that uses a vector layer in iterative mode, the entered file path is used as the base path
for all generated files, which are named using the base name and appending a number representing the index of the
iteration. The file extension (and format) is used for all such generated files.
Apart from raster layers and tables, algorithms also generate graphics and text as HTML files. These results are shown
at the end of the algorithm execution in a new dialog. This dialog will keep the results produced by any algorithm
during the current session, and can be shown at any time by selecting Processing ► Results Viewer from the QGIS
main menu.
Some external applications might have files (with no particular extension restrictions) as output, but they do not belong
to any of the categories above. Those output files will not be processed by QGIS (opened or included into the current
QGIS project), since most of the time they correspond to file formats or elements not supported by QGIS. This is,
for instance, the case with LAS files used for LiDAR data. The files get created, but you won’t see anything new in
your QGIS working session.
For all the other types of output, you will find a checkbox that you can use to tell the algorithm whether to load the
file once it is generated by the algorithm or not. By default, all files are opened.
Optional outputs are not supported. That is, all outputs are created. However, you can uncheck the corresponding
checkbox if you are not interested in a given output, which essentially makes it behave like an optional output (in
other words, the layer is created anyway, but if you leave the text box empty, it will be saved to a temporary file and
deleted once you exit QGIS).
23.4 The history manager
23.4.1 The processing history
Every time you execute an algorithm, information about the process is stored in the history manager. The date and
time of the execution are saved, along with the parameters used, making it is easy to track and control all the work
that has been developed using the Processing framework, and to reproduce it.
Obr. 23.15: Historie
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Process information is kept as a command-line expression, even if the algorithm was launched from the toolbox. This
makes it useful for those learning how to use the command-line interface, since they can call an algorithm using the
toolbox and then check the history manager to see how it could be called from the command line.
Apart from browsing the entries in the registry, you can also re-execute processes by simply double-clicking on the
entry. The algorithm dialog then opens with parameters already set, and you can change any of them to fit your needs
and re-run the algorithm.
The History dialog also provides a convenient way to contribute to the consolidation of the testing infrastructure
of QGIS Processing algorithms and scripts. When you right-click on an entry, you can Create Test… using the
concerned algorithm and parameters, following instructions at https://github.com/qgis/QGIS/blob/release-3_16/
python/plugins/processing/tests/README.md.
23.4.2 The processing log
The history dialog only contains the execution calls, but not the information produced by the algorithm when executed.
That information is written to the QGIS log (View ► Panels ► Log Messages Panel).
Third-party algorithms are usually executed by using their command-line interfaces, which communicate with the
user via the console. Although that console is not shown, usually a full dump of it is written to the log each time you
run one of those algorithms. To avoid cluttering the log with that information, you can disable it for each provider in
the settings dialog.
Some algorithms, even if they can produce a result with the given input data, output comments or additional
information to log when they detect potential problems with the data, in order to warn you. Make sure you check
those messages in the log if you get unexpected results.
23.5 The graphical modeler
The graphical modeler allows you to create complex models using a simple and easy-to-use interface. When working
with a GIS, most analysis operations are not isolated, rather part of a chain of operations. Using the graphical modeler,
that chain of operations can be wrapped into a single process, making it convenient to execute later with a different set
of inputs. No matter how many steps and different algorithms it involves, a model is executed as a single algorithm,
saving time and effort.
The graphical modeler can be opened from the Processing menu (Processing ► Graphical Modeler).
The modeler has a working canvas where the structure of the model and the workflow it represents are shown. The
left part of the window is a section with five panels that can be used to add new elements to the model:
1. Model Properties: you can specify the name of the model and the group that will contain it
2. Inputs: all the inputs that will shape your model
3. Algorithms: the Processing algorithms available
4. Variables: you can also define variables that will only be available in the Processing Modeler
5. Undo History: this panel will register everything that happens in the modeler, making it easy to cancel
things you did wrong.
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Obr. 23.16: Modelář
Creating a model involves two basic steps:
1. Definition of necessary inputs. These inputs will be added to the parameters window, so the user can set their
values when executing the model. The model itself is an algorithm, so the parameters window is generated
automatically as for all algorithms available in the Processing framework.
2. Definition of the workflow. Using the input data of the model, the workflow is defined by adding algorithms
and selecting how they use the defined inputs or the outputs generated by other algorithms in the model.
23.5.1 Definition of inputs
The first step is to define the inputs for the model. The following elements are found in the Inputs panel on the left
side of the modeler window:
• Authentication Configuration
• Boolean
• Color
• Connection Name
• Coordinate Operation
• SRS
• Database Schema
• Database Table
• Datetime
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• Vzdálenost
• Enum
• Výraz
• Rozsah
• Field Aggregates
• Mapovač polí
• Soubor/Složka
• Geometry
• Mapová vrstva
• Map Theme
• Matice
• Mesh Layer
• Vícenásobný vstup
• Číslo
• Bod
• Print Layout
• Print Layout Item
• Rozsah
• Rastrové pásmo
• Rastrová vrstva
• Scale
• Řetězec
• TIN Creation Layers
• Vektorové prvky
• Vektorové pole
• Vektorová vrstva
• Vector Tile Writer Layers
Poznámka: Hovering with the mouse over the inputs will show a tooltip with additional information.
When double-clicking on an element, a dialog is shown that lets you define its characteristics. Depending on the
parameter, the dialog will contain at least one element (the description, which is what the user will see when executing
the model). For example, when adding a numerical value, as can be seen in the next figure, in addition to the description
of the parameter, you have to set a default value and the range of valid values.
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Obr. 23.17: Model Parameters Definition
You can define your input as mandatory for your model by checking the Mandatory option and by checking
the Advanced checkbox you can set the input to be within the Advanced section. This is particularly useful
when the model has many parameters and some of them are not trivial, but you still want to choose them.
The Comments tab allows you to tag the input with more information, to better describe the parameter. Comments
are visible only in the modeler canvas and not in the final algorithm dialog.
For each added input, a new element is added to the modeler canvas.
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Obr. 23.18: Model Parameters
You can also add inputs by dragging the input type from the list and dropping it at the position where you want it
in the modeler canvas. If you want to change a parameter of an existing input, just double click on it, and the same
dialog will pop up.
23.5.2 Definition of the workflow
In the following example we will add two inputs and two algorithms. The aim of the model is to copy the elevation
values from a DEM raster layer to a line layer using the Drape algorithm, and then calculate the total ascent of the
line layer using the Climb Along Line algorithm.
In the Inputs tab, choose the two inputs as Vector Layer for the line and Raster Layer for the DEM. We
are now ready to add the algorithms to the workflow.
Algorithms can be found in the Algorithms panel, grouped much in the same way as they are in the Processing toolbox.
Obr. 23.19: Model Inputs
To add an algorithm to a model, double-click on its name or drag and drop it, just like for inputs. As for the inputs
you can change the description of the algorithm and add a comment. When adding an algorithm, an execution dialog
will appear, with a content similar to the one found in the execution panel that is shown when executing the algorithm
from the toolbox. The following picture shows both the Drape (set Z value from raster) and the
Climb along line algorithm dialogs.
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Obr. 23.20: Model Algorithm parameters
As you can see there are some differences.
You have four choices to define the algorithm inputs:
• Value: allows you to set the parameter from a loaded layer in the QGIS project or to browse a layer from
a folder
• Pre-calculated Value: with this option you can open the Expression Builder and define your own
expression to fill the parameter. Model inputs together with some other layer statistics are available as variables
and are listed at the top of the Search dialog of the Expression Builder
• Model Input: choose this option if the parameter comes from an input of the model you have defined.
Once clicked, this option will list all the suitable inputs for the parameter
• Algorithm Output: is useful when the input parameter of an algorithm is an output of another
algorithm
Algorithm outputs have the addditional Model Output option that makes the output of the algorithm available
in the model.
If a layer generated by the algorithm is only to be used as input to another algorithm, don’t edit that text box.
In the following picture you can see the two input parameters defined as Model Input and the temporary output
layer:
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Obr. 23.21: Algorithm Input and Output parameters
In all cases, you will find an additional parameter named Dependencies that is not available when calling the algorithm
from the toolbox. This parameter allows you to define the order in which algorithms are executed, by explicitly defining
one algorithm as a parent of the current one. This will force the parent algorithm to be executed before the current
one.
When you use the output of a previous algorithm as the input of your algorithm, that implicitly sets the previous
algorithm as parent of the current one (and places the corresponding arrow in the modeler canvas). However, in some
cases an algorithm might depend on another one even if it does not use any output object from it (for instance, an
algorithm that executes a SQL sentence on a PostGIS database and another one that imports a layer into that same
database). In that case, just select the previous algorithm in the Dependencies parameter and they will be executed in
the correct order.
Once all the parameters have been assigned valid values, click on OK and the algorithm will be added to the canvas.
It will be linked to the elements in the canvas (algorithms or inputs) that provide objects that are used as inputs for
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the algorithm.
Elements can be dragged to a different position on the canvas. This is useful to make the structure of the model more
clear and intuitive. You can also resize elements. This is particularly useful if the description of the input or algorithm
is long.
Links between elements are updated automatically and you can see a plus button at the top and at the bottom of each
algorithm. Clicking the button will list all the inputs and outputs of the algorithm so you can have a quick overview.
You can zoom in and out by using the mouse wheel.
Obr. 23.22: A complete model
You can run your algorithm any time by clicking on the button. In order to use the algorithm from the toolbox,
it has to be saved and the modeler dialog closed, to allow the toolbox to refresh its contents.
23.5.3 Interacting with the canvas and elements
You can use the , , and buttons to zoom the modeler canvas. The behavior of the buttons is basically
the same of the main QGIS toolbar.
The Undo History panel together with the and buttons are extremely useful to quickly rollback to
a previous situation. The Undo History panel lists everything you have done when creating the workflow.
You can move or resize many elements at the same time by first selecting them, dragging the mouse.
If you want to snap the elements while moving them in the canvas you can choose View ► Enable Snapping.
The Edit menu contains some very useful options to interact with your model elements:
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• Select All
: select all elements of the model
• Snap Selected Components to Grid: snap and align the elements into a grid
• Undo
: undo the last action
• Redo
: redo the last action
• Cut
: cut the selected elements
• Copy
: copy the selected elements
• Paste
: paste the elements
• Delete Selected Components
: delete all the selected elements from the model
• Add Group Box: add a draggable box to the canvas. This feature is very useful in big models to group
elements in the modeler canvas and to keep the workflow clean. For example we might group together all the
inputs of the example:
Obr. 23.23: Model Group Box
You can change the name and the color of the boxes. Group boxes are very useful when used together with View ►
Zoom To. This allows you to zoom to a specific part of the model.
You might want to change the order of the inputs and how they are listed in the main model dialog. At the bottom of
the Input panel you will find the Reorder Model Inputs... button and by clicking on it a new dialog pops
up allowing you to change the order of the inputs:
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Obr. 23.24: Reorder Model Inputs
23.5.4 Saving and loading models
Use the Save model
button to save the current model and the Open Model
button to open a previously saved model.
Models are saved with the .model3 extension. If the model has already been saved from the modeler window, you
will not be prompted for a filename. Since there is already a file associated with the model, that file will be used for
subsequent saves.
Before saving a model, you have to enter a name and a group for it in the text boxes in the upper part of the window.
Models saved in the models folder (the default folder when you are prompted for a filename to save the model) will
appear in the toolbox in the corresponding branch. When the toolbox is invoked, it searches the models folder for
files with the .model3 extension and loads the models they contain. Since a model is itself an algorithm, it can be
added to the toolbox just like any other algorithm.
Models can also be saved within the project file using the Save model in project
button. Models saved using this method
won’t be written as .model3 files on the disk but will be embedded in the project file.
Project models are available in the Project models menu of the toolbox.
The models folder can be set from the Processing configuration dialog, under the Modeler group.
Models loaded from the models folder appear not only in the toolbox, but also in the algorithms tree in the Algorithms
tab of the modeler window. That means that you can incorporate a model as a part of a bigger model, just like other
algorithms.
Models will show up in the Browser panel and can be run from there.
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Exporting a model as an image, PDF or SVG
A model can also be exported as an image, SVG or PDF (for illustration purposes) by clicking Export as image
,
Export as PDF
or Export as SVG
.
23.5.5 Editing a model
You can edit the model you are currently creating, redefining the workflow and the relationships between the
algorithms and inputs that define the model.
If you right-click on an algorithm in the canvas, you will see a context menu like the one shown next:
Obr. 23.25: Modeler Right Click
Selecting the Remove option will cause the selected algorithm to be removed. An algorithm can be removed only
if there are no other algorithms depending on it. That is, if no output from the algorithm is used in a different one
as input. If you try to remove an algorithm that has others depending on it, a warning message like the one you can
see below will be shown:
Obr. 23.26: Cannot Delete Algorithm
Selecting the Edit… option will show the parameter dialog of the algorithm, so you can change the inputs and
parameter values. Not all input elements available in the model will appear as available inputs. Layers or values
generated at a more advanced step in the workflow defined by the model will not be available if they cause circular
dependencies.
Select the new values and click on the OK button as usual. The connections between the model elements will change
in the modeler canvas accordingly.
The Add comment… allows you to add a comment to the algorithm to better describe the behavior.
A model can be run partially by deactivating some of its algorithms. To do it, select the Deactivate option in the
context menu that appears when right-clicking on an algorithm element. The selected algorithm, and all the ones in
the model that depend on it will be displayed in grey and will not be executed as part of the model.
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Obr. 23.27: Model With Deactivated Algorithms
When right-clicking on an algorithm that is not active, you will see a Activate menu option that you can use to reactivate
it.
23.5.6 Editing model help files and meta-information
You can document your models from the modeler itself. Click on the Edit model help
button, and a dialog like the one
shown next will appear.
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Obr. 23.28: Editing Help
On the right-hand side, you will see a simple HTML page, created using the description of the input parameters and
outputs of the algorithm, along with some additional items like a general description of the model or its author. The
first time you open the help editor, all these descriptions are empty, but you can edit them using the elements on the
left-hand side of the dialog. Select an element on the upper part and then write its description in the text box below.
Model help is saved as part of the model itself.
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23.5.7 Exporting a model as a Python script
As we will see in a later chapter, Processing algorithms can be called from the QGIS Python console, and new
Processing algorithms can be created using Python. A quick way to create such a Python script is to create a model
and then export it as a Python file.
To do so, click on the Export as Script Algorithm…
in the modeler canvas or right click on the name of the model in the
Processing Toolbox and choose Export Model as Python Algorithm…
.
23.5.8 About available algorithms
You might notice that some algorithms that can be executed from the toolbox do not appear in the list of available
algorithms when you are designing a model. To be included in a model, an algorithm must have the correct semantic.
If an algorithm does not have such a well-defined semantic (for instance, if the number of output layers cannot be
known in advance), then it is not possible to use it within a model, and it will not appear in the list of algorithms that
you can find in the modeler dialog.
23.6 The batch processing interface
23.6.1 Úvod
All algorithms (including models) can be executed as a batch process. That is, they can be executed using not just
a single set of inputs, but several of them, executing the algorithm as many times as needed. This is useful when
processing large amounts of data, since it is not necessary to launch the algorithm many times from the toolbox.
To execute an algorithm as a batch process, right-click on its name in the toolbox and select the Execute as batch
process option in the pop-up menu that will appear.
Obr. 23.29: Batch Processing from right-click
If you have the execution dialog of the algorithm open, you can also start the batch processing interface from there,
clicking on the Run as batch process… button.
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Obr. 23.30: Batch Processing From Algorithm Dialog
23.6.2 The parameters table
Executing a batch process is similar to performing a single execution of an algorithm. Parameter values have to be
defined, but in this case we need not just a single value for each parameter, but a set of them instead, one for each
time the algorithm has to be executed. Values are introduced using a table like the one shown next.
Obr. 23.31: Batch Processing
Each line of this table represents a single execution of the algorithm, and each cell contains the value of one of the
parameters. It is similar to the parameters dialog that you see when executing an algorithm from the toolbox, but with
a different arrangement.
By default, the table contains just two rows. You can add or remove rows using the buttons on the lower part of the
window.
Once the size of the table has been set, it has to be filled with the desired values.
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23.6.3 Filling the parameters table
For most parameters, setting the value is trivial. Just type the value or select it from the list of available options,
depending on the parameter type.
Filenames for input data objects are introduced directly typing or, more conveniently, clicking on the … button on
the right hand of the cell, which will show a context menu with two option: one for selecting from the layers currently
opened and another to select from the filesystem. This second option, when selected, shows a typical file chooser
dialog. Multiple files can be selected at once. If the input parameter represents a single data object and several files
are selected, each one of them will be put in a separate row, adding new ones if needed. If the parameter represents
a multiple input, all the selected files will be added to a single cell, separated by semicolons (;).
Layer identifiers can be directly typed in the parameter text box. You can enter the full path to a file or the name of
a layer that is currently loaded in the current QGIS project. The name of the layer will be automatically resolved to its
source path. Notice that, if several layers have the same name, this might cause unexpected results due to ambiguity.
Output data objects are always saved to a file and, unlike when executing an algorithm from the toolbox, saving to
a temporary file or database is not permitted. You can type the name directly or use the file chooser dialog that appears
when clicking on the accompanying button.
Once you select the file, a new dialog is shown to allow for autocompletion of other cells in the same column (same
parameter).
Obr. 23.32: Batch Processing Save
If the default value (‚Do not autocomplete‘) is selected, it will just put the selected filename in the selected cell from
the parameters table. If any of the other options is selected, all the cells below the selected one will be automatically
filled based on a defined criteria. This way, it is much easier to fill the table, and the batch process can be defined
with less effort.
Automatic filling can be done by simply adding correlative numbers to the selected file path, or by appending the
value of another field at the same row. This is particularly useful for naming output data objects according to input
ones.
Obr. 23.33: Batch Processing File Path
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23.6.4 Executing the batch process
To execute the batch process once you have introduced all the necessary values, just click on OK. Progress of the
global batch task will be shown in the progress bar in the lower part of the dialog.
23.7 Using processing algorithms from the console
The console allows advanced users to increase their productivity and perform complex operations that cannot be
performed using any of the other GUI elements of the processing framework. Models involving several algorithms
can be defined using the command-line interface, and additional operations such as loops and conditional sentences
can be added to create more flexible and powerful workflows.
There is not a processing console in QGIS, but all processing commands are available instead from the QGIS built-in
Python console. That means that you can incorporate those commands into your console work and connect processing
algorithms to all the other features (including methods from the QGIS API) available from there.
The code that you can execute from the Python console, even if it does not call any specific processing method,
can be converted into a new algorithm that you can later call from the toolbox, the graphical modeler or any other
component, just like you do with any other algorithm. In fact, some algorithms that you can find in the toolbox are
simple scripts.
In this section, we will see how to use processing algorithms from the QGIS Python console, and also how to write
algorithms using Python.
23.7.1 Calling algorithms from the Python console
The first thing you have to do is to import the processing functions with the following line:
>>> from qgis import processing
Now, there is basically just one (interesting) thing you can do with that from the console: execute an algorithm. That
is done using the run() method, which takes the name of the algorithm to execute as its first parameter, and then
a variable number of additional parameters depending on the requirements of the algorithm. So the first thing you
need to know is the name of the algorithm to execute. That is not the name you see in the toolbox, but rather a unique
command–line name. To find the right name for your algorithm, you can use the processingRegistry. Type
the following line in your console:
>>> for alg in QgsApplication.processingRegistry().algorithms():
print(alg.id(), "->", alg.displayName())
You will see something like this (with some extra dashes added to improve readability).
3d:tessellate --------------> Tessellate
gdal:aspect ----------------> Aspect
gdal:assignprojection ------> Assign projection
gdal:buffervectors ---------> Buffer vectors
gdal:buildvirtualraster ----> Build Virtual Raster
gdal:cliprasterbyextent ----> Clip raster by extent
gdal:cliprasterbymasklayer -> Clip raster by mask layer
gdal:clipvectorbyextent ----> Clip vector by extent
gdal:clipvectorbypolygon ---> Clip vector by mask layer
gdal:colorrelief -----------> Color relief
gdal:contour ---------------> Contour
gdal:convertformat ---------> Convert format
gdal:dissolve --------------> Dissolve
...
That’s a list of all the available algorithm IDs, sorted by provider name and algorithm name, along with their
corresponding names.
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Once you know the command-line name of the algorithm, the next thing to do is to determine the right syntax to
execute it. That means knowing which parameters are needed when calling the run() method.
There is a method to describe an algorithm in detail, which can be used to get a list of the parameters
that an algorithm requires and the outputs that it will generate. To get this information, you can use the
algorithmHelp(id_of_the_algorithm) method. Use the ID of the algorithm, not the full descriptive
name.
Calling the method with native:buffer as parameter (qgis:buffer is an alias for native:buffer and
will also work), you get the following description:
>>> processing.algorithmHelp("native:buffer")
Buffer (native:buffer)
This algorithm computes a buffer area for all the features in an
input layer, using a fixed or dynamic distance.
The segments parameter controls the number of line segments to
use to approximate a quarter circle when creating rounded
offsets.
The end cap style parameter controls how line endings are handled
in the buffer.
The join style parameter specifies whether round, miter or
beveled joins should be used when offsetting corners in a line.
The miter limit parameter is only applicable for miter join
styles, and controls the maximum distance from the offset curve
to use when creating a mitered join.
----------------
Input parameters
----------------
INPUT: Input layer
Parameter type: QgsProcessingParameterFeatureSource
Accepted data types:
- str: layer ID
- str: layer name
- str: layer source
- QgsProcessingFeatureSourceDefinition
- QgsProperty
- QgsVectorLayer
DISTANCE: Distance
Parameter type: QgsProcessingParameterDistance
Accepted data types:
- int
- float
- QgsProperty
SEGMENTS: Segments
Parameter type: QgsProcessingParameterNumber
Accepted data types:
- int
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- float
- QgsProperty
END_CAP_STYLE: End cap style
Parameter type: QgsProcessingParameterEnum
Available values:
- 0: Round
- 1: Flat
- 2: Square
Accepted data types:
- int
- str: as string representation of int, e.g. '1'
- QgsProperty
JOIN_STYLE: Join style
Parameter type: QgsProcessingParameterEnum
Available values:
- 0: Round
- 1: Miter
- 2: Bevel
Accepted data types:
- int
- str: as string representation of int, e.g. '1'
- QgsProperty
MITER_LIMIT: Miter limit
Parameter type: QgsProcessingParameterNumber
Accepted data types:
- int
- float
- QgsProperty
DISSOLVE: Dissolve result
Parameter type: QgsProcessingParameterBoolean
Accepted data types:
- bool
- int
- str
- QgsProperty
OUTPUT: Buffered
Parameter type: QgsProcessingParameterFeatureSink
Accepted data types:
- str: destination vector file, e.g. 'd:/test.shp'
- str: 'memory:' to store result in temporary memory layer
- str: using vector provider ID prefix and destination URI,
e.g. 'postgres:...' to store result in PostGIS table
- QgsProcessingOutputLayerDefinition
- QgsProperty
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----------------
Outputs
----------------
OUTPUT: <QgsProcessingOutputVectorLayer>
Buffered
Now you have everything you need to run any algorithm. As we have already mentioned, algorithms can be run using:
run(). Its syntax is as follows:
>>> processing.run(name_of_the_algorithm, parameters)
Where parameters is a dictionary of parameters that depend on the algorithm you want to run, and is exactly the list
that the algorithmHelp() method gives you.
1 >>> processing.run("native:buffer", {'INPUT': '/data/lines.shp',
2 'DISTANCE': 100.0,
3 'SEGMENTS': 10,
4 'DISSOLVE': True,
5 'END_CAP_STYLE': 0,
6 'JOIN_STYLE': 0,
7 'MITER_LIMIT': 10,
8 'OUTPUT': '/data/buffers.shp'})
If a parameter is optional and you do not want to use it, then don’t include it in the dictionary.
If a parameter is not specified, the default value will be used.
Depending on the type of parameter, values are introduced differently. The next list gives a quick review of how to
introduce values for each type of input parameter:
• Raster Layer, Vector Layer or Table. Simply use a string with the name that identifies the data object to use
(the name it has in the QGIS Table of Contents) or a filename (if the corresponding layer is not opened, it will
be opened but not added to the map canvas). If you have an instance of a QGIS object representing the layer,
you can also pass it as parameter.
• Enumeration. If an algorithm has an enumeration parameter, the value of that parameter should be entered using
an integer value. To know the available options, you can use the algorithmHelp() command, as above.
For instance, the native:buffer algorithm has an enumeration called JOIN_STYLE:
JOIN_STYLE: Join style
Parameter type: QgsProcessingParameterEnum
Available values:
- 0: Round
- 1: Miter
- 2: Bevel
Accepted data types:
- int
- str: as string representation of int, e.g. '1'
- QgsProperty
In this case, the parameter has three options. Notice that ordering is zero-based.
• Boolean. Use True or False.
• Multiple input. The value is a string with input descriptors separated by semicolons (;). As in the case of single
layers or tables, each input descriptor can be the data object name, or its file path.
• Table Field from XXX. Use a string with the name of the field to use. This parameter is case-sensitive.
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• Fixed Table. Type the list of all table values separated by commas (,) and enclosed between quotes ("). Values
start on the upper row and go from left to right. You can also use a 2-D array of values representing the table.
• CRS. Enter the EPSG code number of the desired CRS.
• Extent. You must use a string with xmin, xmax, ymin and ymax values separated by commas (,).
Boolean, file, string and numerical parameters do not need any additional explanations.
Input parameters such as strings, booleans, or numerical values have default values. The default value is used if the
corresponding parameter entry is missing.
For output data objects, type the file path to be used to save it, just as it is done from the toolbox. If the output object
is not specified, the result is saved to a temporary file (or skipped if it is an optional output). The extension of the file
determines the file format. If you enter a file extension not supported by the algorithm, the default file format for that
output type will be used, and its corresponding extension appended to the given file path.
Unlike when an algorithm is executed from the toolbox, outputs are not added to the map canvas if you execute that
same algorithm from the Python console using run(), but runAndLoadResults() will do that.
The run() method returns a dictionary with one or more output names (the ones shown in the algorithm description)
as keys and the file paths of those outputs as values:
1 >>> myresult = processing.run("native:buffer", {'INPUT': '/data/lines.shp',
2 'DISTANCE': 100.0,
3 'SEGMENTS': 10,
4 'DISSOLVE': True,
5 'END_CAP_STYLE': 0,
6 'JOIN_STYLE': 0,
7 'MITER_LIMIT': 10,
8 'OUTPUT': '/data/buffers.shp'})
9 >>> myresult['OUTPUT']
10 /data/buffers.shp
You can load feature output by passing the corresponding file paths to the load() method. Or you could use
runAndLoadResults() instead of run() to load them immediately.
If you want to open an algorithm dialog from the console you can use the createAlgorithmDialog method.
The only mandatory parameter is the algorithm name, but you can also define the dictionary of parameters so that
the dialog will be filled automatically:
1 >>> my_dialog = processing.createAlgorithmDialog("native:buffer", {
2 'INPUT': '/data/lines.shp',
3 'DISTANCE': 100.0,
4 'SEGMENTS': 10,
5 'DISSOLVE': True,
6 'END_CAP_STYLE': 0,
7 'JOIN_STYLE': 0,
8 'MITER_LIMIT': 10,
9 'OUTPUT': '/data/buffers.shp'})
10 >>> my_dialog.show()
The execAlgorithmDialog method opens the dialog immediately:
1 >>> processing.execAlgorithmDialog("native:buffer", {
2 'INPUT': '/data/lines.shp',
3 'DISTANCE': 100.0,
4 'SEGMENTS': 10,
5 'DISSOLVE': True,
6 'END_CAP_STYLE': 0,
7 'JOIN_STYLE': 0,
8 'MITER_LIMIT': 10,
9 'OUTPUT': '/data/buffers.shp'})
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23.7.2 Creating scripts and running them from the toolbox
You can create your own algorithms by writing Python code. Processing scripts extend
QgsProcessingAlgorithm, so you need to add some extra lines of code to implement mandatory functions.
You can find Create new script (clean sheet) and Create New Script from Template (template that includes code
for mandatory functions of QgsProcessingAlgorithm) under the Scripts dropdown menu on the top of the
Processing toolbox. The Processing Script Editor will open, and that’s where you should type your code. Saving the
script from there in the scripts folder (the default folder when you open the save file dialog) with a .py extension
should create the corresponding algorithm.
The name of the algorithm (the one you will see in the toolbox) is defined within the code.
Let’s have a look at the following code, which defines a Processing algorithm that performs a buffer operation with
a user defined buffer distance on a vector layer that is specified by the user, after first smoothing the layer.
1 from qgis.core import (QgsProcessingAlgorithm,
2 QgsProcessingParameterNumber,
3 QgsProcessingParameterFeatureSource,
4 QgsProcessingParameterFeatureSink)
5
6 from qgis import processing
7
8 class algTest(QgsProcessingAlgorithm):
9 INPUT_BUFFERDIST = 'BUFFERDIST'
10 OUTPUT_BUFFER = 'OUTPUT_BUFFER'
11 INPUT_VECTOR = 'INPUT_VECTOR'
12
13 def __init__(self):
14 super().__init__()
15
16 def name(self):
17 return "algTest"
18
19 def displayName(self):
20 return "algTest script"
21
22 def createInstance(self):
23 return type(self)()
24
25 def initAlgorithm(self, config=None):
26 self.addParameter(QgsProcessingParameterFeatureSource(
27 self.INPUT_VECTOR, "Input vector"))
28 self.addParameter(QgsProcessingParameterNumber(
29 self.INPUT_BUFFERDIST, "Buffer distance",
30 QgsProcessingParameterNumber.Double,
31 100.0))
32 self.addParameter(QgsProcessingParameterFeatureSink(
33 self.OUTPUT_BUFFER, "Output buffer"))
34
35 def processAlgorithm(self, parameters, context, feedback):
36 #DO SOMETHING
37 algresult = processing.run("native:smoothgeometry",
38 {'INPUT': parameters[self.INPUT_VECTOR],
39 'ITERATIONS':2,
40 'OFFSET':0.25,
41 'MAX_ANGLE':180,
42 'OUTPUT': 'memory:'},
43 context=context, feedback=feedback, is_child_algorithm=True)
44 smoothed = algresult['OUTPUT']
45 algresult = processing.run('native:buffer',
46 {'INPUT': smoothed,
47 'DISTANCE': parameters[self.INPUT_BUFFERDIST],
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48 'SEGMENTS': 5,
49 'END_CAP_STYLE': 0,
50 'JOIN_STYLE': 0,
51 'MITER_LIMIT': 10,
52 'DISSOLVE': True,
53 'OUTPUT': parameters[self.OUTPUT_BUFFER]},
54 context=context, feedback=feedback, is_child_algorithm=True)
55 buffered = algresult['OUTPUT']
56 return {self.OUTPUT_BUFFER: buffered}
After doing the necessary imports, the following QgsProcessingAlgorithm functions are specified:
• name(): The id of the algorithm (lowercase).
• displayName(): A human readable name for the algorithm.
• createInstance(): Create a new instance of the algorithm class.
• initAlgorithm(): Configure the parameterDefinitions and outputDefinitions.
Here you describe the parameters and output of the algorithm. In this case, a feature source for the input,
a feature sink for the result and a number for the buffer distance.
• processAlgorithm(): Do the work.
Here we first run the smoothgeometry algorithm to smooth the geometry, and then we run the buffer
algorithm on the smoothed output. To be able to run algorithms from within another algorithm we have to set
the is_child_algorithm argument to True. You can see how input and output parameters are used
as parameters to the smoothgeometry and buffer algorithms.
There are a number of different parameter types available for input and output. Below is an alphabetically sorted list:
• QgsProcessingParameterAggregate
• QgsProcessingParameterAuthConfig
• QgsProcessingParameterBand
• QgsProcessingParameterBoolean
• QgsProcessingParameterColor
• QgsProcessingParameterCoordinateOperation
• QgsProcessingParameterCrs
• QgsProcessingParameterDatabaseSchema
• QgsProcessingParameterDatabaseTable
• QgsProcessingParameterDateTime
• QgsProcessingParameterDistance
• QgsProcessingParameterEnum
• QgsProcessingParameterExpression
• QgsProcessingParameterExtent
• QgsProcessingParameterFeatureSink
• QgsProcessingParameterFeatureSource
• QgsProcessingParameterField
• QgsProcessingParameterFieldMapping
• QgsProcessingParameterFile
• QgsProcessingParameterFileDestination
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• QgsProcessingParameterFolderDestination
• QgsProcessingParameterLayout
• QgsProcessingParameterLayoutItem
• QgsProcessingParameterMapLayer
• QgsProcessingParameterMapTheme
• QgsProcessingParameterMatrix
• QgsProcessingParameterMeshLayer
• QgsProcessingParameterMultipleLayers
• QgsProcessingParameterNumber
• QgsProcessingParameterPoint
• QgsProcessingParameterProviderConnection
• QgsProcessingParameterRange
• QgsProcessingParameterRasterDestination
• QgsProcessingParameterRasterLayer
• QgsProcessingParameterScale
• QgsProcessingParameterString
• QgsProcessingParameterVectorDestination
• QgsProcessingParameterVectorLayer
• QgsProcessingParameterVectorTileWriterLayers
The first parameter to the constructors is the name of the parameter, and the second is the description of the parameter
(for the user interface). The rest of the constructor parameters are parameter type specific.
The input can be turned into QGIS classes using the parameterAs functions of QgsProcessingAlgorithm.
For instance to get the number provided for the buffer distance as a double:
self.parameterAsDouble(parameters, self.INPUT_BUFFERDIST, context)).
The processAlgorithm function should return a dictionary containing values for every output defined by the
algorithm. This allows access to these outputs from other algorithms, including other algorithms contained within the
same model.
Well behaved algorithms should define and return as many outputs as makes sense. Non-feature outputs, such
as numbers and strings, are very useful when running your algorithm as part of a larger model, as these values can
be used as input parameters for subsequent algorithms within the model. Consider adding numeric outputs for things
like the number of features processed, the number of invalid features encountered, the number of features output,
etc. The more outputs you return, the more useful your algorithm becomes!
Feedback
The feedback object passed to processAlgorithm() should be used for user feedback / interaction. You
can use the setProgress() function of the feedback object to update the progress bar (0 to 100) to inform
the user about the progress of the algorithm. This is very useful if your algorithm takes a long time to complete.
The feedback object provides an isCanceled() method that should be monitored to enable cancelation of the
algorithm by the user. The pushInfo() method of feedback can be used to send information to the user, and
reportError() is handy for pushing non-fatal errors to users.
Algorithms should avoid using other forms of providing feedback to users, such as print statements or logging to
QgsMessageLog, and should always use the feedback object instead. This allows verbose logging for the algorithm,
and is also thread-safe (which is important, given that algorithms are typically run in a background thread).
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Handling errors
If your algorithm encounters an error which prevents it from executing, such as invalid input values or some other
condition from which it cannot or should not recover, then you should raise a QgsProcessingException. E.g.:
if feature['value'] < 20:
raise QgsProcessingException('Invalid input value {}, must be >= 20'.
→format(feature['value']))
Try to avoid raising QgsProcessingException for non-fatal errors (e.g. when a feature has a null geometry),
and instead just report these errors via feedback.reportError() and skip the feature. This helps make
your algorithm „model-friendly“, as it avoids halting the execution of an entire algorithm when a non-fatal error
is encountered.
Documenting your scripts
As in the case of models, you can create additional documentation for your scripts, to explain what they do and how
to use them.
QgsProcessingAlgorithm provides the helpString(), shortHelpString() and helpUrl()
functions for that purpose. Specify / override these to provide more help to the user.
shortDescription() is used in the tooltip when hovering over the algorithm in the toolbox.
23.7.3 Pre- and post-execution script hooks
Scripts can also be used as pre- and post-execution hooks that are run before and after an algorithm is run, respectively.
This can be used to automate tasks that should be performed whenever an algorithm is executed.
The syntax is identical to the syntax explained above, but an additional global variable named alg is available,
representing the algorithm that has just been (or is about to be) executed.
In the General group of the processing options dialog, you will find two entries named Pre-execution script and Post-execution
script where the filenames of the scripts to be run in each case can be entered.
23.8 Using processing from the command line
QGIS comes with a tool called QGIS Processing Executor which allows you to run Processing algorithms
and models (built-in or provided by plugins) directly from the command line without starting QGIS Desktop itself.
From a command line tool, run qgis_process and you should get:
QGIS Processing Executor - 3.16.8-Hannover 'Hannover' (3.16.8-Hannover)
Usage: C:\OSGeo4W\apps\qgis-ltr\bin\qgis_process.exe [--json] [command] [algorithm␣
→id or path to model file] [parameters]
Options:
--json Output results as JSON objects
Available commands:
plugins list available and active plugins
plugins enable enables an installed plugin. The plugin name must be specified,␣
→e.g. "plugins enable cartography_tools"
plugins disable disables an installed plugin. The plugin name must be specified,
→ e.g. "plugins disable cartography_tools"
list list all available processing algorithms
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help show help for an algorithm. The algorithm id or a path to a␣
→model file must be specified.
run runs an algorithm. The algorithm id or a path to a model file␣
→and parameter values must be specified.
Parameter values are specified after -- with PARAMETER=VALUE␣
→syntax.
Ordered list values for a parameter can be created by␣
→specifying the parameter multiple times,
e.g. --LAYERS=layer1.shp --LAYERS=layer2.shp
If required, the ellipsoid to use for distance and area␣
→calculations can be specified via the "--ELLIPSOID=name" argument.
If required, an existing QGIS project to use during the␣
→algorithm execution can be specified via the "--PROJECT_PATH=path" argument.
Poznámka: Only installed plugins that advertize hasProcessingProvider=yes in their metadata.txt
file are recognized and can be activated or loaded by qgis_process tool.
The command list can be used to get a list of all available providers and algorithms.
qgis_process list
The command help can be used to get further information about commands or algorithms.
qgis_process help qgis:regularpoints
The command run can be used to run an algorithm or model. Specify the name of the algorithm or a path to a model
as first parameter.
qgis_process run qgis:buffer -- INPUT=source.shp DISTANCE=2 OUTPUT=buffered.shp
Where a parameter accepts a list of values, set the same variable multiple times.
qgis_process run native:mergevectorlayers -- LAYERS=input1.shp LAYERS=input2.shp␣
→OUTPUT=merged.shp
While running an algorithm a text-based feedback bar is shown, and the operation can be cancelled via CTRL+C.
The run command also supports further parameters.
• --json will format stdout output in a JSON structured way.
• --ellipsoid will set the ellipsoid to the specified one.
• --distance_units will use the specified distance units.
• --area_units will use the specified area units.
• --project_path will load the specified project for running the algorithm.
23.9 Writing new Processing algorithms as Python scripts
There are two options for writing Processing algorithms using Python.
• Extending QgsProcessingAlgorithm
• Using the @alg decorator
Within QGIS, you can use Create new script in the Scripts menu at the top of the Processing Toolbox to open
the Processing Script Editor where you can write your code. To simplify the task, you can start with a script
template by using Create new script from template from the same menu. This opens a template that extends
QgsProcessingAlgorithm.
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If you save the script in the scripts folder (the default location) with a .py extension, the algorithm will become
available in the Processing Toolbox.
23.9.1 Extending QgsProcessingAlgorithm
The following code
1. takes a vector layer as input
2. counts the number of features
3. does a buffer operation
4. creates a raster layer from the result of the buffer operation
5. returns the buffer layer, raster layer and number of features
1 from qgis.PyQt.QtCore import QCoreApplication
2 from qgis.core import (QgsProcessing,
3 QgsProcessingAlgorithm,
4 QgsProcessingException,
5 QgsProcessingOutputNumber,
6 QgsProcessingParameterDistance,
7 QgsProcessingParameterFeatureSource,
8 QgsProcessingParameterVectorDestination,
9 QgsProcessingParameterRasterDestination)
10 from qgis import processing
11
12
13 class ExampleProcessingAlgorithm(QgsProcessingAlgorithm):
14 """
15 This is an example algorithm that takes a vector layer,
16 creates some new layers and returns some results.
17 """
18
19 def tr(self, string):
20 """
21 Returns a translatable string with the self.tr() function.
22 """
23 return QCoreApplication.translate('Processing', string)
24
25 def createInstance(self):
26 # Must return a new copy of your algorithm.
27 return ExampleProcessingAlgorithm()
28
29 def name(self):
30 """
31 Returns the unique algorithm name.
32 """
33 return 'bufferrasterextend'
34
35 def displayName(self):
36 """
37 Returns the translated algorithm name.
38 """
39 return self.tr('Buffer and export to raster (extend)')
40
41 def group(self):
42 """
43 Returns the name of the group this algorithm belongs to.
44 """
45 return self.tr('Example scripts')
46
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47 def groupId(self):
48 """
49 Returns the unique ID of the group this algorithm belongs
50 to.
51 """
52 return 'examplescripts'
53
54 def shortHelpString(self):
55 """
56 Returns a localised short help string for the algorithm.
57 """
58 return self.tr('Example algorithm short description')
59
60 def initAlgorithm(self, config=None):
61 """
62 Here we define the inputs and outputs of the algorithm.
63 """
64 # 'INPUT' is the recommended name for the main input
65 # parameter.
66 self.addParameter(
67 QgsProcessingParameterFeatureSource(
68 'INPUT',
69 self.tr('Input vector layer'),
70 types=[QgsProcessing.TypeVectorAnyGeometry]
71 )
72 )
73 self.addParameter(
74 QgsProcessingParameterVectorDestination(
75 'BUFFER_OUTPUT',
76 self.tr('Buffer output'),
77 )
78 )
79 # 'OUTPUT' is the recommended name for the main output
80 # parameter.
81 self.addParameter(
82 QgsProcessingParameterRasterDestination(
83 'OUTPUT',
84 self.tr('Raster output')
85 )
86 )
87 self.addParameter(
88 QgsProcessingParameterDistance(
89 'BUFFERDIST',
90 self.tr('BUFFERDIST'),
91 defaultValue = 1.0,
92 # Make distance units match the INPUT layer units:
93 parentParameterName='INPUT'
94 )
95 )
96 self.addParameter(
97 QgsProcessingParameterDistance(
98 'CELLSIZE',
99 self.tr('CELLSIZE'),
100 defaultValue = 10.0,
101 parentParameterName='INPUT'
102 )
103 )
104 self.addOutput(
105 QgsProcessingOutputNumber(
106 'NUMBEROFFEATURES',
107 self.tr('Number of features processed')
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108 )
109 )
110
111 def processAlgorithm(self, parameters, context, feedback):
112 """
113 Here is where the processing itself takes place.
114 """
115 # First, we get the count of features from the INPUT layer.
116 # This layer is defined as a QgsProcessingParameterFeatureSource
117 # parameter, so it is retrieved by calling
118 # self.parameterAsSource.
119 input_featuresource = self.parameterAsSource(parameters,
120 'INPUT',
121 context)
122 numfeatures = input_featuresource.featureCount()
123
124 # Retrieve the buffer distance and raster cell size numeric
125 # values. Since these are numeric values, they are retrieved
126 # using self.parameterAsDouble.
127 bufferdist = self.parameterAsDouble(parameters, 'BUFFERDIST',
128 context)
129 rastercellsize = self.parameterAsDouble(parameters, 'CELLSIZE',
130 context)
131 if feedback.isCanceled():
132 return {}
133 buffer_result = processing.run(
134 'native:buffer',
135 {
136 # Here we pass on the original parameter values of INPUT
137 # and BUFFER_OUTPUT to the buffer algorithm.
138 'INPUT': parameters['INPUT'],
139 'OUTPUT': parameters['BUFFER_OUTPUT'],
140 'DISTANCE': bufferdist,
141 'SEGMENTS': 10,
142 'DISSOLVE': True,
143 'END_CAP_STYLE': 0,
144 'JOIN_STYLE': 0,
145 'MITER_LIMIT': 10
146 },
147 # Because the buffer algorithm is being run as a step in
148 # another larger algorithm, the is_child_algorithm option
149 # should be set to True
150 is_child_algorithm=True,
151 #
152 # It's important to pass on the context and feedback objects to
153 # child algorithms, so that they can properly give feedback to
154 # users and handle cancelation requests.
155 context=context,
156 feedback=feedback)
157
158 # Check for cancelation
159 if feedback.isCanceled():
160 return {}
161
162 # Run the separate rasterization algorithm using the buffer result
163 # as an input.
164 rasterized_result = processing.run(
165 'qgis:rasterize',
166 {
167 # Here we pass the 'OUTPUT' value from the buffer's result
168 # dictionary off to the rasterize child algorithm.
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169 'LAYER': buffer_result['OUTPUT'],
170 'EXTENT': buffer_result['OUTPUT'],
171 'MAP_UNITS_PER_PIXEL': rastercellsize,
172 # Use the original parameter value.
173 'OUTPUT': parameters['OUTPUT']
174 },
175 is_child_algorithm=True,
176 context=context,
177 feedback=feedback)
178
179 if feedback.isCanceled():
180 return {}
181
182 # Return the results
183 return {'OUTPUT': rasterized_result['OUTPUT'],
184 'BUFFER_OUTPUT': buffer_result['OUTPUT'],
185 'NUMBEROFFEATURES': numfeatures}
Processing algorithm standard functions:
• createInstance (mandatory) Must return a new copy of your algorithm. If you change the name of the class,
make sure you also update the value returned here to match!
• name (mandatory) Returns the unique algorithm name, used for identifying the algorithm.
• displayName (mandatory) Returns the translated algorithm name.
• group Returns the name of the group this algorithm belongs to.
• groupId Returns the unique ID of the group this algorithm belongs to.
• shortHelpString Returns a localised short help string for the algorithm.
• initAlgorithm (mandatory) Here we define the inputs and outputs of the algorithm.
INPUT and OUTPUT are recommended names for the main input and main output parameters,
respectively.
If a parameter depends on another parameter, parentParameterName is used to specify this
relationship (could be the field / band of a layer or the distance units of a layer).
• processAlgorithm (mandatory) This is where the processing takes place.
Parameters are retrieved using special purpose functions, for instance parameterAsSource and
parameterAsDouble.
processing.run can be used to run other processing algorithms from a processing algorithm. The
first parameter is the name of the algorithm, the second is a dictionary of the parameters to the algorithm.
is_child_algorithm is normally set to True when running an algorithm from within another
algorithm. context and feedback inform the algorithm about the environment to run in and the
channel for communicating with the user (catching cancel request, reporting progress, providing textual
feedback). When using the (parent) algorithm’s parameters as parameters to „child“ algorithms, the
original parameter values should be used (e.g. parameters['OUTPUT']).
It is good practice to check the feedback object for cancelation as much as is sensibly possible! Doing
so allows for responsive cancelation, instead of forcing users to wait for unwanted processing to occur.
The algorithm should return values for all the output parameters it has defined as a dictionary. In this
case, that’s the buffer and rasterized output layers, and the count of features processed. The dictionary
keys must match the original parameter/output names.
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23.9.2 The @alg decorator
Using the @alg decorator, you can create your own algorithms by writing the Python code and adding a few extra
lines to supply additional information needed to make it a proper Processing algorithm. This simplifies the creation
of algorithms and the specification of inputs and outputs.
One important limitation with the decorator approach is that algorithms created in this way will always be added to
a user’s Processing Scripts provider – it is not possible to add these algorithms to a custom provider, e.g. for use in
plugins.
The following code uses the @alg decorator to
1. use a vector layer as input
2. count the number of features
3. do a buffer operation
4. create a raster layer from the result of the buffer operation
5. returns the buffer layer, raster layer and number of features
1 from qgis import processing
2 from qgis.processing import alg
3 from qgis.core import QgsProject
4
5 @alg(name='bufferrasteralg', label='Buffer and export to raster (alg)',
6 group='examplescripts', group_label='Example scripts')
7 # 'INPUT' is the recommended name for the main input parameter
8 @alg.input(type=alg.SOURCE, name='INPUT', label='Input vector layer')
9 # 'OUTPUT' is the recommended name for the main output parameter
10 @alg.input(type=alg.RASTER_LAYER_DEST, name='OUTPUT',
11 label='Raster output')
12 @alg.input(type=alg.VECTOR_LAYER_DEST, name='BUFFER_OUTPUT',
13 label='Buffer output')
14 @alg.input(type=alg.DISTANCE, name='BUFFERDIST', label='BUFFER DISTANCE',
15 default=1.0)
16 @alg.input(type=alg.DISTANCE, name='CELLSIZE', label='RASTER CELL SIZE',
17 default=10.0)
18 @alg.output(type=alg.NUMBER, name='NUMBEROFFEATURES',
19 label='Number of features processed')
20
21 def bufferrasteralg(instance, parameters, context, feedback, inputs):
22 """
23 Description of the algorithm.
24 (If there is no comment here, you will get an error)
25 """
26 input_featuresource = instance.parameterAsSource(parameters,
27 'INPUT', context)
28 numfeatures = input_featuresource.featureCount()
29 bufferdist = instance.parameterAsDouble(parameters, 'BUFFERDIST',
30 context)
31 rastercellsize = instance.parameterAsDouble(parameters, 'CELLSIZE',
32 context)
33 if feedback.isCanceled():
34 return {}
35 buffer_result = processing.run('native:buffer',
36 {'INPUT': parameters['INPUT'],
37 'OUTPUT': parameters['BUFFER_OUTPUT'],
38 'DISTANCE': bufferdist,
39 'SEGMENTS': 10,
40 'DISSOLVE': True,
41 'END_CAP_STYLE': 0,
42 'JOIN_STYLE': 0,
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43 'MITER_LIMIT': 10
44 },
45 is_child_algorithm=True,
46 context=context,
47 feedback=feedback)
48 if feedback.isCanceled():
49 return {}
50 rasterized_result = processing.run('qgis:rasterize',
51 {'LAYER': buffer_result['OUTPUT'],
52 'EXTENT': buffer_result['OUTPUT'],
53 'MAP_UNITS_PER_PIXEL': rastercellsize,
54 'OUTPUT': parameters['OUTPUT']
55 },
56 is_child_algorithm=True, context=context,
57 feedback=feedback)
58 if feedback.isCanceled():
59 return {}
60 return {'OUTPUT': rasterized_result['OUTPUT'],
61 'BUFFER_OUTPUT': buffer_result['OUTPUT'],
62 'NUMBEROFFEATURES': numfeatures}
As you can see, it involves two algorithms (‚native:buffer‘ and ‚qgis:rasterize‘). The last one (‚qgis:rasterize‘) creates
a raster layer from the buffer layer that was generated by the first one (‚native:buffer‘).
The part of the code where this processing takes place is not difficult to understand if you have read the previous
chapter. The first lines, however, need some additional explanation. They provide the information that is needed to
turn your code into an algorithm that can be run from any of the GUI components, like the toolbox or the graphical
modeler.
These lines are all calls to the @alg decorator functions that help simplify the coding of the algorithm.
• The @alg decorator is used to define the name and location of the algorithm in the Toolbox.
• The @alg.input decorator is used to define the inputs of the algorithm.
• The @alg.output decorator is used to define the outputs of the algorithm.
23.9.3 Input and output types for Processing Algorithms
Here is the list of input and output types that are supported in Processing with their corresponding alg decorator
constants (algfactory.py contains the complete list of alg constants). Sorted on class name.
Input types
Class Alg constant Popis
QgsProcessingParameterAuthConfig alg.AUTH_CFG Allows users to
select from available
authentication
configurations or create
new authentication
configurations
QgsProcessingParameterBand alg.BAND A band of a raster layer
QgsProcessingParameterBoolean alg.BOOL A boolean value
QgsProcessingParameterColor alg.COLOR A color
QgsProcessingParameterCoordinateOperationalg.
COORDINATE_OPERATION
A coordinate
operation (for CRS
transformations)
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Class Alg constant Popis
QgsProcessingParameterCrs alg.CRS A Coordinate Reference
System
QgsProcessingParameterDatabaseSchemaalg.DATABASE_SCHEMA A database schema
QgsProcessingParameterDatabaseTablealg.DATABASE_TABLE A database table
QgsProcessingParameterDateTime alg.DATETIME A datetime (or a pure
date or time)
QgsProcessingParameterDistance alg.DISTANCE A double numeric
parameter for distance
values
QgsProcessingParameterEnum alg.ENUM An enumeration,
allowing for selection
from a set of predefined
values
QgsProcessingParameterExpression alg.EXPRESSION An expression
QgsProcessingParameterExtent alg.EXTENT A spatial extent defined
by xmin, xmax, ymin,
ymax
QgsProcessingParameterField alg.FIELD A field in the attribute
table of a vector layer
QgsProcessingParameterFile alg.FILE A filename of an existing
file
QgsProcessingParameterFileDestinationalg.FILE_DEST A filename for a newly
created output file
QgsProcessingParameterFolderDestinationalg.FOLDER_DEST A folder (destination
folder)
QgsProcessingParameterNumber alg.INT An integer
QgsProcessingParameterLayout alg.LAYOUT A layout
QgsProcessingParameterLayoutItem alg.LAYOUT_ITEM A layout item
QgsProcessingParameterMapLayer alg.MAPLAYER A map layer
QgsProcessingParameterMapTheme alg.MAP_THEME A project map theme
QgsProcessingParameterMatrix alg.MATRIX A matrix
QgsProcessingParameterMeshLayer alg.MESH_LAYER A mesh layer
QgsProcessingParameterMultipleLayersalg.MULTILAYER A set of layers
QgsProcessingParameterNumber alg.NUMBER A numerical value
QgsProcessingParameterPoint alg.POINT A point
QgsProcessingParameterProviderConnectionalg.
PROVIDER_CONNECTION
An available connection
for a database provider
QgsProcessingParameterRange alg.RANGE A number range
QgsProcessingParameterRasterLayer alg.RASTER_LAYER A raster layer
QgsProcessingParameterRasterDestinationalg.RASTER_LAYER_DEST A raster layer
QgsProcessingParameterScale alg.SCALE A map scale
QgsProcessingParameterFeatureSink alg.SINK A feature sink
QgsProcessingParameterFeatureSourcealg.SOURCE A feature source
QgsProcessingParameterString alg.STRING A text string
QgsProcessingParameterVectorLayer alg.VECTOR_LAYER A vector layer
QgsProcessingParameterVectorDestinationalg.VECTOR_LAYER_DEST A vector layer
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Output types
Class Alg constant Popis
QgsProcessingOutputBoolean alg.BOOL A boolean value
QgsProcessingOutputNumber alg.DISTANCE A double numeric parameter
for distance values
QgsProcessingOutputFile alg.FILE A filename of an existing file
QgsProcessingOutputFolder alg.FOLDER A folder
QgsProcessingOutputHtml alg.HTML HTML
QgsProcessingOutputNumber alg.INT A integer
QgsProcessingOutputLayerDefinition alg.LAYERDEF A layer definition
QgsProcessingOutputMapLayer alg.MAPLAYER A map layer
QgsProcessingOutputMultipleLayers alg.MULTILAYER A set of layers
QgsProcessingOutputNumber alg.NUMBER A numerical value
QgsProcessingOutputRasterLayer alg.RASTER_LAYER A raster layer
QgsProcessingOutputString alg.STRING A text string
QgsProcessingOutputVectorLayer alg.VECTOR_LAYER A vector layer
23.9.4 Handing algorithm output
When you declare an output representing a layer (raster or vector), the algorithm will try to add it to QGIS once it
is finished.
• Raster layer output: QgsProcessingParameterRasterDestination / alg.RASTER_LAYER_DEST.
• Vector layer output: QgsProcessingParameterVectorDestination / alg.VECTOR_LAYER_DEST.
So even if the processing.run() method does not add the layers it creates to the user’s current project, the two
output layers (buffer and raster buffer) will be loaded, since they are saved to the destinations entered by the user (or
to temporary destinations if the user does not specify destinations).
If a layer is created as output of an algorithm, it should be declared as such. Otherwise, you will not be able to properly
use the algorithm in the modeler, since what is declared will not match what the algorithm really creates.
You can return strings, numbers and more by specifying them in the result dictionary (as demonstrated for
„NUMBEROFFEATURES“), but they should always be explicitly defined as outputs from your algorithm. We
encourage algorithms to output as many useful values as possible, since these can be valuable for use in later algorithms
when your algorithm is used as part of a model.
23.9.5 Communicating with the user
If your algorithm takes a long time to process, it is a good idea to inform the user about the progress. You can use
feedback (QgsProcessingFeedback) for this.
The progress text and progressbar can be updated using two methods: setProgressText(text) and
setProgress(percent).
You can provide more information by using pushCommandInfo(text), pushDebugInfo(text),
pushInfo(text) and reportError(text).
If your script has a problem, the correct way of handling it is to raise a QgsProcessingException. You can
pass a message as an argument to the constructor of the exception. Processing will take care of handling it and
communicating with the user, depending on where the algorithm is being executed from (toolbox, modeler, Python
console, …)
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23.9.6 Documenting your scripts
You can document your scripts by overloading the helpString() and helpUrl() methods of
QgsProcessingAlgorithm.
23.9.7 Flags
You can override the flags() method of QgsProcessingAlgorithm to tell QGIS more about your algorithm.
You can for instance tell QGIS that the script shall be hidden from the modeler, that it can be canceled, that it is not
thread safe, and more.
Tip: By default, Processing runs algorithms in a separate thread in order to keep QGIS responsive while the processing
task runs. If your algorithm is regularly crashing, you are probably using API calls which are not safe to do in
a background thread. Try returning the QgsProcessingAlgorithm.FlagNoThreading flag from your algorithm’s flags()
method to force Processing to run your algorithm in the main thread instead.
23.9.8 Best practices for writing script algorithms
Here’s a quick summary of ideas to consider when creating your script algorithms and, especially, if you want to share
them with other QGIS users. Following these simple rules will ensure consistency across the different Processing
elements such as the toolbox, the modeler or the batch processing interface.
• Do not load resulting layers. Let Processing handle your results and load your layers if needed.
• Always declare the outputs your algorithm creates.
• Do not show message boxes or use any GUI element from the script. If you want to communicate
with the user, use the methods of the feedback object (QgsProcessingFeedback) or throw
a QgsProcessingException.
There are already many processing algorithms available in QGIS. You can find code on https://github.com/qgis/
QGIS/blob/release-3_16/python/plugins/processing/algs/qgis.
23.10 Configuring external applications
The processing framework can be extended using additional applications. Algorithms that rely on external applications
are managed by their own algorithm providers. Additional providers can be found as separate plugins, and installed
using the QGIS Plugin Manager.
This section will show you how to configure the Processing framework to include these additional applications, and it
will explain some particular features of the algorithms based on them. Once you have correctly configured the system,
you will be able to execute external algorithms from any component like the toolbox or the graphical modeler, just
like you do with any other algorithm.
By default, algorithms that rely on an external application not shipped with QGIS are not enabled. You can enable
them in the Processing settings dialog if they are installed on your system.
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23.10.1 A note for Windows users
If you are not an advanced user and you are running QGIS on Windows, you might not be interested in reading the
rest of this chapter. Make sure you install QGIS in your system using the standalone installer. That will automatically
install SAGA and GRASS in your system and configure them so they can be run from QGIS. All the algorithms from
these providers will be ready to be run without needing any further configuration. If installing with the OSGeo4W
application, make sure that you also select SAGA and GRASS for installation.
23.10.2 A note on file formats
When using external software, opening a file in QGIS does not mean that it can be opened and processed in that other
software. In most cases, other software can read what you have opened in QGIS, but in some cases, that might not
be true. When using databases or uncommon file formats, whether for raster or vector layers, problems might arise.
If that happens, try to use well-known file formats that you are sure are understood by both programs, and check the
console output (in the log panel) to find out what is going wrong.
You might for instance get trouble and not be able to complete your work if you call an external algorithm with
a GRASS raster layers as input. For this reason, such layers will not appear as available to algorithms.
You should, however, not have problems with vector layers, since QGIS automatically converts from the original file
format to one accepted by the external application before passing the layer to it. This adds extra processing time,
which might be significant for large layers, so do not be surprised if it takes more time to process a layer from a DB
connection than a layer from a Shapefile format dataset of similar size.
Providers not using external applications can process any layer that you can open in QGIS, since they open it for
analysis through QGIS.
All raster and vector output formats produced by QGIS can be used as input layers. Some providers do not support
certain formats, but all can export to common formats that can later be transformed by QGIS automatically. As for
input layers, if a conversion is needed, that might increase the processing time.
23.10.3 A note on vector layer selections
External applications may also be made aware of the selections that exist in vector layers within QGIS. However,
that requires rewriting all input vector layers, just as if they were originally in a format not supported by the external
application. Only when no selection exists, or the Use only selected features option is not enabled in the processing
general configuration, can a layer be directly passed to an external application.
In other cases, exporting only selected features is needed, which causes longer execution times.
23.10.4 SAGA
SAGA algorithms can be run from QGIS if SAGA is included with the QGIS installation.
If you are running Windows, both the stand-alone installer and the OSGeo4W installer include SAGA.
About SAGA grid system limitations
Most SAGA algorithms that require several input raster layers require them to have the same grid system. That is, they
must cover the same geographic area and have the same cell size, so their corresponding grids match. When calling
SAGA algorithms from QGIS, you can use any layer, regardless of its cell size and extent. When multiple raster layers
are used as input for a SAGA algorithm, QGIS resamples them to a common grid system and then passes them to
SAGA (unless the SAGA algorithm can operate with layers from different grid systems).
The definition of that common grid system is controlled by the user, and you will find several parameters in the SAGA
group of the settings window to do so. There are two ways of setting the target grid system:
• Setting it manually. You define the extent by setting the values of the following parameters:
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– Resampling min X
– Resampling max X
– Resampling min Y
– Resampling max Y
– Resampling cellsize
Notice that QGIS will resample input layers to that extent, even if they do not overlap with it.
• Setting it automatically from input layers. To select this option, just check the Use min covering grid system
for resampling option. All the other settings will be ignored and the minimum extent that covers all the input
layers will be used. The cell size of the target layer is the maximum of all cell sizes of the input layers.
For algorithms that do not use multiple raster layers, or for those that do not need a unique input grid system, no
resampling is performed before calling SAGA, and those parameters are not used.
Limitations for multi-band layers
Unlike QGIS, SAGA has no support for multi-band layers. If you want to use a multiband layer (such as an RGB or
multispectral image), you first have to split it into single-banded images. To do so, you can use the ‚SAGA/Grid
- Tools/Split RGB image‘ algorithm (which creates three images from an RGB image) or the ‚SAGA/Grid Tools/Extract
band‘ algorithm (to extract a single band).
Limitations in cell size
SAGA assumes that raster layers have the same cell size in the X and Y axis. If you are working with a layer with
different values for horizontal and vertical cell size, you might get unexpected results. In this case, a warning will be
added to the processing log, indicating that an input layer might not be suitable to be processed by SAGA.
Logging
When QGIS calls SAGA, it does so using its command-line interface, thus passing a set of commands to perform all
the required operations. SAGA shows its progress by writing information to the console, which includes the percentage
of processing already done, along with additional content. This output is filtered and used to update the progress bar
while the algorithm is running.
Both the commands sent by QGIS and the additional information printed by SAGA can be logged along with other
processing log messages, and you might find them useful to track what is going on when QGIS runs a SAGA
algorithm. You will find two settings, namely Log console output and Log execution commands, to activate that logging
mechanism.
Most other providers that use external applications and call them through the command-line have similar options,
so you will find them as well in other places in the processing settings list.
23.10.5 R scripts
To enable R in Processing you need to install the Processing R Provider plugin and configure R for QGIS.
Configuration is done in Provider ► R in the Processing tab of Settings ► Options.
Depending on your operating system, you may have to use R folder to specify where your R binaries are located.
Poznámka: On Windows the R executable file is normally in a folder (R-<version>) under C:\Program
Files\R\. Specify the folder and NOT the binary!
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On Linux you just have to make sure that the R folder is in the PATH environment variable. If R in a terminal window
starts R, then you are ready to go.
After installing the Processing R Provider plugin, you will find some example scripts in the Processing Toolbox:
• Scatterplot runs an R function that produces a scatter plot from two numerical fields of the provided vector
layer.
• test_sf does some operations that depend on the sf package and can be used to check if the R package sf
is installed. If the package is not installed, R will try to install it (and all the packages it depends on) for
you, using the Package repository specified in Provider ► R in the Processing options. The default is https:
//cran.at.r-project.org/. Installing may take some time…
• test_sp can be used to check if the R package sp is installed. If the package is not installed, R will try to install
it for you.
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If you have R configured correctly for QGIS, you should be able to run these scripts.
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Adding R scripts from the QGIS collection
R integration in QGIS is different from that of SAGA in that there is not a predefined set of algorithms you can run
(except for some example script that come with the Processing R Provider plugin).
A set of example R scripts is available in the QGIS Repository. Perform the following steps to load and enable them
using the QGIS Resource Sharing plugin.
1. Add the QGIS Resource Sharing plugin (you may have to enable Show also experimental plugins in the Plugin
Manager Settings)
2. Open it (Plugins –> Resource Sharing –> Resource Sharing)
3. Choose the Settings tab
4. Click Reload repositories
5. Choose the All tab
6. Select QGIS R script collection in the list and click on the Install button
7. The collection should now be listed in the Installed tab
8. Close the plugin
9. Open the Processing Toolbox, and if everything is OK, the example scripts will be present under R, in various
groups (only some of the groups are expanded in the screenshot below).
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Obr. 23.34: The Processing Toolbox with some R scripts shown
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The scripts at the top are the example scripts from the Processing R Provider plugin.
10. If, for some reason, the scripts are not available in the Processing Toolbox, you can try to:
1. Open the Processing settings (Settings ► Options ► Processing tab)
2. Go to Providers ► R ► R scripts folder
• On Ubuntu, set the path to (or, better, include in the path):
/home/<user>/.local/share/QGIS/QGIS3/profiles/default/resource_sharing/repositories/github.com/qgis/QGIS-
-Resources/collections/rscripts
• On Windows, set the path to (or, better, include in the path):
C:\Users\<user>\AppData\Roaming\QGIS\QGIS3\profiles\default\resource_sharing\repositories\github.com\qgis
-Resources\collections\rscripts
To edit, double-click. You can then choose to just paste / type the path, or you can navigate to the directory
by using the … button and press the Add button in the dialog that opens. It is possible to provide several
directories here. They will be separated by a semicolon („;“).
If you would like to get all the R scrips from the QGIS 2 on-line collection, you can select QGIS R script collection
(from QGIS 2) instead of QGIS R script collection. You will probably find that scripts that depend on vector data input
or output will not work.
Creating R scripts
You can write scripts and call R commands, as you would do from R. This section shows you the syntax for using R
commands in QGIS, and how to use QGIS objects (layers, tables) in them.
To add an algorithm that calls an R function (or a more complex R script that you have developed and you would like
to have available from QGIS), you have to create a script file that performs the R commands.
R script files have the extension .rsx, and creating them is pretty easy if you just have a basic knowledge of R syntax
and R scripting. They should be stored in the R scripts folder. You can specify the folder (R scripts folder) in the R
settings group in Processing settings dialog).
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Let’s have a look at a very simple script file, which calls the R method spsample to create a random grid within the
boundary of the polygons in a given polygon layer. This method belongs to the maptools package. Since almost
all the algorithms that you might like to incorporate into QGIS will use or generate spatial data, knowledge of spatial
packages like maptools and sp/sf, is very useful.
##Random points within layer extent=name
##Point pattern analysis=group
##Vector_layer=vector
##Number_of_points=number 10
##Output=output vector
library(sp)
spatpoly = as(Vector_layer, "Spatial")
pts=spsample(spatpoly,Number_of_points,type="random")
spdf=SpatialPointsDataFrame(pts, as.data.frame(pts))
Output=st_as_sf(spdf)
The first lines, which start with a double Python comment sign (##), define the display name and group of the script,
and tell QGIS about its inputs and outputs.
Poznámka: To find out more about how to write your own R scripts, have a look at the R Intro section in the training
manual and consult the QGIS R Syntax section.
When you declare an input parameter, QGIS uses that information for two things: creating the user interface to ask the
user for the value of that parameter, and creating a corresponding R variable that can be used as R function input.
In the above example, we have declared an input of type vector, named Vector_layer. When executing the
algorithm, QGIS will open the layer selected by the user and store it in a variable named Vector_layer. So, the
name of a parameter is the name of the variable that you use in R for accessing the value of that parameter (you
should therefore avoid using reserved R words as parameter names).
Spatial parameters such as vector and raster layers are read using the st_read() (or readOGR) and brick()
(or readGDAL) commands (you do not have to worry about adding those commands to your description file – QGIS
will do it), and they are stored as sf (or Spatial*DataFrame) objects.
Table fields are stored as strings containing the name of the selected field.
Vector files can be read using the readOGR() command instead of st_read() by specifying
##load_vector_using_rgdal. This will produce a Spatial*DataFrame object instead of an sf
object.
Raster files can be read using the readGDAL() command instead of brick() by specifying
##load_raster_using_rgdal.
If you are an advanced user and do not want QGIS to create the object for the layer, you can use
##pass_filenames to indicate that you prefer a string with the filename. In this case, it is up to you to open the
file before performing any operation on the data it contains.
With the above information, it is possible to understand the first lines of the R script (the first line not starting with
a Python comment character).
library(sp)
spatpoly = as(Vector_layer, "Spatial")
pts=spsample(polyg,numpoints,type="random")
The spsample function is provided by the sp library, so the first thing we do is to load that library. The variable
Vector_layer contains an sf object. Since we are going to use a function (spsample) from the sp library, we
must convert the sf object to a SpatialPolygonsDataFrame object using the as function.
Then we call the spsample function with this object and the numpoints input parameter (which specifies the
number of points to generate).
Since we have declared a vector output named Output, we have to create a variable named Output containing an
sf object.
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We do this in two steps. First we create a SpatialPolygonsDataFrame object from the result of the function,
using the SpatialPointsDataFrame function, and then we convert that object to an sf object using the st_as_sf
function (of the sf library).
You can use whatever names you like for your intermediate variables. Just make sure that the variable storing your
final result has the defined name (in this case Output), and that it contains a suitable value (an sf object for vector
layer output).
In this case, the result obtained from the spsample method had to be converted explicitly into an sf object
via a SpatialPointsDataFrame object, since it is itself an object of class ppp, which can not be returned
to QGIS.
If your algorithm generates raster layers, the way they are saved will depend on whether or not you have used the
##dontuserasterpackage option. If you have used it, layers are saved using the writeGDAL() method. If
not, the writeRaster() method from the raster package will be used.
If you have used the ##pass_filenames option, outputs are generated using the raster package (with
writeRaster()).
If your algorithm does not generate a layer, but a text result in the console instead, you have to indicate that you want
the console to be shown once the execution is finished. To do so, just start the command lines that produce the results
you want to print with the > (‚greater than‘) sign. Only output from lines prefixed with > are shown. For instance,
here is the description file of an algorithm that performs a normality test on a given field (column) of the attributes
of a vector layer:
##layer=vector
##field=field layer
##nortest=group
library(nortest)
>lillie.test(layer[[field]])
The output of the last line is printed, but the output of the first is not (and neither are the outputs from other command
lines added automatically by QGIS).
If your algorithm creates any kind of graphics (using the plot() method), add the following line
(output_plots_to_html used to be showplots):
##output_plots_to_html
This will cause QGIS to redirect all R graphical outputs to a temporary file, which will be opened once R execution
has finished.
Both graphics and console results will be available through the processing results manager.
For more information, please check the R scripts in the official QGIS collection (you download and install them using
the QGIS Resource Sharing plugin, as explained elsewhere). Most of them are rather simple and will greatly help you
understand how to create your own scripts.
Poznámka: The sf, rgdal and raster libraries are loaded by default, so you do not have to add the corresponding
library() commands. However, other libraries that you might need have to be explicitly loaded by typing:
library(ggplot2) (to load the ggplot2 library). If the package is not already installed on your machine,
Processing will try to download and install it. In this way the package will also become available in R Standalone. Be
aware that if the package has to be downloaded, the script may take a long time to run the first time.
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23.10.6 R libraries
The R script sp_test tries to load the R packages sp and raster.
R libraries installed when running sf_test
The R script sf_test tries to load sf and raster. If these two packages are not installed, R may try to load and
install them (and all the libraries that they depend on).
The following R libraries end up in ~/.local/share/QGIS/QGIS3/profiles/default/
processing/rscripts after sf_test has been run from the Processing Toolbox on Ubuntu with
version 2.0 of the Processing R Provider plugin and a fresh install of R 3.4.4 (apt package r-base-core only):
abind, askpass, assertthat, backports, base64enc, BH, bit, bit64, blob,
brew, callr, classInt, cli, colorspace, covr, crayon, crosstalk, curl, DBI,
deldir, desc, dichromat, digest, dplyr, e1071, ellipsis, evaluate, fansi,
farver, fastmap, gdtools, ggplot2, glue, goftest, gridExtra, gtable, highr,
hms, htmltools, htmlwidgets, httpuv, httr, jsonlite, knitr, labeling, later,
lazyeval, leafem, leaflet, leaflet.providers, leafpop, leafsync, lifecycle,
lwgeom, magrittr, maps, mapview, markdown, memoise, microbenchmark, mime,
munsell, odbc, openssl, pillar, pkgbuild, pkgconfig, pkgload, plogr, plyr,
png, polyclip, praise, prettyunits, processx, promises, ps, purrr, R6,
raster, RColorBrewer, Rcpp, reshape2, rex, rgeos, rlang, rmarkdown, RPostgres,
RPostgreSQL, rprojroot, RSQLite, rstudioapi, satellite, scales, sf, shiny,
sourcetools, sp, spatstat, spatstat.data, spatstat.utils, stars, stringi,
stringr, svglite, sys, systemfonts, tensor, testthat, tibble, tidyselect,
tinytex, units, utf8, uuid, vctrs, viridis, viridisLite, webshot, withr,
xfun, XML, xtable
23.10.7 GRASS
Configuring GRASS is not much different from configuring SAGA. First, the path to the GRASS folder has to be
defined, but only if you are running Windows.
By default, the Processing framework tries to configure its GRASS connector to use the GRASS distribution that
ships along with QGIS. This should work without problems for most systems, but if you experience problems, you
might have to configure the GRASS connector manually. Also, if you want to use a different GRASS installation, you
can change the setting to point to the folder where the other version is installed. GRASS 7 is needed for algorithms
to work correctly.
If you are running Linux, you just have to make sure that GRASS is correctly installed, and that it can be run without
problem from a terminal window.
GRASS algorithms use a region for calculations. This region can be defined manually using values similar to the ones
found in the SAGA configuration, or automatically, taking the minimum extent that covers all the input layers used
to execute the algorithm each time. If the latter approach is the behavior you prefer, just check the Use min covering
region option in the GRASS configuration parameters.
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23.10.8 LAStools
To use LAStools in QGIS, you need to download and install LAStools on your computer and install the LAStools
plugin (available from the official repository) in QGIS.
On Linux platforms, you will need Wine to be able to run some of the tools.
LAStools is activated and configured in the Processing options (Settings ► Options, Processing tab, Providers ►
LAStools), where you can specify the location of LAStools (LAStools folder) and Wine (Wine folder). On Ubuntu,
the default Wine folder is /usr/bin.
23.10.9 OTB Applications
OTB applications are fully supported within the QGIS Processing framework.
OTB (Orfeo ToolBox) is an image processing library for remote sensing data. It also provides applications that provide
image processing functionalities. The list of applications and their documentation are available in OTB CookBook
Poznámka: Note that OTB is not distributed with QGIS and needs to be installed separately. Binary packages for
OTB can be found on the download page.
To configure QGIS processing to find the OTB library:
1. Open the processing settings: Settings ► Options ► Processing (left panel)*
2. You can see OTB under „Providers“:
1. Expand the OTB tab
2. Tick the Activate option
3. Set the OTB folder. This is the location of your OTB installation.
4. Set the OTB application folder. This is the location of your OTB applications (
<PATH_TO_OTB_INSTALLATION>/lib/otb/applications)
5. Click „ok“ to save the settings and close the dialog.
If settings are correct, OTB algorithms will be available in the Processing Toolbox.
Documentation of OTB settings available in QGIS Processing
• Activate: This is a checkbox to activate or deactivate the OTB provider. An invalid OTB setting will uncheck
this when saved.
• OTB folder: This is the directory where OTB is available.
• OTB application folder: This is the location(s) of OTB applications.
Multiple paths are allowed.
• Logger level (optional): Level of logger to use by OTB applications.
The level of logging controls the amount of detail printed during algorithm execution. Possible values for
logger level are INFO, WARNING, CRITICAL, DEBUG. This value is INFO by default. This is an advanced
user configuration.
• Maximum RAM to use (optional): by default, OTB applications use all available system RAM.
You can, however, instruct OTB to use a specific amount of RAM (in MB) using this option. A value of 256
is ignored by the OTB processing provider. This is an advanced user configuration.
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• Geoid file (optional): Path to the geoid file.
This option sets the value of the elev.dem.geoid and elev.geoid parameters in OTB applications. Setting this
value globally enables users to share it across multiple processing algorithms. Empty by default.
• SRTM tiles folder (optional): Directory where SRTM tiles are available.
SRTM data can be stored locally to avoid downloading of files during processing. This option sets the value of
elev.dem.path and elev.dem parameters in OTB applications. Setting this value globally enables users to share
it across multiple processing algorithms. Empty by default.
Compatibility between QGIS and OTB versions
All OTB versions (from OTB 6.6.1) are compatible with the latest QGIS version.
Troubleshoot
If you have issues with OTB applications in QGIS Processing, please open an issue on the OTB bug tracker, using
the qgis label.
Additional information about OTB and QGIS can be found here
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Processing providers and algorithms
Processing algorithms and their parameters (as presented in the user interface) are documented here.
24.1 QGIS algorithm provider
QGIS algorithm provider implements various analysis and geoprocessing operations using mostly only QGIS API.
So almost all algorithms from this provider will work „out of the box“ without any additional configuration.
This provider incorporates some algorithms from plugins and also adds its own algorithms.
24.1.1 Cartography
Align points to features
Calculates the rotation required to align point features with their nearest feature from another reference layer. A new
field is added to the output layer which is filled with the angle (in degrees, clockwise) to the nearest reference feature.
Optionally, the output layer’s symbology can be set to automatically use the calculated rotation field to rotate marker
symbols. If desired, a maximum distance to use when aligning points can be set, to avoid aligning isolated points to
distant features.
Rada: This algorithm is designed for use cases like aligning building point symbols to follow the nearest road
direction.
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Parameters
Label Název Type Popis
Input layer INPUT [vector: point] Point features to calculate the rotation for
Reference layer REFERENCE_LAYER[vector: any] Layer to find the closest feature from for
rotation calculation
Maximum
distance to
consider
Optional
MAX_DISTANCE [number]
Default: Not set
If no reference feature is found within this
distance, no rotation is assigned to the point
feature.
Angle field name FIELD_NAME [string]
Default: ‚rotation‘
Field in which to store the rotation value.
Automatically
apply symbology
APPLY_SYMBOLOGY[boolean]
Default: True
Rotates the symbol marker of the features
using the angle field value
Aligned layer OUTPUT [vector: point]
Default: [Save
to temporary
file]
Specify the rotated output vector layer. One
of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to Database Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Aligned layer OUTPUT [vector: point] The point layer appended with a rotation
field. If loaded to QGIS, it is applied
by default the input layer symbology,
with a data-defined rotation of its marker
symbol.
Python code
Algorithm ID: native:angletonearest
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Combine style databases
Combines multiple QGIS style databases into a single style database. If items of the same type with the same name
exist in different source databases these will be renamed to have unique names in the output combined database.
Viz také:
Create style database from project
Parameters
Label Název Type Popis
Input databases INPUT [file] [list] Files containing QGIS style items
Objects to
combine
OBJECTS [enumeration] [list] Types of style items in the input databases
you would like to put in the new database.
These can be:
• 0 — Symbols
• 1 — Color ramps
• 2 — Text formats
• 3 — Label settings
Output style
database
OUTPUT [file]
Default: [Save
to temporary
file]
Output .XML file combining the selected
style items. One of:
• Save to a Temporary File
• Save to File…
Outputs
Label Název Type Popis
Color ramp count COLORRAMPS [number]
Label settings
count
LABELSETTINGS [number]
Output style
database
OUTPUT [file] Output .XML file combining the selected
style items
Symbol count SYMBOLS [number]
Text format count TEXTFORMATS [number]
Python code
Algorithm ID: native:combinestyles
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Create categorized renderer from styles
Sets a vector layer’s renderer to a categorized renderer using matching symbols from a style database. If no style file
is specified, symbols from the user’s current symbol library are used instead.
A specified expression or field is used to create categories for the renderer. Each category is individually matched to
the symbols which exist within the specified QGIS XML style database. Whenever a matching symbol name is found,
the category’s symbol will be set to this matched symbol.
If desired, outputs can also be tables containing lists of the categories which could not be matched to symbols, and
symbols which were not matched to categories.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Vector layer to apply a categorized style to
Categorize using
expression
FIELD [expression] Field or expression to categorize the
features
Style database
(leave blank to use
saved symbols)
STYLE [file] File (.XML) containing the symbols to
apply to the input layer categories. The file
can be obtained from the Style Manager
Share symbols tool. If no file is specified,
QGIS local symbols library is used.
Use case-sensitive
match to symbol
names
CASE_SENSITIVE [boolean]
Default: False
If True (checked), applies a case sensitive
comparison between the categories and
symbols names
Ignore non-
-alphanumeric
characters while
matching
TOLERANT [boolean]
Default: False
If True (checked), non-alphanumeric
characters in the categories and symbols
names will be ignored, allowing greater
tolerance during the match.
Non-matching
categories
Optional
NON_MATCHING_CATEGORIES[table]
Default: [Skip
output]
Output table for categories which do not
match any symbol in the database. One of:
• Skip Output
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to Database Table…
The file encoding can also be changed here.
Non-matching
symbol names
Optional
NON_MATCHING_SYMBOLS[table]
Default: [Skip
output]
Output table for symbols from the provided
style database which do not match any
category. One of:
• Skip Output
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to Database Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Non-matching
categories
NON_MATCHING_CATEGORIES[table] Lists categories which could not be matched
to any symbol in the provided style database
Non-matching
symbol names
NON_MATCHING_SYMBOLS[table] Lists symbols from the provided style
database which could not match any
category
Categorized layer OUTPUT [same as input] The input vector layer with the categorized
style applied. No new layer is output.
Python code
Algorithm ID: native:categorizeusingstyle
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Create style database from project
Extracts all style objects (symbols, color ramps, text formats and label settings) from a QGIS project.
The extracted symbols are saved to a QGIS style database (XML format), which can be managed and imported via the
Style Manager dialog.
Viz také:
Combine style databases
Parameters
Label Název Type Popis
Input project
(leave blank to use
current)
Optional
INPUT [file] A QGIS project file to extract the style items
from
Objects to extract OBJECTS [enumeration] [list] Types of style items in the input project you
would like to put in the new database. These
can be:
• 0 — Symbols
• 1 — Color ramps
• 2 — Text formats
• 3 — Label settings
Output style
database
OUTPUT [file]
Default: [Save
to temporary
file]
Specify the output .XML file for the
selected style items. One of:
• Save to a Temporary File
• Save to File…
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Outputs
Label Název Type Popis
Color ramp count COLORRAMPS [number] Number of color ramps
Label settings
count
LABELSETTINGS [number] Number of label settings
Output style
database
OUTPUT [file] Output .XML file for the selected style
items
Symbol count SYMBOLS [number] Number of symbols
Text format count TEXTFORMATS [number] Number of text formats
Python code
Algorithm ID: native:stylefromproject
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Export atlas layout as image
Exports the atlas of a print layout as image files (e.g. PNG or JPEG images).
If a coverage layer is set, the selected layout’s atlas settings exposed in this algorithm will be overwritten. In this case,
an empty filter or sort by expression will turn those settings off.
Parameters
Basic parameters
Label Název Type Popis
Atlas layout LAYOUT [layout] Layout to export
Coverage layer
Optional
COVERAGE_LAYER [vector: any] Layer to use to generate the atlas
Filter expression FILTER_EXPRESSION[expression] Expression to use to filter out atlas features
Sort expression
Optional
SORTBY_EXPRESSION[expression] Expression to use to sort the atlas features
Reverse sort order
Optional
SORTBY_REVERSE [boolean] Determines if sorting should be inverted.
Used when a sort expression is provided.
Output filename
expression
FILENAME_EXPRESSION[expression]
Default:
‚output_‘||@atlas_featurenumber
Expression for use to generate filenames
Output folder FOLDER [folder] Destination folder where the images will be
generated
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Advanced parameters
Label Název Type Popis
Map layers to
assign to unlocked
map item(s)
Optional
LAYERS [enumeration]
[layer]
Layers to display in the map item(s) whose
contents are not locked
Image format EXTENSION [list]
Default: png
File format of the generated output(s). The
list of available formats varies depending on
OS and installed drivers.
DPI
Optional
DPI
Default: Not set
[number] DPI of the output file(s). If not set, the value
in the print layout settings will be used.
Generate world
file
GEOREFERENCE [boolean]
Default: True
Determines if a world file should be
generated
Export RDF
metadata
INCLUDE_METADATA[boolean]
Default: True
Determines if RDF metadata (title, author,
…) should be generated
Enable
antialiasing
ANTIALIAS [boolean]
Default: True
Determines if antialiasing should be
enabled
Outputs
Label Název Type Popis
Image file OUTPUT [file] Image files generated by the atlas layout
Python code
Algorithm ID: native:atlaslayouttoimage
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Export atlas layout as PDF
Exports the atlas of a print layout as a PDF file(s).
If a coverage layer is set, the selected layout’s atlas settings exposed in this algorithm will be overwritten. In this case,
an empty filter or sort by expression will turn those settings off.
Parameters
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Basic parameters
Label Název Type Popis
Atlas layout LAYOUT [layout] Layout to export
Coverage layer
Optional
COVERAGE_LAYER [vector: any] Layer to use to generate the atlas
Filter expression FILTER_EXPRESSION[expression] Expression to use to filter out atlas features
Sort expression
Optional
SORTBY_EXPRESSION[expression] Expression to use to sort the atlas features
Reverse sort order
Optional
SORTBY_REVERSE [boolean] Determines if sorting should be inverted.
Used when a sort expression is provided.
Advanced parameters
Label Název Type Popis
Map layers to
assign to unlocked
map item(s)
Optional
LAYERS [enumeration]
[layer]
Layers to display in the map item(s) whose
contents are not locked
DPI
Optional
DPI
Default: Not set
[number] DPI of the output file(s). If not set, the value
in the print layout settings will be used.
Always export
as vectors
FORCE_VECTOR [boolean]
Default: False
Determines if vectorial data should be left
as vectors
Append
georeference
information
GEOREFERENCE [boolean]
Default: True
Determines if a world file should be
generated
Export RDF
metadata
INCLUDE_METADATA[boolean]
Default: True
Determines if RDF metadata (title, author,
…) should be generated
Disable tiled
raster layer
exports
DISABLE_TILED [boolean]
Default: False
Determines if raster should be tiled
Simplify
geometries to
reduce output file
size
SIMPLIFY [boolean]
Default: True
Determines if geometries should be
simplified to reduce output file size
Text export TEXT_FORMAT [list]
Default: 0
Determines if text should be exported
as path or text objects. Possible options are:
• 0 - Always export text as paths
(recommended)
• 1 - Always export texts as text objects
PDF file OUTPUT [file]
Default: [Save to
temporary file]
Name (including path) of the output file.
One of:
• Save to a Temporary File
• Save to File…
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Outputs
Label Název Type Popis
PDF file OUTPUT [file] PDF file corresponding to the exported atlas
layout
Python code
Algorithm ID: native:atlaslayouttopdf
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Export print layout as image
Exports a print layout as an image file (e.g. PNG or JPEG images)
Parameters
Basic parameters
Label Název Type Popis
Print layout LAYOUT [layout] Layout to export
Image file OUTPUT [file]
Default: [Save to
temporary file]
Name (including path) of the output file.
One of:
• Save to a Temporary File
• Save to File…
Advanced parameters
Label Název Type Popis
Map layers to
assign to unlocked
map item(s)
Optional
LAYERS [enumeration]
[layer]
Layers to display in the map item(s) whose
contents are not locked
DPI
Optional
DPI
Default: Not set
[number] DPI of the output file(s). If not set, the value
in the print layout settings will be used.
Generate world
file
GEOREFERENCE [boolean]
Default: True
Determines if a world file should be
generated
Export RDF
metadata
INCLUDE_METADATA[boolean]
Default: True
Determines if RDF metadata (title, author,
…) should be generated
Enable
antialiasing
ANTIALIAS [boolean]
Default: True
Determines if antialiasing should be
enabled
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Outputs
Label Název Type Popis
Image file OUTPUT [file] Image file corresponding to the exported
print layout
Python code
Algorithm ID: native:printlayouttoimage
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Export print layout as pdf
Exports a print layout as a PDF file.
Parameters
Basic parameters
Label Název Type Popis
Print Layout LAYOUT [layout] Layout to export
PDF file OUTPUT [file]
Default: [Save to
temporary file]
Name (including path) of the output file.
One of:
• Save to a Temporary File
• Save to File…
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Advanced parameters
Label Název Type Popis
Map layers to
assign to unlocked
map item(s)
Optional
LAYERS [enumeration]
[layer]
Layers to display in the map item(s) whose
contents are not locked
DPI
Optional
DPI
Default: Not set
[number] DPI of the output file(s). If not set, the value
in the print layout settings will be used.
Always export
as vectors
FORCE_VECTOR [boolean]
Default: False
Determines if vectorial data should be left
as vectors
Append
georeference
information
GEOREFERENCE [boolean]
Default: True
Determines if a world file should be
generated
Export RDF
metadata
INCLUDE_METADATA[boolean]
Default: True
Determines if RDF metadata (title, author,
…) should be generated
Disable tiled
raster layer
exports
DISABLE_TILED [boolean]
Default: False
Determines if raster should be tiled
Simplify
geometries to
reduce output file
size
SIMPLIFY [boolean]
Default: True
Determines if geometries should be
simplified to reduce output file size
Text export TEXT_FORMAT [list]
Default: 0
Determines if text should be exported
as path or text objects. Possible options are:
• 0 - Always export text as paths
(recommended)
• 1 - Always export texts as text objects
Export layers
as separate PDF
files
SEPARATE_LAYERS[boolean]
Default: False
If True, then a separate PDF file will be
created per layer per map item in the layout.
Additionally, separate PDF files may be
created for other complex layout items,
resulting in a set of PDF files which contain
logical atomic components of the layout.
Outputs
Label Název Type Popis
PDF file OUTPUT [file] PDF file(s) corresponding to the exported
print layout
Python code
Algorithm ID: native:printlayouttopdf
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Print layout map extent to layer
Creates a polygon layer containing the extent of a print layout map item (or items), with attributes specifying the map
size (in layout units, i.e. the reference map units), scale and rotation.
If the map item parameter is specified, then only the matching map extent will be exported. If it is not specified, all
map extents from the layout will be exported.
Optionally, a specific output CRS can be specified. If it is not specified, the original map item CRS will be used.
Parameters
Basic parameters
Label Název Type Popis
Print layout LAYOUT [enumeration] A print layout in the current project
Map item
Optional
MAP [enumeration]
Default: All the map
items
The map item(s) whose information you
want to extract. If none is provided then all
the map items are processed.
Extent OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output vector layer for the
extent(s). One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to Database Table…
The file encoding can also be changed here.
Advanced parameters
Label Název Type Popis
Overrride CRS
Optional
CRS [crs]
Default: The layout
CRS
Select the CRS for the layer in which the
information will be reported.
Outputs
Label Název Type Popis
Map height HEIGHT [number]
Extent OUTPUT [vector: polygon] Output polygon vector layer containing
extents of all the input layout map item(s)
Map rotation ROTATION [number]
Map scale SCALE [number]
Map width WIDTH [number]
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Python code
Algorithm ID: native:printlayoutmapextenttolayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Set layer style
Applies a provided style to a layer. The style must be defined in a QML file.
No new output are created: the style is immediately assigned to the layer.
Parameters
Label Název Type Popis
Input Layer INPUT [layer] Input layer you want to apply the style to
Style file STYLE [file] Path to the .qml file of the style
Outputs
Label Název Type Popis
OUTPUT [same as input] The input layer with the new style assigned.
No new layer is created.
Python code
Algorithm ID: native:setlayerstyle
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Topological coloring
Assigns a color index to polygon features in such a way that no adjacent polygons share the same color index, whilst
minimizing the number of colors required.
The algorithm allows choice of method to use when assigning colors.
A minimum number of colors can be specified if desired. The color index is saved to a new attribute named color_id.
The following example shows the algorithm with four different colors chosen; as you can see each color class has the
same amount of features.
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Obr. 24.1: Topological colors example
Parameters
Label Název Type Popis
Input layer INPUT [vector: polygon] The input polygon layer
Minimum number
of colors
MIN_COLORS [number]
Default: 4
The minimum number of colors to assign.
Minimum 1, maximum 1000.
Minimum
distance between
features
MIN_DISTANCE [number]
Default: 0.0
Prevent nearby (but non-touching) features
from being assigned equal colors. Minimum
0.0.
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Label Název Type Popis
Balance color
assignment
BALANCE [enumeration]
Default: 0
Options are:
• 0 — By feature count
Attempts to assign colors so that the
count of features assigned to each
individual color index is balanced.
• 1 — By assigned area
Assigns colors so that the total area
of features assigned to each color
is balanced. This mode can be useful
to help avoid large features resulting
in one of the colors appearing more
dominant on a colored map.
• 2 — By distance between colors
Assigns colors in order to maximize
the distance between features of the
same color. This mode helps to create
a more uniform distribution of colors
across a map.
Colored OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to Database Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Colored OUTPUT [vector: polygon] Polygon vector layer with an added
color_id column
Python code
Algorithm ID: qgis:topologicalcoloring
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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24.1.2 Databáze
Export to PostgreSQL
Exports a vector layer to a PostgreSQL database, creating a new relation. If a relation with the same name exists,
it can be removed before the new relation is created. Prior to this a connection between QGIS and the PostgreSQL
database has to be created (see eg Creating a stored Connection).
Parameters
Label Název Type Popis
Layer to import INPUT [vector: any] Vector layer to add to the database
Database
(connection name)
DATABASE [string] Name of the database connection (not the
database name). Existing connections will
be shown in the combobox.
Schema (schema
name)
Optional
SCHEMA [string]
Default: ‚public‘
Name of the schema to store the data. It can
be a new one or already exist.
Table to import to
(leave blank to use
layer name)
Optional
TABLENAME [string]
Default: ‚‘
Defines a table name for the imported
vector file. If nothing is added, the layer
name will be used.
Primary key field
Optional
PRIMARY_KEY [tablefield: any] Sets the primary key field from an existing
field in the vector layer. A column with
unique values can be used as Primary key
for the database.
Geometry column GEOMETRY_COLUMN[string]
Default: ‚geom‘
Defines the name of the geometry column
in the new PostGIS table. Geometry
information for the features is stored in this
column.
Encoding
Optional
ENCODING [string]
Default: ‚UTF-8‘
Defines the encoding of the output layer
Overwrite OVERWRITE [boolean]
Default: True
If the specified table exists, setting this
option to True will make sure that it
is deleted and a new table will be created
before the features are added. If this option
is False and the table exists, the algorithm
will throw an exception („relation already
exists“).
Create spatial
index
CREATEINDEX [boolean]
Default: True
Specifies whether to create a spatial index
or not
Convert field
names to
lowercase
LOWERCASE_NAMES[boolean]
Default: True
Converts the field names of the input vector
layer to lowercase
Drop length
constraint on
character fields
DROP_STRING_LENGTH[boolean]
Default: False
Should length constraints on character fields
be dropped or not
Create single-part
geometries instead
of multi-part
FORCE_SINGLEPART[boolean]
Default: False
Should the features of the output layer
be single-part instead of multi-part. By
default the existing geometries information
are preserved.
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Outputs
The algorithm has no output.
Python code
Algorithm ID: qgis:importintopostgis
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Export to SpatiaLite
Exports a vector layer to a SpatiaLite database. Prior to this a connection between QGIS and the SpatiaLite database
has to be created (see eg SpatiaLite Layers).
Parameters
Label Název Type Popis
Layer to import INPUT [vector: any] Vector layer to add to the database
File database DATABASE [vector: any] The SQLite/SpatiaLite database file to
connect to
Table to import to
(leave blank to use
layer name)
Optional
TABLENAME [string]
Default: ‚‘
Defines the table name for the imported
vector file. If nothing is specified, the layer
name will be used.
Primary key field
Optional
PRIMARY_KEY [tablefield: any] Use a field in the input vector layer as the
primary key
Geometry column GEOMETRY_COLUMN[string]
Default: ‚geom‘
Defines the name of the geometry column
in the new SpatiaLite table. Geometry
information for the features is stored in this
column.
Encoding
Optional
ENCODING [string]
Default: ‚UTF-8‘
Defines the encoding of the output layer
Overwrite OVERWRITE [boolean]
Default: True
If the specified table exists, setting this
option to True will make sure that it
is deleted and a new table will be created
before the features of the layer is added.
If this option is False and the table
exists, the algorithm will throw an exception
(„table already exists“).
Create spatial
index
CREATEINDEX [boolean]
Default: True
Specifies whether to create a spatial index
or not
Convert field
names to
lowercase
LOWERCASE_NAMES[boolean]
Default: True
Convert the field names of the input vector
layer to lowercase
Drop length
constraint on
character fields
DROP_STRING_LENGTH[boolean]
Default: False
Should length constraints on character fields
be dropped or not
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Label Název Type Popis
Create single-part
geometries instead
of multi-part
FORCE_SINGLEPART[boolean]
Default: False
Should the features of the output layer
be single-part instead of multi-part. By
default the existing geometries information
are preserved.
Outputs
The algorithm has no output.
Python code
Algorithm ID: qgis:importintospatialite
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Package layers
Adds layers to a GeoPackage.
If the GeoPackage exists and Overwrite existing GeoPackage is checked, it will be overwritten (removed
and recreated). If the GeoPackage exists and Overwrite existing GeoPackage is not checked, the layer
will be appended.
Parameters
Label Název Type Popis
Input layers LAYERS [vector: any] [list] The (vector) layers to import into the
GeoPackage. Raster layers are not
supported. If a raster layer is added,
a QgsProcessingException will be
thrown.
Overwrite existing
GeoPackage
OVERWRITE [boolean]
Default: False
If the specified GeoPackage exists, setting
this option to True will make sure that it
is deleted and a new one will be created
before the layers are added. If set to
False, layers will be appended.
Save layer styles
into GeoPackage
SAVE_STYLES [boolean]
Default: True
Save the layer styles
Destination
GeoPackage
OUTPUT [file]
Default: [Save
to temporary
file]
Specify where to store the GeoPackage file.
One of
• Save to a Temporary File
• Save to File…
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Outputs
Label Název Type Popis
Layers within new
package
OUTPUT_LAYERS [string] [list] The list of layers added to the GeoPackage.
Python code
Algorithm ID: native:package
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
PostgreSQL execute and load SQL
Allows a SQL database query to be performed on a PostgreSQL database connected to QGIS and loads the result.
The algorithm won’t create a new layer: it is designed to run queries on the layer itself.
Example
1. Set all the values of an existing field to a fixed value. The SQL query string will be:
UPDATE your_table SET field_to_update=20;
In the example above, the values of the field field_to_update of the table your_table will be all set
to 20.
2. Create a new area column and calculate the area of each feature with the ST_AREA PostGIS function.
-- Create the new column "area" on the table your_table"
ALTER TABLE your_table ADD COLUMN area double precision;
-- Update the "area" column and calculate the area of each feature:
UPDATE your_table SET area=ST_AREA(geom);
Viz také:
PostgreSQL execute SQL, Execute SQL, SpatiaLite execute SQL
Parameters
Label Název Type Popis
Database
(connection name)
DATABASE [string] The database connection (not the database
name). Existing connections will be shown
in the combobox.
SQL query SQL [string] Defines the SQL query, for example
'UPDATE my_table SET
field=10'.
Unique ID field
name
ID_FIELD [string]
Default: id
Sets the primary key field (a column in the
result table)
Geometry field
name
Optional
GEOMETRY_FIELD [string]
Default: ‚geom‘
Name of the geometry column (a column in
the result table)
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Outputs
Label Název Type Popis
SQL layer OUTPUT [vector: any] The resulting vector layer to be loaded into
QGIS.
Python code
Algorithm ID: qgis:postgisexecuteandloadsql
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
PostgreSQL execute SQL
Allows a SQL database query to be performed on a PostgreSQL database connected to QGIS. The algorithm won’t
create a new layer: it is designed to run queries on the layer itself.
Example
1. Set all the values of an existing field to a fixed value. The SQL query string will be:
UPDATE your_table SET field_to_update=20;
In the example above, the values of the field field_to_update of the table your_table will be all set
to 20.
2. Create a new area column and calculate the area of each feature with the ST_AREA PostGIS function.
-- Create the new column "area" on the table your_table"
ALTER TABLE your_table ADD COLUMN area double precision;
-- Update the "area" column and calculate the area of each feature:
UPDATE your_table SET area=ST_AREA(geom);
Viz také:
PostgreSQL execute and load SQL, Execute SQL, SpatiaLite execute SQL
Parameters
Label Název Type Popis
Database
(connection name)
DATABASE [string] The database connection (not the database
name). Existing connections will be shown
in the combobox.
SQL query SQL [string] Defines the SQL query, for example
'UPDATE my_table SET
field=10'.
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Outputs
No output is created. The SQL query is executed in place.
Python code
Algorithm ID: native:postgisexecutesql
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
SpatiaLite execute SQL
Allows a SQL database query to be performed on a SpatiaLite database. The algorithm won’t create a new layer: it
is designed to run queries on the layer itself.
Viz také:
PostgreSQL execute SQL, Execute SQL
For some SQL query examples see PostGIS SQL Query Examples.
Parameters
Label Název Type Popis
File Database DATABASE [vector] The SQLite/SpatiaLite database file to
connect to
SQL query SQL [string]
Default: ‚‘
Defines the SQL query, for example
'UPDATE my_table SET
field=10'.
Outputs
No output is created. The SQL query is executed in place.
Python code
Algorithm ID: native:spatialiteexecutesql
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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SpatiaLite execute SQL (registered DB)
Allows a SQL database query to be performed on a SpatiaLite database connected to QGIS. The algorithm won’t
create a new layer: it is designed to run queries on the layer itself.
Viz také:
PostgreSQL execute SQL, Execute SQL
For some SQL query examples see PostGIS SQL Query Examples.
Parameters
Label Název Type Popis
Database DATABASE [enumeration]
Default: not set
Select a SQLite/SpatiaLite database
connected to the current session
SQL query SQL [string]
Default: ‚‘
Defines the SQL query, for example
'UPDATE my_table SET
field=10'.
Outputs
No output is created. The SQL query is executed in place.
Python code
Algorithm ID: native:spatialiteexecutesqlregistered
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.1.3 File tools
Download file
Downloads a file specified using a URL (using for instance http: or file:). In other words you can copy/paste
a URL and download the file.
Parameters
Label Název Type Popis
URL URL [string] The URL of the file to download.
File destination OUTPUT [string]
Default: [Save
to temporary
file]
Specification of the file destination. One of:
• Skip Output
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
File destination OUTPUT [string] The location of the downloaded file
Python code
Algorithm ID: qgis:filedownloader
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.1.4 Interpolation
Heatmap (kernel density estimation)
Creates a density (heatmap) raster of an input point vector layer using kernel density estimation.
The density is calculated based on the number of points in a location, with larger numbers of clustered points resulting
in larger values. Heatmaps allow easy identification of hotspots and clustering of points.
Parameters
Label Název Type Popis
Point layer INPUT [vector: point] Point vector layer to use for the heatmap
Radius RADIUS [number]
Default: 100.0
Heatmap search radius (or kernel
bandwidth) in map units. The radius
specifies the distance around a point at
which the influence of the point will be felt.
Larger values result in greater smoothing,
but smaller values may show finer details
and variation in point density.
Output raster size PIXEL_SIZE [number]
Default: 0.1
Pixel size of the output raster layer in layer
units.
In the GUI, the size can be specified by the
number of rows (Number of rows)
/ columns (Number of columns) or
the pixel size( Pixel Size X / Pixel
Size Y). Increasing the number of rows
or columns will decrease the cell size and
increase the file size of the output raster.
The values in Rows, Columns, Pixel
Size X and Pixel Size Y will
be updated simultaneously - doubling the
number of rows will double the number of
columns, and the cell size will be halved.
The extent of the output raster will remain
the same (approximately).
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Label Název Type Popis
Radius from field
Optional
RADIUS_FIELD [tablefield:
numeric]
Sets the search radius for each feature from
an attribute field in the input layer.
Weight from field
Optional
WEIGHT_FIELD [tablefield:
numeric]
Allows input features to be weighted by an
attribute field. This can be used to increase
the influence certain features have on the
resultant heatmap.
Kernel shape KERNEL [enumeration]
Default: 0
Controls the rate at which the influence
of a point decreases as the distance from
the point increases. Different kernels decay
at different rates, so a triweight kernel
gives features greater weight for distances
closer to the point then the Epanechnikov
kernel does. Consequently, triweight results
in “sharper” hotspots and Epanechnikov
results in “smoother” hotspots.
There are many shapes available (please
see the Wikipedia page for further
information):
• 0 — Quartic
• 1 — Triangular
• 2 — Uniform
• 3 — Triweight
• 4 — Epanechnikov
Decay ratio
(Triangular
kernels only)
Optional
DECAY [number]
Default: 0.0
Can be used with Triangular kernels to
further control how heat from a feature
decreases with distance from the feature.
• A value of 0 (=minimum) indicates
that the heat will be concentrated in
the center of the given radius and
completely extinguished at the edge.
• A value of 0.5 indicates that pixels at
the edge of the radius will be given
half the heat as pixels at the center of
the search radius.
• A value of 1 means the heat is spread
evenly over the whole search radius
circle. (This is equivalent to the
‘Uniform’ kernel.)
• A value greater than 1 indicates that
the heat is higher towards the edge of
the search radius than at the center.
Output value
scaling
OUTPUT_VALUE [enumeration]
Default: Raw
Allow to change the values of the output
heatmap raster. One of:
• 0 — Raw
• 1 — Scaled
Heatmap OUTPUT [raster]
Default: [Save
to temporary
file]
Specify the output raster layer with kernel
density values. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Heatmap OUTPUT [raster] Raster layer with kernel density values
Example: Creating a Heatmap
For the following example, we will use the airports vector point layer from the QGIS sample dataset
(see Downloading sample data). Another excellent QGIS tutorial on making heatmaps can be found at
http://qgistutorials.com.
In Obr. 24.2, the airports of Alaska are shown.
Obr. 24.2: Airports of Alaska
1. Open the Heatmap (Kernel Density Estimation) algorithm from the QGIS Interpolation group
2. In the Point layer field, select airports from the list of point layers loaded in the current project.
3. Change the Radius to 1000000 meters.
4. Change the Pixel size X to 1000. The Pixel size Y, Rows and Columns will be automatically updated.
5. Click on Run to create and load the airports heatmap (see Obr. 24.4).
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Obr. 24.3: The Heatmap Dialog
QGIS will generate the heatmap and add it to your map window. By default, the heatmap is shaded in greyscale,
with lighter areas showing higher concentrations of airports. The heatmap can now be styled in QGIS to improve its
appearance.
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Obr. 24.4: The heatmap after loading looks like a grey surface
1. Open the properties dialog of the heatmap_airports layer (select the layer heatmap_airports, open
the context menu with the right mouse button and select Properties).
2. Select the Symbology tab.
3. Change the Render type to ‚Singleband pseudocolor‘.
4. Select a suitable Color ramp , for instance YlOrRd.
5. Click the Classify button.
6. Press OK to update the layer.
The final result is shown in Obr. 24.5.
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Obr. 24.5: Styled heatmap of airports of Alaska
Python code
Algorithm ID: qgis:heatmapkerneldensityestimation
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
IDW Interpolation
Generates an Inverse Distance Weighted (IDW) interpolation of a point vector layer.
Sample points are weighted during interpolation such that the influence of one point relative to another declines with
distance from the unknown point you want to create.
The IDW interpolation method also has some disadvantages: the quality of the interpolation result can decrease, if
the distribution of sample data points is uneven.
Furthermore, maximum and minimum values in the interpolated surface can only occur at sample data points.
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Parameters
Label Název Type Popis
Input layer(s) INTERPOLATION_DATA[string] Vector layer(s) and field(s) to use for the
interpolation, coded in a string (see the
ParameterInterpolationData
class in InterpolationWidgets for more
details).
The following GUI elements are provided
to compose the interpolation data string:
• Vector layer [vector: any]
• Interpolation attribute [tablefield:
numeric]: Attribute to use in the
interpolation
• Use Z-coordinate for interpolation
[boolean]: Uses the layer’s stored
Z values (Default: False)
For each of the added layer-field
combinations, a type can be chosen:
• Points
• Structured lines
• Break lines
In the string, the layer-field elements are
separated by '::|::'. The sub-elements
of the layer-field elements are separated by
'::~::'.
Distance
coefficient P
DISTANCE_COEFFICIENT[number]
Default: 2.0
Sets the distance coefficient for the
interpolation. Minimum: 0.0, maximum:
100.0.
Extent (xmin,
xmax, ymin,
ymax)
EXTENT [extent] Extent of the output raster layer. You
have to declare the output extent by either
choosing it from the map canvas, selecting
it from another layer or type it manually.
Output raster size PIXEL_SIZE [number]
Default: 0.1
Pixel size of the output raster layer in layer
units.
In the GUI, the size can be specified by the
number of rows (Number of rows)
/ columns (Number of columns) or
the pixel size( Pixel Size X / Pixel
Size Y). Increasing the number of rows
or columns will decrease the cell size and
increase the file size of the output raster.
The values in Rows, Columns, Pixel
Size X and Pixel Size Y will
be updated simultaneously - doubling the
number of rows will double the number of
columns, and the cell size will be halved.
The extent of the output raster will remain
the same (approximately).
Interpolated OUTPUT [raster]
Default: [Save
to temporary
file]
Raster layer of interpolated values. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Interpolated OUTPUT [raster] Raster layer of interpolated values
Python code
Algorithm ID: qgis:idwinterpolation
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Line Density
Calculates for each raster cell, the density measure of linear features within a circular neighbourhood. This measure
is obtained by summing all the line segments intersecting the circular neighbourhood and dividing this sum by the
area of such neighbourhood. A weighting factor can be applied to the line segments.
Obr. 24.6: Line density example. Input layer source: Roads Overijssel - The Netherlands (OSM).
Parameters
Label Název Type Popis
Input line layer INPUT [vector: any] Input vector layer containing line features
Weight field WEIGHT [number] Field of the layer containing the weight
factor to use during the calculation
Search Radius RADIUS [number]
Default: 10
Radius of the circular neighbourhood. Units
can be specified here.
Pixel size PIXEL_SIZE [number]
Default: 10
Pixel size of the output raster layer in layer
units. The raster has square pixels.
Line density raster OUTPUT [raster]
Default: [Save
to temporary
file]
The output as a raster layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Line density raster OUTPUT [raster] The output line density raster layer.
Python code
Algorithm ID: native:linedensity
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
TIN Interpolation
Generates a Triangulated Irregular Network (TIN) interpolation of a point vector layer.
With the TIN method you can create a surface formed by triangles of nearest neighbor points. To do this, circumcircles
around selected sample points are created and their intersections are connected to a network of non overlapping and
as compact as possible triangles. The resulting surfaces are not smooth.
The algorithm creates both the raster layer of the interpolated values and the vector line layer with the triangulation
boundaries.
Parameters
Label Název Type Popis
Input layer(s) INTERPOLATION_DATA[string] Vector layer(s) and field(s) to use for the
interpolation, coded in a string (see the
ParameterInterpolationData
class in InterpolationWidgets for more
details).
The following GUI elements are provided
to compose the interpolation data string:
• Vector layer [vector: any]
• Interpolation attribute [tablefield:
numeric]: Attribute to use in the
interpolation
• Use Z-coordinate for interpolation
[boolean]: Uses the layer’s stored
Z values (Default: False)
For each of the added layer-field
combinations, a type can be chosen:
• Points
• Structured lines
• Break lines
In the string, the layer-field elements are
separated by '::|::'. The sub-elements
of the layer-field elements are separated by
'::~::'.
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Tabulka 24.11 – pokračujte na předchozí stránce
Label Název Type Popis
Interpolation
method
METHOD [enumeration]
Default: 0
Set the interpolation method to be used.
One of:
• Linear
• Clough-Toucher (cubic)
Extent (xmin,
xmax, ymin,
ymax)
EXTENT [extent] Extent of the output raster layer. You
have to declare the output extent by either
choosing it from the map canvas, selecting
it from another layer or type it manually.
Output raster size PIXEL_SIZE [number]
Default: 0.1
Pixel size of the output raster layer in layer
units.
In the GUI, the size can be specified by the
number of rows (Number of rows)
/ columns (Number of columns) or
the pixel size( Pixel Size X / Pixel
Size Y). Increasing the number of rows
or columns will decrease the cell size and
increase the file size of the output raster.
The values in Rows, Columns, Pixel
Size X and Pixel Size Y will
be updated simultaneously - doubling the
number of rows will double the number of
columns, and the cell size will be halved.
The extent of the output raster will remain
the same (approximately).
Interpolated OUTPUT [raster]
Default: [Save
to temporary
file]
The output TIN interpolation as a raster
layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Triangulation TRIANGULATION [vector: line]
Default: [Skip
output]
The output TIN as a vector layer. One of:
• Skip Output
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
Outputs
Label Název Type Popis
Interpolated OUTPUT [raster] The output TIN interpolation as a raster
layer
Triangulation TRIANGULATION [vector: line] The output TIN as a vector layer.
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Python code
Algorithm ID: qgis:tininterpolation
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.1.5 Layer tools
Extract layer extent
Generates a vector layer with the minimum bounding box (rectangle with N-S orientation) that covers all the input
features.
The output layer contains a single bounding box for the whole input layer.
Obr. 24.7: In red the bounding box of the source layer
Default menu: Vector ► Research Tools
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Parameters
Label Název Type Popis
Layer INPUT [layer] Input layer
Extent OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the polygon vector layer for the
output extent. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Extent OUTPUT [vector: polygon] Output (polygon) vector layer with the
extent (minimum bounding box)
Python code
Algorithm ID: qgis:polygonfromlayerextent
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.1.6 Modeler tools
These tools are only available in the Graphical Modeler. They are not available in the Processing Toolbox.
Conditional branch
Adds a conditional branch into a model, allowing parts of the model to be executed based on the result of an expression
evaluation. Mostly by using tool dependencies to control the flow of a model.
Parameters
Label Název Type Popis
Field BRANCH [string] Name of the condition
Field CONDITION [expression] Expression to evaluate
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Outputs
None.
Python code
Algorithm ID: native:condition
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Load layer into project
Loads a layer to the current project.
Parameters
Label Název Type Popis
Layer INPUT [layer] Layer to load in the legend
Loaded layer
name
NAME [string] Name of the loaded layer
Outputs
Label Název Type Popis
Layer OUTPUT [same as input] The (renamed) loaded layer
Python code
Algorithm ID: qgis:loadlayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Raise exception
Raises an exception and cancels a model’s execution. The exception message can be customized, and optionally an
expression based condition can be specified. If an expression condition is used, then the exception will only be raised
if the expression result is true. A false result indicates that no exception will be raised, and the model execution can
continue uninterrupted.
Parameters
Label Název Type Popis
Message MESSAGE [string] Message to display
Condition CONDITION [expression] Expression to evaluate if true
Outputs
None.
Python code
Algorithm ID: native:raiseexception
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Raise warning
Raises a warning message in the log. The warning message can be customized, and optionally an expression based
condition can be specified. If an expression condition is used, then the warning will only be logged if the expression
result is true. A false result indicates that no warning will be logged.
Parameters
Label Název Type Popis
Message MESSAGE [string] Message to display
Condition CONDITION [expression] Expression to evaluate if true
Outputs
None.
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Python code
Algorithm ID: native:raisewarning
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Rename layer
Renames a layer.
Parameters
Label Název Type Popis
Layer INPUT [layer] Layer to rename
New name NAME [string] The new name of the layer
Outputs
Label Název Type Popis
Layer OUTPUT [same as input] The (renamed) output layer
Python code
Algorithm ID: native:renamelayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Save log to file
Saves the model’s execution log to a file. Optionally, the log can be saved in a HTML formatted version.
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Parameters
Label Název Type Popis
Use HTML USE_HTML [Boolean]
Default: False
Use HTML formatting
Outputs
Label Název Type Popis
File OUTPUT [string] Destination of the log
Python code
Algorithm ID: native:savelog
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Set project variable
Sets an expression variable for the current project.
Parameters
Label Název Type Popis
Variable name NAME [string] Name of the variable
Variable value VALUE [string] Value to be stored
Outputs
None.
Python code
Algorithm ID: native:setprojectvariable
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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String concatenation
Concatenates two strings into a single one in the Processing Modeler.
Parameters
Label Název Type Popis
Input 1 INPUT_1 [string] First string
Input 2 INPUT_2 [string] Second string
Outputs
Label Název Type Popis
Concatenation CONCATENATION [string] The concatenated string
Python code
Algorithm ID: qgis:stringconcatenation
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.1.7 Network analysis
Service area (from layer)
Returns all the edges or parts of edges of a network that can be reached within a distance or a time, starting from
a point layer. This allows evaluation of accessibility within a network, e.g. what are the places I can navigate to on
a road network without spending cost greater than a given value (the cost can be distance or time).
Parameters
Label Název Type Popis
Vector layer
representing
network
INPUT [vector: line] Line vector layer representing the network
to be covered
Vector layer with
start points
START_POINTS [vector: point] Point vector layer whose features are used
as start points to generate the service areas
Path type to
calculate
STRATEGY [enumeration]
Default: 0
The type of path to calculate. One of:
• 0 — Shortest
• 1 — Fastest
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Tabulka 24.13 – pokračujte na předchozí stránce
Label Název Type Popis
Travel cost
(distance for
„Shortest“, time
for „Fastest“)
TRAVEL_COST [number]
Default: 0
The value is estimated as a distance (in the
network layer units) when looking for the
Shortest path and as time (in hours) for the
Fastest path.
Direction field
Optional
DIRECTION_FIELD[tablefield: string]
Default: 0.0
The field used to specify directions for the
network edges.
The values used in this field are specified
with the three parameters Value for
forward direction, Value for
backward direction and Value
for both directions. Forward and
reverse directions correspond to a one-way
edge, „both directions“ indicates a two-way
edge. If a feature does not have
a value in this field, or no field is set then
the default direction setting (provided with
the Default direction parameter)
is used.
Value for forward
direction
Optional
VALUE_FORWARD [string]
Default: ‚‘ (empty
string)
Value set in the direction field to identify
edges with a forward direction
Value for
backward
direction
Optional
VALUE_BACKWARD [string]
Default: ‚‘ (empty
string)
Value set in the direction field to identify
edges with a backward direction
Value for both
directions
Optional
VALUE_BOTH [string]
Default: ‚‘ (empty
string)
Value set in the direction field to identify
bidirectional edges
Default direction
Optional
DEFAULT_DIRECTION[enumeration]
Default: 2
If a feature has no value set in the direction
field or if no direction field is set, then this
direction value is used. One of:
• 0 — Forward direction
• 1 — Backward direction
• 2 — Both directions
Speed field
Optional
SPEED_FIELD [tablefield: string] Field providing the speed value (in km/h)
for the edges of the network when looking
for the fastest path.
If a feature does not have a value in this
field, or no field is set then the default
speed value (provided with the Default
speed parameter) is used.
Default speed
(km/h)
Optional
DEFAULT_SPEED [number]
Default: 50.0
Value to use to calculate the travel time if
no speed field is provided for an edge
Topology
tolerance
Optional
TOLERANCE [number]
Default: 0.0
Two lines with nodes closer than the
specified tolerance are considered
connected
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Include
upper/lower
bound points
INCLUDE_BOUNDS [boolean]
Default: False
Creates a point layer output with two points
for each edge at the boundaries of the
service area. One point is the start of that
edge, the other is the end.
Service area
(lines)
OUTPUT_LINES [vector: line]
Default: [Create
temporary
layer]
Specify the output line layer for the service
area. One of:
• Skip output
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Service area
(boundary nodes)
OUTPUT [vector: point]
Default: [Skip
output]
Specify the output point layer for the
service area boundary nodes. One of:
• Skip output
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Service area
(boundary nodes)
OUTPUT [vector: point] The output point layer with the service area
boundary nodes.
Service area
(lines)
OUTPUT_LINES [vector: line] Line layer representing the parts of the
network that can be serviced by the start
points, for the given cost.
Python code
Algorithm ID: qgis:serviceareafromlayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Service area (from point)
Returns all the edges or parts of edges of a network that can be reached within a given distance or time, starting from
a point feature. This allows the evaluation of accessibility within a network, e.g. what are the places I can navigate to
on a road network without spending a cost greater than a given value (the cost can be distance or time).
Parameters
Label Název Type Popis
Vector layer
representing the
network
INPUT [vector: line] Line vector layer representing the network
to be covered
Start point (x, y) START_POINT [coordinates] Coordinate of the point to calculate the
service area around.
Path type to
calculate
STRATEGY [enumeration]
Default: 0
The type of path to calculate. One of:
• 0 — Shortest
• 1 — Fastest
Travel cost TRAVEL_COST [number]
Default: 0
The value is estimated as a distance (in the
network layer units) when looking for the
Shortest path and as time (in hours) for the
Fastest path.
Advanced
parameters
GUI only Group of advanced network analysis
parameters - see below.
Service area
(lines)
OUTPUT_LINES [vector: line]
Default: [Create
temporary
layer]
Specify the output line layer for the service
area. One of:
• Skip output
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Service area
(boundary nodes)
OUTPUT [vector: point]
Default: [Skip
output]
Specify the output point layer for the
service area boundary nodes. One of:
• Skip output
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Advanced parameters
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Label Název Type Popis
Direction field
Optional
DIRECTION_FIELD[tablefield: string]
Default: 0.0
The field used to specify directions for the
network edges.
The values used in this field are specified
with the three parameters Value for
forward direction, Value for
backward direction and Value
for both directions. Forward and
reverse directions correspond to a one-way
edge, „both directions“ indicates a two-way
edge. If a feature does not have
a value in this field, or no field is set then
the default direction setting (provided with
the Default direction parameter)
is used.
Value for forward
direction
Optional
VALUE_FORWARD [string]
Default: ‚‘ (empty
string)
Value set in the direction field to identify
edges with a forward direction
Value for
backward
direction
Optional
VALUE_BACKWARD [string]
Default: ‚‘ (empty
string)
Value set in the direction field to identify
edges with a backward direction
Value for both
directions
Optional
VALUE_BOTH [string]
Default: ‚‘ (empty
string)
Value set in the direction field to identify
bidirectional edges
Default direction
Optional
DEFAULT_DIRECTION[enumeration]
Default: 2
If a feature has no value set in the direction
field or if no direction field is set, then this
direction value is used. One of:
• 0 — Forward direction
• 1 — Backward direction
• 2 — Both directions
Speed field
Optional
SPEED_FIELD [tablefield: string] Field providing the speed value (in km/h)
for the edges of the network when looking
for the fastest path.
If a feature does not have a value in this
field, or no field is set then the default
speed value (provided with the Default
speed parameter) is used.
Default speed
(km/h)
Optional
DEFAULT_SPEED [number]
Default: 50.0
Value to use to calculate the travel time if
no speed field is provided for an edge
Topology
tolerance
Optional
TOLERANCE [number]
Default: 0.0
Two lines with nodes closer than the
specified tolerance are considered
connected
Include
upper/lower
bound points
INCLUDE_BOUNDS [boolean]
Default: False
Creates a point layer output with two points
for each edge at the boundaries of the
service area. One point is the start of that
edge, the other is the end.
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Outputs
Label Název Type Popis
Service area
(boundary nodes)
OUTPUT [vector: point] The output point layer with the service area
boundary nodes.
Service area
(lines)
OUTPUT_LINES [vector: line] Line layer representing the parts of the
network that can be serviced by the start
point, for the given cost.
Python code
Algorithm ID: qgis:serviceareafrompoint
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Shortest path (layer to point)
Computes the optimal (shortest or fastest) routes from multiple start points defined by a vector layer and a given end
point.
Parameters
Label Název Type Popis
Vector layer
representing
network
INPUT [vector: line] Line vector layer representing the network
to be covered
Path type to
calculate
STRATEGY [enumeration]
Default: 0
The type of path to calculate. One of:
• 0 — Shortest
• 1 — Fastest
Vector layer with
start points
START_POINTS [vector: point] Point vector layer whose features are used
as start points of the routes
End point (x, y) END_POINT [coordinates] Point feature representing the end point of
the routes
Advanced
parameters
GUI only The Advanced parameters group:
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Tabulka 24.18 – pokračujte na předchozí stránce
Label Název Type Popis
Direction field
Optional
DIRECTION_FIELD[tablefield: string]
Default: 0.0
The field used to specify directions for the
network edges.
The values used in this field are specified
with the three parameters Value for
forward direction, Value for
backward direction and Value
for both directions. Forward and
reverse directions correspond to a one-way
edge, „both directions“ indicates a two-way
edge. If a feature does not have
a value in this field, or no field is set then
the default direction setting (provided with
the Default direction parameter)
is used.
Value for forward
direction
Optional
VALUE_FORWARD [string]
Default: ‚‘ (empty
string)
Value set in the direction field to identify
edges with a forward direction
Value for
backward
direction
Optional
VALUE_BACKWARD [string]
Default: ‚‘ (empty
string)
Value set in the direction field to identify
edges with a backward direction
Value for both
directions
Optional
VALUE_BOTH [string]
Default: ‚‘ (empty
string)
Value set in the direction field to identify
bidirectional edges
Default direction
Optional
DEFAULT_DIRECTION[enumeration]
Default: 2
If a feature has no value set in the direction
field or if no direction field is set, then this
direction value is used. One of:
• 0 — Forward direction
• 1 — Backward direction
• 2 — Both directions
Speed field
Optional
SPEED_FIELD [tablefield: string] Field providing the speed value (in km/h)
for the edges of the network when looking
for the fastest path.
If a feature does not have a value in this
field, or no field is set then the default
speed value (provided with the Default
speed parameter) is used.
Default speed
(km/h)
Optional
DEFAULT_SPEED [number]
Default: 50.0
Value to use to calculate the travel time if
no speed field is provided for an edge
Topology
tolerance
Optional
TOLERANCE [number]
Default: 0.0
Two lines with nodes closer than the
specified tolerance are considered
connected
End of the Advanced parameters group
Shortest path OUTPUT [vector: line] Specify the output line layer for the shortest
paths. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Shortest path OUTPUT [vector: line] Line layer of the shortest or fastest path
from each of the start points to the end point
Python code
Algorithm ID: qgis:shortestpathlayertopoint
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Shortest path (point to layer)
Computes the optimal (shortest or fastest) routes between a given start point and multiple end points defined by a point
vector layer.
Parameters
Label Název Type Popis
Vector layer
representing
network
INPUT [vector: line] Line vector layer representing the network
to be covered
Path type to
calculate
STRATEGY [enumeration]
Default: 0
The type of path to calculate. One of:
• 0 — Shortest
• 1 — Fastest
Start point (x, y) START_POINT [coordinates] Point feature representing the start point of
the routes
Vector layer with
end points
END_POINTS [vector: point] Point vector layer whose features are used
as end points of the routes
Direction field
Optional Advanced
DIRECTION_FIELD[tablefield: string]
Default: 0.0
The field used to specify directions for the
network edges.
The values used in this field are specified
with the three parameters Value for
forward direction, Value for
backward direction and Value
for both directions. Forward and
reverse directions correspond to a one-way
edge, „both directions“ indicates a two-way
edge. If a feature does not have
a value in this field, or no field is set then
the default direction setting (provided with
the Default direction parameter)
is used.
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Tabulka 24.19 – pokračujte na předchozí stránce
Label Název Type Popis
Value for forward
direction
Optional Advanced
VALUE_FORWARD [string]
Default: ‚‘ (empty
string)
Value set in the direction field to identify
edges with a forward direction
Value for
backward
direction
Optional Advanced
VALUE_BACKWARD [string]
Default: ‚‘ (empty
string)
Value set in the direction field to identify
edges with a backward direction
Value for both
directions
Optional Advanced
VALUE_BOTH [string]
Default: ‚‘ (empty
string)
Value set in the direction field to identify
bidirectional edges
Default direction
Optional Advanced
DEFAULT_DIRECTION[enumeration]
Default: 2
If a feature has no value set in the direction
field or if no direction field is set, then this
direction value is used. One of:
• 0 — Forward direction
• 1 — Backward direction
• 2 — Both directions
Speed field
Optional Advanced
SPEED_FIELD [tablefield: string] Field providing the speed value (in km/h)
for the edges of the network when looking
for the fastest path.
If a feature does not have a value in this
field, or no field is set then the default
speed value (provided with the Default
speed parameter) is used.
Default speed
(km/h)
Optional Advanced
DEFAULT_SPEED [number]
Default: 50.0
Value to use to calculate the travel time if
no speed field is provided for an edge
Topology
tolerance
Optional Advanced
TOLERANCE [number]
Default: 0.0
Two lines with nodes closer than the
specified tolerance are considered
connected
Shortest path OUTPUT [vector: line] Specify the output line layer for the shortest
paths. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Shortest path OUTPUT [vector: line] Line layer of the shortest or fastest path
from each of the start points to the end point
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Python code
Algorithm ID: qgis:shortestpathpointtolayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Shortest path (point to point)
Computes the optimal (shortest or fastest) route between a given start point and a given end point.
Parameters
Label Název Advanced Type Popis
Vector layer
representing
network
INPUT [vector: line] Line vector layer representing
the network to be covered
Path type to
calculate
STRATEGY [enumeration]
Default: 0
The type of path to calculate.
One of:
• 0 — Shortest
• 1 — Fastest
Start point (x, y) START_POINT [coordinates] Point feature representing the
start point of the routes
End point (x, y) END_POINT [coordinates] Point feature representing the
end point of the routes
Direction field
Optional
DIRECTION_FIELDX [tablefield: string]
Default: 0.0
The field used to specify
directions for the network
edges.
The values used in this field
are specified with the three
parameters Value for
forward direction,
Value for backward
direction and Value
for both directions.
Forward and reverse directions
correspond to a one-way edge,
„both directions“ indicates
a two-way edge. If a feature
does not have a value in this
field, or no field is set then
the default direction setting
(provided with the Default
direction parameter)
is used.
Value for forward
direction
Optional
VALUE_FORWARDX [string]
Default: ‚‘ (empty
string)
Value set in the direction field
to identify edges with a forward
direction
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Tabulka 24.20 – pokračujte na předchozí stránce
Label Název Advanced Type Popis
Value for
backward
direction
Optional
VALUE_BACKWARDX [string]
Default: ‚‘ (empty
string)
Value set in the direction field to
identify edges with a backward
direction
Value for both
directions
Optional
VALUE_BOTH X [string]
Default: ‚‘ (empty
string)
Value set in the direction field to
identify bidirectional edges
Default direction
Optional
DEFAULT_DIRECTIONX [enumeration]
Default: 2
If a feature has no value set
in the direction field or if no
direction field is set, then this
direction value is used. One of:
• 0 — Forward direction
• 1 — Backward direction
• 2 — Both directions
Speed field
Optional
SPEED_FIELD X [tablefield: string] Field providing the speed value
(in km/h) for the edges of the
network when looking for the
fastest path.
If a feature does not have
a value in this field, or no
field is set then the default
speed value (provided with the
Default speed parameter)
is used.
Default speed
(km/h)
Optional
DEFAULT_SPEEDX [number]
Default: 50.0
Value to use to calculate the
travel time if no speed field
is provided for an edge
Topology
tolerance
Optional
TOLERANCE X [number]
Default: 0.0
Two lines with nodes closer
than the specified tolerance are
considered connected
Shortest path OUTPUT [vector: line] Specify the output line layer for
the shortest paths. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be
changed here.
Outputs
Label Název Type Popis
Shortest path OUTPUT [vector: line] Line layer of the shortest or fastest path
from each of the start point to the end point
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Python code
Algorithm ID: qgis:shortestpathpointtopoint
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.1.8 Plots
Bar plot
Creates a bar plot from a category and a layer field.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Category field
name
NAME_FIELD [tablefield: any] Categorical field to use for grouping the
bars (X axis)
Value field VALUE_FIELD [tablefield: any] Value to use for the plot (Y axis).
Bar plot OUTPUT [html]
Default: [Save
to temporary
file]
Specify the HTML file for the plot. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Bar plot OUTPUT [html] HTML file with the plot. Available in the
Processing ► Result Viewer.
Python code
Algorithm ID: qgis:barplot
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Box plot
Creates a box plot from a category field and a numerical layer field.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Category name
field
NAME_FIELD [tablefield: any] Categorical field to use for grouping the
boxes (X axis)
Value field VALUE_FIELD [tablefield: any] Value to use for the plot (Y axis).
Additional
statistic lines
MSD [enumeration]
Default: 0
Additional statistics information to add to
the plot. One of:
• 0 — Show Mean
• 1 — Show Standard Deviation
• 2 — Don’t show mean and standard
deviation
Box plot OUTPUT [html]
Default: [Save
to temporary
file]
Specify the HTML file for the plot. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Box plot OUTPUT [html] HTML file with the plot. Available in the
Processing ► Result Viewer.
Python code
Algorithm ID: qgis:boxplot
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Mean and standard deviation plot
Creates a box plot with mean and standard deviation values.
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Parameters
Label Název Type Popis
Input table INPUT [vector: any] Input vector layer
Category name
field
NAME_FIELD [tablefield: any] Categorical field to use for grouping the
boxes (X axis)
Value field VALUE_FIELD [tablefield: any] Value to use for the plot (Y axis).
Plot OUTPUT [html]
Default: [Save
to temporary
file]
Specify the HTML file for the plot. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Plot OUTPUT [html] HTML file with the plot. Available in the
Processing ► Result Viewer.
Python code
Algorithm ID: qgis:meanandstandarddeviationplot
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Polar plot
Generates a polar plot based on the value of an input vector layer.
Two fields must be entered as parameters: one that defines the category each feature (to group features) and another
one with the variable to plot (this has to be a numeric one).
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Category name
field
NAME_FIELD [tablefield: any] Categorical field to use for grouping the
features (X axis)
Value field VALUE_FIELD [tablefield: any] Value to use for the plot (Y axis).
Polar plot OUTPUT [html]
Default: [Save
to temporary
file]
Specify the HTML file for the plot. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Polar plot OUTPUT [html] HTML file with the plot. Available in the
Processing ► Result Viewer.
Python code
Algorithm ID: qgis:polarplot
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Raster layer histogram
Generates a histogram with the values of a raster layer.
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input raster layer
Band number BAND [raster band] Raster band to use for the histogram
number of bins BINS [number]
Default: 10
The number of bins to use in the histogram
(X axis). Minimum 2.
Histogram OUTPUT [html]
Default: [Save
to temporary
file]
Specify the HTML file for the plot. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Histogram OUTPUT [html] HTML file with the plot. Available in the
Processing ► Result Viewer.
Python code
Algorithm ID: qgis:rasterlayerhistogram
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Vector layer histogram
Generates a histogram with the values of the attribute of a vector layer.
The attribute to use for computing the histogram must be numeric.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Attribute FIELD [tablefield: any] Value to use for the plot (Y axis).
number of bins BINS [number]
Default: 10
The number of bins to use in the histogram
(X axis). Minimum 2.
Histogram OUTPUT [html]
Default: [Save
to temporary
file]
Specify the HTML file for the plot. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Histogram OUTPUT [html] HTML file with the plot. Available in the
Processing ► Result Viewer.
Python code
Algorithm ID: qgis:vectorlayerhistogram
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Vector layer scatterplot
Creates a simple X - Y scatter plot for a vector layer.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
X attribute XFIELD [tablefield: any] Field to use for the X axis
Y attribute YFIELD [tablefield: any] Field to use for the Y axis
Scatterplot OUTPUT [html]
Default: [Save
to temporary
file]
Specify the HTML file for the plot. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Scatterplot OUTPUT [html] HTML file with the plot. Available in the
Processing ► Result Viewer.
Python code
Algorithm ID: qgis:vectorlayerscatterplot
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Vector layer scatterplot 3D
Creates a 3D scatter plot for a vector layer.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
X attribute XFIELD [tablefield: any] Field to use for the X axis
Y attribute YFIELD [tablefield: any] Field to use for the Y axis
Z attribute ZFIELD [tablefield: any] Field to use for the Z axis
Histogram OUTPUT [html]
Default: [Save
to temporary
file]
Specify the HTML file for the plot. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Histogram OUTPUT [html] HTML file with the plot. Available in the
Processing ► Result Viewer.
Python code
Algorithm ID: qgis:scatter3dplot
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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24.1.9 Rastrová analýza
Cell statistics
Computes per-cell statistics based on input raster layers and for each cell writes the resulting statistics to an output
raster. At each cell location, the output value is defined as a function of all overlaid cell values of the input rasters.
By default, a NoData cell in ANY of the input layers will result in a NoData cell in the output raster. If the Ignore
NoData values option is checked, then NoData inputs will be ignored in the statistic calculation. This may result in
NoData output for locations where all cells are NoData.
The Reference layer parameter specifies an existing raster layer to use as a reference when creating the output raster.
The output raster will have the same extent, CRS, and pixel dimensions as this layer.
Calculation details: Input raster layers that do not match the cell size of the reference raster layer will be resampled
using nearest neighbor resampling. The output raster data type will be set to the most complex data type
present in the input datasets except when using the functions Mean, Standard deviation and Variance
(data type is always Float32 or Float64 depending on input float type) or Count and Variety (data type
is always Int32).
• Count: The count statistic will always result in the number of cells without NoData values at the current cell
location.
• Median: If the number of input layers is even, the median will be calculated as the arithmetic mean of the
two middle values of the ordered cell input values.
• Minority/Majority: If no unique minority or majority could be found, the result is NoData, except all
input cell values are equal.
Obr. 24.8: Example with all the statistic functions. NoData cells (grey) are taken into account.
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Parameters
Label Název Type Popis
Input layers INPUT [raster] [list] Input raster layers
Statistic STATISTIC [enumeration]
Default: 0
Available statistics. Options:
• 0 — Sum
• 1 — Count
• 2 — Mean
• 3 — Median
• 4 — Standard deviation
• 5 — Variance
• 6 — Minimum
• 7 — Maximum
• 8 — Minority (least common value)
• 9 — Majority (most common value)
• 10 — Range (max - min)
• 11 — Variety (unique value count)
Ignore NoData
values
IGNORE_NODATA [boolean]
Default: True
Calculate statistics also for all cells stacks,
ignoring NoData occurrence.
Reference layer REF_LAYER [raster] The reference layer to create the output
layer from (extent, CRS, pixel dimensions)
Output no data
value
Optional
OUTPUT_NO_DATA_VALUE[number]
Default: -9999.0
Value to use for nodata in the output layer
Output layer OUTPUT [same as input] Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
CRS authority
identifier
CRS_AUTHID [crs] The coordinate reference system of the
output raster layer
Extent EXTENT [extent] The spatial extent of the output raster layer
Height in pixels HEIGHT_IN_PIXELS[integer] The height in pixels of the output raster
layer
Output raster OUTPUT [raster] Output raster layer containing the result
Total pixel count TOTAL_PIXEL_COUNT[integer] The count of pixels in the output raster layer
Width in pixels WIDTH_IN_PIXELS[integer] The width in pixels of the output raster layer
Python code
Algorithm ID: qgis:cellstatistics
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Equal to frequency
Evaluates on a cell-by-cell basis the frequency (number of times) the values of an input stack of rasters are equal to
the value of a value layer. The output raster extent and resolution are defined by the input raster layer and is always
of Int32 type.
If multiband rasters are used in the data raster stack, the algorithm will always perform the analysis on the first band
of the rasters - use GDAL to use other bands in the analysis. The output NoData value can be set manually.
Obr. 24.9: For each cell in the output raster, the value represents the number of times that the corresponding cells in
the list of rasters are the same as the value raster. NoData cells (grey) are taken into account.
Viz také:
Greater than frequency, Less than frequency
Parameters
Basic parameters
Label Název Type Popis
Input value raster INPUT_VALUE_RASTER[raster] The input value layer serves as reference
layer for the sample layers
Value raster band INPUT_VALUE_RASTER_BAND[raster band]
Default: The first
band of the raster
layer
Select the band you want to use as sample
Input raster layers INPUT_RASTERS [raster] [list] Raster layers to evaluate. If multiband
rasters are used in the data raster stack, the
algorithm will always perform the analysis
on the first band of the rasters
continues on next page
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Tabulka 24.22 – pokračujte na předchozí stránce
Label Název Type Popis
Ignore NoData
values
IGNORE_NODATA [boolean]
Default: False
If unchecked, any NoData cells in the value
raster or the data layer stack will result in
a NoData cell in the output raster
Output layer OUTPUT [same as input]
Default: [Save
to temporary
file]
Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
Advanced parameters
Label Název Type Popis
Output no data
value
Optional
OUTPUT_NO_DATA_VALUE[number]
Default: -9999.0
Value to use for nodata in the output layer
Outputs
Label Název Type Popis
Output layer OUTPUT [raster] Output raster layer containing the result
CRS authority
identifier
CRS_AUTHID [string] The coordinate reference system of the
output raster layer
Extent EXTENT [string] The spatial extent of the output raster layer
Count of cells
with equal value
occurrences
FOUND_LOCATIONS_COUNT[number]
Height in pixels HEIGHT_IN_PIXELS[number] The number of rows in the output raster
layer
Total pixel count TOTAL_PIXEL_COUNT[integer] The count of pixels in the output raster layer
Mean frequency at
valid cell locations
MEAN_FREQUENCY_PER_LOCATION[number]
Count of value
occurrences
OCCURRENCE_COUNT[number]
Width in pixels WIDTH_IN_PIXELS[integer] The number of columns in the output raster
layer
Python code
Algorithm ID: native:equaltofrequency
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Fuzzify raster (gaussian membership)
Transforms an input raster to a fuzzified raster by assigning a membership value to each pixel, using a Gaussian
membership function. Membership values range from 0 to 1. In the fuzzified raster, a value of 0 implies no
membership of the defined fuzzy set, whereas a value of 1 means full membership. The gaussian membership function
is defined as , where f1 is the spread and f2 the midpoint.
Obr. 24.10: Fuzzify raster example. Input raster source: Land Tirol - data.tirol.gv.at.
Viz také:
Fuzzify raster (large membership) Fuzzify raster (linear membership), Fuzzify raster (near membership), Fuzzify raster
(power membership), Fuzzify raster (small membership)
Parameters
Label Název Type Popis
Input Raster INPUT [raster] Input raster layer
Band Number BAND [raster band]
Default: The first
band of the raster
layer
If the raster is multiband, choose the band
that you want to fuzzify.
Function
midpoint
FUZZYMIDPOINT [number]
Default: 10
Midpoint of the gaussian function
Function spread FUZZYSPREAD [number]
Default: 0.01
Spread of the gaussian function
Fuzzified raster OUTPUT [same as input] Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Fuzzified raster OUTPUT [same as input] Output raster layer containing the result
CRS authority
identifier
CRS_AUTHID [crs] The coordinate reference system of the
output raster layer
Extent EXTENT [extent] The spatial extent of the output raster layer
Width in pixels WIDTH_IN_PIXELS[integer] The width in pixels of the output raster layer
Height in pixels HEIGHT_IN_PIXELS[integer] The height in pixels of the output raster
layer
Total pixel count TOTAL_PIXEL_COUNT[integer] The count of pixels in the output raster layer
Python code
Algorithm ID: qgis:fuzzifyrastergaussianmembership
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Fuzzify raster (large membership)
Transforms an input raster to a fuzzified raster by assigning a membership value to each pixel, using a Large
membership function. Membership values range from 0 to 1. In the fuzzified raster, a value of 0 implies no
membership of the defined fuzzy set, whereas a value of 1 means full membership. The large membership function
is defined as , where f1 is the spread and f2 the midpoint.
Viz také:
Fuzzify raster (gaussian membership), Fuzzify raster (linear membership), Fuzzify raster (near membership), Fuzzify
raster (power membership), Fuzzify raster (small membership)
Parameters
Label Název Type Popis
Input Raster INPUT [raster] Input raster layer
Band Number BAND [raster band]
Default: The first
band of the raster
layer
If the raster is multiband, choose the band
that you want to fuzzify.
Function
midpoint
FUZZYMIDPOINT [number]
Default: 50
Midpoint of the large function
Function spread FUZZYSPREAD [number]
Default: 5
Spread of the large function
Fuzzified raster OUTPUT [same as input] Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Fuzzified raster OUTPUT [same as input] Output raster layer containing the result
CRS authority
identifier
CRS_AUTHID [crs] The coordinate reference system of the
output raster layer
Extent EXTENT [extent] The spatial extent of the output raster layer
Width in pixels WIDTH_IN_PIXELS[integer] The width in pixels of the output raster layer
Height in pixels HEIGHT_IN_PIXELS[integer] The height in pixels of the output raster
layer
Total pixel count TOTAL_PIXEL_COUNT[integer] The count of pixels in the output raster layer
Python code
Algorithm ID: qgis:fuzzifyrasterlargemembership
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Fuzzify raster (linear membership)
Transforms an input raster to a fuzzified raster by assigning a membership value to each pixel, using a Linear
membership function. Membership values range from 0 to 1. In the fuzzified raster, a value of 0 implies no
membership of the defined fuzzy set, whereas a value of 1 means full membership. The linear function is defined
as , where a is the low bound and b the high bound. This equation assigns membership values
using a linear transformation for pixel values between the low and high bounds. Pixels values smaller than the low
bound are given 0 membership whereas pixel values greater than the high bound are given 1 membership.
Viz také:
Fuzzify raster (gaussian membership), Fuzzify raster (large membership), Fuzzify raster (near membership), Fuzzify
raster (power membership), Fuzzify raster (small membership)
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Parameters
Label Název Type Popis
Input Raster INPUT [raster] Input raster layer
Band Number BAND [raster band]
Default: The first
band of the raster
layer
If the raster is multiband, choose the band
that you want to fuzzify.
Low fuzzy
membership
bound
FUZZYLOWBOUND [number]
Default: 0
Low bound of the linear function
High fuzzy
membership
bound
FUZZYHIGHBOUND [number]
Default: 1
High bound of the linear function
Fuzzified raster OUTPUT [same as input] Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Fuzzified raster OUTPUT [same as input] Output raster layer containing the result
CRS authority
identifier
CRS_AUTHID [crs] The coordinate reference system of the
output raster layer
Extent EXTENT [extent] The spatial extent of the output raster layer
Width in pixels WIDTH_IN_PIXELS[integer] The width in pixels of the output raster layer
Height in pixels HEIGHT_IN_PIXELS[integer] The height in pixels of the output raster
layer
Total pixel count TOTAL_PIXEL_COUNT[integer] The count of pixels in the output raster layer
Python code
Algorithm ID: qgisfuzzifyrasterlinearmembership
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Fuzzify raster (near membership)
Transforms an input raster to a fuzzified raster by assigning a membership value to each pixel, using a Near
membership function. Membership values range from 0 to 1. In the fuzzified raster, a value of 0 implies no
membership of the defined fuzzy set, whereas a value of 1 means full membership. The near membership function
is defined as , where f1 is the spread and f2 the midpoint.
Viz také:
Fuzzify raster (gaussian membership), Fuzzify raster (large membership), Fuzzify raster (linear membership), Fuzzify
raster (power membership), Fuzzify raster (small membership)
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Parameters
Label Název Type Popis
Input Raster INPUT [raster] Input raster layer
Band Number BAND [raster band]
Default: The first
band of the raster
layer
If the raster is multiband, choose the band
that you want to fuzzify.
Function
midpoint
FUZZYMIDPOINT [number]
Default: 50
Midpoint of the near function
Function spread FUZZYSPREAD [number]
Default: 0.01
Spread of the near function
Fuzzified raster OUTPUT [same as input] Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Fuzzified raster OUTPUT [same as input] Output raster layer containing the result
CRS authority
identifier
CRS_AUTHID [crs] The coordinate reference system of the
output raster layer
Extent EXTENT [extent] The spatial extent of the output raster layer
Width in pixels WIDTH_IN_PIXELS[integer] The width in pixels of the output raster layer
Height in pixels HEIGHT_IN_PIXELS[integer] The height in pixels of the output raster
layer
Total pixel count TOTAL_PIXEL_COUNT[integer] The count of pixels in the output raster layer
Python code
Algorithm ID: qgis:fuzzifyrasternearmembership
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Fuzzify raster (power membership)
Transforms an input raster to a fuzzified raster by assigning a membership value to each pixel, using a Power
membership function. Membership values range from 0 to 1. In the fuzzified raster, a value of 0 implies no
membership of the defined fuzzy set, whereas a value of 1 means full membership. The power function is defined
as , where a is the low bound, b is the high bound, and f1 the exponent. This equation
assigns membership values using the power transformation for pixel values between the low and high bounds. Pixels
values smaller than the low bound are given 0 membership whereas pixel values greater than the high bound are given
1 membership.
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Viz také:
Fuzzify raster (gaussian membership), Fuzzify raster (large membership), Fuzzify raster (linear membership), Fuzzify
raster (near membership), Fuzzify raster (small membership)
Parameters
Label Název Type Popis
Input Raster INPUT [raster] Input raster layer
Band Number BAND [raster band]
Default: The first
band of the raster
layer
If the raster is multiband, choose the band
that you want to fuzzify.
Low fuzzy
membership
bound
FUZZYLOWBOUND [number]
Default: 0
Low bound of the power function
High fuzzy
membership
bound
FUZZYHIGHBOUND [number]
Default: 1
High bound of the power function
High fuzzy
membership
bound
FUZZYEXPONENT [number]
Default: 2
Exponent of the power function
Fuzzified raster OUTPUT [same as input] Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Fuzzified raster OUTPUT [same as input] Output raster layer containing the result
CRS authority
identifier
CRS_AUTHID [crs] The coordinate reference system of the
output raster layer
Extent EXTENT [extent] The spatial extent of the output raster layer
Width in pixels WIDTH_IN_PIXELS[integer] The width in pixels of the output raster layer
Height in pixels HEIGHT_IN_PIXELS[integer] The height in pixels of the output raster
layer
Total pixel count TOTAL_PIXEL_COUNT[integer] The count of pixels in the output raster layer
Python code
Algorithm ID: qgisfuzzifyrasterpowermembership
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Fuzzify raster (small membership)
Transforms an input raster to a fuzzified raster by assigning a membership value to each pixel, using a Small
membership function. Membership values range from 0 to 1. In the fuzzified raster, a value of 0 implies no
membership of the defined fuzzy set, whereas a value of 1 means full membership. The small membership function
is defined as , where f1 is the spread and f2 the midpoint.
Viz také:
Fuzzify raster (gaussian membership), Fuzzify raster (large membership) Fuzzify raster (linear membership), Fuzzify
raster (near membership), Fuzzify raster (power membership)
Parameters
Label Název Type Popis
Input Raster INPUT [raster] Input raster layer
Band Number BAND [raster band]
Default: The first
band of the raster
layer
If the raster is multiband, choose the band
that you want to fuzzify.
Function
midpoint
FUZZYMIDPOINT [number]
Default: 50
Midpoint of the small function
Function spread FUZZYSPREAD [number]
Default: 5
Spread of the small function
Fuzzified raster OUTPUT [same as input] Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Fuzzified raster OUTPUT [same as input] Output raster layer containing the result
CRS authority
identifier
CRS_AUTHID [crs] The coordinate reference system of the
output raster layer
Extent EXTENT [extent] The spatial extent of the output raster layer
Width in pixels WIDTH_IN_PIXELS[integer] The width in pixels of the output raster layer
Height in pixels HEIGHT_IN_PIXELS[integer] The height in pixels of the output raster
layer
Total pixel count TOTAL_PIXEL_COUNT[integer] The count of pixels in the output raster layer
Python code
Algorithm ID: qgisfuzzifyrastersmallmembership
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Greater than frequency
Evaluates on a cell-by-cell basis the frequency (number of times) the values of an input stack of rasters are equal to
the value of a value raster. The output raster extent and resolution is defined by the input raster layer and is always of
Int32 type.
If multiband rasters are used in the data raster stack, the algorithm will always perform the analysis on the first band
of the rasters - use GDAL to use other bands in the analysis. The output NoData value can be set manually.
Obr. 24.11: For each cell in the output raster, the value represents the number of times that the corresponding cells
in the list of rasters are greater than the value raster. NoData cells (grey) are taken into account.
Viz také:
Equal to frequency, Less than frequency
Parameters
Basic parameters
Label Název Type Popis
Input value raster INPUT_VALUE_RASTER[raster] The input value layer serves as reference
layer for the sample layers
Value raster band INPUT_VALUE_RASTER_BAND[raster band]
Default: The first
band of the raster
layer
Select the band you want to use as sample
Input raster layers INPUT_RASTERS [raster] [list] Raster layers to evaluate. If multiband
rasters are used in the data raster stack, the
algorithm will always perform the analysis
on the first band of the rasters
continues on next page
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Tabulka 24.25 – pokračujte na předchozí stránce
Label Název Type Popis
Ignore NoData
values
IGNORE_NODATA [boolean]
Default: False
If unchecked, any NoData cells in the value
raster or the data layer stack will result in
a NoData cell in the output raster
Output layer OUTPUT [same as input]
Default: [Save
to temporary
file]
Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
Advanced parameters
Label Název Type Popis
Output no data
value
Optional
OUTPUT_NO_DATA_VALUE[number]
Default: -9999.0
Value to use for nodata in the output layer
Outputs
Label Název Type Popis
Output layer OUTPUT [raster] Output raster layer containing the result
CRS authority
identifier
CRS_AUTHID [string] The coordinate reference system of the
output raster layer
Extent EXTENT [string] The spatial extent of the output raster layer
Count of cells
with equal value
occurrences
FOUND_LOCATIONS_COUNT[number]
Height in pixels HEIGHT_IN_PIXELS[number] The number of rows in the output raster
layer
Total pixel count TOTAL_PIXEL_COUNT[integer] The count of pixels in the output raster layer
Mean frequency at
valid cell locations
MEAN_FREQUENCY_PER_LOCATION[number]
Count of value
occurrences
OCCURRENCE_COUNT[number]
Width in pixels WIDTH_IN_PIXELS[integer] The number of columns in the output raster
layer
Python code
Algorithm ID: native:greaterthanfrequency
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
844 Kapitola 24. Processing providers and algorithms
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Highest position in raster stack
Evaluates on a cell-by-cell basis the position of the raster with the highest value in a stack of rasters. Position counts
start with 1 and range to the total number of input rasters. The order of the input rasters is relevant for the algorithm.
If multiple rasters feature the highest value, the first raster will be used for the position value.
If multiband rasters are used in the data raster stack, the algorithm will always perform the analysis on the first band
of the rasters - use GDAL to use other bands in the analysis. Any NoData cells in the raster layer stack will result in
a NoData cell in the output raster unless the „ignore NoData“ parameter is checked. The output NoData value can be
set manually. The output rasters extent and resolution is defined by a reference raster layer and is always of Int32
type.
Viz také:
Lowest position in raster stack
Parameters
Basic parameters
Label Název Type Popis
Input raster layers INPUT_RASTERS [raster] [list] List of raster layers to compare with
Reference layer REFERENCE_LAYER[raster] The reference layer for the output layer
creation (extent, CRS, pixel dimensions)
Ignore NoData
values
IGNORE_NODATA [boolean]
Default: False
If unchecked, any NoData cells in the data
layer stack will result in a NoData cell in the
output raster
Output layer OUTPUT [raster]
Default: [Save
to temporary
file]
Specification of the output raster containing
the result. One of:
• Save to a Temporary File
• Save to File…
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Advanced parameters
Label Název Type Popis
Output no data
value
OUTPUT_NODATA_VALUE[number]
Default: -9999.0
Value to use for nodata in the output layer
Outputs
Label Název Type Popis
Output layer OUTPUT [raster] Output raster layer containing the result
CRS authority
identifier
CRS_AUTHID [string] The coordinate reference system of the
output raster layer
Extent EXTENT [string] The spatial extent of the output raster layer
Width in pixels WIDTH_IN_PIXELS[integer] The number of columns in the output raster
layer
Height in pixels HEIGHT_IN_PIXELS[integer] The number of rows in the output raster
layer
Total pixel count TOTAL_PIXEL_COUNT[integer] The count of pixels in the output raster layer
Python code
Algorithm ID: native:highestpositioninrasterstack
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Less than frequency
Evaluates on a cell-by-cell basis the frequency (number of times) the values of an input stack of rasters are less than
the value of a value raster. The output raster extent and resolution is defined by the input raster layer and is always of
Int32 type.
If multiband rasters are used in the data raster stack, the algorithm will always perform the analysis on the first band
of the rasters - use GDAL to use other bands in the analysis. The output NoData value can be set manually.
846 Kapitola 24. Processing providers and algorithms
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Obr. 24.12: For each cell in the output raster, the value represents the number of times that the corresponding cells
in the list of rasters are less than the value raster. NoData cells (grey) are taken into account.
Viz také:
Equal to frequency, Greater than frequency
Parameters
Basic parameters
Label Název Type Popis
Input value raster INPUT_VALUE_RASTER[raster] The input value layer serves as reference
layer for the sample layers
Value raster band INPUT_VALUE_RASTER_BAND[raster band]
Default: The first
band of the raster
layer
Select the band you want to use as sample
Input raster layers INPUT_RASTERS [raster] [list] Raster layers to evaluate. If multiband
rasters are used in the data raster stack, the
algorithm will always perform the analysis
on the first band of the rasters
Ignore NoData
values
IGNORE_NODATA [boolean]
Default: False
If unchecked, any NoData cells in the value
raster or the data layer stack will result in
a NoData cell in the output raster
Output layer OUTPUT [same as input]
Default: [Save
to temporary
file]
Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
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Advanced parameters
Label Název Type Popis
Output no data
value
Optional
OUTPUT_NO_DATA_VALUE[number]
Default: -9999.0
Value to use for nodata in the output layer
Outputs
Label Název Type Popis
Output layer OUTPUT [raster] Output raster layer containing the result
CRS authority
identifier
CRS_AUTHID [string] The coordinate reference system of the
output raster layer
Extent EXTENT [string] The spatial extent of the output raster layer
Count of cells
with equal value
occurrences
FOUND_LOCATIONS_COUNT[number]
Height in pixels HEIGHT_IN_PIXELS[number] The number of rows in the output raster
layer
Total pixel count TOTAL_PIXEL_COUNT[integer] The count of pixels in the output raster layer
Mean frequency at
valid cell locations
MEAN_FREQUENCY_PER_LOCATION[number]
Count of value
occurrences
OCCURRENCE_COUNT[number]
Width in pixels WIDTH_IN_PIXELS[integer] The number of columns in the output raster
layer
Python code
Algorithm ID: native:lessthanfrequency
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Lowest position in raster stack
Evaluates on a cell-by-cell basis the position of the raster with the lowest value in a stack of rasters. Position counts
start with 1 and range to the total number of input rasters. The order of the input rasters is relevant for the algorithm.
If multiple rasters feature the lowest value, the first raster will be used for the position value.
If multiband rasters are used in the data raster stack, the algorithm will always perform the analysis on the first band
of the rasters - use GDAL to use other bands in the analysis. Any NoData cells in the raster layer stack will result in
a NoData cell in the output raster unless the „ignore NoData“ parameter is checked. The output NoData value can be
set manually. The output rasters extent and resolution is defined by a reference raster layer and is always of Int32
type.
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Viz také:
Highest position in raster stack
Parameters
Basic parameters
Label Název Type Popis
Input raster layers INPUT_RASTERS [raster] [list] List of raster layers to compare with
Reference layer REFERENCE_LAYER[raster] The reference layer for the output layer
creation (extent, CRS, pixel dimensions)
Ignore NoData
values
IGNORE_NODATA [boolean]
Default: False
If unchecked, any NoData cells in the data
layer stack will result in a NoData cell in the
output raster
Output layer OUTPUT [raster]
Default: [Save
to temporary
file]
Specification of the output raster containing
the result. One of:
• Save to a Temporary File
• Save to File…
Advanced parameters
Label Název Type Popis
Output no data
value
OUTPUT_NODATA_VALUE[number]
Default: -9999.0
Value to use for nodata in the output layer
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Outputs
Label Název Type Popis
Output layer OUTPUT [raster] Output raster layer containing the result
CRS authority
identifier
CRS_AUTHID [string] The coordinate reference system of the
output raster layer
Extent EXTENT [string] The spatial extent of the output raster layer
Width in pixels WIDTH_IN_PIXELS[integer] The number of columns in the output raster
layer
Height in pixels HEIGHT_IN_PIXELS[integer] The number of rows in the output raster
layer
Total pixel count TOTAL_PIXEL_COUNT[integer] The count of pixels in the output raster layer
Python code
Algorithm ID: native:lowestpositioninrasterstack
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Raster boolean AND
Calculates the boolean AND for a set of input rasters. If all of the input rasters have a non-zero value for a pixel, that
pixel will be set to 1 in the output raster. If any of the input rasters have 0 values for the pixel it will be set to 0 in
the output raster.
The reference layer parameter specifies an existing raster layer to use as a reference when creating the output raster.
The output raster will have the same extent, CRS, and pixel dimensions as this layer.
By default, a nodata pixel in ANY of the input layers will result in a nodata pixel in the output raster. If the Treat
nodata values as false option is checked, then nodata inputs will be treated the same as a 0 input value.
Viz také:
Raster boolean OR
Parameters
Label Název Type Popis
Input layers INPUT [raster] [list] List of input raster layers
Reference layer REF_LAYER [raster] The reference layer to create the output
layer from (extent, CRS, pixel dimensions)
Treat nodata
values as false
NODATA_AS_FALSE[boolean]
Default: False
Treat nodata values in the input files as 0
when performing the operation
Output no data
value
NO_DATA [number]
Default: -9999.0
Value to use for nodata in the output layer
continues on next page
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Tabulka 24.33 – pokračujte na předchozí stránce
Label Název Type Popis
Output data type DATA_TYPE [enumeration]
Default: 5
Output raster data type. Options:
• 0 — Byte
• 1 — Int16
• 2 — UInt16
• 3 — UInt32
• 4 — Int32
• 5 — Float32
• 6 — Float64
• 7 — CInt16
• 8 — CInt32
• 9 — CFloat32
• 10 — CFloat64
Output layer OUTPUT [raster] Output raster layer
Outputs
Label Název Type Popis
Extent EXTENT [extent] The extent of the output raster layer
CRS authority
identifier
CRS_AUTHID [crs] The coordinate reference system of the
output raster layer
Width in pixels WIDTH_IN_PIXELS[integer] The width in pixels of the output raster layer
Height in pixels HEIGHT_IN_PIXELS[integer] The height in pixels of the output raster
layer
Total pixel count TOTAL_PIXEL_COUNT[integer] The count of pixels in the output raster layer
NODATA pixel
count
NODATA_PIXEL_COUNT[integer] The count of nodata pixels in the output
raster layer
True pixel count TRUE_PIXEL_COUNT[integer] The count of True pixels (value = 1) in the
output raster layer
False pixel count FALSE_PIXEL_COUNT[integer] The count of False pixels (value = 0) in the
output raster layer
Output layer OUTPUT [raster] Output raster layer containing the result
Python code
Algorithm ID: qgis:rasterbooleanand
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Raster boolean OR
Calculates the boolean OR for a set of input rasters. If all of the input rasters have a zero value for a pixel, that pixel
will be set to 0 in the output raster. If any of the input rasters have 1 values for the pixel it will be set to 1 in the
output raster.
The reference layer parameter specifies an existing raster layer to use as a reference when creating the output raster.
The output raster will have the same extent, CRS, and pixel dimensions as this layer.
By default, a nodata pixel in ANY of the input layers will result in a nodata pixel in the output raster. If the Treat
nodata values as false option is checked, then nodata inputs will be treated the same as a 0 input value.
Viz také:
Raster boolean AND
Parameters
Label Název Type Popis
Input layers INPUT [raster] [list] List of input raster layers
Reference layer REF_LAYER [raster] The reference layer to create the output
layer from (extent, CRS, pixel dimensions)
Treat nodata
values as false
NODATA_AS_FALSE[boolean]
Default: False
Treat nodata values in the input files as 0
when performing the operation
Output no data
value
NO_DATA [number]
Default: -9999.0
Value to use for nodata in the output layer
Output data type DATA_TYPE [enumeration]
Default: 5
Output raster data type. Options:
• 0 — Byte
• 1 — Int16
• 2 — UInt16
• 3 — UInt32
• 4 — Int32
• 5 — Float32
• 6 — Float64
• 7 — CInt16
• 8 — CInt32
• 9 — CFloat32
• 10 — CFloat64
Output layer OUTPUT [raster] Output raster layer
Outputs
Label Název Type Popis
Extent EXTENT [extent] The extent of the output raster layer
CRS authority
identifier
CRS_AUTHID [crs] The coordinate reference system of the
output raster layer
Width in pixels WIDTH_IN_PIXELS[integer] The width in pixels of the output raster layer
Height in pixels HEIGHT_IN_PIXELS[integer] The height in pixels of the output raster
layer
Total pixel count TOTAL_PIXEL_COUNT[integer] The count of pixels in the output raster layer
NODATA pixel
count
NODATA_PIXEL_COUNT[integer] The count of nodata pixels in the output
raster layer
True pixel count TRUE_PIXEL_COUNT[integer] The count of True pixels (value = 1) in the
output raster layer
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Label Název Type Popis
False pixel count FALSE_PIXEL_COUNT[integer] The count of False pixels (value = 0) in the
output raster layer
Output layer OUTPUT [raster] Output raster layer containing the result
Python code
Algorithm ID: qgis:rasterbooleanor
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Raster calculator
Performs algebraic operations using raster layers.
The resulting layer will have its values computed according to an expression. The expression can contain numerical
values, operators and references to any of the layers in the current project.
Poznámka: When using the calculator in The batch processing interface or from the QGIS Python console the files to
use have to be specified. The corresponding layers are referred using the base name of the file (without the full path).
For instance, if using a layer at path/to/my/rasterfile.tif, the first band of that layer will be referred
as rasterfile.tif@1.
Viz také:
Raster Calculator
Parameters
Label Název Type Popis
Layers GUI only Shows the list of all raster layers loaded
in the legend. These can be used to
fill the expression box (double click
to add). Raster layers are referred by
their name and the number of the band:
layer_name@band_number. For
instance, the first band from a layer named
DEM will be referred as DEM@1.
Operators GUI only Contains some calculator like buttons that
can be used to fill the expression box.
Expression EXPRESSION [string] Expression that will be used to calculate
the output raster layer. You can use the
operator buttons provided to type directly
the expression in this box.
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Label Název Type Popis
Predefined
expressions
GUI only You can use the predefined NDVI
expression or you can define new
expressions for calculations. The Add…
button loads a defined expression (and lets
you set the parameters). The Save… button
lets you define a new expression.
Reference
layer(s) (used
for automated
extent, cellsize,
and CRS)
Optional
LAYERS [raster] [list] Layer(s) that will be used to fetch
extent, cell size and CRS. By choosing
the layer in this box you avoid filling
in all the other parameters by hand.
Raster layers are referred by their
name and the number of the band:
layer_name@band_number. For
instance, the first band from a layer named
DEM will be referred as DEM@1.
Cell size (use 0
or empty to set it
automatically)
Optional
CELLSIZE [number] Cell size of the output raster layer. If the
cell size is not specified, the minimum cell
size of the selected reference layer(s) will
be used. The cell size will be the same for
the X and Y axes.
Output extent
(xmin, xmax,
ymin, ymax)
Optional
EXTENT [extent] Extent of the output raster layer. If the
extent is not specified, the minimum extent
that covers all the selected reference layers
will be used.
Output CRS
Optional
CRS [crs] CRS of the output raster layer. If the output
CRS is not specified, the CRS of the first
reference layer will be used.
Output OUTPUT [raster]
Default: [Save
to temporary
file]
Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Output OUTPUT [raster] Output raster file with the calculated values.
Python code
Algorithm ID: qgis:rastercalculator
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Raster layer statistics
Calculates basic statistics from the values in a given band of the raster layer. The output is loaded in the Processing
► Results viewer menu.
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input raster layer
Band number BAND [raster band]
Default: The first
band of the input
layer
If the raster is multiband, choose the band
you want to get statistics for.
Output OUTPUT_HTML_FILE[html]
Default: [Save
to temporary
file]
Specification of the output file:
• Skip Output
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Maximum value MAX [number]
Mean value MEAN [number]
Minimum value MIN [number]
Output OUTPUT_HTML_FILE[html] The output file contains the following
information:
• Analyzed file: path of the raster layer
• Minimum value: minimum value of
the raster
• Maximum value: maximum value of
the raster
• Range: difference between the
maximum and minimum values
• Sum: total sum of the values
• Mean value: mean of the values
• Standard deviation: standard
deviation of the values
• Sum of the squares: sum of
the squared differences of each
observation from the overall mean
Range RANGE [number]
Standard
deviation
STD_DEV [number]
Sum SUM [number]
Sum of the
squares
SUM_OF_SQUARES [number]
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Python code
Algorithm ID: qgis:rasterlayerstatistics
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Raster layer unique values report
Returns the count and area of each unique value in a given raster layer.
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input raster layer
Band number BAND [raster band]
Default: The first
band of the input
layer
If the raster is multiband, choose the band
you want to get statistics for.
Unique values
report
OUTPUT_HTML_FILE[file]
Default: [Save
to temporary
file]
Specification of the output file:
• Skip Output
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Unique values
table
OUTPUT_TABLE [table]
Default: [Skip
output]
Specification of the table for unique values:
• Skip Output
• Create Temporary Layer
• Save to File…
• Save to GeoPackage…
• Save to PostGIS Table……
The file encoding can also be changed here.
Outputs
Label Název Type Popis
CRS authority
identifier
CRS_AUTHID [crs]
Extent EXTENT [extent]
Height in pixels HEIGHT_IN_PIXELS[number]
NODATA pixel
count
NODATA_PIXEL_COUNT[number]
Total pixel count TOTAL_PIXEL_COUNT[number]
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Label Název Type Popis
Unique values
report
OUTPUT_HTML_FILE[html] The output HTML file contains the
following information:
• Analyzed file: the path of the raster
layer
• Extent: xmin, ymin, xmax, ymax
coordinates of the extent
• Projection: projection of the layer
• Width in pixels: number of columns
and pixel width size
• Height in pixels: number of rows and
pixel width size
• Total pixel count: count of all the
pixels
• NODATA pixel count: count of
pixels with NODATA value
Unique values
table
OUTPUT_TABLE [table] A table with three columns:
• value: pixel value
• count: count of pixels with this value
• m2
: total area in square meters of
pixels with this value.
Width in pixels WIDTH_IN_PIXELS[number]
Python code
Algorithm ID: qgis:rasterlayeruniquevaluesreport
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Raster layer zonal statistics
Calculates statistics for a raster layer’s values, categorized by zones defined in another raster layer.
Viz také:
Zonal statistics
Parameters
Label Název Type Popis
Input Layer INPUT [raster] Input raster layer
Band number BAND [raster band]
Default: The first
band of the raster
layer
If the raster is multiband choose the
band for which you want to calculate the
statistics.
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Label Název Type Popis
Zones layer ZONES [raster] Raster layer defining zones. Zones are given
by contiguous pixels having the same pixel
value.
Zones band
number
ZONES_BAND [raster band]
Default: The first
band of the raster
layer
If the raster is multiband, choose the band
that defines the zones
Reference layer
Optional
REF_LAYER [enumeration]
Default: 0
Raster layer used to calculate the centroids
that will be used as reference when
determining the zones in the output layer.
One of:
• 0 — Input layer
• 1 — Zones layer
Statistics OUTPUT_TABLE [table] Table with the calculated statistics
Outputs
Label Název Type Popis
CRS authority
identifier
CRS_AUTHID [crs]
Extent EXTENT [extent]
Height in pixels HEIGHT_IN_PIXELS[number]
NODATA pixel
count
NODATA_PIXEL_COUNT[number]
Statistics OUTPUT_TABLE [table] The output layer contains the following
information for each zone:
• Area: the area in square raster units
in the zone;
• Sum: the total sum of the pixel values
in the zone;
• Count: the number of pixels in the
zone;
• Min: the minimum pixel value in the
zone;
• Max: the maximum pixel value in the
zone;
• Mean: the mean of the pixel values in
the zone;
Total pixel count TOTAL_PIXEL_COUNT[number]
Width in pixels WIDTH_IN_PIXELS[number]
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Python code
Algorithm ID: qgis:rasterlayerzonalstats
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Raster surface volume
Calculates the volume under a raster surface relative to a given base level. This is mainly useful for Digital Elevation
Models (DEM).
Parameters
Label Název Type Popis
INPUT layer INPUT [raster] Input raster, representing a surface
Band number BAND [raster band]
Default: The first
band of the raster
layer
If the raster is multiband, choose the band
that shall define the surface.
Base level LEVEL [number]
Default: 0.0
Define a base or reference value. This base
is used in the volume calculation according
to the Method parameter (see below).
Method METHOD [enumeration]
Default: 0
Define the method for the volume
calculation given by the difference between
the raster pixel value and the Base
level. Options:
• 0 — Count Only Above Base Level:
only pixels above the base level will
add to the volume.
• 1 — Count Only Below Base Level:
only pixels below the base level will
add to the volume.
• 2 — Subtract Volumes Below Base
level: pixels above the base level
will add to the volume, pixels below
the base level will subtract from the
volume.
• 3 — Add Volumes Below Base level:
Add the volume regardless whether
the pixel is above or below the
base level. This is equivalent to sum
the absolute values of the difference
between the pixel value and the base
level.
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Label Název Type Popis
Surface volume
report
OUTPUT_HTML_FILE[html]
Default: [Save
to temporary
file]
Specification of the output HTML report.
One of:
• Skip output
• Save to Temporary File
• Save to File…
The file encoding can also be changed here.
Surface volume
table
OUTPUT_TABLE [table]
Default: [Skip
output]
Specification of the output table. One of:
• Skip output
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Volume VOLUME [number] The calculated volume
Area AREA [number] The area in square map units
Pixel_count PIXEL_COUNT [number] The total number of pixels that have been
analyzed
Surface volume
report
OUTPUT_HTML_FILE[html] The output report (containing volume, area
and pixel count) in HTML format
Surface volume
table
OUTPUT_TABLE [table] The output table (containing volume, area
and pixel count)
Python code
Algorithm ID: qgis:rastersurfacevolume
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Reclassify by layer
Reclassifies a raster band by assigning new class values based on the ranges specified in a vector table.
Parameters
Label Název Type Popis
Raster layer INPUT_RASTER [raster] Raster layer to reclassify
Band number RASTER_BAND [raster band]
Default: The first
band of the raster
layer
If the raster is multiband, choose the band
you want to reclassify.
Layer containing
class breaks
INPUT_TABLE [vector: any] Vector layer containing the values to use for
classification.
Minimum class
value field
MIN_FIELD [tablefield:
numeric]
Field with the minimum value of the range
for the class.
Maximum class
value field
MAX_FIELD [tablefield:
numeric]
Field with the maximum value of the range
for the class.
Output value field VALUE_FIELD [tablefield:
numeric]
Field with the value that will be assigned to
the pixels that fall in the class (between the
corresponding min and max values).
Output no data
value
NO_DATA [number]
Default: -9999.0
Value to apply to no data values.
Range boundaries RANGE_BOUNDARIES[enumeration]
Default: 0
Defines comparison rules for the
classification. Options:
• 0 — min < value <= max
• 1 — min <= value < max
• 2 — min <= value <= max
• 3 — min < value < max
Use no data when
no range matches
value
NODATA_FOR_MISSING[boolean]
Default: False
Values that do not belong to a class will
result in the no data value. If False, the
original value is kept.
Output data type DATA_TYPE [enumeration]
Default: 5
Defines the data type of the output raster
file. Options:
• 0 — Byte
• 1 — Int16
• 2 — UInt16
• 3 — UInt32
• 4 — Int32
• 5 — Float32
• 6 — Float64
• 7 — CInt16
• 8 — CInt32
• 9 — CFloat32
• 10 — CFloat64
Reclassified raster OUTPUT [raster] Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Reclassified raster OUTPUT [raster] Output raster layer with reclassified band
values
Python code
Algorithm ID: qgis:reclassifybylayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Reclassify by table
Reclassifies a raster band by assigning new class values based on the ranges specified in a fixed table.
Parameters
Label Název Type Popis
Raster layer INPUT_RASTER [raster] Raster layer to reclassify
Band number RASTER_BAND [raster band]
Default: 1
Raster band for which you want to
recalculate values.
Reclassification
table
TABLE [table] A 3-columns table to fill with the values to
set the boundaries of each class (Minimum
and Maximum) and the new Value to
assign to the band values that fall in the
class.
Output no data
value
NO_DATA [number]
Default: -9999.0
Value to apply to no data values.
Range boundaries RANGE_BOUNDARIES[enumeration]
Default: 0
Defines comparison rules for the
classification. Options:
• 0 — min < value <= max
• 1 — min <= value < max
• 2 — min <= value <= max
• 3 — min < value < max
Use no data when
no range matches
value
NODATA_FOR_MISSING[boolean]
Default: False
Applies the no data value to band values that
do not fall in any class. If False, the original
value is kept.
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Label Název Type Popis
Output data type DATA_TYPE [enumeration]
Default: 5
Defines the format of the output raster file.
Options:
• 0 — Byte
• 1 — Int16
• 2 — UInt16
• 3 — UInt32
• 4 — Int32
• 5 — Float32
• 6 — Float64
• 7 — CInt16
• 8 — CInt32
• 9 — CFloat32
• 10 — CFloat64
Reclassified raster OUTPUT [raster]
Default: ‚[Save to
temporary file]‘
Specification of the output raster layer. One
of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here
Outputs
Label Název Type Popis
Reclassified raster OUTPUT [raster]
Default: ‚[Save to
temporary file]‘
The output raster layer.
Python code
Algorithm ID: qgis:reclassifybytable
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Rescale raster
Rescales raster layer to a new value range, while preserving the shape (distribution) of the raster’s histogram (pixel
values). Input values are mapped using a linear interpolation from the source raster’s minimum and maximum pixel
values to the destination minimum and miximum pixel range.
By default the algorithm preserves the original NODATA value, but there is an option to override it.
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Obr. 24.13: Rescaling values of a raster layer from [0 - 50] to [100 - 1000]
Parameters
Label Název Type Popis
Input Raster INPUT [raster] Raster layer to use for rescaling
Band number Band [raster band]
Default: The first
band of the input
layer
If the raster is multiband,
choose a band.
New minimum value MINIMUM [number]
Default value: 0.0
Minimum pixel value to use in
the rescaled layer
New maximum value MAXIMUM [number]
Default value: 255.0
Maximum pixel value to use in
the rescaled layer
New NODATA value
Optional
NODATA [number]
Default value: Not
set
Value to assign to the
NODATA pixels. If unset,
original NODATA values are
preserved.
Rescaled OUTPUT [raster]
Default: [Save
to temporary
file]
Specification of the output
raster layer. One of:
• Save to a Temporary File
• Save to File…
Outputs
Label Název Type Popis
Rescaled OUTPUT [raster] Output raster layer with rescaled band
values
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Python code
Algorithm ID: native:rescaleraster
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Round raster
Rounds the cell values of a raster dataset according to the specified number of decimals.
Alternatively, a negative number of decimal places may be used to round values to powers of a base n. For example,
with a Base value n of 10 and Decimal places of -1, the algorithm rounds cell values to multiples of 10, -2 rounds
to multiples of 100, and so on. Arbitrary base values may be chosen, the algorithm applies the same multiplicative
principle. Rounding cell values to multiples of a base n may be used to generalize raster layers.
The algorithm preserves the data type of the input raster. Therefore byte/integer rasters can only be rounded to
multiples of a base n, otherwise a warning is raised and the raster gets copied as byte/integer raster.
Obr. 24.14: Rounding values of a raster
Parameters
Basic parameters
Label Název Type Popis
Input raster INPUT [raster] The raster to process.
Band number BAND [number]
Default: 1
The band of the raster
Rounding
direction
ROUNDING_DIRECTION[list]
Default: 1
How to choose the target rounded value.
Options are:
0 - Round up 1 - Round to nearest 2 - Round
down
Number of
decimals places
DECIMAL_PLACES [number]
Default: 2
Number of decimals places to round to.
Use negative values to round cell values to
a multiple of a base n
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Label Název Type Popis
Output raster OUTPUT [raster]
Default: [Save
to temporary
file]
Specification of the output file. One of:
• Save to a Temporary File
• Save to File…
Advanced parameters
Label Název Type Popis
Base n for
rounding to
multiples of n
BASE_N [number]
Default: 10
When the DECIMAL_PLACES parameter
is negative, raster values are rounded to
multiples of the base n value
Outputs
Label Název Type Popis
Output raster OUTPUT [raster] The output raster layer with values rounded
for the selected band.
Python code
Algorithm ID: native:roundrastervalues
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Sample raster values
Extracts raster values at the point locations. If the raster layer is multiband, each band is sampled.
The attribute table of the resulting layer will have as many new columns as the raster layer band count.
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Parameters
Label Název Type Popis
Input Point Layer INPUT [vector: point] Point vector layer to use for
sampling
Raster Layer to sample RASTERCOPY [raster] Raster layer to sample at the
given point locations.
Output column prefix COLUMN_PREFIX [string]
Default: ‚rvalue‘
Prefix for the names of the
added columns.
Sampled Points
Optional
OUTPUT [vector: point]
Default: [Create
temporary
layer]
Specify the output layer
containing the sampled values.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to Database
Table…
The file encoding can also be
changed here.
Outputs
Label Název Type Popis
Sampled Points
Optional
OUTPUT [vector: point] The output layer containing the sampled
values.
Python code
Algorithm ID: qgis:rastersampling
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Zonal histogram
Appends fields representing counts of each unique value from a raster layer contained within polygon features.
The output layer attribute table will have as many fields as the unique values of the raster layer that intersects the
polygon(s).
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Obr. 24.15: Raster layer histogram example
Parameters
Label Název Type Popis
Raster layer INPUT_RASTER [raster] Input raster layer.
Band number RASTER_BAND [raster band]
Default: The first
band of the input
layer
If the raster is multiband, choose a band.
Vector layer
containing zones
INPUT_VECTOR [vector: polygon] Vector polygon layer that defines the zones.
Output column
prefix
COLUMN_PREFIX
Optional
[string]
Default: ‚HISTO_‘
Prefix for the output columns names.
Output zones OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output vector polygon layer.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to Database Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Output zones
Optional
OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
The output vector polygon layer.
Python code
Algorithm ID: qgis:zonalhistogram
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Zonal statistics
Calculates statistics of a raster layer for each feature of an overlapping polygon vector layer.
Prior to QGIS 3.16, the algorithm edited the layer in-place, adding the new statistics fields to it. Now, it outputs a new
layer with these statistics.
Parameters
Label Název Type Popis
Input layer INPUT [vector: polygon] Vector polygon layer that contains the
zones.
Raster layer INPUT_RASTER [raster] Input raster layer.
Raster band RASTER_BAND [raster band]
Default: The first
band of the input
layer
If the raster is multiband, choose a band for
the statistics.
Output column
prefix
COLUMN_PREFIX [string]
Default: ‚_‘
Prefix for the output columns names.
Statistics to
calculate
STATISTICS [enumeration] [list]
Default: [0,1,2]
List of statistical operator for the output.
Options:
• 0 — Count
• 1 — Sum
• 2 — Mean
• 3 — Median
• 4 — St. dev.
• 5 — Minimum
• 6 — Maximum
• 7 — Range
• 8 — Minority
• 9 — Majority
• 10 — Variety
• 11 — Variance
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Tabulka 24.48 – pokračujte na předchozí stránce
Label Název Type Popis
Zonal Statistics
NEW in 3.16
OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output vector polygon layer.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to Database Table…
• Append to Layer…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Zonal Statistics
NEW in 3.16
OUTPUT [vector: polygon] The zone vector layer with added statistics.
Python code
Algorithm ID: qgis:zonalstatisticsfb
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.1.10 Raster Creation
Create constant raster layer
Generates raster layer for given extent and cell size filled with the specified value.
Additionally an output data type can be specified. The algorithm will abort if a value has been entered that cannot be
represented by the selected output raster data type.
Parameters
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Basic parameters
Label Name Type Description
Desired extent EXTENT [extent] Specify the extent (xmin, xmax, ymin,
ymax) of the output raster layer. One of:
• Use Canvas Extent
• Select Extent on Canvas
• Use Layer Extent…
It will internally be extended to a multiple
of the tile size.
Target CRS TARGET_CRS [crs]
Default: Project
CRS
CRS for the output raster layer
Pixel size PIXEL_SIZE [number]
Default: 0.1
Pixel size (X=Y) in map units. Minimum
value: 0.01
Constant value NUMBER [number]
Default: 1
Constant pixel value for the output raster
layer.
Constant OUTPUT [raster]
Default: [Save
to temporary
file]
Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
Advanced parameters
Label Name Type Description
Output raster
data type
OUTPUT_TYPE
Default: 5
[enumeration] Defines the data type of the output raster
file. Options:
• 0 — Byte
• 1 — Integer16
• 2 — Unsigned Integer16
• 3 — Integer32
• 4 — Unsigned Integer32
• 5 — Float32
• 6 — Float64
Outputs
Label Name Type Description
Constant OUTPUT [raster] Raster covering the desired extent with the
specified pixel size and value.
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Python code
Algorithm ID: native:createconstantrasterlayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Create random raster layer (binomial distribution)
Generates a raster layer for given extent and cell size filled with binomially distributed random values.
By default, the values will be chosen given an N of 10 and a probability of 0.5. This can be overridden by using the
advanced parameter for N and probability. The raster data type is set to Integer types (Integer16 by default). The
binomial distribution random values are defined as positive integer numbers. A floating point raster will represent
a cast of integer values to floating point.
Parameters
Basic parameters
Label Name Type Description
Desired extent EXTENT [extent] Specify the extent (xmin, xmax, ymin,
ymax) of the output raster layer. One of:
• Use Canvas Extent
• Select Extent on Canvas
• Use Layer Extent…
It will internally be extended to a multiple
of the tile size.
Target CRS TARGET_CRS [crs]
Default: Project
CRS
CRS for the output raster layer
Pixel size PIXEL_SIZE [number]
Default: 0.1
Pixel size (X=Y) in map units. Minimum
value: 0.01
Output raster OUTPUT [raster]
Default: [Save
to temporary
file]
Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
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Advanced parameters
Label Name Type Description
Output raster
data type
OUTPUT_TYPE
Default: 0
[enumeration] Defines the data type of the output raster
file. Options:
• 0 — Integer16
• 1 — Unsigned Integer16
• 2 — Integer32
• 3 — Unsigned Integer32
• 4 — Float32
• 5 — Float64
N N [number]
Default: 10
Probability PROBABILITY [number]
Default: 0.5
Outputs
Label Name Type Description
Output raster OUTPUT [raster] Raster covering the desired extent with the
cell size filled with random values
Python code
Algorithm ID: native:createrandombinomialrasterlayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Create random raster layer (exponential distribution)
Generates a raster layer for given extent and cell size filled with exponentially distributed random values.
By default, the values will be chosen given a lambda of 1.0. This can be overridden by using the advanced parameter
for lambda. The raster data type is set to Float32 by default as the exponential distribution random values are floating
point numbers.
Parameters
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Basic parameters
Label Name Type Description
Desired extent EXTENT [extent] Specify the extent (xmin, xmax, ymin,
ymax) of the output raster layer. One of:
• Use Canvas Extent
• Select Extent on Canvas
• Use Layer Extent…
It will internally be extended to a multiple
of the tile size.
Target CRS TARGET_CRS [crs]
Default: Project
CRS
CRS for the output raster layer
Pixel size PIXEL_SIZE [number]
Default: 1.0
Pixel size (X=Y) in map units. Minimum
value: 0.01
Output raster OUTPUT [raster]
Default: [Save
to temporary
file]
Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
Advanced parameters
Label Name Type Description
Output raster
data type
OUTPUT_TYPE
Default: 0
[enumeration] Defines the data type of the output raster
file. Options:
• 0 — Float32
• 1 — Float64
Lambda LAMBDA [number]
Default: 1.0
Outputs
Label Name Type Description
Output raster OUTPUT [raster] Raster covering the desired extent with the
cell size filled with random values
Python code
Algorithm ID: native:createrandomexponentialrasterlayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Create random raster layer (gamma distribution)
Generates a raster layer for given extent and cell size filled with gamma distributed random values.
By default, the values will be chosen given an alpha and beta value of 1.0. This can be overridden by using the
advanced parameter for alpha and beta. The raster data type is set to Float32 by default as the gamma distribution
random values are floating point numbers.
Parameters
Basic parameters
Label Name Type Description
Desired extent EXTENT [extent] Specify the extent (xmin, xmax, ymin,
ymax) of the output raster layer. One of:
• Use Canvas Extent
• Select Extent on Canvas
• Use Layer Extent…
It will internally be extended to a multiple
of the tile size.
Target CRS TARGET_CRS [crs]
Default: Project
CRS
CRS for the output raster layer
Pixel size PIXEL_SIZE [number]
Default: 1.0
Pixel size (X=Y) in map units. Minimum
value: 0.01
Output raster OUTPUT [raster]
Default: [Save
to temporary
file]
Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
Advanced parameters
Label Name Type Description
Output raster
data type
OUTPUT_TYPE
Default: 0
[enumeration] Defines the data type of the output raster
file. Options:
• 0 — Float32
• 1 — Float64
Alpha ALPHA [number]
Default: 1.0
Beta BETA [number]
Default: 1.0
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Outputs
Label Name Type Description
Output raster OUTPUT [raster] Raster covering the desired extent with the
cell size filled with randomly distributed
values
Python code
Algorithm ID: native:createrandomgammarasterlayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Create random raster layer (geometric distribution)
Generates a raster layer for given extent and cell size filled with geometrically distributed random values.
By default, the values will be chosen given a probability of 0.5. This can be overridden by using the advanced parameter
for mean value. The raster data type is set to Integer types (Integer16 by default). The geometric distribution random
values are defined as positive integer numbers. A floating point raster will represent a cast of integer values to floating
point.
Parameters
Basic parameters
Label Name Type Description
Desired extent EXTENT [extent] Specify the extent (xmin, xmax, ymin,
ymax) of the output raster layer. One of:
• Use Canvas Extent
• Select Extent on Canvas
• Use Layer Extent…
It will internally be extended to a multiple
of the tile size.
Target CRS TARGET_CRS [crs]
Default: Project
CRS
CRS for the output raster layer
Pixel size PIXEL_SIZE [number]
Default: 1.0
Pixel size (X=Y) in map units. Minimum
value: 0.01
Output raster OUTPUT [raster]
Default: [Save
to temporary
file]
Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
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Advanced parameters
Label Name Type Description
Output raster
data type
OUTPUT_TYPE
Default: 0
[enumeration] Defines the data type of the output raster
file. Options:
• 0 — Integer16
• 1 — Unsigned Integer16
• 2 — Integer32
• 3 — Unsigned Integer32
• 4 — Float32
• 5 — Float64
Probability PROBABILITY [number]
Default: 0.5
Outputs
Label Name Type Description
Output raster OUTPUT [raster] Raster covering the desired extent with the
cell size filled with randomly distributed
values
Python code
Algorithm ID: native:createrandomgeometricrasterlayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Create random raster layer (negative binomial distribution)
Generates a raster layer for given extent and cell size filled with negative binomially distributed random values.
By default, the values will be chosen given a distribution parameter k of 10.0 and a probability of 0.5. This can
be overridden by using the advanced parameters for k and probability. The raster data type is set to Integer types
(Integer16 by default). The negative binomial distribution random values are defined as positive integer numbers.
A floating point raster will represent a cast of integer values to floating point.
Parameters
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Basic parameters
Label Name Type Description
Desired extent EXTENT [extent] Specify the extent (xmin, xmax, ymin,
ymax) of the output raster layer. One of:
• Use Canvas Extent
• Select Extent on Canvas
• Use Layer Extent…
It will internally be extended to a multiple
of the tile size.
Target CRS TARGET_CRS [crs]
Default: Project
CRS
CRS for the output raster layer
Pixel size PIXEL_SIZE [number]
Default: 1.0
Pixel size (X=Y) in map units. Minimum
value: 0.01
Output raster OUTPUT [raster]
Default: [Save
to temporary
file]
Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
Advanced parameters
Label Name Type Description
Output raster
data type
OUTPUT_TYPE
Default: 0
[enumeration] Defines the data type of the output raster
file. Options:
• 0 — Integer16
• 1 — Unsigned Integer16
• 2 — Integer32
• 3 — Unsigned Integer32
• 4 — Float32
• 5 — Float64
Distribution
parameter k
K_PARAMETER [number]
Default: 10
Probability PROBABILITY [number]
Default: 0.5
Outputs
Label Name Type Description
Output raster OUTPUT [raster] Raster covering the desired extent with the
cell size filled with randomly distributed
values
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Python code
Algorithm ID: native:createrandomnegativebinomialrasterlayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Create random raster layer (normal distribution)
Generates a raster layer for given extent and cell size filled with normally distributed random values.
By default, the values will be chosen given a mean of 0.0 and a standard deviation of 1.0. This can be overridden by
using the advanced parameters for mean and standard deviation value. The raster data type is set to Float32 by default
as the normal distribution random values are floating point numbers.
Parameters
Basic parameters
Label Name Type Description
Desired extent EXTENT [extent] Specify the extent (xmin, xmax, ymin,
ymax) of the output raster layer. One of:
• Use Canvas Extent
• Select Extent on Canvas
• Use Layer Extent…
It will internally be extended to a multiple
of the tile size.
Target CRS TARGET_CRS [crs]
Default: Project
CRS
CRS for the output raster layer
Pixel size PIXEL_SIZE [number]
Default: 1.0
Pixel size (X=Y) in map units. Minimum
value: 0.01
Output raster OUTPUT [raster]
Default: [Save
to temporary
file]
Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
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Advanced parameters
Label Name Type Description
Output raster
data type
OUTPUT_TYPE
Default: 0
[enumeration] Defines the data type of the output raster
file. Options:
• 0 — Float32
• 1 — Float64
Mean of normal
distribution
MEAN [number]
Default: 0.0
Standard
deviation
of normal
distribution
STDDEV [number]
Default: 1.0
Outputs
Label Name Type Description
Output raster OUTPUT [raster] Raster covering the desired extent with the
cell size filled with randomly distributed
values
Python code
Algorithm ID: native:createrandomnormalrasterlayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Create random raster layer (poisson distribution)
Generates a raster layer for given extent and cell size filled with poisson distributed random values.
By default, the values will be chosen given a mean of 1.0. This can be overridden by using the advanced parameter
for mean value. The raster data type is set to Integer types (Integer16 by default). The poisson distribution random
values are positive integer numbers. A floating point raster will represent a cast of integer values to floating point.
Parameters
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Basic parameters
Label Name Type Description
Desired extent EXTENT [extent] Specify the extent (xmin, xmax, ymin,
ymax) of the output raster layer. One of:
• Use Canvas Extent
• Select Extent on Canvas
• Use Layer Extent…
It will internally be extended to a multiple
of the tile size.
Target CRS TARGET_CRS [crs]
Default: Project
CRS
CRS for the output raster layer
Pixel size PIXEL_SIZE [number]
Default: 1.0
Pixel size (X=Y) in map units. Minimum
value: 0.01
Output raster OUTPUT [raster]
Default: [Save
to temporary
file]
Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
Advanced parameters
Label Name Type Description
Output raster
data type
OUTPUT_TYPE
Default: 0
[enumeration] Defines the data type of the output raster
file. Options:
• 0 — Integer16
• 1 — Unsigned Integer16
• 2 — Integer32
• 3 — Unsigned Integer32
• 4 — Float32
• 5 — Float64
Mean MEAN [number]
Default: 1.0
Outputs
Label Name Type Description
Output raster OUTPUT [raster] Raster covering the desired extent with the
cell size filled with randomly distributed
values
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Python code
Algorithm ID: native:createrandompoissonrasterlayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Create random raster layer (uniform distribution)
Generates a raster layer for given extent and cell size filled with random values.
By default, the values will range between the minimum and maximum value of the specified output raster type. This
can be overridden by using the advanced parameters for lower and upper bound value. If the bounds have the same
value or both are zero (default) the algorithm will create random values in the full value range of the chosen raster
data type. Choosing bounds outside the acceptable range of the output raster type will abort the algorithm.
Parameters
Basic parameters
Label Name Type Description
Desired extent EXTENT [extent] Specify the extent (xmin, xmax, ymin,
ymax) of the output raster layer. One of:
• Use Canvas Extent
• Select Extent on Canvas
• Use Layer Extent…
It will internally be extended to a multiple
of the tile size.
Target CRS TARGET_CRS [crs]
Default: Project
CRS
CRS for the output raster layer
Pixel size PIXEL_SIZE [number]
Default: 1.0
Pixel size (X=Y) in map units. Minimum
value: 0.01
Output raster OUTPUT [raster]
Default: [Save
to temporary
file]
Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
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Advanced parameters
Label Name Type Description
Output raster
data type
OUTPUT_TYPE
Default: 5
[enumeration] Defines the data type of the output raster
file. Options:
• 0 — Byte
• 1 — Integer16
• 2 — Unsigned Integer16
• 3 — Integer32
• 4 — Unsigned Integer32
• 5 — Float32
• 6 — Float64
Lower bound for
random number
range
LOWER_BOUND [number]
Default: 0.0
Upper bound for
random number
range
UPPER_BOUND [number]
Default: 0.0
Outputs
Label Name Type Description
Output raster OUTPUT [raster] Raster covering the desired extent with the
cell size filled with randomly distributed
values
Python code
Algorithm ID: native:createrandomuniformrasterlayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.1.11 Raster terrain analysis
Aspect
Calculates the aspect of the Digital Terrain Model in input. The final aspect raster layer contains values from 0 to 360
that express the slope direction, starting from north (0°) and continuing clockwise.
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Obr. 24.16: Aspect values
The following picture shows the aspect layer reclassified with a color ramp:
Obr. 24.17: Aspect layer reclassified
Parameters
Label Název Type Popis
Elevation layer INPUT [raster] Digital Terrain Model raster layer
Z factor Z_FACTOR [number]
Default: 1.0
Vertical exaggeration. This parameter
is useful when the Z units differ from the X
and Y units, for example feet and meters.
You can use this parameter to adjust for
this. The default is 1 (no exaggeration).
Aspect OUTPUT [raster] Specify the output aspect raster layer. One
of:
• Save to a Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Aspect OUTPUT [raster] The output aspect raster layer
Python code
Algorithm ID: qgis:aspect
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Hillshade
Calculates the hillshade raster layer given an input Digital Terrain Model.
The shading of the layer is calculated according to the sun position: you have the options to change both the horizontal
angle (azimuth) and the vertical angle (sun elevation) of the sun.
Obr. 24.18: Azimuth and vertical angle
The hillshade layer contains values from 0 (complete shadow) to 255 (complete sun). Hillshade is used usually to
better understand the relief of the area.
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Obr. 24.19: Hillshade layer with azimuth 300 and vertical angle 45
Particularly interesting is to give the hillshade layer a transparency value and overlap it with the elevation raster:
Obr. 24.20: Overlapping the hillshade with the elevation layer
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Parameters
Label Název Type Popis
Elevation layer INPUT [raster] Digital Terrain Model raster layer
Z factor Z_FACTOR [number]
Default: 1.0
Vertical exaggeration. This parameter
is useful when the Z units differ from the X
and Y units, for example feet and meters.
You can use this parameter to adjust for
this. Increasing the value of this parameter
will exaggerate the final result (making it
look more „hilly“). The default is 1 (no
exaggeration).
Azimuth
(horizontal angle)
AZIMUTH [number]
Default: 300.0
Set the horizontal angle (in degrees) of the
sun (clockwise direction). Range: 0 to 360.
0 is north.
Vertical angle V_ANGLE [number]
Default: 40.0
Set the vertical angle (in degrees) of the
sun, that is the height of the sun. Values
can go from 0 (minimum elevation) to 90
(maximum elevation).
Hillshade OUTPUT [raster] Specify the output hillshade raster layer.
One of:
• Save to a Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Hillshade OUTPUT [raster] The output hillshade raster layer
Python code
Algorithm ID: qgis:hillshade
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Hypsometric curves
Calculates hypsometric curves for an input Digital Elevation Model. Curves are produced as CSV files in an output
folder specified by the user.
A hypsometric curve is a cumulative histogram of elevation values in a geographical area.
You can use hypsometric curves to detect differences in the landscape due to the geomorphology of the territory.
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Parameters
Label Název Type Popis
DEM to analyze INPUT_DEM [raster] Digital Terrain Model raster layer to use for
calculating altitudes
Boundary layer BOUNDARY_LAYER [vector: polygon] Polygon vector layer with boundaries of
areas used to calculate hypsometric curves
Step STEP [number]
Default: 100.0
Vertical distance between curves
Use % of area
instead of absolute
value
USE_PERCENTAGE [boolean]
Default: False
Write area percentage to “Area” field of the
CSV file instead of the absolute area
Hypsometric
curves
OUTPUT_DIRECTORY[folder] Specify the output folder for the
hypsometric curves. One of:
• Save to a Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Hypsometric
curves
OUTPUT_DIRECTORY[folder] Directory containing the files with the
hypsometric curves. For each feature from
the input vector layer, a CSV file with area
and altitude values will be created.
The file names start with histogram_,
followed by layer name and feature ID.
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Python code
Algorithm ID: qgis:hypsometriccurves
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Relief
Creates a shaded relief layer from digital elevation data. You can specify the relief color manually, or you can let the
algorithm choose automatically all the relief classes.
Obr. 24.21: Relief layer
Parameters
Label Název Type Popis
Elevation layer INPUT [raster] Digital Terrain Model raster layer
Z factor Z_FACTOR [number]
Default: 1.0
Vertical exaggeration. This parameter
is useful when the Z units differ from the X
and Y units, for example feet and meters.
You can use this parameter to adjust for
this. Increasing the value of this parameter
will exaggerate the final result (making it
look more „hilly“). The default is 1 (no
exaggeration).
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Tabulka 24.51 – pokračujte na předchozí stránce
Label Název Type Popis
Generate
relief classes
automatically
AUTO_COLORS [boolean]
Default: False
If you check this option the algorithm
will create all the relief color classes
automatically
Relief colors
Optional
COLORS [table widget] Use the table widget if you want to
choose the relief colors manually. You
can add as many color classes as you
want: for each class you can choose the
lower and upper bound and finally by
clicking on the color row you can choose
the color thanks to the color widget.
Obr. 24.22: Manually setting of relief color
classes
The buttons in the right side panel give you
the chance to: add or remove color classes,
change the order of the color classes already
defined, open an existing file with color
classes and save the current classes as file.
Relief OUTPUT [raster]
Default: [Save
to temporary
file]
Specify the output relief raster layer. One
of:
• Save to a Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
The file encoding can also be changed here.
Frequency
distribution
FREQUENCY_DISTRIBUTION[table]
Default: [Skip
output]
Specify the CSV table for the output
frequency distribution. One of:
• Skip Output
• Save to a Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Relief OUTPUT [raster] The output relief raster layer
Frequency
distribution
OUTPUT [table] The output frequency distribution
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Python code
Algorithm ID: qgis:relief
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Ruggedness index
Calculates the quantitative measurement of terrain heterogeneity described by Riley et al. (1999). It is calculated for
every location, by summarizing the change in elevation within the 3x3 pixel grid.
Each pixel contains the difference in elevation from a center cell and the 8 cells surrounding it.
Obr. 24.23: Ruggedness layer from low (red) to high values (green)
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Parameters
Label Název Type Popis
Elevation layer INPUT [raster] Digital Terrain Model raster layer
Z factor Z_FACTOR [number]
Default: 1.0
Vertical exaggeration. This parameter
is useful when the Z units differ from the X
and Y units, for example feet and meters.
You can use this parameter to adjust for
this. Increasing the value of this parameter
will exaggerate the final result (making it
look more rugged). The default is 1 (no
exaggeration).
Ruggedness OUTPUT [raster]
Default: [Save
to temporary
file]
Specify the output ruggedness raster layer.
One of:
• Save to a Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Ruggedness OUTPUT [raster] The output ruggedness raster layer
Python code
Algorithm ID: qgis:ruggednessindex
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Slope
Calculates the slope from an input raster layer. The slope is the angle of inclination of the terrain and is expressed in
degrees.
In the following picture you can see to the left the DTM layer with the elevation of the terrain while to the right the
calculated slope:
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Obr. 24.24: Flat areas in red, steep areas in blue
Parameters
Label Název Type Popis
Elevation layer INPUT [raster] Digital Terrain Model raster layer
Z factor Z_FACTOR [number]
Default: 1.0
Vertical exaggeration. This parameter
is useful when the Z units differ from the X
and Y units, for example feet and meters.
You can use this parameter to adjust for
this. Increasing the value of this parameter
will exaggerate the final result (making it
steeper). The default is 1 (no exaggeration).
Slope OUTPUT [raster]
Default: [Save
to temporary
file]
Specify the output slope raster layer. One
of:
• Save to a Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Slope OUTPUT [raster] The output slope raster layer
Python code
Algorithm ID: qgis:slope
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.1.12 Raster tools
Convert map to raster
Creates a raster image of map canvas content.
A map theme can be selected to render a predetermined set of layers with a defined style for each layer.
Alternatively, a single layer can be selected if no map theme is set.
If neither map theme nor layer is set, the current map content will be rendered. The minimum extent entered will
internally be extended to be a multiple of the tile size.
Parameters
Label Název Type Popis
Minimum extent
to render (xmin,
xmax, ymin,
ymax)
EXTENT [extent] Specify the extent of the output raster layer.
One of:
• Use Canvas Extent
• Select Extent on Canvas
• Use Layer Extent…
It will internally be extended to a multiple
of the tile size.
Tile size TILE_SIZE [number]
Default: 1024
Size of the tile of the output raster layer.
Minimum value: 64.
Map units per
pixel
MAP_UNITS_PER_PIXEL[number]
Default: 100.0
Pixel size (in map units). Minimum value:
0.0
Make background
transparent
MAKE_BACKGROUND_TRANSPARENT[boolean]
Default: False
Allows exporting the map with
a transparent background. Outputs an
RGBA (instead of RGB) image if set to
True.
Map theme to
render
Optional
MAP_THEME [enumeration] Use an existing map theme for the
rendering.
Single layer to
render
Optional
LAYER [enumeration] Choose a single layer for the rendering
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Label Název Type Popis
Output layer OUTPUT [raster]
Default: Save to
temporary file
Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Output layer OUTPUT [raster] Output raster layer
Python code
Algorithm ID: qgis:rasterize
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Fill NoData cells
Resets the NoData values in the input raster to a chosen value, resulting in raster dataset with no NoData pixels.
The algorithm respects the input raster data type, e.g. a floating point fill value will be truncated when applied to an
integer raster.
Obr. 24.25: Filling NoData values (in grey) of a raster
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Parameters
Label Název Type Popis
Input raster INPUT [raster] The raster to process.
Band number BAND [number]
Default: 1
The band of the raster
Fill value FILL_VALUE [number]
Default: 1.0
Set the value to use for the NoData pixels
Output raster OUTPUT [raster]
Default: [Save
to temporary
file]
Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
Outputs
Label Název Type Popis
Output raster OUTPUT [raster] The output raster layer with filled data cells.
Python code
Algorithm ID: native:fillnodata
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Generate XYZ tiles (Directory)
Generates raster “XYZ” tiles using the current QGIS project as individual images to a directory structure.
Parameters
Label Název Type Popis
Extent (xmin,
xmax, ymin,
ymax)
EXTENT [extent] Specify the extent of the tiles. One of:
• Use Canvas Extent
• Select Extent on Canvas
• Use Layer Extent…
It will internally be extended to a multiple
of the tile size.
Minimum zoom ZOOM_MIN [number]
Default: 12
Minimum 0, maximum 25.
Maximum zoom ZOOM_MAX [number]
Default: 12
Minimum 0, maximum 25.
DPI DPI [number]
Default: 96
Minimum 48, maximum 600.
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Label Název Type Popis
Background color
Optional
BACKGROUND_COLOR[color]
Default: QColor(0,
0, 0, 0)
Choose the background color for the tiles
Tile format TILE_FORMAT [enumeration]
Default: 0
One of:
• 0 — PNG
• 1 — JPG
Quality (JPG
only)
Optional
QUALITY [number]
Default: 75
Minimum 1, maximum 100.
Metatile size
Optional
METATILESIZE [number]
Default: 4
Specify a custom metatile size when
generating XYZ tiles. Larger values may
speed up the rendering of tiles and provide
better labelling (fewer gaps without labels)
at the expense of using more memory.
Minimum 1, maximum 20.
Tile width
Optional
TILE_WIDTH [number]
Default: 256
Minimum 1, maximum 4096.
Tile height
Optional
TILE_HEIGHT [number]
Default: 256
Minimum 1, maximum 4096.
Use inverted tile
Y axis (TMS
conventions)
Optional
TMS_CONVENTION [boolean]
Default: False
Output directory OUTPUT_DIRECTORY[folder]
Default: [Save
to temporary
folder]
Specification of the output raster. One of:
• Skip Output
• Save to a Temporary Directory
• Save to Directory…
The file encoding can also be changed here.
Output html
(Leaflet)
OUTPUT_HTML [html]
Default: [Save
to temporary
file]
Specification of the output HTML file. One
of:
• Skip Output
• Save to a Temporary File
• Save to File…
Outputs
Label Název Type Popis
Output directory OUTPUT_DIRECTORY[folder] Output directory (for the tiles)
Output html
(Leaflet)
OUTPUT_HTML [html] The output HTML (Leaflet) file
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Python code
Algorithm ID: qgis:tilesxyzdirectory
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Generate XYZ tiles (MBTiles)
Generates raster “XYZ” tiles using the current QGIS project as a single file in the “MBTiles” format.
Parameters
Label Název Type Popis
Extent (xmin,
xmax, ymin,
ymax)
EXTENT [extent] Specify the extent of the tiles. One of:
• Use Canvas Extent
• Select Extent on Canvas
• Use Layer Extent…
It will internally be extended to a multiple
of the tile size.
Minimum zoom ZOOM_MIN [number]
Default: 12
Minimum 0, maximum 25.
Maximum zoom ZOOM_MAX [number]
Default: 12
Minimum 0, maximum 25.
DPI DPI [number]
Default: 96
Minimum 48, maximum 600.
Background color
Optional
BACKGROUND_COLOR[color]
Default: QColor(0,
0, 0, 0)
Choose the background color for the tiles
Tile format TILE_FORMAT [enumeration]
Default: 0
One of:
• 0 — PNG
• 1 — JPG
Quality (JPG
only)
Optional
QUALITY [number]
Default: 75
Minimum 1, maximum 100.
Metatile size
Optional
METATILESIZE [number]
Default: 4
Specify a custom metatile size when
generating XYZ tiles. Larger values may
speed up the rendering of tiles and provide
better labelling (fewer gaps without labels)
at the expense of using more memory.
Minimum 1, maximum 20.
Output file (for
MBTiles)
OUTPUT_FILE [file]
Default: [Save
to temporary
file]
Specification of the output file. One of:
• Skip Output
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Output file (for
MBTiles)
OUTPUT_FILE [file] The output file.
Python code
Algorithm ID: qgis:tilesxyzmbtiles
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.1.13 Vector analysis
Basic statistics for fields
Generates basic statistics for a field of the attribute table of a vector layer.
Numeric, date, time and string fields are supported.
The statistics returned will depend on the field type.
Statistics are generated as an HTML file and are available in the Processing ► Results viewer.
Default menu: Vector ► Analysis Tools
Parameters
Label Název Type Popis
Input vector INPUT_LAYER [vector: any] Vector layer to calculate the statistics on
Field to calculate
statistics on
FIELD_NAME [tablefield: any] Any supported table field to calculate the
statistics
Statistics OUTPUT_HTML_FILE[html] HTML file for the calculated statistics
Outputs
Label Název Type Popis
Statistics OUTPUT_HTML_FILE[html] HTML file with the
calculated statistics
Count COUNT [number]
Number of unique values UNIQUE [number]
Number of empty (null) values EMPTY [number]
Number of non-empty values FILLED [number]
Minimum value MIN [same as input]
Maximum value MAX [same as input]
Minimum length MIN_LENGTH [number]
Maximum length MAX_LENGTH [number]
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Label Název Type Popis
Mean length MEAN_LENGTH [number]
Coefficient of Variation CV [number]
Sum SUM [number]
Mean value MEAN [number]
Standard deviation STD_DEV [number]
Range RANGE [number]
Median MEDIAN [number]
Minority (rarest occurring value) MINORITY [same as input]
Majority (most frequently
occurring value)
MAJORITY [same as input]
First quartile FIRSTQUARTILE [number]
Third quartile THIRDQUARTILE [number]
Interquartile Range (IQR) IQR [number]
Python code
Algorithm ID: qgis:basicstatisticsforfields
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Climb along line
Calculates the total climb and descent along line geometries. The input layer must have Z values present. If Z values
are not available, the Drape (set Z value from raster) algorithm may be used to add Z values from a DEM layer.
The output layer is a copy of the input layer with additional fields that contain the total climb (climb), total descent
(descent), the minimum elevation (minelev) and the maximum elevation (maxelev) for each line geometry.
If the input layer contains fields with the same names as these added fields, they will be renamed (field names will be
altered to „name_2“, „name_3“, etc, finding the first non-duplicate name).
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Parameters
Label Název Type Popis
Line layer INPUT [vector: line] Line layer to calculate the climb for. Must
have Z values
Climb layer OUTPUT [vector: line] The output (line) layer
Outputs
Label Název Type Popis
Climb layer OUTPUT [vector: line] Line layer containing new attributes with
the results from climb calculations.
Total climb TOTALCLIMB [number] The sum of the climb for all the line
geometries in the input layer
Total descent TOTALDESCENT [number] The sum of the descent for all the line
geometries in the input layer
Minimum
elevation
MINELEVATION [number] The minimum elevation for the geometries
in the layer
Maximum
elevation
MAXELEVATION [number] The maximum elevation for the geometries
in the layer
Python code
Algorithm ID: qgis:climbalongline
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Count points in polygon
Takes a point and a polygon layer and counts the number of points from the point layer in each of the polygons of the
polygon layer.
A new polygon layer is generated, with the exact same content as the input polygon layer, but containing an additional
field with the points count corresponding to each polygon.
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Obr. 24.26: The labels in the polygons show the point count
An optional weight field can be used to assign weights to each point. Alternatively, a unique class field can be specified.
If both options are used, the weight field will take precedence and the unique class field will be ignored.
Default menu: Vector ► Analysis Tools
Parameters
Label Název Type Popis
Polygons POLYGONS [vector: polygon] Polygon layer whose features are associated
with the count of points they contain
Points POINTS [vector: point] Point layer with features to count
Weight field
Optional
WEIGHT [tablefield: any] A field from the point layer. The count
generated will be the sum of the weight field
of the points contained by the polygon. If
the weight field is not numeric, the count
will be 0.
Class field
Optional
CLASSFIELD [tablefield: any] Points are classified based on the selected
attribute and if several points with the same
attribute value are within the polygon, only
one of them is counted. The final count of
the points in a polygon is, therefore, the
count of different classes that are found in
it.
Count field name FIELD [string]
Default:
‚NUMPOINTS‘
The name of the field to store the count of
points
Count OUTPUT [vector: polygon] Specification of the output layer
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Outputs
Label Název Type Popis
Count OUTPUT [vector: polygon] Resulting layer with the attribute table
containing the new column with the points
count
DBSCAN clustering
Clusters point features based on a 2D implementation of Density-based spatial clustering of applications with noise
(DBSCAN) algorithm.
The algorithm requires two parameters, a minimum cluster size, and the maximum distance allowed between clustered
points.
Viz také:
K-means clustering
Parameters
Label Název Type Popis
Input layer INPUT [vector: point] Layer to analyze
Minimum cluster
size
MIN_SIZE [number]
Default: 5
Minimum number of features to generate
a cluster
Maximum
distance between
clustered points
EPS [number]
Default: 1.0
Distance beyond which two features can not
belong to the same cluster (eps)
Cluster field name FIELD_NAME [string]
Default:
‚CLUSTER_ID‘
Name of the field where the associated
cluster number shall be stored
Treat border
points as noise
(DBSCAN*)
Optional
DBSCAN* [boolean]
Default: False
If checked, points on the border of a cluster
are themselves treated as unclustered
points, and only points in the interior of
a cluster are tagged as clustered.
Clusters OUTPUT [vector: point] Vector layer for the result of the clustering
Outputs
Label Název Type Popis
Clusters OUTPUT [vector: point] Vector layer containing the original features
with a field setting the cluster they belong to
Number of
clusters
NUM_CLUSTERS [number] The number of clusters discovered
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Python code
Algorithm ID: qgis:dbscanclustering
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Distance matrix
Calculates for point features distances to their nearest features in the same layer or in another layer.
Default menu: Vector ► Analysis Tools
Viz také:
Join attributes by nearest
Parameters
Label Název Type Popis
Input point layer INPUT [vector: point] Point layer for which the distance matrix
is calculated (from points)
Input unique ID
field
INPUT_FIELD [tablefield: any] Field to use to uniquely identify features of
the input layer. Used in the output attribute
table.
Target point layer TARGET [vector: point] Point layer containing the nearest point(s)
to search (to points)
Target unique ID
field
TARGET_FIELD [tablefield: any] Field to use to uniquely identify features of
the target layer. Used in the output attribute
table.
Output matrix
type
MATRIX_TYPE [enumeration]
Default: 0
Different types of calculation are available:
• 0 — Linear (N * k x 3) distance
matrix: for each input point, reports
the distance to each of the k nearest
target points. The output matrix
consists of up to k rows per input
point, and each row has three
columns: InputID, TargetID and
Distance.
• 1 — Standard (N x T) distance
matrix
• 2 — Summary distance matrix
(mean, std. dev., min, max): for each
input point, reports statistics on the
distances to its target points.
Use only the
nearest (k) target
points
NEAREST_POINTS [number]
Default: 0
You can choose to calculate the distance to
all the points in the target layer (0) or limit
to a number (k) of closest features.
Distance matrix OUTPUT [vector: point]
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Outputs
Label Název Type Popis
Distance matrix OUTPUT [vector: point] Point (or MultiPoint for the „Linear (N *
k x 3)“ case) vector layer containing the
distance calculation for each input feature.
Its features and attribute table depend on the
selected output matrix type.
Python code
Algorithm ID: qgis:distancematrix
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Distance to nearest hub (line to hub)
Creates lines that join each feature of an input vector to the nearest feature in a destination layer. Distances are
calculated based on the center of each feature.
Obr. 24.27: Display the nearest hub for the red input features
Viz také:
Distance to nearest hub (points), Join attributes by nearest
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Parameters
Label Název Type Popis
Source points
layer
INPUT [vector: any] Vector layer for which the nearest feature
is searched
Destination hubs
layer
HUBS [vector: any] Vector layer containing the features to
search for
Hub layer name
attribute
FIELD [tablefield: any] Field to use to uniquely identify features
of the destination layer. Used in the output
attribute table
Measurement unit UNIT [enumeration]
Default: 0
Units in which to report the distance to the
closest feature:
• 0 — Meters
• 1 — Feet
• 2 — Miles
• 3 — Kilometers
• 4 — Layer units
Hub distance OUTPUT [vector: line] Line vector layer for the distance matrix
output
Outputs
Label Název Type Popis
Hub distance OUTPUT [vector: line] Line vector layer with the attributes of the
input features, the identifier of their closest
feature and the calculated distance.
Python code
Algorithm ID: qgis:distancetonearesthublinetohub
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Distance to nearest hub (points)
Creates a point layer representing the center of the input features with the addition of two fields containing the identifier
of the nearest feature (based on its center point) and the distance between the points.
Viz také:
Distance to nearest hub (line to hub), Join attributes by nearest
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Parameters
Label Název Type Popis
Source points
layer
INPUT [vector: any] Vector layer for which the nearest feature
is searched
Destination hubs
layer
HUBS [vector: any] Vector layer containing the features to
search for
Hub layer name
attribute
FIELD [tablefield: any] Field to use to uniquely identify features
of the destination layer. Used in the output
attribute table
Measurement unit UNIT [enumeration]
Default: 0
Units in which to report the distance to the
closest feature:
• 0 — Meters
• 1 — Feet
• 2 — Miles
• 3 — Kilometers
• 4 — Layer units
Hub distance OUTPUT [vector: point] Point vector layer for the distance matrix
output.
Outputs
Label Název Type Popis
Hub distance OUTPUT [vector: point] Point vector layer with the attributes of the
input features, the identifier of their closest
feature and the calculated distance.
Python code
Algorithm ID: qgis:distancetonearesthubpoints
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Join by lines (hub lines)
Creates hub and spoke diagrams by connecting lines from points on the Spoke layer to matching points in the Hub
layer.
Determination of which hub goes with each point is based on a match between the Hub ID field on the hub points
and the Spoke ID field on the spoke points.
If input layers are not point layers, a point on the surface of the geometries will be taken as the connecting location.
Optionally, geodesic lines can be created, which represent the shortest path on the surface of an ellipsoid. When
geodesic mode is used, it is possible to split the created lines at the antimeridian (±180 degrees longitude), which
can improve rendering of the lines. Additionally, the distance between vertices can be specified. A smaller distance
results in a denser, more accurate line.
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Obr. 24.28: Join points based on a common field / attribute
Parameters
Label Název Type Popis
Hub layer HUBS [vector: any] Input layer
Hub ID field HUB_FIELD [tablefield: any] Field of the hub layer with ID to join
Hub layer fields to
copy (leave empty
to copy all fields)
Optional
HUB_FIELDS [tablefield: any]
[list]
The field(s) of the hub layer to be copied. If
no field(s) are chosen all fields are taken.
Spoke layer SPOKES [vector: any] Additional spoke point layer
Spoke ID field SPOKE_FIELD [tablefield: any] Field of the spoke layer with ID to join
Spoke layer fields
to copy (leave
empty to copy all
fields)
Optional
SPOKE_FIELDS [tablefield: any]
[list]
Field(s) of the spoke layer to be copied. If
no fields are chosen all fields are taken.
Create geodesic
lines
GEODESIC [boolean]
Default: False
Create geodesic lines (the shortest path on
the surface of an ellipsoid)
Distance between
vertices (geodesic
lines only)
GEODESIC_DISTANCE[number]
Default: 1000.0
(kilometers)
Distance between consecutive vertices (in
kilometers). A smaller distance results in
a denser, more accurate line
Split lines at
antimeridian
(±180 degrees
longitude)
ANTIMERIDIAN_SPLIT[boolean]
Default: False
Split lines at ±180 degrees longitude (to
improve rendering of the lines)
Hub lines OUTPUT [vector: line] The resulting line layer
Outputs
Label Název Type Popis
Hub lines OUTPUT [vector: line] The resulting line layer
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Python code
Algorithm ID: qgis:hublines
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
K-means clustering
Calculates the 2D distance based k-means cluster number for each input feature.
K-means clustering aims to partition the features into k clusters in which each feature belongs to the cluster with the
nearest mean. The mean point is represented by the barycenter of the clustered features.
If input geometries are lines or polygons, the clustering is based on the centroid of the feature.
Obr. 24.29: A five class point clusters
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Viz také:
DBSCAN clustering
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Layer to analyze
Number of
clusters
CLUSTERS [number]
Default: 5
Number of clusters to create with the
features
Cluster field name FIELD_NAME [string]
Default:
‚CLUSTER_ID‘
Name of the cluster number field
Clusters OUTPUT [vector: any] Vector layer for generated the clusters
Outputs
Label Název Type Popis
Clusters OUTPUT [vector: any] Vector layer containing the original features
with a field specifying the cluster they
belong to
Python code
Algorithm ID: qgis:kmeansclustering
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
List unique values
Lists unique values of an attribute table field and counts their number.
Default menu: Vector ► Analysis Tools
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Layer to analyze
Target field(s) FIELDS [tablefield: any] Field to analyze
Unique values OUTPUT [table] Summary table layer with unique values
HTML report OUTPUT_HTML_FILE[html] HTML report of unique values in the
Processing ► Results viewer
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Outputs
Label Název Type Popis
Unique values OUTPUT [table] Summary table layer with unique values
HTML report OUTPUT_HTML_FILE[html] HTML report of unique values. Can be
opened from the Processing ► Results
viewer
Total unique
values
TOTAL_VALUES [number] The number of uniqe values in the input
field
UNIQUE_VALUES Unique values [string] A string with the comma separated list of
unique values found in the input field
Python code
Algorithm ID: qgis:listuniquevalues
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Mean coordinate(s)
Computes a point layer with the center of mass of geometries in an input layer.
An attribute can be specified as containing weights to be applied to each feature when computing the center of mass.
If an attribute is selected in the parameter, features will be grouped according to values in this field. Instead of a single
point with the center of mass of the whole layer, the output layer will contain a center of mass for the features in each
category.
Default menu: Vector ► Analysis Tools
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Weight field
Optional
WEIGHT [tablefield:
numeric]
Field to use if you want to perform
a weighted mean
Unique ID field UID [tablefield:
numeric]
Unique field on which the calculation of the
mean will be made
Mean coordinates OUTPUT [vector: point] The (point vector) layer for the result
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Outputs
Label Název Type Popis
Mean coordinates OUTPUT [vector: point] Resulting point(s) layer
Python code
Algorithm ID: qgis:meancoordinates
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Nearest neighbour analysis
Performs nearest neighbor analysis for a point layer. The output tells you how your data are distributed (clustered,
randomly or distributed).
Output is generated as an HTML file with the computed statistical values:
• Observed mean distance
• Expected mean distance
• Nearest neighbour index
• Number of points
• Z-Score: Comparing the Z-Score with the normal distribution tells you how your data are distributed. A low
Z-Score means that the data are unlikely to be the result of a spatially random process, while a high Z-Score
means that your data are likely to be a result of a spatially random process.
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Default menu: Vector ► Analysis Tools
Viz také:
Join attributes by nearest
Parameters
Label Název Type Popis
Input layer INPUT [vector: point] Point vector layer to calculate the statistics
on
Nearest neighbour OUTPUT_HTML_FILE[html] HTML file for the computed statistics
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Outputs
Label Název Type Popis
Nearest neighbour OUTPUT_HTML_FILE[html] HTML file with the computed statistics
Observed mean
distance
OBSERVED_MD [number] Observed mean distance
Expected mean
distance
EXPECTED_MD [number] Expected mean distance
Nearest neighbour
index
NN_INDEX [number] Nearest neighbour index
Number of points POINT_COUNT [number] Number of points
Z-Score Z_SCORE [number] Z-Score
Python code
Algorithm ID: qgis:nearestneighbouranalysis
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Overlap analysis
Calculates the area and percentage cover by which features from an input layer are overlapped by features from
a selection of overlay layers.
New attributes are added to the output layer reporting the total area of overlap and percentage of the input feature
overlapped by each of the selected overlay layers.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] The input layer.
Overlap layers LAYERS [vector: any] [list] The overlay layers.
Output layer OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Output layer OUTPUT [same as input] The output layer with additional fields
reporting the overlap (in map units and
percentage) of the input feature overlapped
by each of the selected layers.
Python code
Algorithm ID: qgis:calculatevectoroverlaps
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Statistics by categories
Calculates statistics of a field depending on a parent class. The parent class is a combination of values from other
fields.
Parameters
Label Název Type Popis
Input vector layer INPUT [vector: any] Input vector layer with unique classes and
values
Field to calculate
statistics on (if
empty, only count
is calculated)
Optional
VALUES_FIELD_NAME[tablefield: any] If empty only the count will be calculated
Field(s) with
categories
CATEGORIES_FIELD_NAME[vector: any] [list] The fields that (combined) define the
categories
Statistics by
category
OUTPUT [table] Table for the generated statistics
Outputs
Label Název Type Popis
Statistics by
category
OUTPUT [table] Table containing the statistics
Depending on the type of the field being analyzed, the following statistics are returned for each grouped value:
Statistics Řetězec Numeric Datum
Count (COUNT)
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Tabulka 24.61 – pokračujte na předchozí stránce
Statistics Řetězec Numeric Datum
Unique values (UNIQUE)
Empty (null) values (EMPTY)
Non-empty values (FILLED)
Minimal value (MIN)
Maximal value (MAX)
Range (RANGE)
Sum (SUM)
Mean value (MEAN)
Median value (MEDIAN)
Standard Deviation (STD_DEV)
Coefficient of variation (CV)
Minority (rarest occurring value - MINORITY)
Majority (most frequently occurring value - MAJORITY)
First Quartile (FIRSTQUARTILE)
Third Quartile (THIRDQUARTILE)
Inter Quartile Range (IQR)
Minimum Length (MIN_LENGTH)
Mean Length (MEAN_LENGTH)
Maximum Length (MAX_LENGTH)
Python code
Algorithm ID: qgis:statisticsbycategories
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Sum line lengths
Takes a polygon layer and a line layer and measures the total length of lines and the total number of them that cross
each polygon.
The resulting layer has the same features as the input polygon layer, but with two additional attributes containing the
length and count of the lines across each polygon.
Default menu: Vector ► Analysis Tools
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Parameters
Label Název Type Popis
Lines LINES [vector: line] Input vector line layer
Polygons POLYGONS [vector: polygon] Polygon vector layer
Lines length field
name
LEN_FIELD [string]
Default: ‚LENGTH‘
Name of the field for the lines length
Lines count field
name
COUNT_FIELD [string]
Default: ‚COUNT‘
Name of the field for the lines count
Line length OUTPUT [vector: polygon] The output polygon vector layer
Outputs
Label Název Type Popis
Line length OUTPUT [vector: polygon] Polygon output layer with fields of lines
length and line count
Python code
Algorithm ID: qgis:sumlinelengths
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.1.14 Vector creation
Array of offset (parallel) lines
Creates copies of line features in a layer, by creating multiple offset versions of each feature. Each new version
is incrementally offset by a specified distance.
Positive distance will offset lines to the left, and negative distances will offset them to the right.
Obr. 24.30: In blue the source layer, in red the offset one
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Allows features in-place modification
Viz také:
Offset lines, Array of translated features
Parameters
Label Název Type Popis
Input layer INPUT [vector: line] Input line vector layer to use for the offsets.
Number of
features to create
COUNT [number ]
Default: 10
Number of offset copies to generate for
each feature
Offset step
distance
OFFSET [number ]
Default: 1.0
Distance between two consecutive offset
copies
Segments SEGMENTS [number]
Default: 8
Number of line segments to use to
approximate a quarter circle when creating
rounded offsets
Join style JOIN_STYLE [enumeration]
Default: 0
Specify whether round, miter or beveled
joins should be used when offsetting corners
in a line. One of:
• 0 — Round
• 1 — Miter
• 2 — Bevel
Miter limit MITER_LIMIT [number]
Default: 2.0
Only applicable for mitered join styles, and
controls the maximum distance from the
offset curve to use when creating a mitered
join.
Offset lines OUTPUT [vector: line]
Default: [Create
temporary
layer]
Specify the output line layer with offset
features. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Offset lines OUTPUT [vector: line] Output line layer with offset features. The
original features are also copied.
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Python code
Algorithm ID: qgis:arrayoffsetlines
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Array of translated features
Creates copies of features in a layer by creating multiple translated versions of each. Each copy is incrementally
displaced by a preset amount in the X, Y and/or Z axis.
M values present in the geometry can also be translated.
Obr. 24.31: Input layers in blue tones, output layers with translated features in red tones
Allows features in-place modification
Viz také:
Translate, Array of offset (parallel) lines
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer to translate
Number of
features to create
COUNT [number ]
Default: 10
Number of copies to generate for each
feature
Step distance (x-
-axis)
DELTA_X [number ]
Default: 0.0
Displacement to apply on the X axis
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Tabulka 24.64 – pokračujte na předchozí stránce
Label Název Type Popis
Step distance (y-
-axis)
DELTA_Y [number ]
Default: 0.0
Displacement to apply on the Y axis
Step distance (z-
axis)
DELTA_Z [number ]
Default: 0.0
Displacement to apply on the Z axis
Step distance (m
values)
DELTA_M [number ]
Default: 0.0
Displacement to apply on M
Translated OUTPUT [same as input]
Default: [Create
temporary
layer]
Output vector layer with translated (moved)
copies of the features. The original features
are also copied. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Translated OUTPUT [same as input] Output vector layer with translated (moved)
copies of the features. The original features
are also copied.
Python code
Algorithm ID: qgis:arraytranslatedfeatures
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Create grid
Creates a vector layer with a grid covering a given extent. Grid cells can have different shapes:
Obr. 24.32: Different grid cell shapes
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The size of each element in the grid is defined using a horizontal and vertical spacing.
The CRS of the output layer must be defined.
The grid extent and the spacing values must be expressed in the coordinates and units of this CRS.
Default menu: Vector ► Research Tools
Parameters
Label Název Type Popis
Grid type TYPE [enumeration]
Default: 0
Shape of the grid. One of:
• 0 — Point
• 1 — Line
• 2 — Rectangle (polygon)
• 3 — Diamond (polygon)
• 4 — Hexagon (polygon)
Grid extent EXTENT [extent] Extent of the grid
Horizontal
spacing
HSPACING [number]
Default: 1.0
Size of a grid cell on the X-axis
Vertical spacing VSPACING [number]
Default: 1.0
Size of a grid cell on the Y-axis
Horizontal overlay HOVERLAY [number]
Default: 0.0
Overlay distance between two consecutive
grid cells on the X-axis
Vertical overlay VOVERLAY [number]
Default: 0.0
Overlay distance between two consecutive
grid cells on the Y-axis
Grid CRS CRS [crs]
Default: Project CRS
Coordinate reference system to apply to the
grid
Grid OUTPUT [vector: any]
Default: [Create
temporary
layer]
Resulting vector grid layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Grid OUTPUT [vector: any] Resulting vector grid layer. The output
geometry type (point, line or polygon)
depends on the Grid type.
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Python code
Algorithm ID: qgis:creategrid
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Create points layer from table
Creates points layer from a table with columns that contain coordinates fields.
Besides X and Y coordinates you can also specify Z and M fields.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer or a table.
X field XFIELD [tablefield: any] Field containing the X coordinate
Y field YFIELD [tablefield: any] Field containing the Y coordinate
Z field
Optional
ZFIELD [tablefield: any] Field containing the Z coordinate
M field
Optional
MFIELD [tablefield: any] Field containing the M value
Target CRS TARGET_CRS [crs]
Default:
EPSG:4326
Coordinate reference system to use for
layer. The provided coordinates are
assumed to be compliant.
Points from table OUTPUT [vector: point]
Default: [Create
temporary
layer]
Specify the resulting point layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Points from table OUTPUT [vector: point] The resulting point layer
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Python code
Algorithm ID: qgis:createpointslayerfromtable
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Generate points (pixel centroids) along line
Generates a point vector layer from an input raster and line layer.
The points correspond to the pixel centroids that intersect the line layer.
Obr. 24.33: Points of the pixel centroids
Parameters
Label Název Type Popis
Raster layer INPUT_RASTER [raster] Input raster layer
Vector layer INPUT_VECTOR [vector: line] Input line vector layer
Points along line OUTPUT [vector: point]
Default: [Create
temporary
layer]
Resulting point layer with pixel centroids.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Points along line OUTPUT [vector: point] Resulting point layer with pixel centroids
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Python code
Algorithm ID: qgis:generatepointspixelcentroidsalongline
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Generate points (pixel centroids) inside polygon
Generates a point vector layer from an input raster and polygon layer.
The points correspond to the pixel centroids that intersect the polygon layer.
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Obr. 24.34: Points of the pixel centroids
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Parameters
Label Název Type Popis
Raster layer INPUT_RASTER [raster] Input raster layer
Vector layer INPUT_VECTOR [vector: polygon] Input polygon vector layer
Points inside
polygons
OUTPUT [vector: point]
Default: [Create
temporary
layer]
Resulting point layer of pixel centroids. One
of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Points inside
polygons
OUTPUT [vector: point] Resulting point layer of pixel centroids
Python code
Algorithm ID: qgis:generatepointspixelcentroidsinsidepolygons
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Import geotagged photos
Creates a point layer corresponding to the geotagged locations from JPEG images from a source folder.
The point layer will contain a single PointZ feature per input file from which the geotags could be read. Any altitude
information from the geotags will be used to set the point’s Z value.
Besides longitude and latitude also altitude, direction and timestamp information, if present in the photo, will be
added to the point as attributes.
Parameters
Label Název Type Popis
Input folder FOLDER [folder] Path to the source folder containing the
geotagged photos
Scan recursively RECURSIVE [boolean]
Default: False
If checked, the folder and its subfolders will
be scanned
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Tabulka 24.67 – pokračujte na předchozí stránce
Label Název Type Popis
Photos OUTPUT [vector: point]
Default: [Create
temporary
layer]
Specify the point vector layer for the
geotagged photos. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Invalid photos
table
Optional
INVALID [table]
Default: [Skip
output]
Specify the table of unreadable or non-geotagged
photos. One of:
• Skip Output
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Photos OUTPUT [vector: point] Point vector layer with geotagged photos.
The form of the layer is automatically filled
with paths and photo previews settings.
Invalid photos
table
Optional
INVALID [table] Table of unreadable or non-geotagged
photos can also be created.
Python code
Algorithm ID: qgis:importphotos
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Points to path
Converts a point layer to a line layer, by joining points in an order defined by a field in the input point layer (if the
order field is a date/time field, the format must be specified).
Points can be grouped by a field to distinguish line features.
In addition to the line vector layer, a text file is output that describes the resulting line as a start point and a sequence
of bearings / directions (relative to azimuth) and distances.
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Parameters
Label Název Type Popis
Input point layer INPUT [vector: point] Input point vector layer
Close path CLOSE_PATH [boolean]
Default: False
If checked, the first and last points of
the line will be connected and close the
generated path
Order field ORDER_FIELD [tablefield: any] Field containing the order to connect the
points in the path
Group field
Optional
GROUP_FIELD [tablefield: any] Point features of the same value in the field
will be grouped in the same line. If not set,
a single path is drawn with all the input
points.
Date format
(if order field
is DateTime)
Optional
DATE_FORMAT [string] The format to use for the Order field
parameter. Specify this only if the Order
field is of type Date/Time.
Paths OUTPUT [vector: line]
Default: [Create
temporary
layer]
Specify the line vector layer of the path.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Directory for text
output
OUTPUT_TEXT_DIR[folder]
Default: [Skip
output]
Specify the directory that will contain the
description files of points and paths. One of:
• Skip Output
• Save to a Temporary Directory
• Save to Directory…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Paths OUTPUT [vector: line] Line vector layer of the path
Directory for text
output
OUTPUT_TEXT_DIR[folder] Directory containing description files of
points and paths
Python code
Algorithm ID: qgis:pointstopath
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Random points along line
Creates a new point layer, with points placed on the lines of another layer.
For each line in the input layer, a given number of points is added to the resulting layer. The procedure for adding
a point is to:
1. randomly select a line feature from the input layer
2. if the feature is multi-part, randomly select a part of it
3. randomly select a segment of that line
4. randomly select a position on that segment.
The procedure means that curved parts of the lines (with relatively short segments) will get more points than straight
parts (with relatively long segments), as demonstrated in the illustration below, where the output of the Random points
along lines algorithm can be compared with the output of the Random points on lines algorithm (that produces points
with an, on average, even distribution along the lines).
Obr. 24.35: Example algorithm output. Left: Random points along line, right: Random points on lines
A minimum distance can be specified, to avoid points being too close to each other.
Viz také:
Random points on lines
Parameters
Label Název Type Popis
Input point layer INPUT [vector: line] Input line vector layer
Number of points POINTS_NUMBER [number]
Default: 1
Number of points to create
Minimum
distance between
points
MIN_DISTANCE [number]
Default: 0.0
The minimum distance between points
Random points OUTPUT [vector: point]
Default: [Create
temporary
layer]
The output random points. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Random points OUTPUT [vector: point] The output random points layer.
Python code
Algorithm ID: qgis:qgisrandompointsalongline
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Random points in extent
Creates a new point layer with a given number of random points, all of them within a given extent.
A distance factor can be specified, to avoid points being too close to each other. If the minimum distance between
points makes it impossible to create new points, either distance can be decreased or the maximum number of attempts
may be increased.
Default menu: Vector ► Research Tools
Parameters
Label Název Type Popis
Input extent EXTENT [extent] Map extent for the random points
Number of points POINTS_NUMBER [number]
Default: 1
Number of point to create
Minimum
distance between
points
MIN_DISTANCE [number]
Default: 0.0
The minimum distance between points
Target CRS TARGET_CRS [crs]
Default: Project CRS
CRS of the random points layer
Maximum
number of search
attempts given
the minimum
distance
MAX_ATTEMPTS [number]
Default: 200
Maximum number of attempts to place the
points
Random points OUTPUT [vector: point]
Default: [Create
temporary
layer]
The output random points. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Random points OUTPUT [vector: point] The output random points layer.
Python code
Algorithm ID: native:randompointsinextent
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Random points in layer bounds
Creates a new point layer with a given number of random points, all of them within the extent of a given layer.
A minimum distance can be specified, to avoid points being too close to each other.
Default menu: Vector ► Research Tools
Parameters
Label Název Type Popis
Input layer INPUT [vector: polygon] Input polygon layer defining the area
Number of points POINTS_NUMBER [number]
Default: 1
Number of points to create
Minimum
distance between
points
MIN_DISTANCE [number]
Default: 0.0
The minimum distance between points
Random points OUTPUT [vector: point]
Default: [Create
temporary
layer]
The output random points. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Random points OUTPUT [vector: point] The output random points layer.
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Python code
Algorithm ID: qgis:randompointsinlayerbounds
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Random points in polygons
Creates a point layer with points placed inside the polygons of another layer.
For each feature (polygon / multi-polygon) geometry in the input layer, the given number of points is added to the
result layer.
Per feature and global minimum distances can be specified in order to avoid points being too close in the output point
layer. If a minimum distance is specified, it may not be possible to generate the specified number of points for each
feature. The total number of generated points and missed points are available as output from the algorithm.
The illustration below shows the effect of per feature and global minimum distances and zero/non-zero minimum
distances (generated with the same seed, so at least the first point generated will be the same).
Obr. 24.36: Ten points per polygon feature, left: min. distances = 0, middle: min.distances = 1, right: min. distance =
1, global min. distance = 0
The maximum number of tries per point can be specified. This is only relevant for non-zero minimum distance.
A seed for the random number generator can be provided, making it possible to get identical random number
sequences for different runs of the algorithm.
The attributes of the polygon feature on which a point was generated can be included (Include polygon attributes).
If you want approximately the same point density for all the features, you can data-define the number of points using
the area of the polygon feature geometry.
Viz také:
Random points inside polygons
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Parameters
Label Název Type Popis
Input polygon
layer
INPUT [vector: line] Input polygon vector layer
Number of points
for each feature
POINTS_NUMBER [number ]
Default: 1
Number of points to create
Minimum
distance between
points
Optional
MIN_DISTANCE [number ]
Default: 0.0
The minimum distance between points
within one polygon feature
Global minimum
distance between
points
Optional
MIN_DISTANCE_GLOBAL[number ]
Default: 0.0
The global minimum distance between
points. Should be smaller than the Minimum
distance between points (per feature) for that
parameter to have an effect.
Maximum
number of search
attempts (for Min.
dist. > 0)
Optional
MAX_TRIES_PER_POINT[number ]
Default: 10
The maximum number of tries per point.
Only relevant if the minimum distance
between points is set (and greater than 0).
Random seed
Optional
SEED [number]
Default: Not set
The seed to use for the random number
generator.
Include polygon
attributes
INCLUDE_POLYGON_ATTRIBUTES[boolean]
Default: True
If set, a point will get the attributes from the
line on which it is placed.
Random points in
polygons
OUTPUT [vector: point]
Default: [Create
temporary
layer]
The output random points. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Random points in
polygons
OUTPUT [vector: point] The output random points layer.
Number of
features with
empty or no
geometry
FEATURES_WITH_EMPTY_OR_NO_GEOMETRY[number]
Total number of
points generated
OUTPUT_POINTS [number]
Number of missed
points
POINTS_MISSED [number] The number of points that could not be
generated due to the minimum distance
constraint.
Number of
features with
missed points
POLYGONS_WITH_MISSED_POINTS[number] Not including features with empty or no
geometry
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Python code
Algorithm ID: qgis:randompointsinpolygons
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Random points inside polygons
Creates a new point layer with a given number of random points inside each polygon of the input polygon layer.
Two sampling strategies are available:
• Points count: number of points for each feature
• Points density: density of points for each feature
A minimum distance can be specified, to avoid points being too close to each other.
Default menu: Vector ► Research Tools
Viz také:
Random points in polygons
Parameters
Label Název Type Popis
Input layer INPUT [vector: polygon] Input polygon vector layer
Sampling strategy STRATEGY [enumeration]
Default: 0
Sampling strategy to use. One of:
• 0 — Points count: number of points
for each feature
• 1 — Points density: density of points
for each feature
Point count or
density
VALUE [number ]
Default: 1.0
The number or density of points, depending
on the chosen Sampling strategy.
Minimum
distance between
points
MIN_DISTANCE [number]
Default: 0.0
The minimum distance between points
Random points OUTPUT [vector: point]
Default: [Create
temporary
layer]
The output random points. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Random points OUTPUT [vector: point] The output random points layer.
Python code
Algorithm ID: qgis:randompointsinsidepolygons
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Random points on lines
Creates a point layer with points placed on the lines of another layer.
For each feature (line / multi-line) geometry in the input layer, the given number of points is added to the result layer.
Per feature and global minimum distances can be specified in order to avoid points being too close in the output point
layer. If a minimum distance is specified, it may not be possible to generate the specified number of points for each
feature. The total number of generated points and missed points are available as output from the algorithm.
The illustration below shows the effect of per feature and global minimum distances and zero/non-zero minimum
distances (generated with the same seed, so at least the first point generated will be the same).
Obr. 24.37: Five points per line feature, left: min. distances = 0, middle: min.distances != 0, right: min. distance !=
0, global min. distance = 0
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The maximum number of tries per point can be specified. This is only relevant for non-zero minimum distance.
A seed for the random number generator can be provided, making it possible to get identical random number
sequences for different runs of the algorithm.
The attributes of the line feature on which a point was generated can be included (Include line attributes).
If you want approximately the same point density for all the line features, you can data-define the number of points
using the length of the line feature geometry.
Viz také:
Random points along line
Parameters
Label Název Type Popis
Input line layer INPUT [vector: line] Input line vector layer
Number of points
for each feature
POINTS_NUMBER [number ]
Default: 1
Number of points to create
Minimum
distance between
points (per
feature)
Optional
MIN_DISTANCE [number ]
Default: 0.0
The minimum distance between points
within one line feature
Global minimum
distance between
points
Optional
MIN_DISTANCE_GLOBAL[number ]
Default: 0.0
The global minimum distance between
points. Should be smaller than the Minimum
distance between points (per feature) for that
parameter to have an effect.
Maximum
number of search
attempts (for Min.
dist. > 0)
Optional
MAX_TRIES_PER_POINT[number ]
Default: 10
The maximum number of tries per point.
Only relevant if the minimum distance
between points is set (and greater than 0).
Random seed
Optional
SEED [number]
Default: Not set
The seed to use for the random number
generator.
Include line
attributes
INCLUDE_LINE_ATTRIBUTES[boolean]
Default: True
If set, a point will get the attributes from the
line on which it is placed.
Random points on
lines
OUTPUT [vector: point]
Default: [Create
temporary
layer]
The output random points. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Random points on
lines
OUTPUT [vector: point] The output random points layer.
Number of
features with
empty or no
geometry
FEATURES_WITH_EMPTY_OR_NO_GEOMETRY[number]
Number of
features with
missed points
LINES_WITH_MISSED_POINTS[number] Not including features with empty or no
geometry
Total number of
points generated
OUTPUT_POINTS [number]
Number of missed
points
POINTS_MISSED [number] The number of points that could not be
generated due to the minimum distance
constraint.
Python code
Algorithm ID: qgis:randompointsonlines
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Raster pixels to points
Creates a vector layer of points corresponding to each pixel in a raster layer.
Converts a raster layer to a vector layer, by creating point features for each individual pixel’s center in the raster layer.
Any nodata pixels are skipped in the output.
Parameters
Label Název Type Popis
Raster layer INPUT_RASTER [raster] Input raster layer
Band number RASTER_BAND [raster band] Raster band to extract data from
Field name FIELD_NAME [string]
Default: ‚VALUE‘
Name of the field to store the raster band
value
Vector points OUTPUT [vector: point]
Default: [Create
temporary
layer]
Specify the resulting point layer of pixels
centroids. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Vector points OUTPUT [vector: point] Resulting point layer with pixels centroids
Python code
Algorithm ID: qgis:pixelstopoints
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Raster pixels to polygons
Creates a vector layer of polygons corresponding to each pixel in a raster layer.
Converts a raster layer to a vector layer, by creating polygon features for each individual pixel’s extent in the raster
layer. Any nodata pixels are skipped in the output.
Parameters
Label Název Type Popis
Raster layer INPUT_RASTER [raster] Input raster layer
Band number RASTER_BAND [raster band] Raster band to extract data from
Field name FIELD_NAME [string]
Default: ‚VALUE‘
Name of the field to store the raster band
value
Vector polygons OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the resulting polygon layer of pixel
extents. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Vector polygons OUTPUT [vector: polygon] Resulting polygon layer of pixel extents
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Python code
Algorithm ID: qgis:pixelstopolygons
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Regular points
Creates a new point layer with its points placed in a regular grid within a given extent.
The grid is specified either by the spacing between the points (same spacing for all dimensions) or by the number
of points to generate. In the latter case, the spacing will be determined from the extent. In order to generate a full
rectangular grid, at least the number of points specified by the user is generated for the latter case.
Random offsets to the point spacing can be applied, resulting in a non-regular point pattern.
Default menu: Vector ► Research Tools
Parameters
Label Název Type Popis
Input extent
(xmin, xmax,
ymin, ymax)
EXTENT [extent] Map extent for the random points
Point
spacing/count
SPACING [number]
Default: 100
Spacing between the points, or the number
of points, depending on whether Use
point spacing is checked or not.
Initial inset from
corner (LH side)
INSET [number]
Default: 0.0
Offsets the points relative to the upper left
corner. The value is used for both the X and
Y axis.
Apply random
offset to point
spacing
RANDOMIZE [boolean]
Default: False
If checked the points will have a random
spacing
Use point spacing IS_SPACING [boolean]
Default: True
If unchecked the point spacing is not taken
into account
Output layer CRS CRS [crs]
Default: Project CRS
CRS of the random points layer
Regular points OUTPUT [vector: point]
Default: [Create
temporary
layer]
Specify the output regular point layer. One
of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Regular points OUTPUT [vector: point] The output regular point layer.
Python code
Algorithm ID: qgis:regularpoints
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.1.15 Vector general
Assign projection
Assigns a new projection to a vector layer.
It creates a new layer with the exact same features and geometries as the input one, but assigned to a new CRS. The
geometries are not reprojected, they are just assigned to a different CRS.
This algorithm can be used to repair layers which have been assigned an incorrect projection.
Attributes are not modified by this algorithm.
Viz také:
Define Shapefile projection, Find projection, Reproject layer
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Vector layer with wrong or missing CRS
Assigned CRS CRS [crs]
Default:
EPSG:4326
- WGS84
Select the new CRS to assign to the vector
layer
Assigned CRS
Optional
OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output layer containing only the
duplicates. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Assigned CRS OUTPUT [same as input] Vector layer with assigned projection
Python code
Algorithm ID: native:assignprojection
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Convert layer to spatial bookmarks
Creates spatial bookmarks corresponding to the extent of features contained in a layer.
Parameters
Label Název Type Popis
Input Layer INPUT [vector: line,
polygon]
The input vector layer
Bookmark
destination
DESTINATION [enumeration]
Default: 0
Select the destination for the bookmarks.
One of:
• 0 — Project bookmarks
• 1 — User bookmarks
Name field NAME_EXPRESSION[expression] Field or expression that will give names to
the generated bookmarks
Group field GROUP_EXPRESSION[expression] Field or expression that will provide groups
for the generated bookmarks
Outputs
Label Název Type Popis
Count of
bookmarks added
COUNT [number]
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Python code
Algorithm ID: native:layertobookmarks
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Convert spatial bookmarks to layer
Creates a new layer containing polygon features for stored spatial bookmarks. The export can be filtered to only
bookmarks belonging to the current project, to all user bookmarks, or a combination of both.
Parameters
Label Název Type Popis
Bookmark source SOURCE [enumeration] [list]
Default: [0,1]
Select the source(s) of the bookmarks. One
or more of:
• 0 — Project bookmarks
• 1 — User bookmarks
Output CRS CRS [crs]
Default:
EPSG:4326
- WGS 84
The CRS of the output layer
Output OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Output OUTPUT [vector: polygon] The output (bookmarks) vector layer
Python code
Algorithm ID: native:bookmarkstolayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Create attribute index
Creates an index against a field of the attribute table to speed up queries. The support for index creation depends on
both the layer’s data provider and the field type.
No outputs are created: the index is stored on the layer itself.
Parameters
Label Název Type Popis
Input Layer INPUT [vector: any] Select the vector layer you want to create an
attribute index for
Attribute to index FIELD [tablefield: any] Field of the vector layer
Outputs
Label Název Type Popis
Indexed layer OUTPUT [same as input] A copy of the input vector layer with an
index for the specified field
Python code
Algorithm ID: native:createattributeindex
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Create spatial index
Creates an index to speed up access to the features in a layer based on their spatial location. Support for spatial index
creation is dependent on the layer’s data provider.
No new output layers are created.
Default menu: Vector ► Data Management Tools
Parameters
Label Název Type Popis
Input Layer INPUT [vector: any] Input vector layer
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Outputs
Label Název Type Popis
Indexed layer OUTPUT [same as input] A copy of the input vector layer with
a spatial index
Python code
Algorithm ID: native:createspatialindex
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Define Shapefile projection
Sets the CRS (projection) of an existing Shapefile format dataset to the provided CRS. It is very useful when
a Shapefile format dataset is missing the prj file and you know the correct projection.
Contrary to the Assign projection algorithm, it modifies the current layer and will not output a new layer.
Poznámka: For Shapefile datasets, the .prj and .qpj files will be overwritten - or created if missing - to match
the provided CRS.
Default menu: Vector ► Data Management Tools
Viz také:
Assign projection, Find projection, Reproject layer
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Vector layer with missing projection
information
CRS CRS [crs] Select the CRS to assign to the vector layer
Outputs
Label Název Type Popis
INPUT [same as input] The input vector layer with the defined
projection
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Python code
Algorithm ID: qgis:definecurrentprojection
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Delete duplicate geometries
Finds and removes duplicated geometries.
Attributes are not checked, so in case two features have identical geometries but different attributes, only one of them
will be added to the result layer.
Viz také:
Drop geometries, Remove null geometries, Delete duplicates by attribute
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] The layer with duplicate geometries you
want to clean
Cleaned OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Count of
discarded
duplicate records
DUPLICATE_COUNT[number] Count of discarded duplicate records
Cleaned OUTPUT [same as input] The output layer without any duplicated
geometries
Count of retained
records
RETAINED_COUNT [number] Count of unique records
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Python code
Algorithm ID: native:deleteduplicategeometries
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Delete duplicates by attribute
Deletes duplicate rows by only considering the specified field / fields. The first matching row will be retained, and
duplicates will be discarded.
Optionally, these duplicate records can be saved to a separate output for analysis.
Viz také:
Delete duplicate geometries
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] The input layer
Fields to match
duplicates by
FIELDS [tablefield: any]
[list]
Fields defining duplicates. Features with
identical values for all these fields are
considered duplicates.
Filtered (no
duplicates)
OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output layer containing the
unique features. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Filtered
(duplicates)
Optional
DUPLICATES [same as input]
Default: [Skip
output]
Specify the output layer containing only the
duplicates. One of:
• Skip output
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Filtered
(duplicates)
Optional
DUPLICATES [same as input]
Default: [Skip
output]
Vector layer containing the removed
features. Will not be produced if not
specified (left as [Skip output]).
Count of
discarded
duplicate records
DUPLICATE_COUNT[number] Count of discarded duplicate records
Filtered (no
duplicates)
OUTPUT [same as input] Vector layer containing the unique features.
Count of retained
records
RETAINED_COUNT [number] Count of unique records
Python code
Algorithm ID: native:removeduplicatesbyattribute
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Detect dataset changes
Compares two vector layers, and determines which features are unchanged, added or deleted between the two. It
is designed for comparing two different versions of the same dataset.
Obr. 24.38: Detect dataset change example
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Parameters
Label Název Type Popis
Original layer ORIGINAL [vector: any] The vector layer considered as the original
version
Revised layer REVISED [vector: any] The revised or modified vector layer
Attributes to
consider for
match
Optional
COMPARE_ATTRIBUTES[tablefield: any]
[list]
Attributes to consider for match. By default,
all attributes are compared.
Geometry
comparison
behavior
Optional
MATCH_TYPE [enumeration]
Default: 1
Defines the criteria for comparison.
Options:
• 0 — Exact Match: includes the order
and vertices count of geometries
• 1 — Tolerant Match (Topological
Equality): geometries are considered
equal
Unchanged
features
UNCHANGED [vector: same
as Original layer]
Specify the output vector layer containing
the unchanged features. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Added features ADDED [vector: same
as Original layer]
Specify the output vector layer containing
the added features. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Deleted features DELETED [vector: same
as Original layer]
Specify the output vector layer containing
the deleted features. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Unchanged
features
UNCHANGED [vector: same
as Original layer]
Vector layer containing the unchanged
features.
Added features ADDED [vector: same
as Original layer]
Vector layer containing the added features.
Deleted features DELETED [vector: same
as Original layer]
Vector layer containing the deleted features.
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Tabulka 24.78 – pokračujte na předchozí stránce
Label Název Type Popis
Count of
unchanged
features
UNCHANGED_COUNT[number] Count of unchanged features.
Count of features
added in revised
layer
ADDED_COUNT [number] Count of features added in revised layer.
Count of features
deleted from
original layer
DELETED_COUNT [number] Count of features deleted from original
layer.
Python code
Algorithm ID: native:detectvectorchanges
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Drop geometries
Creates a simple geometryless copy of the input layer attribute table. It keeps the attribute table of the source layer.
If the file is saved in a local folder, you can choose between many file formats.
Allows features in-place modification
Viz také:
Delete duplicate geometries, Remove null geometries
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] The input vector layer
Dropped
geometries
OUTPUT [table] Specify the output geometryless layer. One
of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Dropped
geometries
OUTPUT [table] The output geometryless layer. A copy of
the original attribute table.
Python code
Algorithm ID: native:dropgeometries
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Execute SQL
Runs a simple or complex query with SQL syntax on the source layer.
Input datasources are identified with input1, input2… inputN and a simple query will look like SELECT *
FROM input1.
Beside a simple query, you can add expressions or variables within the SQL query parameter itself. This
is particulary useful if this algorithm is executed within a Processing model and you want to use a model input
as a parameter of the query. An example of a query will then be SELECT * FROM [% @table %] where
@table is the variable that identifies the model input.
The result of the query will be added as a new layer.
Viz také:
SpatiaLite execute SQL, PostgreSQL execute SQL
Parameters
Label Název Type Popis
Additional input
datasources
(called input1,
.., inputN in the
query)
INPUT_DATASOURCES[vector: any] [list] List of layers to query. In the SQL editor
you can refer these layers with their real
name or also with input1, input2, inputN
depending on how many layers have been
chosen.
SQL query INPUT_QUERY [string] Type the string of your SQL query, e.g.
SELECT * FROM input1.
Unique identifier
field
Optional
INPUT_UID_FIELD[string] Specify the column with unique ID
Geometry field
Optional
INPUT_GEOMETRY_FIELD[string] Specify the geometry field
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Tabulka 24.79 – pokračujte na předchozí stránce
Label Název Type Popis
Geometry type
Optional
INPUT_GEOMETRY_TYPE[enumeration]
Default: 0
Choose the geometry of the result. By
default the algorithm will autodetect it. One
of:
• 0 — Autodetect
• 1 — No geometry
• 2 — Point
• 3 — LineString
• 4 — Polygon
• 5 — MultiPoint
• 6 — MultiLineString
• 7 — MultiPolygon
CRS
Optional
INPUT_GEOMETRY_CRS[crs] The CRS to assign to the output layer
SQL Output OUTPUT [vector: any]
Default: [Create
temporary
layer]
Specify the output layer created by the
query. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
SQL Output OUTPUT [vector: any] Vector layer created by the query
Python code
Algorithm ID: qgis:executesql
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Extract selected features
Saves the selected features as a new layer.
Poznámka: If the selected layer has no selected features, the newly created layer will be empty.
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Parameters
Label Název Type Popis
Input Layer INPUT [vector: any] Layer to save the selection from
Selected features OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the vector layer for the selected
features. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Selected features OUTPUT [same as input] Vector layer with only the selected features,
or no feature if none was selected.
Python code
Algorithm ID: native:saveselectedfeatures
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Extract Shapefile encoding
Extracts the attribute encoding information embedded in a Shapefile. Both the encoding specified by an optional
.cpg file and any encoding details present in the .dbf LDID header block are considered.
Parameters
Label Název Type Popis
Input Layer INPUT [vector: any] ESRI Shapefile (.SHP) Layer to extract the
encoding information.
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Outputs
Label Název Type Popis
Shapefile
encoding
ENCODING [string] Encoding information specified in the input
file
CPG encoding CPG_ENCODING [string] Encoding information specified in any
optional .CPG file
LDID encoding LDID_ENCODING [string] Encoding information specified in .dbf
LDID header block
Python code
Algorithm ID: native:shpencodinginfo
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Find projection
Creates a shortlist of candidate coordinate reference systems, for instance for a layer with an unknown projection.
The area that the layer is expected to cover must be specified via the target area parameter. The coordinate reference
system for this target area must be known to QGIS.
The algorithm operates by testing the layer’s extent in every known reference system and then listing any for which
the bounds would be near the target area if the layer was in this projection.
Viz také:
Assign projection, Define Shapefile projection, Reproject layer
Parameters
Label Název Type Popis
Input Layer INPUT [vector: any] Layer with unknown projection
Target area for
layer (xmin, xmax,
ymin, ymax)
TARGET_AREA [extent] The area that the layer covers. The options
for specifying the extent are:
• Use Canvas Extent
• Select Extent on Canvas
• Use Layer Extent
It is also possible to provide the extent
coordinates directly (xmin, xmax, ymin,
ymax).
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Tabulka 24.81 – pokračujte na předchozí stránce
Label Název Type Popis
CRS candidates OUTPUT [table]
Default: [Create
temporary
layer]
Specify the table (geometryless layer) for
the CRS suggestions (EPSG codes). One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
CRS candidates OUTPUT [table] A table with all the CRS (EPSG codes) of
the matching criteria.
Python code
Algorithm ID: qgis:findprojection
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Flatten relationship
Flattens a relationship for a vector layer, exporting a single layer containing one parent feature per related child feature.
This master feature contains all the attributes for the related features. This allows to have the relation as a plain table
that can be e.g. exported to CSV.
Obr. 24.39: Form of a region with related children (left) - A duplicate region feature for each related child, with
joined attributes (right)
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Parameters
Label Název Type Popis
Input Layer INPUT [vector: any] Layer with the relationship that should be
de-normalized
Flattened Layer
Optional
OUTPUT [same as input]
Default: [Save
to temporary
file]
Specify the output (flattened) layer. One of:
• Save to a Temporary File
• Save to File…
• Save To GeoPackage…
• Save to Database Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Flattened layer OUTPUT [same as input] A layer containing master features with all
the attributes for the related features
Python code
Algorithm ID: native:flattenrelationships
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Join attributes by field value
Takes an input vector layer and creates a new vector layer that is an extended version of the input one, with additional
attributes in its attribute table.
The additional attributes and their values are taken from a second vector layer. An attribute is selected in each of
them to define the join criteria.
Viz také:
Join attributes by nearest, Join attributes by location
Parameters
Label Název Type Popis
Input Layer INPUT [vector: any] Input vector layer. The output layer will
consist of the features of this layer with
attributes from matching features in the
second layer.
Table field FIELD [tablefield: any] Field of the source layer to use for the join
Input layer 2 INPUT_2 [vector: any] Layer with the attribute table to join
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Label Název Type Popis
Table field 2 FIELD_2 [tablefield: any] Field of the second (join) layer to use for
the join The type of the field must be equal
to (or compatible with) the input table field
type.
Layer 2 fields to
copy
Optional
FIELDS_TO_COPY [tablefield: any]
[list]
Select the specific fields you want to add. By
default all the fields are added.
Join type METHOD [enumeration]
Default: 1
The type of the final joined layer. One of:
• 0 — Create separate feature for each
matching feature (one-to-many)
• 1 — Take attributes of the first
matching feature only (one-to-one)
Discard records
which could not
be joined
DISCARD_NONMATCHING[boolean]
Default: True
Check if you don’t want to keep the features
that could not be joined
Joined field prefix
Optional
PREFIX [string] Add a prefix to joined fields in order to
easily identify them and avoid field name
collision
Joined layer OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer for the join.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Unjoinable
features from
first layer
NON_MATCHING [same as input]
Default: [Skip
output]
Specify the output vector layer for
unjoinable features from first layer. One of:
• Skip output
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Number of joined
features from
input table
JOINED_COUNT [number]
Unjoinable
features from
first layer
Optional
NON_MATCHING [same as input] Vector layer with the non-matched features
Joined layer OUTPUT [same as input] Output vector layer with added attributes
from the join
Number of
unjoinable
features from
input table
Optional
UNJOINABLE_COUNT[number]
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Python code
Algorithm ID: native:joinattributestable
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Join attributes by location
Takes an input vector layer and creates a new vector layer that is an extended version of the input one, with additional
attributes in its attribute table.
The additional attributes and their values are taken from a second vector layer. A spatial criteria is applied to select
the values from the second layer that are added to each feature from the first layer.
Default menu: Vector ► Data Management Tools
Viz také:
Join attributes by nearest, Join attributes by field value, Join attributes by location (summary)
Parameters
Label Název Type Popis
Input Layer INPUT [vector: any] Input vector layer. The output layer will
consist of the features of this layer with
attributes from matching features in the
second layer.
Join layer JOIN [vector: any] The attributes of this vector layer will be
added to the source layer attribute table.
Geometric
predicate
PREDICATE [enumeration] [list]
Default: [0]
Select the geometric criteria. One or more
of:
• 0 — intersects
• 1 — contains
• 2 — equals
• 3 — touches
• 4 — overlaps
• 5 — within
• 6 — crosses
Fields to add
(leave empty to
use all fields)
Optional
JOIN_FIELDS [tablefield: any]
[list]
Select the specific fields you want to add. By
default all the fields are added.
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Label Název Type Popis
Join type METHOD [enumeration] The type of the final joined layer. One of:
• 0 — Create separate feature for each
matching feature (one-to-many)
• 1 — Take attributes of the first
matching feature only (one-to-one)
• 2 — Take attributes of the feature
with largest overlap only (one-to-
-one)
Discard records
which could not
be joined
DISCARD_NONMATCHING[boolean]
Default: False
Remove from the output the input layer
records which could not be joined
Joined field prefix
Optional
PREFIX [string] Add a prefix to joined fields in order to
easily identify them and avoid field name
collision
Joined layer OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer for the join.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Unjoinable
features from
first layer
NON_MATCHING [same as input]
Default: [Skip
output]
Specify the output vector layer for
unjoinable features from first layer. One of:
• Skip output
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Number of joined
features from
input table
JOINED_COUNT [number]
Unjoinable
features from
first layer
Optional
NON_MATCHING [same as input] Vector layer of the non-matched features
Joined layer OUTPUT [same as input] Output vector layer with added attributes
from the join
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Python code
Algorithm ID: native:joinattributesbylocation
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Join attributes by location (summary)
Takes an input vector layer and creates a new vector layer that is an extended version of the input one, with additional
attributes in its attribute table.
The additional attributes and their values are taken from a second vector layer. A spatial criteria is applied to select
the values from the second layer that are added to each feature from the first layer.
The algorithm calculates a statistical summary for the values from matching features in the second layer (e.g.
maximum value, mean value, etc).
Viz také:
Join attributes by location
Parameters
Label Název Type Popis
Input Layer INPUT [vector: any] Input vector layer. The output layer will
consist of the features of this layer with
attributes from matching features in the
second layer.
Join layer JOIN [vector: any] The attributes of this vector layer will be
added to the source layer attribute table.
Geometric
predicate
PREDICATE [enumeration] [list]
Default: [0]
Select the geometric criteria. One or more
of:
• 0 — intersects
• 1 — contains
• 2 — equals
• 3 — touches
• 4 — overlaps
• 5 — within
• 6 — crosses
Fields to
summarize (leave
empty to use all
fields)
Optional
JOIN_FIELDS [tablefield: any]
[list]
Select the specific fields you want to add
and summarize. By default all the fields are
added.
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Label Název Type Popis
Summaries to
calculate (leave
empty to use all
fields)
Optional
SUMMARIES [enumeration] [list]
Default: []
Choose which type of summary you want to
add to each field and for each feature. One
or more of:
• 0 — count
• 1 — unique
• 2 — min
• 3 — max
• 4 — range
• 5 — sum
• 6 — mean
• 7 — median
• 8 — stddev
• 9 — minority
• 10 — majority
• 11 — q1
• 12 — q3
• 13 — iqr
• 14 — empty
• 15 — filled
• 16 — min_length
• 17 — max_length
• 18 — mean_length
Discard records
which could not
be joined
DISCARD_NONMATCHING[boolean]
Default: False
Remove from the output the input layer
records which could not be joined
Joined layer OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer for the join.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Joined layer OUTPUT [same as input] Output vector layer with summarized
attributes from the join
Python code
Algorithm ID: qgis:joinbylocationsummary
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Join attributes by nearest
Takes an input vector layer and creates a new vector layer with additional fields in its attribute table. The additional
attributes and their values are taken from a second vector layer. Features are joined by finding the closest features
from each layer.
By default only the nearest feature is joined, but the join can also join to the k-nearest neighboring features.
If a maximum distance is specified, only features which are closer than this distance will be matched.
Viz také:
Nearest neighbour analysis, Join attributes by field value, Join attributes by location, Distance matrix
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] The input layer.
Input layer 2 INPUT_2 [vector: any] The join layer.
Layer 2 fields to
copy (leave empty
to copy all fields)
FIELDS_TO_COPY [fields] Join layer fields to copy (if empty, all fields
will be copied).
Discard records
which could not
be joined
DISCARD_NONMATCHING[boolean]
Default: False
Remove from the output the input layer
records which could not be joined
Joined field prefix PREFIX [string] Joined field prefix
Maximum nearest
neighbors
NEIGHBORS [number]
Default: 1
Maximum number of nearest neighbors
Maximum
distance
MAX_DISTANCE [number] Maximum search distance
Joined layer OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the vector layer containing the
joined features. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Unjoinable
features from
first layer
NON_MATCHING [same as input]
Default: [Skip
output]
Specify the vector layer containing the
features that could not be joined. One of:
• Skip output
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Joined layer OUTPUT [same as input] The output joined layer.
Unjoinable
features from
first layer
NON_MATCHING [same as input] Layer containing the features from first
layer that could not be joined to any features
in the join layer.
Number of joined
features from
input table
JOINED_COUNT [number] Number of features from the input table
that have been joined.
Number of
unjoinable
features from
input table
UNJOINABLE_COUNT[number] Number of features from the input table
that could not be joined.
Python code
Algorithm ID: native:joinbynearest
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Merge vector layers
Combines multiple vector layers of the same geometry type into a single one.
The attribute table of the resulting layer will contain the fields from all input layers. If fields with the same name but
different types are found then the exported field will be automatically converted into a string type field. New fields
storing the original layer name and source are also added.
If any input layers contain Z or M values, then the output layer will also contain these values. Similarly, if any of the
input layers are multi-part, the output layer will also be a multi-part layer.
Optionally, the destination coordinate reference system (CRS) for the merged layer can be set. If it is not set, the CRS
will be taken from the first input layer. All layers will be reprojected to match this CRS.
Default menu: Vector ► Data Management Tools
Viz také:
Split vector layer
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Parameters
Label Název Type Popis
Input Layers LAYERS [vector: any] [list] The layers that are to be merged into
a single layer. Layers should be of the same
geometry type.
Destination CRS
Optional
CRS [crs] Choose the CRS for the output layer. If not
specified, the CRS of the first input layer
is used.
Merged OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Merged OUTPUT [same as input] Output vector layer containing all the
features and attributes from the input layers.
Python code
Algorithm ID: native:mergevectorlayers
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Order by expression
Sorts a vector layer according to an expression: changes the feature index according to an expression.
Be careful, it might not work as expected with some providers, the order might not be kept every time.
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Parameters
Label Název Type Popis
Input Layer INPUT [vector: any] Input vector layer to sort
Expression EXPRESSION [expression] Expression to use for the sorting
Sort ascending ASCENDING [boolean]
Default: True
If checked the vector layer will be sorted
from small to large values.
Sort nulls first NULLS_FIRST [boolean]
Default: False
If checked, Null values are placed first
Ordered OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Ordered OUTPUT [same as input] Output (sorted) vector layer
Python code
Algorithm ID: native:orderbyexpression
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Repair Shapefile
Repairs a broken ESRI Shapefile dataset by (re)creating the SHX file.
Parameters
Label Název Type Popis
Input Shapefile INPUT [file] Full path to the ESRI Shapefile dataset with
a missing or broken SHX file
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Outputs
Label Název Type Popis
Repaired layer OUTPUT [vector: any] The input vector layer with the SHX file
repaired
Python code
Algorithm ID: native:repairshapefile
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Reproject layer
Reprojects a vector layer in a different CRS. The reprojected layer will have the same features and attributes of the
input layer.
Allows features in-place modification
Viz také:
Assign projection, Define Shapefile projection, Find projection
Parameters
Label Název Type Popis
Input Layer INPUT [vector: any] Input vector layer to reproject
Target CRS TARGET_CRS [crs]
Default:
EPSG:4326
- WGS 84
Destination coordinate reference system
Coordinate
Operation
Optional
OPERATION [string] Specific operation to use for a particular
reprojection task, instead of always
forcing use of the current project’s
transformation settings. Useful when
reprojecting a particular layer and control
over the exact transformation pipeline
is required. Requires proj version >= 6.
Read more at Datum Transformations.
Reprojected OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Reprojected OUTPUT [same as input] Output (reprojected) vector layer
Python code
Algorithm ID: native:reprojectlayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Save vector features to file
Saves vector features to a specified file dataset.
For dataset formats supporting layers, an optional layer name parameter can be used to specify a custom string.
Optional GDAL-defined dataset and layer options can be specified. For more information on this, read the online
GDAL documentation on the format.
Parameters
Basic parameters
Label Název Type Popis
Vector features INPUT [vector: any] Input vector layer.
Saved features OUTPUT [same as input]
Default: [Save
to temporary
file]
Specify the file to save the features to. One
of:
• Save to a Temporary File
• Save to File…
Advanced parameters
Label Název Type Popis
Layer name
Optional
LAYER_NAME [string] Name to use for the output layer
GDAL dataset
options
Optional
DATASOURCE_OPTIONS[string] GDAL dataset creation options of the
output format. Separate individual options
with semicolons.
GDAL layer
options
Optional
LAYER_OPTIONS [string] GDAL layer creation options of the output
format. Separate individual options with
semicolons.
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Outputs
Label Název Type Popis
Saved features OUTPUT [same as input] Vector layer with the saved features.
File name and
path
FILE_PATH [string] Output file name and path.
Layer name LAYER_NAME [string] Name of the layer, if any.
Python code
Algorithm ID: native:savefeatures
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Set layer encoding
Sets the encoding used for reading a layer’s attributes. No permanent changes are made to the layer, rather it affects
only how the layer is read during the current session.
Poznámka: Changing the encoding is only supported for some vector layer data sources.
Parameters
Label Název Type Popis
Saved features INPUT [vector: any] Vector layer to set the encoding.
Encoding ENCODING [string] Text encoding to assign to the layer in the
current QGIS session.
Outputs
Label Název Type Popis
Output layer OUTPUT [same as input] Input vector layer with the set encoding.
Python code
Algorithm ID: native:setlayerencoding
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Split features by character
Features are split into multiple output features by splitting a field’s value at a specified character. For instance, if
a layer contains features with multiple comma separated values contained in a single field, this algorithm can be used
to split these values up across multiple output features. Geometries and other attributes remain unchanged in the
output. Optionally, the separator string can be a regular expression for added flexibility.
Parameters
Label Název Type Popis
Input Layer INPUT [vector: any] Input vector layer
Split using values
in the field
FIELD [tablefield: any] Field to use for splitting
Split value using
character
CHAR [string] Character to use for splitting
Use regular
expression
separator
REGEX [boolean]
Default: False
Split OUTPUT [same as input]
Default: Create
temporary
layer
Specify output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Split OUTPUT [same as input] The output vector layer.
Python code
Algorithm ID: native:splitfeaturesbycharacter
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Split vector layer
Creates a set of vectors in an output folder based on an input layer and an attribute. The output folder will contain
as many layers as the unique values found in the desired field.
The number of files generated is equal to the number of different values found for the specified attribute.
It is the opposite operation of merging.
Default menu: Vector ► Data Management Tools
Viz také:
Merge vector layers
Parameters
Label Název Type Popis
Input Layer INPUT [vector: any] Input vector layer
Unique ID field FIELD [tablefield: any] Field to use for splitting
Output directory OUTPUT [folder]
Default: [Save
to temporary
folder]
Specify the directory for the output layers.
One of:
• Save to a Temporary Directory
• Save to Directory…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Output directory OUTPUT [folder] The directory for the output layers
Output layers OUTPUT_LAYERS [same as input]
[list]
The output vector layers resulting from the
split.
Python code
Algorithm ID: native:splitvectorlayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Truncate table
Truncates a layer, by deleting all features from within the layer.
Varování: This algorithm modifies the layer in place, and deleted features cannot be restored!
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Parameters
Label Název Type Popis
Input Layer INPUT [vector: any] Input vector layer
Outputs
Label Název Type Popis
Truncated layer OUTPUT [folder] The truncated (empty) layer
Python code
Algorithm ID: native:truncatetable
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.1.16 Vector geometry
Add geometry attributes
Computes geometric properties of the features in a vector layer and includes them in the output layer.
It generates a new vector layer with the same content as the input one, but with additional attributes, containing
geometric measurements based on a selected CRS.
The attributes added to the table depend on the geometry type and dimension of the input layer:
• for point layers: X (xcoord), Y (ycoord), Z (zcoord) coordinates and/or M value (mvalue)
• for line layers: length and, for the LineString and CompoundCurve geometry types, the feature
sinuosity and straight distance (straightdis)
• for polygon layers: perimeter and area
Default menu: Vector ► Geometry Tools
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Calculate using CALC_METHOD [enumeration]
Default: 0
Calculation parameters to use for the
geometric properties. One of:
• 0 — Layer CRS
• 1 — Project CRS
• 2 — Ellipsoidal
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Tabulka 24.89 – pokračujte na předchozí stránce
Label Název Type Popis
Added geom info OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output (input copy with
geometry) layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Added geom info OUTPUT [same as input] Copy of the input vector layer with the
addition of the geometry fields
Python code
Algorithm ID: qgis:exportaddgeometrycolumns
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Affine transform
Applies an affine transformation to the layer geometries. Affine transformations can include translation, scaling and
rotation. The operations are performed in the following order: scale, rotation, and translation.
Z and M values (if present) can be translated and scaled.
Obr. 24.40: Vector point layer (green dots) before (left), and after (rigth) an affine transformation (translation).
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Viz také:
Translate
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Translation (x-
-axis)
DELTA_X [number ]
Default: 0
Displacement to apply on the X axis.
Translation (y-
-axis)
DELTA_Y [number ]
Default: 0
Displacement to apply on the Y axis.
Translation (z-
axis)
DELTA_Z [number ]
Default: 0
Displacement to apply on the Z axis.
Translation (m-
-values)
DELTA_M [number ]
Default: 0
Offset to apply on m values.
Scale factor
(x-axis)
SCALE_X [number ]
Default: 1
Scaling value (expansion or contraction) to
apply on the X axis.
Scale factor
(y-axis)
SCALE_Y [number ]
Default: 1
Scaling value (expansion or contraction) to
apply on the Y axis.
Scale factor
(z-axis)
SCALE_Z [number ]
Default: 1
Scaling value (expansion or contraction) to
apply on the Z axis.
Scale factor
(m-values)
SCALE_M [number ]
Default: 1
Scaling value (expansion or contraction) to
apply on m values.
Rotation
around z-axis
(degrees counter-
-clockwise)
ROTATION_Z [number ]
Default: 0
Angle of the rotation in degrees.
Transformed OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Transformed OUTPUT [same as input] Output (transformed) vector layer.
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Python code
Algorithm ID: native:affinetransform
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Aggregate
Takes a vector or table layer and creates a new layer by aggregating features based on a group by expression.
Features for which group by expression returns the same value are grouped together.
It is possible to group all source features together using constant value in group by parameter, example: NULL.
It is also possible to group features by multiple fields using Array function, example: Array(„Field1“, „Field2“).
Geometries (if present) are combined into one multipart geometry for each group. Output attributes are computed
depending on each given aggregate definition.
This algorithm allows to use the default aggregates functions of the QGIS Expression engine.
Viz také:
Collect geometries, Dissolve
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Group by
expression
GROUP_BY [tablefield: any]
Default: ‚NULL‘
Choose the grouping field. If NULL all
features will be grouped.
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Tabulka 24.93 – pokračujte na předchozí stránce
Label Název Type Popis
Aggregates AGGREGATES [list] List of output layer field definitions.
Example of a field definition:
{‚aggregate‘: ‚sum‘, ‚delimiter‘: ‚,‘, ‚input‘:
‚ $area‘, ‚length‘: 10, ‚name‘: ‚totarea‘,
‚precision‘: 0, ‚type‘: 6}
By default, the list contains all the fields of
the input layer. In the GUI, you can edit
these fields and their definitions, and you
can also:
• Click the button to add a new
field.
• Click to delete the selected field.
• Use and to change order of
the fields.
• Click to reset to the default (the
fields of the input layer).
For each of the fields you’d like to retrieve
information from, you need to define the
following:
Input expression [expression] (input)
Field or expression from the input
layer.
Aggregate function [enumeration] (aggregate)
Function to use on the input
expression to return the aggregated
value.
Default: concatenate (for string data
type), sum (for numeric data type)
Delimiter [string] (delimiter)
Text string to separate aggregated
values, for example in case of
concatenation.
Default: ,
Output field name [string] (name)
Name of the aggregated field in the
output layer. By default input field
name is kept.
Type [enumeration] (type) Data type
of the output field. One of:
• 1 — Boolean
• 2 — Integer
• 4 — Integer64
• 6 — Double
• 10 — String
• 14 — Date
• 16 — DateTime
Length [number] (length) Length of
the output field.
Precision [number] (precision)
Precision of the output field.
Load fields from
layer
GUI only [vector: any] You can load fields from another layer and
use them for the aggregation
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Label Název Type Popis
Aggregated OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output (aggregate) layer One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Aggregated OUTPUT [same as input] Multigeometry vector layer with the
aggregated values
Python code
Algorithm ID: native:aggregate
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Boundary
Returns the closure of the combinatorial boundary of the input geometries (i.e. the topological boundary of the
geometry).
Only for polygon and line layers.
For polygon geometries , the boundary consists of all the lines making up the rings of the polygon.
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Obr. 24.41: Boundaries (black dashed line) of the source polygon layer
For lines geometries, the boundaries are their end points.
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Obr. 24.42: Boundary layer (red points) for lines. In yellow a selected feature.
Parameters
Label Název Type Popis
Input layer INPUT [vector: line,
polygon]
Input line or polygon vector layer
Boundary OUTPUT [vector: point, line]
Default: [Create
temporary
layer]
Specify the output (boundary) layer. One
of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Boundary OUTPUT [vector: point, line] Boundaries from the input layer (point for
line, and line for polygon)
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Python code
Algorithm ID: native:boundary
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Bounding boxes
Calculates the bounding box (envelope) of each feature in an input layer. Polygon and line geometries are supported.
Obr. 24.43: Black lines represent the bounding boxes of each polygon feature
Allows features in-place modification
Viz také:
Minimum bounding geometry
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Parameters
Label Název Type Popis
Input layer INPUT [vector: line,
polygon]
Input line or polygon vector layer
Bounds OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output (bounding box) layer.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Bounds OUTPUT [vector: polygon] Bounding boxes of input layer
Python code
Algorithm ID: native:boundingboxes
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Buffer
Computes a buffer area for all the features in an input layer, using a fixed distance.
It is possible to use a negative distance for polygon input layers. In this case the buffer will result in a smaller polygon
(setback).
Obr. 24.44: Buffer (in yellow) of points, line and polygon
Allows features in-place modification
Default menu: Vector ► Geoprocessing Tools
Viz také:
Variable distance buffer, Multi-ring buffer (constant distance), Variable width buffer (by M value)
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Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Distance DISTANCE [number ]
Default: 10.0
Buffer distance (from the boundary of each
feature). You can use the Data Defined
button on the right to choose a field from
which the radius will be calculated. This
way you can have different radius for each
feature (see Variable distance buffer).
Segments SEGMENTS [number]
Default: 5
Controls the number of line segments to
use to approximate a quarter circle when
creating rounded offsets.
End cap style END_CAP_STYLE [enumeration]
Default: 0
Controls how line endings are handled in
the buffer. One of:
• 0 — Round
• 1 — Flat
• 2 — Square
Obr. 24.45: Round, flat and square cap
styles
Join style JOIN_STYLE [enumeration]
Default: 0
Specifies whether round, miter or beveled
joins should be used when offsetting corners
in a line. Options are:
• 0 — Round
• 1 — Miter
• 2 — Bevel
Miter limit MITER_LIMIT [number]
Default: 2.0
Controls the maximum distance from the
offset curve to use when creating a mitered
join (only applicable for miter join styles).
Minimum: 1.
Dissolve result DISSOLVE [boolean]
Default: False
Dissolve the final buffer. If True
(checked), overlapping buffers will be
dissolved (combined) into a new feature.
Obr. 24.46: Standard and dissolved buffer
Buffered OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output (buffer) layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Buffered OUTPUT [vector: polygon] Output (buffer) polygon layer
Python code
Algorithm ID: native:buffer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Centroids
Creates a new point layer, with points representing the centroids of the geometries of the input layer.
The centroid is a single point representing the barycenter (of all parts) of the feature, so it can be outside the feature
borders. But can also be a point on each part of the feature.
The attributes of the points in the output layer are the same as for the original features.
Obr. 24.47: The red stars represent the centroids of the features of the input layer.
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Allows features in-place modification
Default menu: Vector ► Geometry Tools
Viz také:
Point on Surface
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Create centroid
for each part
ALL_PARTS [boolean ]
Default: False
If True (checked), a centroid will be created
for each part of the geometry
Centroids OUTPUT [vector: point]
Default: [Create
temporary
layer]
Specify the output (centroid) layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Centroids OUTPUT [vector: point] Output point vector layer (centroids)
Python code
Algorithm ID: native:centroids
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Check validity
Performs a validity check on the geometries of a vector layer.
The geometries are classified in three groups (valid, invalid and error) and for each group, a vector layer with its
features is generated:
• The Valid output layer contains only the valid features (without topological errors).
• The Invalid output layer contains all the invalid features found by the algorithm.
• The Error output layer is a point layer that points to where the invalid features were found.
The attribute tables of the generated layers will contain some additional information („message“ for the error layer,
„FID“ and „_errors“ for the invalid layer and only „FID“ for the valid layer):
The attribute table of each generated vector layer will contain some additional information (number of errors found
and types of error):
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Obr. 24.48: Left: the input layer. Right: the valid layer (green), the invalid layer (orange)
Default menu: Vector ► Geometry Tools
Viz také:
Fix geometries and the core plugin Geometry Checker Plugin
Parameters
Label Název Type Popis
Input layer INPUT_LAYER [vector: any] Input vector layer
Method METHOD [enumeration]
Default: 2
Method to use to check validity. Options:
• 0: The one selected in digitizing
settings
• 1: QGIS
• 2: GEOS
Ignore ring self
intersection
IGNORE_RING_SELF_INTERSECTION[boolean]
Default: False
Ignore self intersecting rings when
checking for validity.
Valid output VALID_OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the vector layer to contain a copy of
the valid features of the source layer. One
of:
• Skip output
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Invalid output INVALID_OUTPUT [same as input]
Default: [Create
temporary
layer]
Vector layer containing copy of the invalid
features of the source layer with the field
_errors listing the summary of the
error(s) found. One of:
• Skip output
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Tabulka 24.95 – pokračujte na předchozí stránce
Label Název Type Popis
Error output ERROR_OUTPUT [vector: point]
Default: [Create
temporary
layer]
Point layer of the exact position of the
validity problems detected with the
message field describing the error(s)
found. One of:
• Skip output
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Count of errors ERROR_COUNT [number] The number of geometries that caused
errors.
Error output ERROR_OUTPUT [vector: point] Point layer of the exact position of the
validity problems detected with the
message field describing the error(s)
found.
Count of invalid
features
INVALID_COUNT [number] The number of invalid geometries.
Invalid output INVALID_OUTPUT [same as input] Vector layer containing copy of the invalid
features of the source layer with the field
_errors listing the summary of the
error(s) found.
Count of valid
features
VALID_COUNT [number] The number of valid geometries.
Valid output VALID_OUTPUT [same as input] Vector layer containing a copy of the valid
features of the source layer.
Python code
Algorithm ID: qgis:checkvalidity
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Types of error messages and their meanings
Tabulka 24.97: If the GEOS method is used the following error messages
can occur:
Error message Explanation Example
Repeated point This error happens when a given
vertex is repeated.
Ring self-intersection This error happens when
a geometry touches itself and
generates a ring.
Self-intersection This error happens when
a geometry touches itself.
Topology validation error
Hole lies outside shell
Holes are nested
Interior is disconnected
Nested shells This error happens when
a polygon geometry is on top of
another polygon geometry.
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Tabulka 24.97 – pokračujte na předchozí stránce
Error message Explanation Example
Duplicate rings This error happens when two
rings (exterior or interior)
of a polygon geometry are
identical
Too few points in geometry
component
Invalid coordinate For a point geometry, this error
happens when the geometry
does not have a proper
coordinate pair. The coordinate
pair does not contain a latitude
value and a longitude value in
that order.
Ring is not closed
Tabulka 24.98: If the QGIS method is used the following error messages
can occur:
Error message Explanation Example
Segment %1 of ring %2 of polygon
%3 intersects segment %4 of ring
%5 of polygon %6 at %7
Ring %1 with less than four points
Ring %1 not closed
Line %1 with less than two points
Line %1 contains %n duplicate
node(s) at %2
This error happens when
consecutive points on a line
have the same coordinates.
Segments %1 and %2 of line %3
intersect at %4
This error happens when a line self
intersects (two segments of the line
intersect each other).
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Tabulka 24.98 – pokračujte na předchozí stránce
Error message Explanation Example
Ring self-intersection This error happens when an outer
or inner (island) ring / boundary of
a polygon geometry intersects itself.
Ring %1 of polygon %2 not in
exterior ring
Polygon %1 lies inside polygon %2 This error happens when a part of
a MultiPolygon geometry is inside
a hole of a MultiPolygon geometry.
Collect geometries
Takes a vector layer and collects its geometries into new multipart geometries.
One or more attributes can be specified to collect only geometries belonging to the same class (having the same value
for the specified attributes), alternatively all geometries can be collected.
All output geometries will be converted to multi geometries, even those with just a single part. This algorithm does
not dissolve overlapping geometries - they will be collected together without modifying the shape of each geometry
part.
See the ‚Promote to multipart‘ or ‚Aggregate‘ algorithms for alternative options.
Default menu: Vector ► Geometry Tools
Viz také:
Aggregate, Promote to multipart, Dissolve
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Unique ID fields FIELD [tablefield: any]
[list]
Choose one or more attributes to collect the
geometries
Collected OUTPUT [same as input] Vector layer with collected geometries
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Outputs
Label Název Type Popis
Collected OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer for the
collected geometries. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Python code
Algorithm ID: native:collect
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Concave hull (alpha shapes)
Computes the concave hull of the features in an input point layer.
Obr. 24.49: Concave hulls with different thresholds (0.3, 0.6, 0.9)
Viz také:
Convex hull, Concave hull (k-nearest neighbor)
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Parameters
Label Název Type Popis
Input point layer INPUT [vector: point] Input point vector layer
Threshold ALPHA [number]
Default: 0.3
Number from 0 (maximum concave hull) to
1 (convex hull).
Allow holes HOLES [boolean]
Default: True
Choose whether to allow holes in the final
concave hull
Split multipart
geometry into
singlepart
geometries
NO_MULTIGEOMETRY[boolean]
Default: True
Check if you want to have singlepart
geometries instead of multipart ones.
Concave hull OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Concave hull OUTPUT [vector: polygon] The output vector layer
Python code
Algorithm ID: qgis:concavehull
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Concave hull (k-nearest neighbor)
Generates a concave hull polygon from a set of points. If the input layer is a line or polygon layer, it will use the
vertices.
The number of neighbors to consider determines the concaveness of the output polygon. A lower number will result in
a concave hull that follows the points very closely, while a higher number will have a smoother shape. The minimum
number of neighbor points to consider is 3. A value equal to or greater than the number of points will result in a convex
hull.
If a field is selected, the algorithm will group the features in the input layer using unique values in that field and
generate individual polygons in the output layer for each group.
Viz také:
Concave hull (alpha shapes)
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Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Number of
neighboring
points to consider
(a lower number
is more concave,
a higher number
is smoother)
KNEIGHBORS [number]
Default: 3
Determines the concaveness of the output
polygon. A small number will result in
a concave hull that follows the points very
closely, while a high number will make the
polygon look more like the convex hull (if
the number is equal to or larger than the
number of features, the result will be the
convex hull). Minimum value: 3.
Field
Optional
FIELD [tablefield: any]
Default: None
If specified, one concave hull polygon
is generated for each unique value of the
field (by selecting features using this value).
Concave hull OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Concave hull OUTPUT [vector: polygon] The output vector layer
Python code
Algorithm ID: qgis:knearestconcavehull
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Convert geometry type
Generates a new layer based on an existing one, with a different type of geometry.
The attribute table of the output layer is the same as the one of the input layer.
Not all conversions are possible. For instance, a line layer can be converted to a point layer, but a point layer cannot
be converted to a line layer.
Viz také:
Polygonize, Lines to polygons, Polygons to lines, Points to path
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Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
New geometry
type
TYPE [enumeration]
Default: 0
Geometry type to apply to the output
features. One of:
• 0 — Centroids
• 1 — Nodes
• 2 — Linestrings
• 3 — Multilinestrings
• 4 — Polygons
Converted OUTPUT [vector: any]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Converted OUTPUT [vector: any] Output vector layer - the type depends on
the parameters
Python code
Algorithm ID: qgis:convertgeometrytype
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Convert to curved geometries
Converts a geometry into its curved geometry equivalent.
Already curved geometries will be retained without change.
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Parameters
Label Název Type Popis
Input layer INPUT [vector: line or
polygon]
Input vector layer
Maximum
distance tolerance
DISTANCE [number]
Default: 0.000001
The maximum distance allowed between
the original location of vertices and where
they would fall on the converted curved
geometries
Maximum angle
tolerance
ANGLE [number]
Default: 0.000001
Segments are considered as suitable for
replacing with an arc if the points are all
regularly spaced on the candidate arc. This
parameter specifies the maximum angular
deviation (in degrees) allowed when testing
for regular point spacing. Between 0 and
45°.
Curves OUTPUT [vector:
compoundcurve
or curvepolygon]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to Database Table…
• Append to Layer…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Curves OUTPUT [vector:
compoundcurve
or curvepolygon]
Output vector layer with curved geometries
Python code
Algorithm ID: native:converttocurves
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Convex hull
Calculates the convex hull for each feature in an input layer.
See the ‚Minimum bounding geometry‘ algorithm for a convex hull calculation which covers the whole layer or grouped
subsets of features.
Obr. 24.50: Black lines identify the convex hull for each layer feature
Allows features in-place modification
Default menu: Vector ► Geoprocessing Tools
Viz také:
Minimum bounding geometry, Concave hull (alpha shapes)
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Convex hull OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Convex hull OUTPUT [vector: polygon] The output (convex hull) vector layer
Python code
Algorithm ID: native:convexhull
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Create layer from extent
Creates a new vector layer that contains a single feature with geometry matching the extent of the input layer.
It can be used in models to convert a literal extent (xmin, xmax, ymin, ymax format) into a layer which can be
used for other algorithms which require a layer based input.
Viz také:
Create layer from point
Parameters
Label Název Type Popis
Extent (xmin,
xmax, ymin,
ymax)
INPUT [extent] Input extent
Extent OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Extent OUTPUT [vector: polygon] The output (extent) vector layer
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Python code
Algorithm ID: native:extenttolayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Create layer from point
Creates a new vector layer that contains a single feature with geometry matching a point parameter. It can be used in
models to convert a point into a point layer for algorithms which require a layer based input.
Viz také:
Create layer from extent
Parameters
Label Název Type Popis
Point INPUT [coordinates] Input point, including CRS info (example:
397254,6214446 [EPSG:32632]).
If the CRS is not provided, the Project CRS
will be used.
The point can be specified by clicking on
the map canvas.
Point OUTPUT [vector: point]
Default: [Create
temporary
layer]
Specify the output layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Point OUTPUT [vector: point] The output point vector layer containing the
input point.
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Python code
Algorithm ID: native:pointtolayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Create wedge buffers
Creates wedge shaped buffers from input points.
Obr. 24.51: Wedge buffers
The native output from this algorithm are CurvePolygon geometries, but these may be automatically segmentized to
Polygons depending on the output format.
Viz také:
Buffer, Variable width buffer (by M value), Tapered buffers
Parameters
Label Název Type Popis
Input layer INPUT [vector: point] Input point vector layer
Azimuth (degrees
from North)
AZIMUTH [number ]
Default: 0.0
Angle (in degrees) as the middle value of
the wedge
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Tabulka 24.101 – pokračujte na předchozí stránce
Label Název Type Popis
Wedge width (in
degrees)
WIDTH [number ]
Default: 45.0
Width (in degrees) of the buffer. The
wedge will extend to half of the angular
width either side of the azimuth direction.
Obr. 24.52: Azimuth and width values of
the wedge buffer
Outer radius OUTER_RADIUS [number ]
Default: 1.0
The outer size (length) of the wedge: the size
is meant from the source point to the edge
of the wedge shape.
Inner radius
Optional
INNER_RADIUS [number ]
Default: 0.0
Inner radius value. If 0 the wedge will begin
from the source point.
Buffers OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Buffers OUTPUT [vector: polygon] The output (wedge buffer) vector layer
Python code
Algorithm ID: native:wedgebuffers
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Delaunay triangulation
Creates a polygon layer with the Delaunay triangulation corresponding to the input point layer.
Obr. 24.53: Delaunay triangulation on points
Default menu: Vector ► Geometry Tools
Parameters
Label Název Type Popis
Input layer INPUT [vector: point] Input point vector layer
Delaunay
triangulation
OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Delaunay
triangulation
OUTPUT [vector: polygon] The output (Delaunay triangulation) vector
layer
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Python code
Algorithm ID: qgis:delaunaytriangulation
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Delete holes
Takes a polygon layer and removes holes in polygons. It creates a new vector layer in which polygons with holes have
been replaced by polygons with only their external ring. Attributes are not modified.
An optional minimum area parameter allows removing only holes which are smaller than a specified area threshold.
Leaving this parameter at 0.0 results in all holes being removed.
Obr. 24.54: Before and after the cleaning
Allows features in-place modification
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Parameters
Label Název Type Popis
Input layer INPUT [vector: polygon] Input polygon vector layer
Remove holes with
area less than
Optional
MIN_AREA [number ]
Default: 0.0
Only holes with an area less than this
threshold will be deleted. With a value of
0.0, all the holes will be deleted.
Cleaned OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Cleaned OUTPUT [same as input] The output (cleaned) vector layer
Python code
Algorithm ID: native:deleteholes
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Densify by count
Takes a polygon or line layer and generates a new one in which the geometries have a larger number of vertices than
the original one.
If the geometries have Z or M values present then these will be linearly interpolated at the added vertices.
The number of new vertices to add to each segment is specified as an input parameter.
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Obr. 24.55: Red points show the vertices before and after the densify
Allows features in-place modification
Default menu: Vector ► Geometry Tools
Viz také:
Densify by interval
Parameters
Label Název Type Popis
Input layer INPUT [vector: line,
polygon]
Input line or polygon vector layer
Vertices to add VERTICES [number]
Default: 1
Number of vertices to add to each segment
Densified OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Densified OUTPUT [same as input] The output (densified) vector layer
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Python code
Algorithm ID: native:densifygeometries
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Densify by interval
Takes a polygon or line layer and generates a new one in which the geometries have a larger number of vertices than
the original one.
The geometries are densified by adding regularly placed extra vertices inside each segment so that the maximum
distance between any two vertices does not exceed the specified distance.
If the geometries have Z or M values present then these will be linearly interpolated at the added vertices.
Example
Specifying a distance of 3 would cause the segment [0 0] -> [10 0] to be converted to [0 0] -> [2.5
0] -> [5 0] -> [7.5 0] -> [10 0], since 3 extra vertices are required on the segment and spacing these
at 2.5 increments allows them to be evenly spaced over the segment.
Obr. 24.56: Densify geometry at a given interval
Allows features in-place modification
Viz také:
Densify by count
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Parameters
Label Název Type Popis
Input layer INPUT [vector: line,
polygon]
Input line or polygon vector layer
Interval between
vertices to add
INTERVAL [number ]
Default: 1.0
Maximum distance between two
consecutive vertices
Densified OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Densified OUTPUT [same as input] The output (densified) vector layer
Python code
Algorithm ID: native:densifygeometriesgivenaninterval
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Dissolve
Takes a vector layer and combines its features into new features. One or more attributes can be specified to dissolve
features belonging to the same class (having the same value for the specified attributes), alternatively all features can
be dissolved to a single feature.
All output geometries will be converted to multi geometries. In case the input is a polygon layer, common boundaries
of adjacent polygons being dissolved will get erased.
The resulting attribute table will have the same fields as the input layer. The values in the output layer’s fields are the
ones of the first input feature that happens to be processed.
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Obr. 24.57: Dissolve the polygon layer on a common attribute
Default menu: Vector ► Geoprocessing Tools
Viz také:
Aggregate, Collect geometries
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Dissolve field(s)
Optional
FIELD [tablefield: any]
[list]
Default: []
Features having the same value for the
selected field(s) will be replaced with
a single one and their geometries are
merged.
If no field is provided then all the
features are dissolved, resulting in a single
(multipart) feature.
Dissolved OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Dissolved OUTPUT [same as input] The output vector layer with dissolved
geometries
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Python code
Algorithm ID: native:dissolve
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Drape (set Z value from raster)
Uses values sampled from a band within a raster layer to set the Z value for every overlapping vertex in the feature
geometry. The raster values can optionally be scaled by a preset amount.
If Z values already exist in the layer, they will be overwritten with the new value. If no Z values exist, the geometry
will be upgraded to include the Z dimension.
Viz také:
Set M value from raster, Set Z value
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Raster layer RASTER [raster] Raster layer with Z values
Band number BAND [raster band]
Default: 1
The raster band to take the Z values from
Value for
nodata or non-
-intersecting
vertices
NODATA [number ]
Default: 0
Value to use in case the vertex does not
intersect (a valid pixel of) the raster
Scale factor SCALE [number ]
Default: 1.0
Scaling value: the band values are
multiplied by this value.
Updated OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer (with
Z values from the raster layer). One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Updated OUTPUT [same as input] The output vector layer with Z values from
the raster layer
Python code
Algorithm ID: native:setzfromraster
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Drop M/Z values
Removes M (measure) or Z (altitude) values from input geometries.
Viz také:
Set M value, Set Z value
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer with M or Z values
Drop M Values DROP_M_VALUES [boolean]
Default: False
Removes the M values from the geometries
Drop Z Values DROP_Z_VALUES [boolean]
Default: False
Removes the Z values from the geometries
Z/M Dropped OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Z/M Dropped OUTPUT [same as input] The output vector layer (identical to the
input layer, except that the M and/or
Z dimensions have been removed from the
geometries).
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Python code
Algorithm ID: native:dropmzvalues
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Eliminate selected polygons
Combines selected polygons of the input layer with certain adjacent polygons by erasing their common boundary.
The adjacent polygon can be either the one with the largest or smallest area or the one sharing the largest common
boundary with the polygon to be eliminated.
Eliminate is normally used to get rid of sliver polygons, i.e. tiny polygons that are a result of polygon intersection
processes where boundaries of the inputs are similar but not identical.
Default menu: Vector ► Geoprocessing Tools
Viz také:
Fix geometries
Parameters
Label Název Type Popis
Input layer INPUT [vector: polygon] Input polygon vector layer
Merge selection
with the
neighboring
polygon with the
MODE [enumeration]
Default: None
Choose the parameter to use in order to get
rid of the selected polygons:
• 0 — Largest Area
• 1 — Smallest Area
• 2 — Largest Common Boundary
Eliminated OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Eliminated OUTPUT [vector: polygon] The output polygon vector layer.
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Python code
Algorithm ID: qgis:eliminateselectedpolygons
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Explode lines
Takes a lines layer and creates a new one in which each line layer is replaced by a set of lines representing the segments
in the original line.
Each line in the resulting layer contains only a start and an end point, with no intermediate vertices between them.
Obr. 24.58: The original line layer and the exploded one
Allows features in-place modification
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Viz také:
Subdivide, Line substring
Parameters
Label Název Type Popis
Input layer INPUT [vector: line] Input line vector layer
Exploded OUTPUT [vector: line]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Exploded OUTPUT [vector: line] The output line vector layer with features
representing each segment of the input
layer.
Python code
Algorithm ID: native:explodelines
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Extend lines
Extends line geometry by a specified amount at the start and end of the line.
Lines are extended using the bearing of the first and last segment in the line.
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Obr. 24.59: The red dashes represent the initial and final extension of the original layer
Allows features in-place modification
Viz také:
Line substring
Parameters
Label Název Type Popis
Input layer INPUT [vector: line] Input line vector layer
Start distance START_DISTANCE [number ] Distance by which to extend the first
segment of the line (starting point)
End distance END_DISTANCE [number ] Distance by which to extend the last
segment of the line (ending point)
Extended OUTPUT [vector: line]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Extended OUTPUT [vector: line] The output (extended) line vector layer.
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Python code
Algorithm ID: native:extendlines
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Extract M values
Extracts M values from geometries into feature attributes.
By default only the M value from the first vertex of each feature is extracted, however the algorithm can optionally
calculate statistics on all of the geometry’s M values, including sum, mean, minimum and maximum.
Viz také:
Extract Z values, Set M value, Drop M/Z values
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Summaries to
calculate
SUMMARIES [enumeration]
Default: [0]
Statistics on the M values of a geometry.
One or more of:
• 0 — First
• 1 — Last
• 2 — Count
• 3 — Sum
• 4 — Mean
• 5 — Median
• 6 — St.dev (pop)
• 7 — Minimum
• 8 — Maximum
• 9 — Range
• 10 — Minority
• 11 — Majority
• 12 — Variety
• 13 — Q1
• 14 — Q3
• 15 — IQR
Output column
prefix
COLUMN_PREFIX [string]
Default: ‚m_‘
The prefix for the output (M) column
Extracted OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Extracted OUTPUT [same as input] The output vector layer (with M values)
Python code
Algorithm ID: native:extractmvalues
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Extract specific vertices
Takes a vector layer and generates a point layer with points representing specific vertices in the input geometries.
For instance, this algorithm can be used to extract the first or last vertices in the geometry. The attributes associated
to each point are the same ones associated to the feature that the vertex belongs to.
The vertex indices parameter accepts a comma separated string specifying the indices of the vertices to extract. The
first vertex corresponds to an index of 0, the second vertex has an index of 1, etc. Negative indices can be used to find
vertices at the end of the geometry, e.g., an index of -1 corresponds to the last vertex, -2 corresponds to the second
last vertex, etc.
Additional fields are added to the vertices indicating the specific vertex position (e.g., 0, -1, etc), the original vertex
index, the vertex’s part and its index within the part (as well as its ring for polygons), distance along the original
geometry and bisector angle of vertex for the original geometry.
Viz také:
Extract vertices, Filter vertices by M value, Filter vertices by Z value
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Vertex indices VERTICES [string]
Default: ‚0‘
Comma-separated string of the indices of
the vertices to extract.
Vertices OUTPUT [vector: point]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Vertices OUTPUT [vector: point] The output (point) vector layer containing
the specified vertices from the input layer
geometries.
Python code
Algorithm ID: native:extractspecificvertices
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Extract vertices
Takes a vector layer and generates a point layer with points representing the vertices in the input geometries.
The attributes associated to each point are the same ones associated to the feature that the vertex belongs to.
Additional fields are added to the vertices indicating the vertex index (beginning at 0), the feature’s part and its index
within the part (as well as its ring for polygons), distance along original geometry and bisector angle of vertex for
original geometry.
Obr. 24.60: Vertices extracted for line and polygon layer
Default menu: Vector ► Geometry Tools
Viz také:
Extract specific vertices, Filter vertices by M value, Filter vertices by Z value
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Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Vertices OUTPUT [vector: point]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Vertices OUTPUT [vector: point] The output (point) vector layer containing
the vertices from the input layer geometries.
Python code
Algorithm ID: native:extractvertices
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Extract Z values
Extracts Z values from geometries into feature attributes.
By default only the Z value from the first vertex of each feature is extracted, however the algorithm can optionally
calculate statistics on all of the geometry’s Z values, including sum, mean, minimum and maximum.
Viz také:
Extract M values, Set Z value, Drop M/Z values
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
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Tabulka 24.104 – pokračujte na předchozí stránce
Label Název Type Popis
Summaries to
calculate
SUMMARIES [enumeration]
Default: [0]
Statistics on the Z values of a geometry.
One or more of:
• 0 — First
• 1 — Last
• 2 — Count
• 3 — Sum
• 4 — Mean
• 5 — Median
• 6 — St.dev (pop)
• 7 — Minimum
• 8 — Maximum
• 9 — Range
• 10 — Minority
• 11 — Majority
• 12 — Variety
• 13 — Q1
• 14 — Q3
• 15 — IQR
Output column
prefix
COLUMN_PREFIX [string]
Default: ‚z_‘
The prefix for the output (Z) column
Extracted OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Extracted OUTPUT [same as input] The output vector layer (with Z values)
Python code
Algorithm ID: native:extractzvalues
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Filter vertices by M value
Filters away vertices based on their M value, returning geometries with only vertex points that have a M value greater
than or equal to the specified minimum value and/or less than or equal to the maximum value.
If the minimum value is not specified then only the maximum value is tested, and similarly if the maximum value
is not specified then only the minimum value is tested.
Obr. 24.61: The red line represents the black line with only vertices whose M value is <=10.
Poznámka: Depending on the input geometry attributes and the filters used, the resultant geometries created by this
algorithm may no longer be valid.
Viz také:
Filter vertices by Z value, Extract vertices, Extract specific vertices
Parameters
Label Název Type Popis
Input layer INPUT [vector: line,
polygon]
Input line or polygon vector layer to remove
vertices from
Minimum
Optional
MIN [number ]
Default: Not set
Minimum of M values allowed
Maximum
Optional
MAX [number ]
Default: Not set
Maximum of M values allowed
Filtered OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Filtered OUTPUT [same as input] The output vector layer of features with
only the filtered vertices.
Python code
Algorithm ID: native:filterverticesbym
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Filter vertices by Z value
Filters away vertices based on their Z value, returning geometries with only vertex points that have a Z value greater
than or equal to the specified minimum value and/or less than or equal to the maximum value.
If the minimum value is not specified then only the maximum value is tested, and similarly if the maximum value
is not specified then only the minimum value is tested.
Obr. 24.62: The red line represents the black line with only vertices whose Z value is <=10.
Poznámka: Depending on the input geometry attributes and the filters used, the resultant geometries created by this
algorithm may no longer be valid. You may need to run the Fix geometries algorithm to ensure their validity.
Viz také:
Filter vertices by M value, Extract vertices, Extract specific vertices
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Parameters
Label Název Type Popis
Input layer INPUT [vector: line,
polygon]
Input line or polygon vector layer to remove
vertices from
Minimum
Optional
MIN [number ]
Default: Not set
Minimum of Z values allowed
Maximum
Optional
MAX [number ]
Default: Not set
Maximum of Z values allowed
Filtered OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Filtered OUTPUT [same as input] The output vector layer of features with
only the filtered vertices.
Python code
Algorithm ID: native:filterverticesbyz
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Fix geometries
Attempts to create a valid representation of a given invalid geometry without losing any of the input vertices. Already
valid geometries are returned without further intervention. Always outputs multi-geometry layer.
Poznámka: M values will be dropped from the output.
Allows features in-place modification
Viz také:
Check validity
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Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Fixed geometries OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Fixed geometries OUTPUT [same as input] The output vector layer with fixed
geometries.
Python code
Algorithm ID: native:fixgeometries
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Force right-hand-rule
Forces polygon geometries to respect the Right-Hand-Rule, in which the area that is bounded by a polygon is to the
right of the boundary. In particular, the exterior ring is oriented in a clockwise direction and any interior rings in
a counter-clockwise direction.
Parameters
Label Název Type Popis
Input layer INPUT [vector: polygon] Input vector layer
Reoriented OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Reoriented OUTPUT [vector: polygon] The output vector layer with reoriented
geometries.
Python code
Algorithm ID: native:forcerhr
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Geodesic line split at antimeridian
Splits a line into multiple geodesic segments, whenever the line crosses the antimeridian (±180 degrees longitude).
Splitting at the antimeridian helps the visual display of the lines in some projections. The returned geometry will
always be a multi-part geometry.
Whenever line segments in the input geometry cross the antimeridian, they will be split into two segments, with the
latitude of the breakpoint being determined using a geodesic line connecting the points either side of this segment.
The current project ellipsoid setting will be used when calculating this breakpoint.
If the input geometry contains M or Z values, these will be linearly interpolated for the new vertices created at the
antimeridian.
Parameters
Label Název Type Popis
Input layer INPUT [vector: line] Input line vector layer
Split OUTPUT [vector: line]
Default: [Create
temporary
layer]
Specify the output line vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Split OUTPUT [vector: line] The output line vector layer split at the
antimeridian.
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Python code
Algorithm ID: native:antimeridiansplit
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Geometry by expression
Updates existing geometries (or creates new geometries) for input features by use of a QGIS expression.
This allows complex geometry modifications which can utilize all the flexibility of the QGIS expression engine to
manipulate and create geometries for output features.
For help with QGIS expression functions, see the inbuilt help available in the expression builder.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Output geometry
type
OUTPUT_GEOMETRY[enumeration]
Default: 0
The output geometry strongly depends on
the expression: for instance, if you create
a buffer the geometry type has to be
polygon. One of:
• 0 — Polygon
• 1 — Line
• 2 — Point
Output geometry
has z values
WITH_Z [boolean]
Default: False
Choose if the output geometry should
include the Z dimension
Output geometry
has m values
WITH_M [boolean]
Default: False
Choose if the output geometry should
include the M dimension
Geometry
expression
EXPRESSION [expression]
Default:
‚$geometry‘
Add the geometry expression you want
to use. You can use the button to open
the Expression Dialog. The dialog lists all
the relevant expressions, together with their
help and guide.
Modified
geometry
OUTPUT [vector: any]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Modified
geometry
OUTPUT [vector: any] The output vector layer
Python code
Algorithm ID: native:geometrybyexpression
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Interpolate point on line
Creates a point geometry interpolated at a set distance along line or curve geometries.
Z and M values are linearly interpolated from existing values.
If a multipart geometry is encountered, only the first part is considered when calculating the substring.
If the specified distance is greater than the input feature’s length, the resultant feature will have a null geometry.
Obr. 24.63: Interpolated point at 500m of the beginning of the line
Viz také:
Points along geometry
Parameters
Label Název Type Popis
Input layer INPUT [vector: line,
polygon]
Input line or polygon vector layer
Distance DISTANCE [number ]
Default: 0.0
Distance from the beginning of the line
Interpolated
points
OUTPUT [vector: point]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Interpolated
points
OUTPUT [vector: point] The output point vector layer with features
at a set distance along the line or polygon
boundary
Python code
Algorithm ID: native:interpolatepoint
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Keep N biggest parts
Takes a layer with polygons or multipolygons and returns a new layer in which only the n largest polygons of each
multipolygon feature are kept. If a feature has n or fewer parts, the feature will just be copied.
Obr. 24.64: Clockwise from top left: original multipart feature, one, two and three biggest parts kept
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Parameters
Label Název Type Popis
Polygons INPUT [vector: polygon] Input polygon vector layer
Parts to keep PARTS [number]
Default: 1
Number of parts to keep. If 1, only the
biggest part of the feature will be kept.
Parts OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output polygon vector layer.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Parts OUTPUT [vector: polygon] The output polygon vector layer with the N
biggest parts of each feature
Python code
Algorithm ID: qgis:keepnbiggestparts
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Line substring
Returns the portion of a line (or curve) which falls between the specified start and end distances (measured from the
beginning of the line).
Z and M values are linearly interpolated from existing values.
If a multipart geometry is encountered, only the first part is considered when calculating the substring.
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Obr. 24.65: Substring line with starting distance set at 0 meters and the ending distance at 250 meters.
Allows features in-place modification
Viz také:
Extend lines
Parameters
Label Název Type Popis
Input layer INPUT [vector: line] Input line vector layer
Start distance START_DISTANCE [number ] Distance along the input line to the start
point of the output feature
End distance END_DISTANCE [number ] Distance along the input line to the end
point of the output feature
Substring OUTPUT [vector: line]
Default: [Create
temporary
layer]
Specify the output line vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Substring OUTPUT [vector: line] The output line vector layer.
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Python code
Algorithm ID: native:linesubstring
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Lines to polygons
Generates a polygon layer using as polygon rings the lines from an input line layer.
The attribute table of the output layer is the same as the one of the input layer.
Default menu: Vector ► Geometry Tools
Viz také:
Polygons to lines, Polygonize, Convert geometry type
Parameters
Label Název Type Popis
Input layer INPUT [vector: line] Input line vector layer
Polygons OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output polygon vector layer.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Polygons OUTPUT [vector: polygon] The output polygon vector layer.
Python code
Algorithm ID: qgis:linestopolygons
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Merge lines
Joins all connected parts of MultiLineString geometries into single LineString geometries.
If any parts of the input MultiLineString geometries are not connected, the resultant geometry will be
a MultiLineString containing any lines which could be merged and any non-connected line parts.
Allows features in-place modification
Parameters
Label Název Type Popis
Input layer INPUT [vector: line] Input line vector layer
Merged OUTPUT [vector: line]
Default: [Create
temporary
layer]
Specify the output line vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Merged OUTPUT [vector: line] The output (merged) line vector layer.
Python code
Algorithm ID: native:mergelines
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Minimum bounding geometry
Creates geometries which enclose the features from an input layer. The features can be grouped by a field. The output
layer will then contain one feature per group value with a geometry (MBB) that covers the geometries of the features
with matching value.
The following enclosing geometry types are supported:
• bounding box (envelope)
• oriented rectangle
• circle
• convex hull
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Obr. 24.66: Clockwise from top left: envelope, oriented rectangle, circle, convex hull
Viz také:
Minimum enclosing circles
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Field
Optional
FIELD [tablefield: any] Features can be grouped by a field. If set,
this causes the output layer to contain one
feature per grouped value with a minimal
geometry covering only the features with
matching values.
Geometry type TYPE [enumeration]
Default: 0
Enclosing geometry types. One of:
• 0 — Envelope (Bounding Box)
• 1 — Minimum Oriented Rectangle
• 2 — Minimum Enclosing Circle
• 3 — Convex Hull
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Tabulka 24.107 – pokračujte na předchozí stránce
Label Název Type Popis
Bounding
geometry
OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output polygon vector layer.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Bounding
geometry
OUTPUT [vector: polygon] The output (bounding) polygon vector
layer.
Python code
Algorithm ID: qgis:minimumboundinggeometry
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Minimum enclosing circles
Calculates the minimum enclosing circles of the features in the input layer.
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Obr. 24.67: Enclosing circles for each feature
Allows features in-place modification
Viz také:
Minimum bounding geometry
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Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Number of
segment in circles
SEGMENTS [number]
Default: 72
The number of segment used to
approximate a circle. Minimum 8,
maximum 100000.
Minimum
enclosing circles
OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output polygon vector layer.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Minimum
enclosing circles
OUTPUT [vector: polygon] The output polygon vector layer.
Python code
Algorithm ID: native:minimumenclosingcircle
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Multi-ring buffer (constant distance)
Computes multi-ring (donut) buffer for the features of the input layer, using a fixed or dynamic distance and number
of rings.
Obr. 24.68: Multi-ring buffer for a line, point and polygon layer
Allows features in-place modification
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Viz také:
Buffer, Variable distance buffer, Rectangles, ovals, diamonds, Single sided buffer
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Number of rings RINGS [number ]
Default: 1
The number of rings. It can be a unique
value (same number of rings for all the
features) or it can be taken from features
data (the number of rings depends on
feature values).
Distance between
rings
DISTANCE [number ]
Default: 1.0
Distance between the rings. It can be
a unique value (same distance for all the
features) or it can be taken from features
data (the distance depends on feature
values).
Multi-ring
buffer (constant
distance)
OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output polygon vector layer.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Multi-ring
buffer (constant
distance)
OUTPUT [vector: polygon] The output polygon vector layer.
Python code
Algorithm ID: native:multiringconstantbuffer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Multipart to singleparts
Splits multipart features in the input layer into singlepart features.
The attributes of the output layer are the same as the original ones but divided into single features.
Obr. 24.69: Left the multipart source layer and right the single part output result
Allows features in-place modification
Default menu: Vector ► Geometry Tools
Viz také:
Collect geometries, Promote to multipart
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Single parts OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output polygon vector layer.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Single parts OUTPUT [same as input] The output vector layer.
Python code
Algorithm ID: native:multiparttosingleparts
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Offset lines
Offsets lines by a specified distance. Positive distances will offset lines to the left, and negative distances will offset
them to the right.
Obr. 24.70: In blue the source layer, in red the offset one
Allows features in-place modification
Viz také:
Array of offset (parallel) lines, Translate
Parameters
Label Název Type Popis
Input layer INPUT [vector: line] Input line vector layer
Distance DISTANCE [number ]
Default: 10.0
Offset distance. You can use the Data
Defined button on the right to choose a field
from which the radius will be calculated.
This way you can have different radius for
each feature (see Variable distance buffer).
Segments SEGMENTS [number]
Default: 8
Controls the number of line segments to
use to approximate a quarter circle when
creating rounded offsets.
Join style JOIN_STYLE [enumeration]
Default: 0
Specifies whether round, miter or beveled
joins should be used when offsetting corners
in a line. Options are:
• 0 — Round
• 1 — Miter
• 2 — Bevel
Miter limit MITER_LIMIT [number]
Default: 2.0
Controls the maximum distance from the
offset curve to use when creating a mitered
join (only applicable for miter join styles).
Minimum: 1.
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Tabulka 24.109 – pokračujte na předchozí stránce
Label Název Type Popis
Offset OUTPUT [vector: line]
Default: [Create
temporary
layer]
Specify the output (offset) layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Offset OUTPUT [vector: line] Output (offset) line layer
Python code
Algorithm ID: native:offsetline
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Oriented minimum bounding box
Calculates the minimum area rotated rectangle for each feature in the input layer.
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Obr. 24.71: Oriented minimum bounding box
Allows features in-place modification
Viz také:
Minimum bounding geometry
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Bounding boxes OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output polygon vector layer.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Bounding boxes OUTPUT [vector: polygon] The output polygon vector layer.
Python code
Algorithm ID: native:orientedminimumboundingbox
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Orthogonalize
Attempts to orthogonalize the geometries of the input line or polygon layer. This process shifts the vertices in the
geometries to try to make every angle in the geometry either a right angle or a straight line.
Obr. 24.72: In blue the source layer and in the red orthogonalized result
Allows features in-place modification
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Parameters
Label Název Type Popis
Input layer INPUT [vector: line,
polygon]
Input line or polygon vector layer
Maximum
angle tolerance
(degrees)
ANGLE_TOLERANCE[number]
Default: 15
Specify the maximum deviation from
a right angle or straight line a vertex
can have for it to be adjusted. Smaller
tolerances mean that only vertices which
are already closer to right angles will be
adjusted, and larger tolerances mean that
vertices which deviate further from right
angles will also be adjusted.
Maximum
algorithm
iterations
MAX_ITERATIONS [number]
Default: 1000
Setting a larger number for the maximum
number of iterations will result in a more
orthogonal geometry at the cost of extra
processing time.
Orthogonalized OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output polygon vector layer.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Orthogonalized OUTPUT [same as input] The output polygon vector layer with
adjusted angles.
Python code
Algorithm ID: native:orthogonalize
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Point on Surface
For each feature of the input layer, returns a point that is guaranteed to lie on the surface of the feature geometry.
Allows features in-place modification
Viz také:
Centroids
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Create point on
surface for each
part
ANGLE_TOLERANCE[boolean ] If checked, a point will be created for each
part of the geometry.
Point OUTPUT [vector: point]
Default: [Create
temporary
layer]
Specify the output point vector layer. One
of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Point OUTPUT [vector: point] The output point vector layer.
Python code
Algorithm ID: native:pointonsurface
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Points along geometry
Creates points at regular intervals along line or polygon geometries. Created points will have new attributes added for
the distance along the geometry and the angle of the line at the point.
An optional start and end offset can be specified, which controls how far from the start and end of the geometry the
points should be created.
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Obr. 24.73: Points created along the source line layer
Viz také:
Interpolate point on line
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Parameters
Label Název Type Popis
Input layer INPUT [vector: line,
polygon]
Input line or polygon vector layer
Distance DISTANCE [number ]
Default: 1.0
Distance between two consecutive points
along the line
Start offset START_OFFSET [number ]
Default: 0.0
Distance from the beginning of the input
line, representing the position of the first
point.
End offset END_OFFSET [number ]
Default: 0.0
Distance from the end of the input line,
representing the position beyond which no
point feature shoud be created.
Interpolated
points
OUTPUT [vector: point]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Interpolated
points
OUTPUT [vector: point] Point vector layer with features placed along
lines or polygon boundaries of the input
layer.
Python code
Algorithm ID: native:pointsalonglines
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Points displacement
Given a distance of proximity, identifies nearby point features and radially distributes them over a circle whose center
represents their barycenter. A convenient tool to scatter overlaid features.
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Parameters
Label Název Type Popis
Input layer INPUT [vector: point] Input point vector layer
Minimum
distance to other
points
PROXIMITY [number]
Default: 1.0
Distance below which point features
are considered close. Close features are
distributed altogether.
Displacement
distance
DISTANCE [number]
Default: 1.0
Radius of the circle on which close features
are placed
Horizontal
distribution
for two point case
HORIZONTAL [boolean]
Default: False
When only two points are identified
as close, aligns them horizontally on the
circle instead of vertically.
Displaced OUTPUT [vector: point]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Displaced OUTPUT [vector: point] Output point vector layer
Python code
Algorithm ID: qgis:pointsdisplacement
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Pole of inaccessibility
Calculates the pole of inaccessibility for a polygon layer, which is the most distant internal point from the boundary
of the surface.
This algorithm uses the ‚polylabel‘ algorithm (Vladimir Agafonkin, 2016), which is an iterative approach guaranteed
to find the true pole of inaccessibility within a specified tolerance. A more precise tolerance (lower value) requires
more iterations and will take longer to calculate.
The distance from the calculated pole to the polygon boundary will be stored as a new attribute in the output layer.
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Obr. 24.74: Pole of inaccessibility
Parameters
Label Název Type Popis
Input layer INPUT [vector: polygon] Input vector layer
Tolerance TOLERANCE [number]
Default: 1.0
Set the tolerance for the calculation
Point OUTPUT [vector: point]
Default: [Create
temporary
layer]
Specify the output polygon vector layer.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Point OUTPUT [vector: point] The output point vector layer
Python code
Algorithm ID: native:poleofinaccessibility
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Polygonize
Creates a polygon layer whose features boundaries are generated from a line layer of closed features.
Obr. 24.75: The yellow polygons generated from the closed lines
Poznámka: The line layer must have closed shapes in order to be transformed into a polygon.
Viz také:
Polygons to lines, Lines to polygons, Convert geometry type
Parameters
Label Název Type Popis
Input layer INPUT [vector: line] Input line vector layer
Keep table
structure of
line layer
Optional
KEEP_FIELDS [boolean]
Default: False
Check to keep the fields (only the table
structure, not the values) of the input layer
Polygons from
lines
OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output polygon vector layer.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Polygons from
lines
OUTPUT [vector: polygon] The output polygon vector layer from lines
Python code
Algorithm ID: native:polygonize
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Polygons to lines
Takes a polygon layer and creates a line layer, with lines representing the boundaries of the polygons in the input
layer.
The attribute table of the output layer is the same as the one of the input layer.
Obr. 24.76: Black lines as the result of the algorithm
Default menu: Vector ► Geometry Tools
Viz také:
Lines to polygons, Polygonize, Convert geometry type
Parameters
Label Název Type Popis
Input layer INPUT [vector: polygon] Input polygon vector layer
Lines OUTPUT [vector: line]
Default: [Create
temporary
layer]
Specify the output line vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Lines OUTPUT [vector: line] The output line vector layer from polygons
Python code
Algorithm ID: native:polygonstolines
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Project points (Cartesian)
Projects point geometries by a specified distance and bearing (azimuth).
Allows features in-place modification
Parameters
Label Název Type Popis
Input layer INPUT [vector: point] Input point vector layer
Bearing (degrees
from North)
BEARING [number ]
Default: 0.0
Clockwise angle starting from North, in
degree (°) unit
Distance DISTANCE [number ]
Default: 1.0
Distance to offset geometries, in layer units
Projected OUTPUT [vector: point]
Default: [Create
temporary
layer]
Specify the output point vector layer. One
of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Projected OUTPUT [vector: point] The output (projected) point vector layer
Python code
Algorithm ID: native:projectpointcartesian
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Promote to multipart
Takes a vector layer with singlepart geometries and generates a new one in which all geometries are multipart.
Input features which are already multipart features will remain unchanged.
This algorithm can be used to force geometries to multipart types in order to be compatible with data providers that
require multipart features.
Allows features in-place modification
Viz také:
Aggregate, Collect geometries
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Multiparts OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output multipart vector layer.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Multiparts OUTPUT [same as input] The output multipart vector layer
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Python code
Algorithm ID: native:promotetomulti
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Rectangles, ovals, diamonds
Creates a buffer area with a rectangle, oval or diamond shape for each feature of the input point layer.
The shape parameters can be fixed for all features or dynamic using a field or an expression.
Obr. 24.77: Different buffer shapes with dynamic parameters
Parameters
Label Název Type Popis
Input layer INPUT [vector: point] Input point vector layer
Buffer shape SHAPE [enumeration] The shape to use. One of:
• 0 — Rectangles
• 1 — Ovals
• 2 — Diamonds
Width WIDTH [number ]
Default: 1.0
Width of the buffer shape
Height HEIGHT [number ]
Default: 1.0
Height of the buffer shape
Rotation
Optional
ROTATION [number ]
Default: None
Rotation of the buffer shape
Number of
segment
SEGMENTS [number]
Default: 36
Number of segments for a full circle (Ovals
shape)
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Tabulka 24.114 – pokračujte na předchozí stránce
Label Název Type Popis
Output OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Output OUTPUT [vector: polygon] The output vector layer (with the buffer
shapes)
Python code
Algorithm ID: native:rectanglesovalsdiamonds
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Remove duplicate vertices
Removes duplicate vertices from features, wherever removing the vertices does not result in a degenerate geometry.
The tolerance parameter specifies the tolerance for coordinates when determining whether vertices are identical.
By default, Z values are not considered when detecting duplicate vertices. E.g. two vertices with the same X and
Y coordinate but different Z values will still be considered duplicate and one will be removed. If the Use Z Value
parameter is true, then the Z values are also tested and vertices with the same X and Y but different Z will be
maintained.
Poznámka: Duplicate vertices are not tested between different parts of a multipart geometry, e.g. a multipoint
geometry with overlapping points will not be changed by this method.
Allows features in-place modification
Viz také:
Extract vertices, Extract specific vertices, Delete duplicate geometries
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Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Tolerance TOLERANCE [number ]
Default: 0.000001
Vertices closer than the specified distance
are considered duplicates
Use Z value USE_Z_VALUE [boolean ]
Default: False
If the Use Z Value parameter is true, then
the Z values are also tested and vertices with
the same X and Y but different Z will be
maintained.
Cleaned OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Cleaned OUTPUT [same as input] The output vector layer (without duplicate
vertices)
Python code
Algorithm ID: native:removeduplicatevertices
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Remove null geometries
Removes any features which do not have a geometry from a vector layer. All other features will be copied unchanged.
The features with null geometries can be saved to a separate layer.
If Also remove empty geometries is checked, the algorithm removes features whose geometries have no coordinates,
i.e., geometries that are empty. In that case, also the null output will reflect this option, containing both null and empty
geometries.
Viz také:
Delete duplicate geometries
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Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer (with non-NULL
geometries)
Also remove
empty geometries
REMOVE_EMPTY [boolean]
Non null
geometries
OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer for the non-NULL
(and non-empty) geometries. One
of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Null geometries NULL_OUTPUT [same as input]
Default: [Skip
output]
Specify the output vector layer for the
NULL (and empty) geometries. One of:
• Skip Output
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Null geometries NULL_OUTPUT [same as input] Output vector layer (for NULL and, if
chosen, empty geometries)
Non null
geometries
OUTPUT [same as input] The output vector layer (without NULL
and, if chosen, empty geometries)
Python code
Algorithm ID: native:removenullgeometries
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Reverse line direction
Inverts the direction of a line layer.
Obr. 24.78: Before and after the direction inversion
Allows features in-place modification
Parameters
Label Název Type Popis
Input layer INPUT [vector: line] Input line vector layer
Reversed OUTPUT [vector: line]
Default: [Create
temporary
layer]
Specify the output line vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Reversed OUTPUT [vector: line] The output line vector layer (with reversed
lines)
Python code
Algorithm ID: native:reverselinedirection
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Rotate
Rotates feature geometries by the specified angle clockwise. The rotation occurs around each feature’s centroid, or
optionally around a unique preset point.
Allows features in-place modification
Viz také:
Translate, Swap X and Y coordinates
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Rotation (degrees
clockwise)
ANGLE [number ]
Default: 0.0
Angle of the rotation in degrees
Rotation anchor
point (x, y)
Optional
ANCHOR [point]
Default: None
X,Y coordinates of the point to rotate the
features around. If not set the rotation
occurs around each feature’s centroid.
Rotated OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer (with rotated
geometries). One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Rotated OUTPUT [same as input] The output vector layer with rotated
geometries
Python code
Algorithm ID: native:rotatefeatures
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Segmentize by maximum angle
Segmentizes a geometry by converting curved sections to linear sections.
The segmentization is performed by specifying the maximum allowed radius angle between vertices on the
straightened geometry (e.g the angle of the arc created from the original arc center to consecutive output vertices
on the linearized geometry). Non-curved geometries will be retained without change.
Viz také:
Segmentize by maximum distance, Simplify, Smooth
Parameters
Label Název Type Popis
Input layer INPUT [vector: line,
polygon]
Input line or polygon vector layer
Maximum angle
between vertices
(degrees)
ANGLE [number ]
Default: 5.0
Maximum allowed radius angle between
vertices on the straightened geometry
Segmentized OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer (with
segmentized geometries). One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Segmentized OUTPUT [same as input] The output vector layer with segmentized
geometries
Python code
Algorithm ID: native:segmentizebymaxangle
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Segmentize by maximum distance
Segmentizes a geometry by converting curved sections to linear sections.
The segmentization is performed by specifying the maximum allowed offset distance between the original curve and
the segmentized representation. Non-curved geometries will be retained without change.
Viz také:
Segmentize by maximum angle, Simplify, Smooth
Parameters
Label Název Type Popis
Input layer INPUT [vector: line,
polygon]
Input line or polygon vector layer
Maximum offset
distance
DISTANCE [number ]
Default: 1.0
Maximum allowed offset distance between
the original curve and the segmentized
representation, in the layer units.
Segmentized OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer (with
segmentized geometries). One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Segmentized OUTPUT [same as input] The output vector layer with segmentized
geometries
Python code
Algorithm ID: native:segmentizebymaxdistance
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Set M value
Sets the M value for geometries in a layer.
If M values already exist in the layer, they will be overwritten with the new value. If no M values exist, the geometry
will be upgraded to include M values and the specified value used as the initial M value for all geometries.
Tip: Use the Identify Features
button to check the added M value: the results are available in the Identify Results
dialog.
Viz také:
Set M value from raster, Set Z value, Drop M/Z values
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
M Value M_VALUE [number ]
Default: 0.0
M value to assign to the feature geometries
M Added OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
M Added OUTPUT [same as input] The output vector layer (with M values
assigned to the geometries)
Python code
Algorithm ID: native:setmvalue
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Set M value from raster
Uses values sampled from a band within a raster layer to set the M value for every overlapping vertex in the feature
geometry. The raster values can optionally be scaled by a preset amount.
If M values already exist in the layer, they will be overwritten with the new value. If no M values exist, the geometry
will be upgraded to include M values.
Viz také:
Drape (set Z value from raster), Set M value
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Raster layer RASTER [raster] Raster layer with M values
Band number BAND [raster band]
Default: 1
The raster band from which the M values
are taken
Value for
nodata or non-
-intersecting
vertices
NODATA [number ]
Default: 0.0
Value to use in case the vertex does not
intersect (a valid pixel of) the raster
Scale factor SCALE [number ]
Default: 1.0
Scaling value: the band values are
multiplied by this value.
Updated OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer (with
updated M values). One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Updated OUTPUT [same as input] The output vector layer (with updated M
values)
Python code
Algorithm ID: native:setmfromraster
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Set Z value
Sets the Z value for geometries in a layer.
If Z values already exist in the layer, they will be overwritten with the new value. If no Z values exist, the geometry
will be upgraded to include Z values and the specified value used as the initial Z value for all geometries.
Tip: Use the Identify Features
button to check the added Z value: the results are available in the Identify Results dialog.
Viz také:
Drape (set Z value from raster), Set M value, Drop M/Z values
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Z Value Z_VALUE [number ]
Default: 0.0
Z value to assign to the feature geometries
Z Added OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Z Added OUTPUT [same as input] The output vector layer (with Z values
assigned)
Python code
Algorithm ID: native:setzvalue
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Simplify
Simplifies the geometries in a line or polygon layer. It creates a new layer with the same features as the ones in the
input layer, but with geometries containing a lower number of vertices.
The algorithm gives a choice of simplification methods, including distance based (the „Douglas-Peucker“ algorithm),
area based („Visvalingam“ algorithm) and snapping geometries to grid.
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Obr. 24.79: Clockwise from top left: source layer and increasing simplification tolerances
Allows features in-place modification
Default menu: Vector ► Geometry Tools
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Viz také:
Smooth, Densify by count, Densify by interval
Parameters
Label Název Type Popis
Input layer INPUT [vector: line,
polygon]
Input line or polygon vector layer
Simplification
method
METHOD [enumeration]
Default: 0
Simplification method. One of:
• 0 — Distance (Douglas-Peucker)
• 1 — Snap to grid
• 2 — Area (Visvalingam)
Tolerance TOLERANCE [number ]
Default: 1.0
Threshold tolerance (in units of the layer):
if the distance between two nodes is smaller
than the tolerance value, the segment will be
simplified and vertices will be removed.
Simplified OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output (simplified) vector layer.
One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Simplified OUTPUT [same as input] The output (simplified) vector layer
Python code
Algorithm ID: native:simplifygeometries
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Single sided buffer
Computes a buffer on lines by a specified distance on one side of the line only.
Buffer always results in a polygon layer.
Obr. 24.80: Left versus right side buffer on the same vector line layer
Viz také:
Buffer
Parameters
Label Název Type Popis
Input layer INPUT [vector: line] Input line vector layer
Distance DISTANCE [number]
Default: 10.0
Buffer distance.
Side SIDE [enumeration] Which side to create the buffer on. One of:
• 0 – Left
• 1 – Right
Segments SEGMENTS [number]
Default: 8
Controls the number of line segments to
use to approximate a quarter circle when
creating rounded offsets.
Join style JOIN_STYLE [enumeration] Specifies whether round, miter or beveled
joins should be used when offsetting corners
in a line. Options are:
• 0 — Round
• 1 — Miter
• 2 — Bevel
Miter limit MITER_LIMIT [number]
Default: 2.0
Controls the maximum distance from the
offset curve to use when creating a mitered
join (only applicable for miter join styles).
Minimum: 1.0
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Tabulka 24.119 – pokračujte na předchozí stránce
Label Název Type Popis
Buffer OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output (buffer) layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Buffer OUTPUT [vector: polygon] Output (buffer) polygon layer
Python code
Algorithm ID: native:singlesidedbuffer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Smooth
Smooths the geometries in a line or polygon layer by adding more vertices and corners to the feature geometries.
The iterations parameter dictates how many smoothing iterations will be applied to each geometry. A higher number
of iterations results in smoother geometries with the cost of greater number of nodes in the geometries.
Obr. 24.81: Increasing number of iterations causes smoother geometries
The offset parameter controls how „tightly“ the smoothed geometries follow the original geometries. Smaller values
results in a tighter fit, and larger values will create a looser fit.
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Obr. 24.82: Blue: the input layer. Offset 0.25 gives the red line, while offset 0.50 gives the green line.
The maximum angle parameter can be used to prevent smoothing of nodes with large angles. Any node where the
angle of the segments to either side is larger than this will not be smoothed. For example, setting the maximum angle
to 90 degrees or lower would preserve right angles in the geometry.
Allows features in-place modification
Viz také:
Simplify, Densify by count, Densify by interval
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Parameters
Label Název Type Popis
Input layer INPUT [vector: line,
polygon]
Input line or polygon vector layer
Iterations ITERATIONS [number ]
Default: 1
Increasing the number of iterations will give
smoother geometries (and more vertices).
Offset OFFSET [number ]
Default: 0.25
Increasing values will move the smoothed
lines / boundaries further away from the
input lines / boundaries.
Maximum node
angle to smooth
MAX_ANGLE [number ]
Default: 180.0
Every node below this value will be
smoothed
Smoothed OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output (smoothed) layer. One
of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Smoothed OUTPUT [same as input] Output (smoothed) vector layer
Python code
Algorithm ID: native:smoothgeometry
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Snap geometries to layer
Snaps the geometries in a layer either to the geometries from another layer, or to geometries within the same layer.
Matching is done based on a tolerance distance, and vertices will be inserted or removed as required to make the
geometries match the reference geometries.
Viz také:
Snap points to grid
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Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Reference layer REFERENCE_LAYER[vector: any] Vector layer to snap to
Tolerance TOLERANCE [number]
Default: 10.0
Control how close input vertices need to
be to the reference layer geometries before
they are snapped.
Behavior BEHAVIOR [enumeration]
Default: 0
Snapping can be done to an existing node or
a segment (its closest point to the vertex to
move). Available snapping options:
• 0 — Prefer aligning nodes, insert
extra vertices where required
Prefer to snap to nodes, even when
a segment may be closer than a node.
New nodes will be inserted to make
geometries follow each other exactly
when inside allowable tolerance.
• 1 — Prefer closest point, insert extra
vertices where required
Snap to closest point, regardless of it
is a node or a segment. New nodes
will be inserted to make geometries
follow each other exactly when inside
allowable tolerance.
• 2 — Prefer aligning nodes, don’t
insert new vertices
Prefer to snap to nodes, even when
a segment may be closer than a node.
No new nodes will be inserted.
• 3 — Prefer closest point, don’t insert
new vertices
Snap to closest point, regardless of it
is a node or a segment. No new nodes
will be inserted.
• 4 — Move end points only, prefer
aligning nodes
Only snap start/end points of
lines (point features will also be
snapped, polygon features will not be
modified), prefer to snap to nodes.
• 5 — Move end points only, prefer
closest point
Only snap start/end points of
lines (point features will also be
snapped, polygon features will not
be modified), snap to closest point
• 6 — Snap end points to end points
only
Only snap the start/end points of lines
to other start/end points of lines
• 7 — Snap to anchor nodes (single
layer only)
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Tabulka 24.121 – pokračujte na předchozí stránce
Label Název Type Popis
Snapped geometry OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output (snapped) layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Snapped geometry OUTPUT [same as input] Output (snapped) vector layer
Python code
Algorithm ID: native:snapgeometries
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Snap points to grid
Modifies the coordinates of geometries in a vector layer, so that all points or vertices are snapped to the closest point
of a grid.
If the snapped geometry cannot be calculated (or is totally collapsed) the feature’s geometry will be cleared.
Snapping can be performed on the X, Y, Z or M axis. A grid spacing of 0 for any axis will disable snapping for that
axis.
Poznámka: Snapping to grid may generate an invalid geometry in some corner cases.
Allows features in-place modification
Viz také:
Snap geometries to layer
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Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
X Grid Spacing HSPACING [number ]
Default: 1.0
Grid spacing on the X axis
Y Grid Spacing VSPACING [number ]
Default: 1.0
Grid spacing on the Y axis
Z Grid Spacing ZSPACING [number ]
Default: 0.0
Grid spacing on the Z axis
M Grid Spacing MSPACING [number ]
Default: 0.0
Grid spacing on the M axis
Snapped OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output (snapped) layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Snapped OUTPUT [same as input] Output (snapped) vector layer
Python code
Algorithm ID: native:snappointstogrid
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Split lines by maximum length
Takes a line (or curve) layer and splits each feature into multiple parts, where each part is of a specified maximum
length. Z and M values at the start and end of the new line substrings are linearly interpolated from existing values.
Parameters
Label Název Type Popis
Input layer INPUT [vector: line] The input line vector layer
Maximum line
length
LENGTH [number ]
Default: 10.0
The maximum length of a line in the output.
Split OUTPUT [vector: line]
Default: [Create
temporary
layer]
Specify the output line vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Split OUTPUT [vector: line] The new line vector layer - the length of
the feature geometries is less than or equal
to the length specified in the LENGTH
parameter.
Python code
Algorithm ID: native:splitlinesbylength
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Subdivide
Subdivides the geometry. The returned geometry will be a collection containing subdivided parts from the original
geometry, where no part has more than the specified maximum number of nodes.
This is useful for dividing a complex geometry into less complex parts, easier to spatially index and faster to perform
spatial operations. Curved geometries will be segmentized before subdivision.
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Obr. 24.83: Left the input layer, middle maximum nodes value is 100 and right maximum value is 200
Poznámka: Subdividing a geometry can generate geometry parts that may not be valid and may contain self-
-intersections.
Allows features in-place modification
Viz také:
Explode lines, Line substring
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] The input vector layer
Maximum nodes
in parts
MAX_NODES [number ]
Default: 256
Maximum number of vertices each new
geometry part is allowed to have. Fewer
sub-parts for higher values.
Subdivided OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output (subdivided) vector
layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Subdivided OUTPUT [same as input] Output vector layer
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Python code
Algorithm ID: native:subdivide
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Swap X and Y coordinates
Switches the X and Y coordinate values in input geometries.
It can be used to repair geometries which have accidentally had their latitude and longitude values reversed.
Allows features in-place modification
Viz také:
Translate, Rotate
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] The input vector layer
Swapped OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Swapped OUTPUT [same as input] Output (swapped) vector layer
Python code
Algorithm ID: native:swapxy
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Tapered buffers
Creates tapered buffer along line geometries, using a specified start and end buffer diameter.
Obr. 24.84: Tapered buffer example
Viz také:
Variable width buffer (by M value), Buffer, Create wedge buffers
Parameters
Label Název Type Popis
Input layer INPUT [vector: line] Input line vector layer
Start width START_WIDTH [number ]
Default: 0.0
Represents the radius of the buffer applied
at the start point of the line feature
End width END_WIDTH [number ]
Default: 0.0
Represents the radius of the buffer applied
at the end point of the line feature.
Segments SEGMENTS [number ]
Default: 16
Controls the number of line segments to
use to approximate a quarter circle when
creating rounded offsets.
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Tabulka 24.123 – pokračujte na předchozí stránce
Label Název Type Popis
Buffered OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output (buffer) layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Buffered OUTPUT [vector: polygon] Output (buffer) polygon layer
Python code
Algorithm ID: native:taperedbuffer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Tessellate
Tessellates a polygon geometry layer, dividing the geometries into triangular components.
The output layer consists of multipolygon geometries for each input feature, with each multipolygon consisting of
multiple triangle component polygons.
Obr. 24.85: Tessellated polygon (right)
Allows features in-place modification
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Parameters
Label Název Type Popis
Input layer INPUT [vector: polygon] Input polygon vector layer
Tesselated OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Tesselated OUTPUT [vector: polygon] Output multipolygonZ layer
Python code
Algorithm ID: 3d:tessellate
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Transect
Creates transects on vertices for (multi)linestring.
A transect is a line oriented from an angle (by default perpendicular) to the input polylines (at vertices).
Field(s) from feature(s) are returned in the transect with these new fields:
• TR_FID: ID of the original feature
• TR_ID: ID of the transect. Each transect have an unique ID
• TR_SEGMENT: ID of the segment of the linestring
• TR_ANGLE: Angle in degrees from the original line at the vertex
• TR_LENGTH: Total length of the transect returned
• TR_ORIENT: Side of the transect (only on the left or right of the line, or both side)
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Obr. 24.86: Dashed red lines represent the transect of the input line layer
Parameters
Label Název Type Popis
Input layer INPUT [vector: line] Input line vector layer
Length of the
transect
LENGTH [number ]
Default: 5.0
Length in map unit of the transect
Angle in degrees
from the original
line at the vertices
ANGLE [number ]
Default: 90.0
Change the angle of the transect
Side to create the
transect
SIDE [enumeration] Choose the side of the transect. Available
options are:
• 0 — Left
• 1 — Right
• 2 — Both
Transect OUTPUT [vector: line]
Default: [Create
temporary
layer]
Specify the output line layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Transect OUTPUT [vector: line] Output line layer
Python code
Algorithm ID: native:transect
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Translate
Moves the geometries within a layer, by offsetting with a predefined X and Y displacement.
Z and M values present in the geometry can also be translated.
Obr. 24.87: Dashed lines represent the translated geometry of the input layer
Allows features in-place modification
Viz také:
Array of translated features, Offset lines, Rotate, Swap X and Y coordinates
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Offset distance (x-
-axis)
DELTA_X [number ]
Default: 0.0
Displacement to apply on the X axis
Offset distance (y-
-axis)
DELTA_Y [number ]
Default: 0.0
Displacement to apply on the Y axis
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Tabulka 24.125 – pokračujte na předchozí stránce
Label Název Type Popis
Offset distance (z-
axis)
DELTA_Z [number ]
Default: 0.0
Displacement to apply on the Z axis
Offset distance (m
values)
DELTA_M [number ]
Default: 0.0
Displacement to apply on the M axis
Translated OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Translated OUTPUT [same as input] Output vector layer
Python code
Algorithm ID: native:translategeometry
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Variable distance buffer
Computes a buffer area for all the features in an input layer.
The size of the buffer for a given feature is defined by an attribute, so it allows different features to have different
buffer sizes.
Poznámka: This algorithm is only available from the Graphical modeler.
Viz také:
Buffer
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Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Distance field DISTANCE [tablefield:
numeric]
Attribute for the distance radius of the
buffer
Segments SEGMENTS [number]
Default: 5
Controls the number of line segments to
use to approximate a quarter circle when
creating rounded offsets.
Dissolve result DISSOLVE [boolean]
Default: False
Choose to dissolve the final
buffer, resulting in a single
feature covering all input features.
Obr. 24.88: Normal and dissolved buffer
End cap style END_CAP_STYLE [enumeration] Controls how line endings
are handled in the buffer.
Obr. 24.89: Round, flat and square cap
styles
Join style JOIN_STYLE [enumeration] Specifies whether round, miter or beveled
joins should be used when offsetting corners
in a line.
Miter limit MITER_LIMIT [number]
Default: 2.0
Only applicable for mitered join styles, and
controls the maximum distance from the
offset curve to use when creating a mitered
join.
Outputs
Label Název Type Popis
Buffer OUTPUT [vector: polygon] Buffer polygon vector layer.
Python code
Algorithm ID: qgis:variabledistancebuffer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Variable width buffer (by M value)
Creates variable width buffers along lines, using the M value of the line geometries as the diameter of the buffer at
each vertex.
Obr. 24.90: Variable buffer example
Viz také:
Tapered buffers, Buffer, Set M value
Parameters
Label Název Type Popis
Input layer INPUT [vector: line] Input line vector layer
Segments SEGMENTS [number ]
Default: 16
Number of the buffer segments per quarter
circle. It can be a unique value (same value
for all the features), or it can be taken
from features data (the value can depend on
feature attributes).
Buffered OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output (buffer) layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Buffered OUTPUT [vector: polygon] Variable buffer polygon layer
Python code
Algorithm ID: native:bufferbym
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Voronoi polygons
Takes a point layer and generates a polygon layer containing the Voronoi polygons (known also as Thiessen polygons)
corresponding to those input points.
Any location within a Voronoi polygon is closer to the associated point than to any other point.
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Obr. 24.91: Voronoi polygons
Default menu: Vector ► Geometry Tools
Parameters
Label Název Type Popis
Input layer INPUT [vector: point] Input point vector layer
Buffer region (%
of extent)
BUFFER [number]
Default: 0.0
The extent of the output layer will be this
much bigger than the extent of the input
layer
Voronoi polygons OUTPUT [vector: polygon]
Default: [Create
temporary
layer]
Specify the output layer (with the Voronoi
polygons). One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Voronoi polygons OUTPUT [vector: polygon] Voronoi polygons of the input point vector
layer
Python code
Algorithm ID: qgis:voronoipolygons
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.1.17 Vector overlay
Clip
Clips a vector layer using the features of an additional polygon layer.
Only the parts of the features in the input layer that fall within the polygons of the overlay layer will be added to the
resulting layer.
Varování: Feature modification
The attributes of the features are not modified, although properties such as area or length of the features will
be modified by the clipping operation. If such properties are stored as attributes, those attributes will have to be
manually updated.
This algorithm uses spatial indexes on the providers, prepared geometries and apply a clipping operation if the
geometry isn’t wholly contained by the mask geometry.
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Obr. 24.92: Clipping operation between a two-features input layer and a single feature overlay layer (left) - resulting
features are moved for clarity (right)
Allows features in-place modification
Default menu: Vector ► Geoprocessing Tools
Viz také:
Intersection, Difference
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Layer containing the features to be clipped
Overlay layer OVERLAY [vector: polygon] Layer containing the clipping features
Clipped OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the layer to contain the features
from the input layer that are inside the
overlay (clipping) layer. One of:
• Create Temporary Layer
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table……
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Clipped OUTPUT [same as input] Layer containing features from the input
layer split by the overlay layer.
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Python code
Algorithm ID: qgis:clip
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Difference
Extracts features from the input layer that don’t fall within the boundaries of the overlay layer.
Input layer features that partially overlap the overlay layer feature(s) are split along the boundary of those feature(s)
and only the portions outside the overlay layer features are retained.
Attributes are not modified (see warning).
Obr. 24.93: Difference operation between a two-features input layer and a single feature overlay layer (left) - resulting
features are moved for clarity (right)
Allows features in-place modification
Default menu: Vector ► Geoprocessing Tools
Viz také:
Symmetrical difference, Clip
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Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Layer to extract (parts of) features from.
Overlay layer OVERLAY [vector: any] Layer containing the geometries that
will be subtracted from the input layer
geometries. It is expected to have at least
as many dimensions (point: 0D, line: 1D,
polygon: 2D, volume: 3D) as the input
layer geometries.
Difference OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the layer to contain the (parts of)
features from the input layer that are not
inside the overlay layer. One of:
• Create Temporary Layer
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table……
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Difference OUTPUT [same as input] Layer containing (parts of) features from
the input layer not overlapping the overlay
layer.
Python code
Algorithm ID: qgis:difference
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Extract/clip by extent
Creates a new vector layer that only contains features which fall within a specified extent.
Any features which intersect the extent will be included.
Viz také:
Clip
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Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Layer to extract (parts of) features from.
Extent (xmin,
xmax, ymin,
ymax)
EXTENT [extent] Extent for clipping.
Clip features to
extent
CLIP [boolean]
Default: False
If checked, output geometries will be
automatically converted to multi geometries
to ensure uniform output types. Moreover
the geometries will be clipped to the
extent chosen instead of taking the whole
geometry as output.
Extracted OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the layer to contain the features
from the input layer that are inside the clip
extent. One of:
• Create Temporary Layer
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table……
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Extracted OUTPUT [same as input] Layer containing the clipped features.
Python code
Algorithm ID: qgis:extractbyextent
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Intersection
Extracts the portions of features from the input layer that overlap features in the overlay layer.
Features in the intersection layer are assigned the attributes of the overlapping features from both the input and overlay
layers.
Attributes are not modified (see warning).
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Obr. 24.94: The intersection operation: A two-features input layer and a single feature overlay layer (left) - resulting
features are moved for clarity (right)
Default menu: Vector ► Geoprocessing Tools
Viz také:
Clip, Difference
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Layer to extract (parts of) features from.
Overlay layer OVERLAY [vector: any] Layer containing the features to check for
overlap. Its features‘ geometry is expected
to have at least as many dimensions (point:
0D, line: 1D, polygon: 2D, volume: 3D)
as the input layer’s.
Input fields to
keep (leave empty
to keep all fields)
Optional
INPUT_FIELDS [tablefield: any]
[list]
Default: None
Field(s) of the input layer to keep in the
output. If no fields are chosen all fields are
taken.
Overlay fields to
keep (leave empty
to keep all fields)
Optional
OVERLAY_FIELDS [tablefield: any]
[list]
Default: None
Field(s) of the overlay layer to keep in the
output. If no fields are chosen all fields are
taken.
Overlay fields
prefix
Optional
OVERLAY_FIELDS_PREFIX[string] Prefix to add to the field names of
the intersect layer’s fields to avoid name
collisions with fields in the input layer.
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Tabulka 24.127 – pokračujte na předchozí stránce
Label Název Type Popis
Intersection OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the layer to contain (the parts of)
the features from the input layer that overlap
one or more features from the overlay layer.
One of:
• Create Temporary Layer
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table……
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Intersection OUTPUT [same as input] Layer containing (parts of) features from
the input layer that overlap the overlay layer.
Python code
Algorithm ID: qgis:intersection
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Line intersections
Creates point features where the lines from the two layers intersect.
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Obr. 24.95: Points of intersection
Default menu: Vector ► Analysis Tools
Parameters
Label Název Type Popis
Input layer INPUT [vector: line] Input line layer.
Intersect layer INTERSECT [vector: line] Layer to use to find line intersections.
Input fields to
keep (leave empty
to keep all fields)
Optional
INPUT_FIELDS [tablefield: any]
[list]
Default: None
Field(s) of the input layer to keep in the
output. If no fields are chosen all fields are
taken.
Intersect fields to
keep (leave empty
to keep all fields)
Optional
INTERSECT_FIELDS[tablefield: any]
[list]
Default: None
Field(s) of the intersect layer to keep in the
output. If no fields are chosen all fields are
taken.
Intersect fields
prefix
Optional
OVERLAY_FIELDS_PREFIX[string] Prefix to add to the field names of
the intersect layer’s fields to avoid name
collisions with fields in the input layer.
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Tabulka 24.129 – pokračujte na předchozí stránce
Label Název Type Popis
Intersection OUTPUT [vector: point]
Default: [Create
temporary
layer]
Specify the layer to contain the intersection
points of the lines from the input and
overlay layers. One of:
• Create Temporary Layer
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table……
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Intersections OUTPUT [vector: point] Point vector layer with the intersections.
Python code
Algorithm ID: qgis:lineintersections
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Split with lines
Splits the lines or polygons in one layer using the lines in another layer to define the breaking points. Intersection
between geometries in both layers are considered as split points.
Output will contain multi geometries for split features.
Obr. 24.96: Split lines
Allows features in-place modification
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Parameters
Label Název Type Popis
Input layer INPUT [vector: line,
polygon]
Layer containing the lines or polygons to
split.
Split layer LINES [vector: line] Line layer whose lines are used to define the
breaking points.
Split OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the layer to contain the splitted (in
case they are intersected by a line in the split
layer) line/polygon features from the input
layer. One of:
• Create Temporary Layer
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table……
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Split OUTPUT [same as input] Output vector layer with split lines or
polygons from input layer.
Python code
Algorithm ID: qgis:splitwithlines
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Symmetrical difference
Creates a layer containing features from both the input and overlay layers but with the overlapping areas between the
two layers removed.
The attribute table of the symmetrical difference layer contains attributes and fields from both the input and overlay
layers.
Attributes are not modified (see warning).
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Obr. 24.97: Symmetrical difference operation between a two-features input layer and a single feature overlay layer
(left) - resulting features are moved for clarity (right)
Default menu: Vector ► Geoprocessing Tools
Viz také:
Difference, Clip, Intersection
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] First layer to extract (parts of) features
from.
Overlay layer OVERLAY [vector: any] Second layer to extract (parts of) features
from. Ideally the geometry type should be
the same as input layer.
Overlay fields
prefix
Optional
OVERLAY_FIELDS_PREFIX[string] Prefix to add to the field names of
the overlay layer’s fields to avoid name
collisions with fields in the input layer.
Symmetrical
difference
OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the layer to contain (the parts of)
the features from the input and overlay
layers that do not overlap features from the
other layer. One of:
• Create Temporary Layer
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table……
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Symmetrical
difference
OUTPUT [same as input] Layer containing (parts of) features from
each layer not overlapping the other layer.
Python code
Algorithm ID: qgis:symmetricaldifference
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Union
Checks overlaps between features within the input layer and creates separate features for overlapping and non-overlapping
parts. The area of overlap will create as many identical overlapping features as there are features that
participate in that overlap.
Obr. 24.98: Union operation with a single input layer of three overlapping features (left) - resulting features are moved
for clarity (right)
An overlay layer can also be used, in which case features from each layer are split at their overlap with features from
the other one, creating a layer containing all the portions from both input and overlay layers. The attribute table of the
union layer is filled with attribute values from the respective original layer for non-overlapping features, and attribute
values from both layers for overlapping features.
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Obr. 24.99: Union operation between a two-features input layer and a single feature overlay layer (left) - resulting
features are moved for clarity (right)
Poznámka: For union(A,B) algorithm, if there are overlaps among geometries of layer A or among geometries
of layer B, these are not resolved: you need to do union(union(A,B)) to resolve all overlaps, i.e. run single
layer union(X) on the produced result X=union(A,B).
Default menu: Vector ► Geoprocessing Tools
Viz také:
Clip, Difference, Intersection
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer to split at any
intersections.
Overlay layer
Optional
OVERLAY [vector: any] Layer that will be combined to the first
one. Ideally the geometry type should be the
same as input layer.
Overlay fields
prefix
Optional
OVERLAY_FIELDS_PREFIX[string] Prefix to add to the field names of
the overlay layer’s fields to avoid name
collisions with fields in the input layer.
Union OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the layer to contain the (split and
duplicated) features from the input layer
and the overlay layer. One of:
• Create Temporary Layer
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table……
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Union OUTPUT [same as input] Layer containing all the overlapping and
non-overlapping parts from the processed
layer(s).
Python code
Algorithm ID: qgis:union
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.1.18 Vector selection
Extract by attribute
Creates two vector layers from an input layer: one will contain only matching features while the second will contain
all the non-matching features.
The criteria for adding features to the resulting layer is based on the values of an attribute from the input layer.
Viz také:
Select by attribute
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Layer to extract features from.
Selection attribute FIELD [tablefield: any] Filtering field of the layer
Operator OPERATOR [enumeration]
Default: 0
Many different operators are available:
• 0 — =
• 1 — ̸=
• 2 — >
• 3 — >=
• 4 — <
• 5 — <=
• 6 — begins with
• 7 — contains
• 8 — is null
• 9 — is not null
• 10 — does not contain
Value
Optional
VALUE [string] Value to be evaluated
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Tabulka 24.130 – pokračujte na předchozí stránce
Label Název Type Popis
Extracted
(attribute)
OUTPUT [same as input]
Default: [Create
Temporary
Layer]
Specify the output vector layer for matching
features. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Extracted (non-
-matching)
FAIL_OUTPUT [same as input]
Default: [Skip
output]
Specify the output vector layer for non-matching
features. One of:
• Skip Output
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
Outputs
Label Název Type Popis
Extracted
(attribute)
OUTPUT [same as input] Vector layer with matching features from
the input layer
Extracted (non-
-matching)
FAIL_OUTPUT [same as input] Vector layer with non-matching features
from the input layer
Python code
Algorithm ID: qgis:extractbyattribute
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Extract by expression
Creates two vector layers from an input layer: one will contain only matching features while the second will contain
all the non-matching features.
The criteria for adding features to the resulting layer is based on a QGIS expression. For more information about
expressions see the Výrazy.
Viz také:
Select by expression
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Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Expression EXPRESSION [expression] Expression to filter the vector layer
Matching features OUTPUT [same as input]
Default: [Create
Temporary
Layer]
Specify the output vector layer for matching
features. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Non-matching FAIL_OUTPUT [same as input]
Default: [Skip
output]
Specify the output vector layer for non-matching
features. One of:
• Skip Output
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
Outputs
Label Název Type Popis
Matching features OUTPUT [same as input] Vector layer with matching features from
the input layer
Non-matching FAIL_OUTPUT [same as input] Vector layer with non-matching features
from the input layer
Python code
Algorithm ID: qgis:extractbyexpression
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Extract by location
Creates a new vector layer that only contains matching features from an input layer.
The criteria for adding features to the resulting layer is based on the spatial relationship between each feature and the
features in an additional layer.
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Obr. 24.100: In this example, the dataset from which we want to select (the source vector layer) consists of the green
circles, the orange rectangle is the dataset that it is being compared to (the intersection vector layer).
Available geometric predicates are:
Intersect Tests whether a geometry intersects another. Returns 1 (true) if the geometries spatially intersect (share
any portion of space - overlap or touch) and 0 if they don’t. In the picture above, this will select circles 1, 2 and
3.
Contain Returns 1 (true) if and only if no points of b lie in the exterior of a, and at least one point of the interior of
b lies in the interior of a. In the picture, no circle is selected, but the rectangle would be if you would select it
the other way around, as it contains a circle completely. This is the opposite of are within.
Disjoint Returns 1 (true) if the geometries do not share any portion of space (no overlap, not touching). Only circle
4 is selected.
Equal Returns 1 (true) if and only if geometries are exactly the same. No circles will be selected.
Touch Tests whether a geometry touches another. Returns 1 (true) if the geometries have at least one point in
common, but their interiors do not intersect. Only circle 3 is selected.
Overlap Tests whether a geometry overlaps another. Returns 1 (true) if the geometries share space, are of the same
dimension, but are not completely contained by each other. Only circle 2 is selected.
Are within Tests whether a geometry is within another. Returns 1 (true) if geometry a is completely inside geometry
b. Only circle 1 is selected.
Cross Returns 1 (true) if the supplied geometries have some, but not all, interior points in common and the actual
crossing is of a lower dimension than the highest supplied geometry. For example, a line crossing a polygon will
cross as a line (selected). Two lines crossing will cross as a point (selected). Two polygons cross as a polygon
(not selected).
Viz také:
Select by location
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Parameters
Label Název Type Popis
Extract features
from
INPUT [vector: any] Input vector layer
Where the
features
(geometric
predicate)
PREDICATE [enumeration] [list]
Default: [0]
Spatial condition for the selection. One or
more of:
• 0 — intersect
• 1 — contain
• 2 — disjoint
• 3 — equal
• 4 — touch
• 5 — overlap
• 6 — are within
• 7 — cross
If more than one condition is chosen, at
least one of them (OR operation) has to be
met for a feature to be extracted.
By comparing to
the features from
INTERSECT [vector: any] Intersection vector layer
Extracted
(location)
OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer for the
features that have the chosen spatial
relationship(s) with one or more features in
the comparison layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
Outputs
Label Název Type Popis
Extracted
(location)
OUTPUT [same as input] Vector layer with features from the
input layer that have the chosen spatial
relationship(s) with one or more features in
the comparison layer.
Python code
Algorithm ID: qgis:extractbylocation
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Random extract
Takes a vector layer and generates a new one that contains only a subset of the features in the input layer.
The subset is defined randomly, based on feature IDs, using a percentage or count value to define the total number of
features in the subset.
Viz také:
Random selection
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Source vector layer to select the features
from
Method METHOD [enumeration]
Default: 0
Random selection methods. One of:
• 0 — Number of selected features
• 1 — Percentage of selected features
Number/percentage
of selected
features
NUMBER [number]
Default: 10
Number or percentage of features to select
Extracted
(random)
OUTPUT [vector: any]
Default: [Create
temporary
layer]
Specify the output vector layer for the
randomly selected features. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
Vector layer containing randomly selected
features
Outputs
Label Název Type Popis
Extracted
(random)
OUTPUT [same as input] Vector layer containing randomly selected
features from the input layer
Python code
Algorithm ID: qgis:randomextract
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Random extract within subsets
Takes a vector layer and generates a new one that contains only a subset of the features in the input layer.
The subset is defined randomly, based on feature IDs, using a percentage or count value to define the total number
of features in the subset. The percentage/count value is not applied to the whole layer, but instead to each category.
Categories are defined according to a given attribute.
Viz také:
Random selection within subsets
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Vector layer to select the features from
ID field FIELD [tablefield: any] Category of the source vector layer to select
the features from
Method METHOD [enumeration]
Default: 0
Random selection method. One of:
• 0 — Number of selected features
• 1 — Percentage of selected features
Number/percentage
of selected
features
NUMBER [number]
Default: 10
Number or percentage of features to select
Extracted
(random
stratified)
OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer for the
randomly selected features. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Extracted
(random
stratified)
OUTPUT [same as input] Vector layer containing randomly selected
features from the input layer
Python code
Algorithm ID: qgis:randomextractwithinsubsets
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Random selection
Takes a vector layer and selects a subset of its features. No new layer is generated by this algorithm.
The subset is defined randomly, based on feature IDs, using a percentage or count value to define the total number of
features in the subset.
Default menu: Vector ► Research Tools
Viz také:
Random extract
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Vector layer for the selection
Method METHOD [enumeration]
Default: 0
Random selection method. One of:
• 0 — Number of selected features
• 1 — Percentage of selected features
Number/percentage
of selected
features
NUMBER [number]
Default: 10
Number or percentage of features to select
Outputs
Label Název Type Popis
Input layer INPUT [same as input] The input layer with features selected
Python code
Algorithm ID: qgis:randomselection
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Random selection within subsets
Takes a vector layer and selects a subset of its features. No new layer is generated by this algorithm.
The subset is defined randomly, based on feature IDs, using a percentage or count value to define the total number of
features in the subset.
The percentage/count value is not applied to the whole layer, but instead to each category.
Categories are defined according to a given attribute, which is also specified as an input parameter for the algorithm.
No new outputs are created.
Default menu: Vector ► Research Tools
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Viz také:
Random extract within subsets
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Vector layer to select features in
ID field FIELD [tablefield: any] Category of the input layer to select the
features from
Method METHOD [enumeration]
Default: 0
Random selection method. One of:
• 0 — Number of selected features
• 1 — Percentage of selected features
Number/percentage
of selected
features
NUMBER [number]
Default: 10
Number or percentage of features to select
Outputs
Label Název Type Popis
Input layer INPUT [same as input] The input layer with features selected
Python code
Algorithm ID: qgis:randomselectionwithinsubsets
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Select by attribute
Creates a selection in a vector layer.
The criteria for selecting features is based on the values of an attribute from the input layer.
Viz také:
Extract by attribute
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Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Vector layer to select features in
Selection attribute FIELD [tablefield: any] Filtering field of the layer
Operator OPERATOR [enumeration]
Default: 0
Many different operators are available:
• 0 — =
• 1 — ̸=
• 2 — >
• 3 — >=
• 4 — <
• 5 — <=
• 6 — begins with
• 7 — contains
• 8 — is null
• 9 — is not null
• 10 — does not contain
Value
Optional
VALUE [string] Value to be evaluated
Modify current
selection by
METHOD [enumeration]
Default: 0
How the selection of the algorithm should
be managed. One of:
• 0 — creating new selection
• 1 — adding to current selection
• 2 — removing from current selection
• 3 — selecting within current
selection
Outputs
Label Název Type Popis
Input layer INPUT [same as input] The input layer with features selected
Python code
Algorithm ID: qgis:selectbyattribute
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Select by expression
Creates a selection in a vector layer.
The criteria for selecting features is based on a QGIS expression. For more information about expressions see the
Výrazy.
Viz také:
Extract by expression
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Expression EXPRESSION [expression] Expression to filter the input layer
Modify current
selection by
METHOD [enumeration]
Default: 0
How the selection of the algorithm should
be managed. One of:
• 0 — creating new selection
• 1 — adding to current selection
• 2 — removing from current selection
• 3 — selecting within current
selection
Outputs
Label Název Type Popis
Input layer INPUT [same as input] The input layer with features selected
Python code
Algorithm ID: qgis:selectbyexpression
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Select by location
Creates a selection in a vector layer.
The criteria for selecting features is based on the spatial relationship between each feature and the features in an
additional layer.
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Obr. 24.101: In this example, the dataset from which we want to select (the source vector layer) consists of the green
circles, the orange rectangle is the dataset that it is being compared to (the intersection vector layer).
Available geometric predicates are:
Intersect Tests whether a geometry intersects another. Returns 1 (true) if the geometries spatially intersect (share
any portion of space - overlap or touch) and 0 if they don’t. In the picture above, this will select circles 1, 2 and
3.
Contain Returns 1 (true) if and only if no points of b lie in the exterior of a, and at least one point of the interior of
b lies in the interior of a. In the picture, no circle is selected, but the rectangle would be if you would select it
the other way around, as it contains a circle completely. This is the opposite of are within.
Disjoint Returns 1 (true) if the geometries do not share any portion of space (no overlap, not touching). Only circle
4 is selected.
Equal Returns 1 (true) if and only if geometries are exactly the same. No circles will be selected.
Touch Tests whether a geometry touches another. Returns 1 (true) if the geometries have at least one point in
common, but their interiors do not intersect. Only circle 3 is selected.
Overlap Tests whether a geometry overlaps another. Returns 1 (true) if the geometries share space, are of the same
dimension, but are not completely contained by each other. Only circle 2 is selected.
Are within Tests whether a geometry is within another. Returns 1 (true) if geometry a is completely inside geometry
b. Only circle 1 is selected.
Cross Returns 1 (true) if the supplied geometries have some, but not all, interior points in common and the actual
crossing is of a lower dimension than the highest supplied geometry. For example, a line crossing a polygon will
cross as a line (selected). Two lines crossing will cross as a point (selected). Two polygons cross as a polygon
(not selected).
Default menu: Vector ► Research Tools
Viz také:
Extract by location
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Parameters
Label Název Type Popis
Select features
from
INPUT [vector: any] Input vector layer
Where the
features
(geometric
predicate)
PREDICATE [enumeration] [list]
Default: [0]
Spatial condition for the selection. One or
more of:
• 0 — intersect
• 1 — contain
• 2 — disjoint
• 3 — equal
• 4 — touch
• 5 — overlap
• 6 — are within
• 7 — cross
If more than one condition is chosen, at
least one of them (OR operation) has to be
met for a feature to be extracted.
By comparing to
the features from
INTERSECT [vector: any] Intersection vector layer
Modify current
selection by
METHOD [enumeration]
Default: 0
How the selection of the algorithm should
be managed. One of:
• 0 — creating new selection
• 1 — adding to current selection
• 2 — selecting within current
selection
• 3 — removing from current selection
Outputs
Label Název Type Popis
Input layer INPUT [same as input] The input layer with features selected
Python code
Algorithm ID: qgis:selectbylocation
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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24.1.19 Vector table
Add autoincremental field
Adds a new integer field to a vector layer, with a sequential value for each feature.
This field can be used as a unique ID for features in the layer. The new attribute is not added to the input layer but
a new layer is generated instead.
The initial starting value for the incremental series can be specified. Optionally, the incremental series can be based
on grouping fields and a sort order for features can also be specified.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] The input vector layer.
Field name FIELD_NAME [string]
Default: ‚AUTO‘
Name of the field with autoincremental
values
Start values at
Optional
START [number]
Default: 0
Choose the initial number of the
incremental count
Group values by
Optional
GROUP_FIELDS [tablefield: any]
[list]
Select grouping field(s): instead of a single
count run for the whole layer, a separate
count is processed for each value returned
by the combination of these fields.
Sort expression
Optional
SORT_EXPRESSION[expression] Use an expression to sort the features in the
layer either globally or if set, based on group
fields.
Sort ascending SORT_ASCENDING [boolean]
Default: True
When a sort expression is set, use
this option to control the order in which
features are assigned values.
Sort nulls first SORT_NULLS_FIRST[boolean]
Default: False
When a sort expression is set, use
this option to set whether Null values are
counted first or last.
Incremented OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer with the auto
increment field. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Incremented OUTPUT [same as input] Vector layer with auto incremental field
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Python code
Algorithm ID: qgis:addautoincrementalfield
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Add field to attributes table
Adds a new field to a vector layer.
The name and characteristics of the attribute are defined as parameters.
The new attribute is not added to the input layer but a new layer is generated instead.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] The input layer
Field name FIELD_NAME [string] Name of the new field
Field type FIELD_TYPE [enumeration]
Default: 0
Type of the new field. You can choose
between:
• 0 — Integer
• 1 — Float
• 2 — String
Field length FIELD_LENGTH [number]
Default: 10
Length of the field
Field precision FIELD_PRECISION[number]
Default: 0
Precision of the field. Useful with Float field
type.
Added OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table……
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Added OUTPUT [same as input] Vector layer with new field added
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Python code
Algorithm ID: qgis:addfieldtoattributestable
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Add unique value index field
Takes a vector layer and an attribute and adds a new numeric field.
Values in this field correspond to values in the specified attribute, so features with the same value for the attribute
will have the same value in the new numeric field.
This creates a numeric equivalent of the specified attribute, which defines the same classes.
The new attribute is not added to the input layer but a new layer is generated instead.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] The input layer.
Class field FIELD [tablefield: any] Features that have the same value for this
field will get the same index.
Output field name FIELD_NAME [string]
Default:
‚NUM_FIELD‘
Name of the new field containing the
indexes.
Layer with index
field
OUTPUT [vector: any]
Default: [Create
temporary
layer]
Vector layer with the numeric field
containing indexes. One of:
• Skip Output
• Create Temporary Layer
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table……
The file encoding can also be changed here.
Class summary SUMMARY_OUTPUT [table]
Default: [Skip
output]
Specify the table to contain the summary of
the class field mapped to the corresponding
unique value. One of:
• Skip Output
• Create Temporary Layer
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table……
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Layer with index
field
OUTPUT [same as input] Vector layer with the numeric field
containing indexes.
Class summary SUMMARY_OUTPUT [table]
Default: [Skip
Output]
Table with summary of the class field
mapped to the corresponding unique value.
Python code
Algorithm ID: qgis:adduniquevalueindexfield
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Add X/Y fields to layer
Adds X and Y (or latitude/longitude) fields to a point layer. The X/Y fields can be calculated in a different CRS to
the layer (e.g. creating latitude/longitude fields for a layer in a projected CRS).
Parameters
Label Název Type Popis
Input layer INPUT [vector: point] The input layer.
Coordinate system CRS [crs]
Default:
„EPSG:4326“
Coordinate reference system to use for the
generated x and y fields.
Field prefix
Optional
PREFIX [string] Prefix to add to the new field names to avoid
name collisions with fields in the input layer.
Added fields OUTPUT [vector: point]
Default: [Create
temporary
layer]
Specify the output layer. One of:
• Create Temporary Layer
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Added fields OUTPUT [vector: point] The output layer - identical to the input layer
but with two new double fields, x and y.
Python code
Algorithm ID: qgis:addxyfieldstolayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Advanced Python field calculator
Adds a new attribute to a vector layer, with values resulting from applying an expression to each feature.
The expression is defined as a Python function.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Result field name FIELD_NAME [string]
Default: ‚NewField‘
Name of the new field
Field type FIELD_TYPE [enumeration]
Default: 0
Type of the new field. One of:
• 0 — Integer
• 1 — Float
• 2 — String
Field length FIELD_LENGTH [number]
Default: 10
Length of the field
Field precision FIELD_PRECISION[number]
Default: 3
Precision of the field. Useful with Float field
type.
Global expression
Optional
GLOBAL [string] The code in the global expression section
will be executed only once before the
calculator starts iterating through all the
features of the input layer. Therefore, this
is the correct place to import necessary
modules or to calculate variables that will
be used in subsequent calculations.
Formula FORMULA [string] The Python formula to evaluate. Example:
To calculate the area of an input polygon
layer you can add:
value = $geom.area()
continues on next page
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Tabulka 24.140 – pokračujte na předchozí stránce
Label Název Type Popis
Calculated OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the vector layer with the new
calculated field. One of:
• Create Temporary Layer
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table……
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Calculated OUTPUT [same as input] Vector layer with the new calculated field
Python code
Algorithm ID: qgis:advancedpythonfieldcalculator
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Drop field(s)
Takes a vector layer and generates a new one that has the same features but without the selected columns.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer to drop field(s) from
Fields to drop COLUMN [tablefield: any]
[list]
The field(s) to drop
Remaining fields OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer with the
remaining fields. One of:
• Create Temporary Layer
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table……
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Remaining fields OUTPUT [same as input] Vector layer with the remaining fields
Python code
Algorithm ID: qgis:deletecolumn
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Explode HStore Field
Creates a copy of the input layer and adds a new field for every unique key in the HStore field.
The expected field list is an optional comma separated list. If this list is specified, only these fields are added and the
HStore field is updated. By default, all unique keys are added.
The PostgreSQL HStore is a simple key-value store used in PostgreSQL and OGR (when reading an OSM file with
the other_tags field.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
HStore field FIELD [tablefield: any] The field(s) to drop
Expected list of
fields separated by
a comma
Optional
EXPECTED_FIELDS[string]
Default: ‚‘
Comma-separated list of fields to extract.
The HStore field will be updated by
removing these keys.
Exploded OUTPUT [same as input]
Default: [Create
temporary
layer]
Specify the output vector layer. One of:
• Create Temporary Layer
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table……
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Exploded OUTPUT [same as input] Output vector layer
Python code
Algorithm ID: qgis:explodehstorefield
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Extract binary field
Extracts contents from a binary field, saving them to individual files. Filenames can be generated using values taken
from an attribute in the source table or based on a more complex expression.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer containing the binary data
Binary field FIELD [tablefield: any] Field containing the binary data
File name FILENAME [expression] Field or expression-based text to name each
output file
Destination folder FOLDER [folder]
Default:
[Save to
a temporary
folder]
Folder in which to store the output files. One
of:
• Save to a Temporary Directory
• Save to Directory…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Folder FOLDER [folder] The folder that contains the output files.
Python code
Algorithm ID: qgis:extractbinary
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Feature filter
Filters features from the input layer and redirects them to one or several outputs. If you do not know about any
attribute names that are common to all possible input layers, filtering is only possible on the feature geometry and
general record mechanisms, such as $id and uuid.
Poznámka: This algorithm is only available from the Graphical modeler.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] The input layer.
Outputs and
filters
(one or more)
OUTPUT_<name
of the
filter>
[same as input] The output layers with filters (as many
as there are filters).
Outputs
Label Název Type Popis
Output
(one or more)
native:filter_1:OUTPUT_<name
of filter>
[same as input] The output layers with filtered features
(as many as there are filters).
Python code
Algorithm ID: qgis:featurefilter
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Field calculator
Opens the field calculator (see Výrazy). You can use all the supported expressions and functions.
A new layer is created with the result of the expression.
The field calculator is very useful when used in The graphical modeler.
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Parameters
Label Název Type Popis
Input layer INPUT [vector: any] The layer to calculate on
Output field name FIELD_NAME [string] The name of the field for the results
Output field type FIELD_TYPE [enumeration]
Default: 0
The type of the field. One of:
• 0 — Float
• 1 — Integer
• 2 — String
• 3 — Date
Output field width FIELD_LENGTH [number]
Default: 10
The length of the result field (minimum 0)
Field precision FIELD_PRECISION[number]
Default: 3
The precision of the result field (minimum
0, maximum 15)
Create new field NEW_FIELD [boolean]
Default: True
Should the result field be a new field
Formula FORMULA [expression] The formula to use to calculate the result
Output file OUTPUT [vector: any]
Default: [Save
to temporary
file]
Specification of the output layer.
Outputs
Label Název Type Popis
Calculated OUTPUT [vector: any] Output layer with the calculated field values
Python code
Algorithm ID: qgis:fieldcalculator
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Refactor fields
Allows editing the structure of the attribute table of a vector layer.
Fields can be modified in their type and name, using a fields mapping.
The original layer is not modified. A new layer is generated, which contains a modified attribute table, according to
the provided fields mapping.
Refactor layer fields allows to:
• Change field names and types
• Add and remove fields
• Reorder fields
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• Calculate new fields based on expressions
• Load field list from another layer
Obr. 24.102: Refactor fields dialog
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] The layer to modify
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Tabulka 24.143 – pokračujte na předchozí stránce
Label Název Type Popis
Fields mapping FIELDS_MAPPING [list] List of output fields with their definitions.
The embedded table lists all the fields of the
source layer and allows you to edit them:
• Click to create a new field.
• Click to remove a field.
• Use and to change the
selected field order.
• Click to reset to the default view.
For each of the fields you’d like to reuse,
you need to fill the following options:
Source expression (expression) [expression]
Field or expression from the input
layer.
Field name (name) [string] Name of the
field in the output layer. By default
input field name is kept.
Type (type) [enumeration] Data type of
the output field. One of:
• Date (14)
• DateTime (16)
• Double (6)
• Integer (2)
• Integer64 (4)
• String (10)
• Boolean (1)
Length (length) [number] Length of
the output field.
Precision (precision) [number]
Precision of the output field.
Fields from another layer can be loaded into
the field list in Load fields from layer.
Refactored OUTPUT [vector: any]
Default: [Create
temporary
layer]
Specification of the output layer. One of:
• Create Temporary Layer
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table……
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Refactored OUTPUT [vector: any] Output layer with refactored fields
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Python code
Algorithm ID: qgis:refactorfields
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Rename vector field
Renames an existing field from a vector layer.
The original layer is not modified. A new layer is generated where the attribute table contains the renamed field.
Viz také:
Refactor fields
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] The input vector layer
Field to rename FIELD [string] The field to be altered
New field name NEW_NAME [string] The new field name
Renamed OUTPUT [vector: same
as input]
Default: [Create
temporary
layer]
Specification of the output layer. One of:
• Create Temporary Layer
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table……
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Renamed OUTPUT [vector: same
as input]
Output layer with the renamed field
Python code
Algorithm ID: qgis:renametablefield
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Text to float
Modifies the type of a given attribute in a vector layer, converting a text attribute containing numeric strings into
a numeric attribute (e.g. ‚1‘ to 1.0).
The algorithm creates a new vector layer so the source one is not modified.
If the conversion is not possible the selected column will have NULL values.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] The input vector layer.
Text attribute to
convert to float
FIELD [tablefield: string] The string field for the input layer that is to
be converted to a float field.
Float from text OUTPUT [same as input]
Default: [Create
Temporary
Layer]
Specify the output layer. One of:
• Create Temporary Layer
• Save to File…
• Save to Geopackage…
• Save to PostGIS Table……
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Float from text OUTPUT [same as input] Output vector layer with the string field
converted into a float field
Python code
Algorithm ID: qgis:texttofloat
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.1.20 Vector Tiles
Write vector tiles (MBTiles)
Exports one or more vector layers to vector tiles, a data format optimized for fast map rendering and small data size.
MBTiles is a specification for storing tiled map data in SQLite databases for immediate usage and for transfer.
MBTiles files are known as tilesets.
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Parameters
Label Name Type Description
Input layers INPUT [vector: any][list] A list of layers to combine to generate the
vector tiles
Minimum zoom
level
MIN_ZOOM [number]
Default: 0
The lowest zoom level for which the tileset
provides data. Set between 0 and 24.
Maximum zoom
level
MAX_ZOOM [number]
Default: 3
The highest zoom level for which the tileset
provides data. Set between 0 and 24.
Extent
Optional
EXTENT [extent]
Default: Not set
The maximum extent of the rendered map
area. Bounds must define an area covered
by all zoom levels.
Metadata: Name
Optional
META_NAME [string] Name of the tileset
Metadata:
Description
Optional
META_DESCRIPTION[string] A description of the tileset’s contents
Metadata:
Attribution
Optional
META_ATTRIBUTION[string] An attribution string, which explains the
sources of data and/or style for the map.
Metadata:
Version
Optional
META_VERSION [string] The version of the tileset. This refers to
a revision of the tileset itself, not of the
MBTiles specification.
Metadata: Type
Optional
META_TYPE [string] Type of tileset. Possible values are
overlay or baselayer.
Metadata: Center
Optional
META_CENTER [string] The center (string of comma-separated
numbers: the longitude, latitude, and zoom
level) of the default view of the map.
Example: -122.1906,37.7599,11
Destination
MBTiles
OUTPUT [vector tiles]
Default: [Save to
temporary file]
Specification of the output MBTiles file.
One of:
• Save to a Temporary File
• Save to File…
Outputs
Label Name Type Description
Destination
MBTiles
OUTPUT [file] Output vector tiles .mbtiles file.
Python code
Algorithm ID: native:writevectortiles_mbtiles
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Write vector tiles (XYZ)
Exports one or more vector layers to vector tiles, a data format optimized for fast map rendering and small data size.
Parameters
Label Name Type Description
File template XYZ_TEMPLATE [string]
Default:
‚{z}/{x}/{y}.pbf‘
Template to generate the vector tiles url
Input layers INPUT [vector: any][list] A list of layers to combine to generate the
vector tiles
Minimum zoom
level
MIN_ZOOM [number]
Default: 0
The lowest zoom level for which the tileset
provides data. Set between 0 and 24.
Maximum zoom
level
MAX_ZOOM [number]
Default: 3
The highest zoom level for which the tileset
provides data. Set between 0 and 24.
Extent
Optional
EXTENT [extent]
Default: Not set
The maximum extent of the rendered map
area. Bounds must define an area covered
by all zoom levels.
Output directory OUTPUT_DIRECTORY[folder]
Default: [Save to
temporary folder]
Specification of the output vector tiles
folder. One of:
• Save to a Temporary Directory
• Save to Directory
Outputs
Label Name Type Description
Output directory OUTPUT_DIRECTORY[folder] A folder containing different subsets of the
vector tiles files (.pbf) stored in subfolders
corresponding to the zoom levels.
Python code
Algorithm ID: native:writevectortiles_xyz
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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24.2 GDAL algorithm provider
GDAL (Geospatial Data Abstraction Library) is a translator library for raster and vector geospatial data formats.
Algorithms in the Processing Framework are derived from the GDAL raster programs and GDAL vector programs.
24.2.1 Rastrová analýza
Aspect
Generates an aspect map from any GDAL-supported elevation raster. Aspect is the compass direction that a slope
faces. The pixels will have a value from 0-360° measured in degrees from north indicating the azimuth. On the
northern hemisphere, the north side of slopes is often shaded (small azimuth from 0°-90°), while the southern side
receives more solar radiation (higher azimuth from 180°-270°).
This algorithm is derived from the GDAL DEM utility.
Default menu: Raster ► Analysis
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input elevation raster layer
Band number BAND [raster band]
Default: 1
The number of the band to use as elevation
Return
trigonometric
angle instead of
azimuth
TRIG_ANGLE [boolean]
Default: False
Activating the trigonometric angle results in
different categories: 0° (East), 90° (North),
180° (West), 270° (South).
Return 0 for flat
instead of -9999
ZERO_FLAT [boolean]
Default: False
Activating this option will insert a 0-value
for the value -9999 on flat areas.
Compute edges COMPUTE_EDGES [boolean]
Default: False
Generates edges from the elevation raster
Use
Zevenbergen&Thorne
formula instead of
the Horn’s one
ZEVENBERGEN [boolean]
Default: False
Activates Zevenbergen&Thorne formula
for smooth landscapes
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options
Aspect OUTPUT [raster]
Default: [Save
to temporary
file]
Output raster layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Aspect OUTPUT [raster] Output raster with angle values in degrees
Python code
Algorithm ID: gdal:aspect
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Color relief
Generates a color relief map from any GDAL-supported elevation raster. Color reliefs can particularly be used to
depict elevations. The Algorithm outputs a 4-band raster with values computed from the elevation and a text-based
color configuration file. By default, the colors between the given elevation values are blended smoothly and the result
is a nice colorized elevation raster.
This algorithm is derived from the GDAL DEM utility.
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input elevation raster layer
Band number BAND [raster band]
Default: 1
The number of the band to use as elevation
Compute edges COMPUTE_EDGES [boolean]
Default: False
Generates edges from the elevation raster
Color
configuration
file
COLOR_TABLE [file] A text-based color configuration file
Matching mode MATCH_MODE [enumeration]
Default: 2
One of:
• 0 — Use strict color matching
• 1 — Use closest RGBA quadruples
• 2 — Use smoothly blended colours
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options
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Label Název Type Popis
Color relief OUTPUT [raster]
Default: [Save
to temporary
file]
Output raster layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Color relief OUTPUT [raster] A 4-band output raster
Python code
Algorithm ID: gdal:colorrelief
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Fill nodata
Fill raster regions with no data values by interpolation from edges. The values for the no-data regions are calculated by
the sourrounding pixel values using inverse distance weighting. After the interpolation a smoothing of the results takes
placce. Input can be any GDAL-supported raster layer. This algorithm is generally suitable for interpolating missing
regions of fairly continuously varying rasters (such as elevation models for instance). It is also suitable for filling small
holes and cracks in more irregularly varying images (like airphotos). It is generally not so great for interpolating
a raster from sparse point data.
This algorithm is derived from the GDAL fillnodata utility.
Default menu: Raster ► Analysis
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input raster layer
Band number BAND [raster band]
Default: 1
The band to operate on. Nodata values must
be represented by the value 0.
Maximum
distance (in
pixels) to search
out for values to
interpolate
DISTANCE [number]
Default: 10
The number of pixels to search in all
directions to find values to interpolate from
Number of
smoothing
iterations to
run after the
interpolation
ITERATIONS [number]
Default: 0
The number of 3x3 filter passes to run (0
or more) to smoothen the results of the
interpolation.
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Label Název Type Popis
Do not use default
validity mask for
the input band
NO_MASK [boolean]
Default: False
Activates the user-defined validity mask
Validity mask MASK_LAYER [raster] A raster layer that defines the areas to fill.
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options
Filled OUTPUT [raster]
Default: [Save
to temporary
file]
Specification of the output raster layer. One
of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Filled OUTPUT [raster] Output raster
Python code
Algorithm ID: gdal:fillnodata
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Grid (Data metrics)
Computes some data metrics using the specified window and output grid geometry.
This algorithm is derived from the GDAL grid utility.
Default menu: Raster ► Analysis
Viz také:
GDAL grid tutorial
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Parameters
Label Název Type Popis
Point layer INPUT [vector: point] Input point vector layer
Data metric to use METRIC [enumeration]
Default: 0
One of:
• 0 — Minimum, minimum value
found in grid node search ellipse
• 1 — Maximum, maximum value
found in grid node search ellipse
• 2 — Range, a difference between
the minimum and maximum values
found in grid node search ellipse
• 3 — Count, a number of data points
found in grid node search ellipse
• 4 — Average distance, an average
distance between the grid node
(center of the search ellipse) and all
of the data points found in grid node
search ellipse
• 5 — Average distance between
points, an average distance between
the data points found in grid node
search ellipse. The distance between
each pair of points within ellipse
is calculated and average of all
distances is set as a grid node value
The first radius of
search ellipse
RADIUS_1 [number]
Default: 0.0
The first radius (X axis if rotation angle is 0)
of the search ellipse
The second radius
of search ellipse
RADIUS_2 [number]
Default: 0.0
The second radius (Y axis if rotation angle
is 0) of the search ellipse
Angle of search
ellipse rotation in
degrees (counter
clockwise)
ANGLE [number]
Default: 0.0
Angle of ellipse rotation in degrees. Ellipse
rotated counter clockwise.
Minimum number
of data points to
use
MIN_POINTS [number]
Default: 0.0
Minimum number of data points to average.
If less amount of points found the grid node
considered empty and will be filled with
NODATA marker.
Nodata NODATA [number]
Default: 0.0
No data marker to fill empty points
Z value from field
Optional
Z_FIELD [tablefield:
numeric]
Field for the interpolation
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options
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Label Název Type Popis
Output data type DATA_TYPE [enumeration]
Default: 5
Defines the data type of the output raster
file. Options:
• 0 — Byte
• 1 — Int16
• 2 — UInt16
• 3 — UInt32
• 4 — Int32
• 5 — Float32
• 6 — Float64
• 7 — CInt16
• 8 — CInt32
• 9 — CFloat32
• 10 — CFloat64
Interpolated (data
metrics)
OUTPUT [raster]
Default: [Save
to temporary
file]
Specify the output raster layer with
interpolated values. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Interpolated (data
metrics)
OUTPUT [raster] Output raster with interpolated values
Python code
Algorithm ID: gdal:griddatametrics
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Grid (IDW with nearest neighbor searching)
Computes the Inverse Distance to a Power gridding combined to the nearest neighbor method. Ideal when a maximum
number of data points to use is required.
This algorithm is derived from the GDAL grid utility.
Viz také:
GDAL grid tutorial
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Parameters
Label Název Type Popis
Point layer INPUT [vector: point] Input point vector layer
Weighting power POWER [number]
Default: 2.0
Weighting power
Smoothing SMOOTHING [number]
Default: 0.0
Smoothing parameter
The radius of the
search circle
RADIUS [number]
Default: 1.0
The radius of the search circle
Maximum
number of data
points to use
MAX_POINTS [number]
Default: 12
Do not search for more points than this
number.
Minimum number
of data points to
use
MIN_POINTS [number]
Default: 0
Minimum number of data points to average.
If less amount of points found the grid node
considered empty and will be filled with
NODATA marker.
Nodata NODATA [number]
Default: 0.0
No data marker to fill empty points
Z value from field
Optional
Z_FIELD [tablefield:
numeric]
Field for the interpolation
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options
Output data type DATA_TYPE [enumeration]
Default: 5
Defines the data type of the output raster
file. Options:
• 0 — Byte
• 1 — Int16
• 2 — UInt16
• 3 — UInt32
• 4 — Int32
• 5 — Float32
• 6 — Float64
• 7 — CInt16
• 8 — CInt32
• 9 — CFloat32
• 10 — CFloat64
Interpolated
(IDW with NN
search)
OUTPUT [raster]
Default: [Save
to temporary
file]
Specify the output raster layer with
interpolated values. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Interpolated
(IDW with NN
search)
OUTPUT [raster] Output raster with interpolated values
Python code
Algorithm ID: gdal:gridinversedistancenearestneighbor
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Grid (Inverse distance to a power)
The Inverse Distance to a Power gridding method is a weighted average interpolator.
You should supply the input arrays with the scattered data values including coordinates of every data point and output
grid geometry. The function will compute interpolated value for the given position in output grid.
This algorithm is derived from the GDAL grid utility.
Default menu: Raster ► Analysis
Viz také:
GDAL grid tutorial
Parameters
Label Název Type Popis
Point layer INPUT [vector: point] Input point vector layer
Weighting power POWER [number]
Default: 2.0
Weighting power
Smothing SMOOTHING [number]
Default: 0.0
Smoothing parameter
The first radius of
search ellipse
RADIUS_1 [number]
Default: 0.0
The first radius (X axis if rotation angle is 0)
of the search ellipse
The second radius
of search ellipse
RADIUS_2 [number]
Default: 0.0
The second radius (Y axis if rotation angle
is 0) of the search ellipse
Angle of search
ellipse rotation in
degrees (counter
clockwise)
ANGLE [number]
Default: 0.0
Angle of ellipse rotation in degrees. Ellipse
rotated counter clockwise.
Maximum
number of data
points to use
MAX_POINTS [number]
Default: 0
Do not search for more points than this
number.
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Label Název Type Popis
Minimum number
of data points to
use
MIN_POINTS [number]
Default: 0
Minimum number of data points to average.
If less amount of points found the grid node
considered empty and will be filled with
NODATA marker.
Nodata NODATA [number]
Default: 0.0
No data marker to fill empty points
Z value from field
Optional
Z_FIELD [tablefield:
numeric]
Field for the interpolation
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options
Output data type DATA_TYPE [enumeration]
Default: 5
Defines the data type of the output raster
file. Options:
• 0 — Byte
• 1 — Int16
• 2 — UInt16
• 3 — UInt32
• 4 — Int32
• 5 — Float32
• 6 — Float64
• 7 — CInt16
• 8 — CInt32
• 9 — CFloat32
• 10 — CFloat64
Interpolated
(IDW)
OUTPUT [raster]
Default: [Save
to temporary
file]
Specify the output raster layer with
interpolated values. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Interpolated
(IDW)
OUTPUT [raster] Output raster with interpolated values
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Python code
Algorithm ID: gdal:gridinversedistance
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Grid (Linear)
The Linear method perform linear interpolation by computing a Delaunay triangulation of the point cloud, finding
in which triangle of the triangulation the point is, and by doing linear interpolation from its barycentric coordinates
within the triangle. If the point is not in any triangle, depending on the radius, the algorithm will use the value of the
nearest point or the NODATA value.
This algorithm is derived from the GDAL grid utility.
Parameters
Label Název Type Popis
Point layer INPUT [vector: point] Input point vector layer
Search distance RADIUS [number]
Default: -1.0
In case the point to be interpolated does
not fit into a triangle of the Delaunay
triangulation, use that maximum distance to
search a nearest neighbour, or use nodata
otherwise. If set to -1, the search distance
is infinite. If set to 0, no data value will be
used.
Nodata NODATA [number]
Default: 0.0
No data marker to fill empty points
Z value from field
Optional
Z_FIELD [tablefield:
numeric]
Field for the interpolation
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options
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Label Název Type Popis
Output data type DATA_TYPE [enumeration]
Default: 5
Defines the data type of the output raster
file. Options:
• 0 — Byte
• 1 — Int16
• 2 — UInt16
• 3 — UInt32
• 4 — Int32
• 5 — Float32
• 6 — Float64
• 7 — CInt16
• 8 — CInt32
• 9 — CFloat32
• 10 — CFloat64
Interpolated
(Linear)
OUTPUT [raster]
Default: [Save
to temporary
file]
Specify the output raster layer with
interpolated values. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Interpolated
(Linear)
OUTPUT [raster] Output raster with interpolated values
Python code
Algorithm ID: gdal:gridlinear
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Grid (Moving average)
The Moving Average is a simple data averaging algorithm. It uses a moving window of elliptic form to search values
and averages all data points within the window. Search ellipse can be rotated by specified angle, the center of ellipse
located at the grid node. Also the minimum number of data points to average can be set, if there are not enough
points in window, the grid node considered empty and will be filled with specified NODATA value.
This algorithm is derived from the GDAL grid utility.
Default menu: Raster ► Analysis
Viz také:
GDAL grid tutorial
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Parameters
Label Název Type Popis
Point layer INPUT [vector: point] Input point vector layer
The first radius of
search ellipse
RADIUS_1 [number]
Default: 0.0
The first radius (X axis if rotation angle is 0)
of the search ellipse
The second radius
of search ellipse
RADIUS_2 [number]
Default: 0.0
The second radius (Y axis if rotation angle
is 0) of the search ellipse
Angle of search
ellipse rotation in
degrees (counter
clockwise)
ANGLE [number]
Default: 0.0
Angle of ellipse rotation in degrees. Ellipse
rotated counter clockwise.
Minimum number
of data points to
use
MIN_POINTS [number]
Default: 0.0
Minimum number of data points to average.
If less amount of points found the grid node
considered empty and will be filled with
NODATA marker.
Nodata NODATA [number]
Default: 0.0
No data marker to fill empty points
Z value from field
Optional
Z_FIELD [tablefield:
numeric]
Field for the interpolation
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options
Output data type DATA_TYPE [enumeration]
Default: 5
Defines the data type of the output raster
file. Options:
• 0 — Byte
• 1 — Int16
• 2 — UInt16
• 3 — UInt32
• 4 — Int32
• 5 — Float32
• 6 — Float64
• 7 — CInt16
• 8 — CInt32
• 9 — CFloat32
• 10 — CFloat64
Interpolated
(moving average)
OUTPUT [raster]
Default: [Save
to temporary
file]
Specify the output raster layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Interpolated
(moving average)
OUTPUT [raster] Output raster with interpolated values
Python code
Algorithm ID: gdal:gridaverage
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Grid (Nearest neighbor)
The Nearest Neighbor method doesn’t perform any interpolation or smoothing, it just takes the value of nearest point
found in grid node search ellipse and returns it as a result. If there are no points found, the specified NODATA value
will be returned.
This algorithm is derived from the GDAL grid utility.
Default menu: Raster ► Analysis
Viz také:
GDAL grid tutorial
Parameters
Label Název Type Popis
Point layer INPUT [vector: point] Input point vector layer
The first radius of
search ellipse
RADIUS_1 [number]
Default: 0.0
The first radius (X axis if rotation angle is 0)
of the search ellipse
The second radius
of search ellipse
RADIUS_2 [number]
Default: 0.0
The second radius (Y axis if rotation angle
is 0) of the search ellipse
Angle of search
ellipse rotation in
degrees (counter
clockwise)
ANGLE [number]
Default: 0.0
Angle of ellipse rotation in degrees. Ellipse
rotated counter clockwise.
Nodata NODATA [number]
Default: 0.0
No data marker to fill empty points
Z value from field
Optional
Z_FIELD [tablefield:
numeric]
Field for the interpolation
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
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Label Název Type Popis
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options
Output data type DATA_TYPE [enumeration]
Default: 5
Defines the data type of the output raster
file. Options:
• 0 — Byte
• 1 — Int16
• 2 — UInt16
• 3 — UInt32
• 4 — Int32
• 5 — Float32
• 6 — Float64
• 7 — CInt16
• 8 — CInt32
• 9 — CFloat32
• 10 — CFloat64
Interpolated
(Nearest
neighbour)
OUTPUT [raster]
Default: [Save
to temporary
file]
Specify the output raster layer with
interpolated values. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Interpolated
(Nearest
neighbour)
OUTPUT [raster] Output raster with interpolated values
Python code
Algorithm ID: gdal:gridnearestneighbor
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Hillshade
Outputs a raster with a nice shaded relief effect. It’s very useful for visualizing the terrain. You can optionally specify
the azimuth and altitude of the light source, a vertical exaggeration factor and a scaling factor to account for differences
between vertical and horizontal units.
This algorithm is derived from the GDAL DEM utility .
Default menu: Raster ► Analysis
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input Elevation raster layer
Band number BAND [raster band]
Default: 1
Band containing the elevation information
Z factor (vertical
exaggeration)
Z_FACTOR [number]
Default: 1.0
The factor exaggerates the height of the
output elevation raster
Scale (ratio of
vert. units to
horiz.)
SCALE [number]
Default: 1.0
The ratio of vertical units to horizontal units
Azimuth of the
light
AZIMUTH [number]
Default: 315.0
Defines the azimuth of the light shining on
the elevation raster in degrees. If it comes
from the top of the raster the value is 0, if
it comes from the east it is 90 a.s.o.
Altitude of the
light
ALTITUDE [number]
Default: 45.0
Defines the altitude of the light, in degrees.
90 if the light comes from above the
elevation raster, 0 if it is raking light.
Compute edges COMPUTE_EDGES [boolean]
Default: False
Generates edges from the elevation raster
Use
Zevenbergen&Thorne
formula (instead
of the Horn’s one)
ZEVENBERGEN [boolean]
Default: False
Activates Zevenbergen&Thorne formula
for smooth landscapes
Combined
shading
COMBINED [boolean]
Default: False
Multidirectional
shading
MULTIDIRECTIONAL[boolean]
Default: False
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options
Hillshade OUTPUT [raster]
Default: [Save
to temporary
file]
Specify the output raster layer with
interpolated values. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
1138 Kapitola 24. Processing providers and algorithms
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Outputs
Label Název Type Popis
Hillshade OUTPUT [raster] Output raster with interpolated values
Python code
Algorithm ID: gdal:hillshade
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Near black
Converts nearly black/white borders to black.
This algorithm will scan an image and try to set all pixels that are nearly or exactly black, white or one or more custom
colors around the collar to black or white. This is often used to „fix up“ lossy compressed airphotos so that color pixels
can be treated as transparent when mosaicking.
This algorithm is derived from the GDAL nearblack utility.
Default menu: Raster ► Analysis
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input Elevation raster layer
How far from
black (white)
NEAR [number]
Default: 15
Select how far from black, white or custom
colors the pixel values can be and still
considered near black, white or custom
color.
Search for nearly
white pixels
instead of nearly
black
WHITE [boolean]
Default: False
Search for nearly white (255) pixels instead
of nearly black pixels
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options
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Label Název Type Popis
Nearblack OUTPUT [raster]
Default: [Save
to temporary
file]
Specify the output raster layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Nearblack OUTPUT [raster] Output raster
Python code
Algorithm ID: gdal:nearblack
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Proximity (raster distance)
Generates a raster proximity map indicating the distance from the center of each pixel to the center of the nearest
pixel identified as a target pixel. Target pixels are those in the source raster for which the raster pixel value is in the
set of target pixel values.
This algorithm is derived from the GDAL proximity utility.
Default menu: Raster ► Analysis
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input Elevation raster layer
Band number BAND [raster band]
Default: 1
Band containing the elevation information
A list of pixel
values in the
source image to be
considered target
pixels
Optional
VALUES [string]
Default: ‚‘
A list of target pixel values in the source
image to be considered target pixels. If
not specified, all non-zero pixels will be
considered target pixels.
Distance units UNITS [enumeration]
Default: 1
Indicate whether distances generated should
be in pixel or georeferenced coordinates.
One of:
• 0 — Georeferenced coordinates
• 1 — Pixel coordinates
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Label Název Type Popis
The maximum
distance to be
generated
Optional
MAX_DISTANCE [number]
Default: 0.0
The maximum distance to be generated.
The nodata value will be used for pixels
beyond this distance. If a nodata value is not
provided, the output band will be queried
for its nodata value. If the output band does
not have a nodata value, then the value
65535 will be used. Distance is interpreted
according to the value of Distance units.
Value to be
applied to all
pixels that are
within the maxdist
of target pixels
Optional
REPLACE [number]
Default: 0.0
Specify a value to be applied to all pixels
that are closer than the maximum distance
from target pixels (including the target
pixels) instead of a distance value.
Nodata value
to use for the
destination
proximity raster
Optional
NODATA [number]
Default: 0.0
Specify the nodata value to use for the
output raster
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options
Output data type DATA_TYPE [enumeration]
Default: 5
Defines the data type of the output raster
file. Options:
• 0 — Byte
• 1 — Int16
• 2 — UInt16
• 3 — UInt32
• 4 — Int32
• 5 — Float32
• 6 — Float64
• 7 — CInt16
• 8 — CInt32
• 9 — CFloat32
• 10 — CFloat64
Proximity map OUTPUT [raster]
Default: [Save
to temporary
file]
Specify the output raster layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Proximity map OUTPUT [raster] Output raster
Python code
Algorithm ID: gdal:proximity
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Roughness
Outputs a single-band raster with values computed from the elevation. Roughness is the degree of irregularity of the
surface. It’s calculated by the largest inter-cell difference of a central pixel and its surrounding cell. The determination
of the roughness plays a role in the analysis of terrain elevation data, it’s useful for calculations of the river morphology,
in climatology and physical geography in general.
This algorithm is derived from the GDAL DEM utility.
Default menu: Raster ► Analysis
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input elevation raster layer
Band number BAND [raster band]
Default: 1
The number of the band to use as elevation
Compute edges COMPUTE_EDGES [boolean]
Default: False
Generates edges from the elevation raster
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Roughness OUTPUT [raster]
Default: [Save
to temporary
file]
Specify the output raster layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
1142 Kapitola 24. Processing providers and algorithms
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Outputs
Label Název Type Popis
Roughness OUTPUT [raster] Single-band output roughness raster. The
value -9999 is used as nodata value.
Python code
Algorithm ID: gdal:roughness
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Sieve
Removes raster polygons smaller than a provided threshold size (in pixels) and replaces them with the pixel value of
the largest neighbour polygon. It is useful if you have a large amount of small areas on your raster map.
This algorithm is derived from the GDAL sieve utility.
Default menu: Raster ► Analysis
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input elevation raster layer
Threshold THRESHOLD [number]
Default: 10
Only raster polygons smaller than this size
will be removed
Use 8-
-connectedness
EIGHT_CONNECTEDNESS[boolean]
Default: False
Use eight connectedness instead of four
connectedness
Do not use the
default validity
mask for the input
band
NO_MASK [boolean]
Default: False
Validity mask
Optional
MASK_LAYER [raster] Validity mask to use instead of the default
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options
Sieved OUTPUT [raster]
Default: [Save
to temporary
file]
Specify the output raster layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Sieved OUTPUT [raster] Output raster layer.
Python code
Algorithm ID: gdal:sieve
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Slope
Generates a slope map from any GDAL-supported elevation raster. Slope is the angle of inclination to the horizontal.
You have the option of specifying the type of slope value you want: degrees or percent slope.
This algorithm is derived from the GDAL DEM utility.
Default menu: Raster ► Analysis
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input Elevation raster layer
Band number BAND [raster band]
Default: 1
Band containing the elevation information
Ratio of vertical
units to horizontal
SCALE [number]
Default: 1.0
The ratio of vertical units to horizontal units
Slope expressed
as percent (instead
of degrees)
AS_PERCENT [boolean]
Default: False
Express slope as percent instead of degrees
Compute edges COMPUTE_EDGES [boolean]
Default: False
Generates edges from the elevation raster
Use
Zevenbergen&Thorne
formula (instead
of the Horn’s one)
ZEVENBERGEN [boolean]
Default: False
Activates Zevenbergen&Thorne formula
for smooth landscapes
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options
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Label Název Type Popis
Slope OUTPUT [raster]
Default: [Save
to temporary
file]
Specify the output raster layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Slope OUTPUT [raster] Output raster
Python code
Algorithm ID: gdal:slope
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Terrain Ruggedness Index (TRI)
Outputs a single-band raster with values computed from the elevation. TRI stands for Terrain Ruggedness Index,
which is defined as the mean difference between a central pixel and its surrounding cells.
This algorithm is derived from the GDAL DEM utility.
Default menu: Raster ► Analysis
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input elevation raster layer
Band number BAND [raster band]
Default: 1
The number of the band to use as elevation
Compute edges COMPUTE_EDGES [boolean]
Default: False
Generates edges from the elevation raster
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Terrain
Ruggedness
Index
OUTPUT [raster]
Default: [Save
to temporary
file]
Specify the output raster layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Terrain
Ruggedness
Index
OUTPUT [raster] Output ruggedness raster. The value -9999
is used as nodata value.
Python code
Algorithm ID: gdal:triterrainruggednessindex
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Topographic Position Index (TPI)
Outputs a single-band raster with values computed from the elevation. TPI stands for Topographic Position Index,
which is defined as the difference between a central pixel and the mean of its surrounding cells.
This algorithm is derived from the GDAL DEM utility.
Default menu: Raster ► Analysis
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input elevation raster layer
Band number BAND [raster band]
Default: 1
The number of the band to use for elevation
values
Compute edges COMPUTE_EDGES [boolean]
Default: False
Generates edges from the elevation raster
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Terrain
Ruggedness
Index
OUTPUT [raster]
Default: [Save
to temporary
file]
Specify the output raster layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
1146 Kapitola 24. Processing providers and algorithms
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Outputs
Label Název Type Popis
Terrain
Ruggedness
Index
OUTPUT [raster] Output raster.
Python code
Algorithm ID: gdal:tpitopographicpositionindex
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.2.2 Raster conversion
gdal2xyz
Converts raster data to XYZ ASCII file format.
Parameters
Label Název Type Popis
Input layer INPUT [raster] Raster layer to convert
Band number BAND [raster band]
Default: The first
band of the input
layer
If the raster is multiband, choose the band
you want to convert
Output comma-separated
values
CSV [boolean]
Default: False
Sets whether the output file should be of
type comma-separated values (csv).
XYZ ASCII file OUTPUT [file]
Default: [Save
to temporary
file]
Specification of the output file. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
XYZ ASCII file INPUT [table] Table file containing the values exported
from the raster band.
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Python code
Algorithm ID: gdal:gdal2xyz
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
PCT to RGB
Converts an 8 bit paletted image to a 24 bit RGB. It will convert a pseudocolor band from the input file to an RGB
file of the desired format.
This algorithm is derived from the GDAL pct2rgb utility.
Default menu: Raster ► Conversion
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input 8 bit raster image
Band number BAND [raster band]
Default: The first
band of the input
layer
If the raster is multiband, choose the band
you want to convert
Generate a RGBA
file
RGBA [boolean]
Default: False
Sets whether the output file should be of
type RGBA.
PCT to RGB OUTPUT [file]
Default: [Save
to temporary
file]
Specification of the output file. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
PCT to RGB OUTPUT [raster] 24 bit RGB raster image
Python code
Algorithm ID: gdal:pcttorgb
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Polygonize (raster to vector)
Creates vector polygons for all connected regions of pixels in the raster sharing a common pixel value. Each polygon
is created with an attribute indicating the pixel value of that polygon.
This algorithm is derived from the GDAL polygonize utility.
Default menu: Raster ► Conversion
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input raster layer
Band number BAND [raster band]
Default: The first
band of the input
layer
If the raster is multiband, choose the band
you want to use
Name of the field
to create
FIELD [string]
Default: ‚DN‘
Specify the field name for the attributes of
the connected regions.
Use 8-
-connectedness
EIGHT_CONNECTEDNESS[boolean]
Default: False
If not set, raster cells must have a common
border to be considered connected (4-connected).
If set, touching raster cells are
also considered connected (8-connected).
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options
Vectorized OUTPUT [vector: polygon]
Default: [Save
to temporary
file]
Specification of the output (polygon) vector
layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Vectorized OUTPUT [vector: polygon] Output vector layer
Python code
Algorithm ID: gdal:polygonize
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Rearrange bands
Creates a new raster using selected band(s) from a given raster layer. The algorithm also makes it possible to reorder
the bands for the newly-created raster.
This algorithm is derived from the GDAL translate utility.
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input raster layer
Selected band(s) BANDS [raster band] [list]
Default: None
Ordered list of the bands to use to create the
new raster
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Output data type DATA_TYPE [enumeration]
Default: 0
Defines the data type of the output raster
file. Options:
• 0 — Use Input Layer Data Type
• 1 — Byte
• 2 — Int16
• 3 — UInt16
• 4 — UInt32
• 5 — Int32
• 6 — Float32
• 7 — Float64
• 8 — CInt16
• 9 — CInt32
• 10 — CFloat32
• 11 — CFloat64
Converted OUTPUT [raster]
Default: Save to
temporary file
Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Converted OUTPUT [raster] Output raster layer with rearranged bands.
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Python code
Algorithm ID: gdal:rearrange_bands
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
RGB to PCT
Converts a 24 bit RGB image into a 8 bit paletted. Computes an optimal pseudo-color table for the given RGB-image
using a median cut algorithm on a downsampled RGB histogram. Then it converts the image into a pseudo-colored
image using the color table. This conversion utilizes Floyd-Steinberg dithering (error diffusion) to maximize output
image visual quality.
If you want to classify a raster map and want to reduce the number of classes it can be helpful to downsample your
image with this algorithm before.
This algorithm is derived from the GDAL rgb2pct utility.
Default menu: Raster ► Conversion
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input (RGB) raster layer
Number of colors NCOLORS [number]
Default: 2
The number of colors the resulting image
will contain. A value from 2-256 is possible.
RGB to PCT OUTPUT [raster]
Default: [Save
to temporary
file]
Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
RGB to PCT OUTPUT [raster] Output raster layer.
Python code
Algorithm ID: gdal:rgbtopct
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Translate (convert format)
Converts raster data between different formats.
This algorithm is derived from the GDAL translate utility.
Default menu: Raster ► Conversion
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input raster layer
Override the
projection of the
output file
Optional
TARGET_CRS [crs] Specify a projection for the output file
Assign a specified
nodata value to
output bands
Optional
NODATA [number]
Default: Not set
Defines the value to use for nodata in the
output raster
Copy all
subdatasets of this
file to individual
output files
COPY_SUBDATASETS[boolean]
Default: False
Create individual files for subdatasets
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options
Output data type DATA_TYPE [enumeration]
Default: 0
Defines the data type of the output raster
file. Options:
• 0 — Use Input Layer Data Type
• 1 — Byte
• 2 — Int16
• 3 — UInt16
• 4 — UInt32
• 5 — Int32
• 6 — Float32
• 7 — Float64
• 8 — CInt16
• 9 — CInt32
• 10 — CFloat32
• 11 — CFloat64
Converted OUTPUT [raster]
Default: [Save
to temporary
file]
Specification of the output (translated)
raster layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Converted OUTPUT [raster] Output (translated) raster layer.
Python code
Algorithm ID: gdal:translate
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.2.3 Raster extraction
Clip raster by extent
Clips any GDAL-supported raster file to a given extent.
This algorithm is derived from the GDAL warp utility.
Default menu: Raster ► Extraction
Parameters
Label Název Type Popis
Input layer INPUT [raster] The input raster
Clipping extent EXTENT [extent] Extent that should be used for the output
raster. Only pixels within the specified
bounding box will be included in the output.
Assign a specified
nodata value to
output bands
Optional
NODATA [number]
Default: None
Defines a value that should be inserted for
the nodata values in the output raster
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
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Label Název Type Popis
Output data type DATA_TYPE [enumeration]
Default: 0
Defines the format of the output raster file.
Options:
• 0 — Use Input Layer Data Type
• 1 — Byte
• 2 — Int16
• 3 — UInt16
• 4 — UInt32
• 5 — Int32
• 6 — Float32
• 7 — Float64
• 8 — CInt16
• 9 — CInt32
• 10 — CFloat32
• 11 — CFloat64
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options
Clipped (extent) OUTPUT [raster]
Default: ‚[Save to
temporary file]‘
Specification of the output raster layer. One
of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here
Outputs
Label Název Type Popis
Clipped (extent) OUTPUT [raster] Output raster layer clipped by the given
extent
Python code
Algorithm ID: gdal:cliprasterbyextent
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Clip raster by mask layer
Clips any GDAL-supported raster by a vector mask layer.
This algorithm is derived from the GDAL warp utility.
Default menu: Raster ► Extraction
Parameters
Label Název Type Popis
Input layer INPUT [raster] The input raster
Mask layer MASK [vector: polygon] Vector mask for clipping the
raster
Source CRS SOURCE_CRS [crs] Set the coordinate reference to
use for the input raster
Target CRS TARGET_CRS [crs] Set the coordinate reference to
use for the mask layer
Assign a specified nodata
value to output bands
Optional
NODATA [number]
Default: None
Defines a value that should be
inserted for the nodata values in
the output raster
Create an output alpha band ALPHA_BAND [boolean]
Default: False
Creates an alpha band for the
result. The alpha band then
includes the transparency values
of the pixels.
Match the extent of the
clipped raster to the extent of
the mask layer
CROP_TO_CUTLINE[boolean]
Default: True
Applies the vector layer extent
to the output raster if checked.
Keep resolution of input
raster
KEEP_RESOLUTION[boolean]
Default: False
The resolution of the output
raster will not be changed
Set output file resolution SET_RESOLUTION [boolean]
Default: False
Shall the output resolution (cell
size) be specified
X Resolution to output bands
Optional
X_RESOLUTION [number]
Default: None
The width of the cells in the
output raster
Y Resolution to output band
Optional
Y_RESOLUTION [number]
Default: None
The height of the cells in the
output raster
Use multithreaded warping
implementation
MULTITHREADING [boolean]
Default: False
Two threads will be used
to process chunks of image
and perform input/output
operation simultaneously.
Note that computation is not
multithreaded itself.
Additional creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation
options that control the raster
to be created (colors, block
size, file compression…). For
convenience, you can rely on
predefined profiles (see GDAL
driver options section).
For Batch Process: separate
multiple options with a pipe
character (|).
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Label Název Type Popis
Output data type DATA_TYPE [enumeration]
Default: 0
Defines the format of the output
raster file.
Options:
• 0 — Use Input Layer
Data Type
• 1 — Byte
• 2 — Int16
• 3 — UInt16
• 4 — UInt32
• 5 — Int32
• 6 — Float32
• 7 — Float64
• 8 — CInt16
• 9 — CInt32
• 10 — CFloat32
• 11 — CFloat64
Additional command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command
line options
Clipped (mask) OUTPUT [raster] Default:
‚[Save to temporary
file]‘
Specification of the output
raster layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be
changed here
Outputs
Label Název Type Popis
Clipped (mask) OUTPUT [raster] Output raster layer clipped by the vector
layer
Python code
Algorithm ID: gdal:cliprasterbymasklayer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Contour
Extracts contour lines from any GDAL-supported elevation raster.
This algorithm is derived from the GDAL contour utility.
Default menu: Raster ► Extraction
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input raster
Band number BAND [raster band]
Default: 1
Raster band to create the contours from
Interval between
contour lines
INTERVAL [number]
Default: 10.0
Defines the interval between the contour
lines in the given units of the elevation raster
(minimum value 0)
Attribute name
(if not set, no
elevation attribute
is attached)
Optional
FIELD_NAME [string]
Default: ‚ELEV‘
Provides a name for the attribute in which
to put the elevation.
Offset from zero
relative to which to
interpret intervals
Optional
OFFSET [number]
Default: 0.0
Produce 3D vector CREATE_3D [boolean]
Default: False
Forces production of 3D vectors instead of
2D. Includes elevation at every vertex.
Treat all raster
values as valid
IGNORE_NODATA [boolean]
Default: False
Ignores any nodata values in the dataset.
Input pixel
value to treat
as „nodata“
Optional
NODATA [number]
Default: None
Defines a value that should be inserted for
the nodata values in the output raster
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options.
Refer to the corresponding GDAL utility
documentation.
Contours OUTPUT [vector: line]
Default: ‚[Save to
temporary file]‘
Specification of the output vector layer. One
of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Contours OUTPUT [vector: line] Output vector layer with contour lines
Python code
Algorithm ID: gdal:contour
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Contour Polygons
Extracts contour polygons from any GDAL-supported elevation raster.
This algorithm is derived from the GDAL contour utility.
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input raster
Band number BAND [raster band]
Default: 1
Raster band to create the contours from
Interval between
contour lines
INTERVAL [number]
Default: 10.0
Defines the interval between the contour
lines in the given units of the elevation raster
(minimum value 0)
Offset from zero
relative to which to
interpret intervals
Optional
OFFSET [number]
Default: 0.0
Attribute name
for minimum
elevation of
contour polygon
Optional
FIELD_NAME_MIN [string]
Default:
‚ELEV_MIN‘
Provides a name for the attribute in which
to put the minimum elevation of contour
polygon. If not provided no minimum
elevation attribute is attached.
Attribute name
for maximum
elevation of
contour polygon
Optional
FIELD_NAME_MAX [string]
Default:
‚ELEV_MAX‘
Provides a name for the attribute in which
to put the maximum elevation of contour
polygon. If not provided no maximum
elevation attribute is attached.
Produce 3D vector CREATE_3D [boolean]
Default: False
Forces production of 3D vectors instead of
2D. Includes elevation at every vertex.
Treat all raster
values as valid
IGNORE_NODATA [boolean]
Default: False
Ignores any nodata values in the dataset.
Input pixel
value to treat
as „nodata“
Optional
NODATA [number]
Default: None
Defines a value that should be inserted for
the nodata values in the output raster
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Label Název Type Popis
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options.
Refer to the corresponding GDAL utility
documentation.
Contours OUTPUT [vector: polygon]
Default: ‚[Save to
temporary file]‘
Specification of the output vector layer. One
of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Contours OUTPUT [vector: polygon] Output vector layer with contour polygons
Python code
Algorithm ID: gdal:contour_polygon
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.2.4 Raster miscellaneous
Build overviews (pyramids)
To speed up rendering time of raster layers overviews (pyramids) can be created. Overviews are lower resolution
copies of the data which QGIS uses depending of the level of zoom.
This algorithm is derived from the GDAL addo utility.
Default menu: Raster ► Miscellaneous
Parameters
Basic parameters
Label Název Type Popis
Input layer INPUT [raster] Input raster layer
Remove all
existing overviews
CLEAN [boolean]
Default: False
Removes existing overviews from the
raster. By default these are not removed.
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Advanced parameters
Label Název Type Popis
Overview levels LEVELS [string]
Default: ‚2 4 8 16‘
Defines the number of overview levels
calculated by the original resolution of the
input raster layer. By default 4 levels will be
taken into consideration.
Resampling
method
Optional
RESAMPLING [enumeration]
Default: 0
Calculates the overviews with a defined
resampling method. Possible resampling
methods are:
• 0 – Nearest Neighbour (nearest)
• 1 – Average (average)
• 2 – Gaussian (gauss)
• 3 – Cubic Convolution (cubic)
• 4 – B-Spline Convolution
(cubicspline)
• 5 – Lanczos Windowed Sinc
(lanczos)
• 6 – Average MP (average_mp)
• 7 – Average in Mag/Phase Space
(average_magphase)
• 8 – Mode (mode)
Overviews format
Optional
FORMAT [enumeration]
Default: 0
The overviews can be stored internally, or
externally as GTiff or ERDAS Imagine file.
By default the overviews are stored in the
output raster. Possible formats methods are:
• 0 – Internal (if possible)
• 1 – External (GTiff .ovr)
• 2 – External (ERDAS Imagine .aux)
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options
Outputs
Label Název Type Popis
Pyramidized OUTPUT [raster] Output raster layer with overviews
Python code
Algorithm ID: gdal:overviews
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Build virtual raster
Builds a VRT (Virtual Dataset) that is a mosaic of the list of input GDAL-supported rasters. With a mosaic you can
merge several raster files.
This algorithm is derived from the GDAL buildvrt utility.
Default menu: Raster ► Miscellaneous
Parameters
Basic parameters
Label Název Type Popis
Input layers INPUT [raster] [list] GDAL-supported raster layers.
Resolution RESOLUTION [enumeration]
Default: 0
The output resolution of the mosaic. By
default the average resolution of the raster
files will be chosen.
Options:
• 0 — Average (average)
• 1 — Highest (highest)
• 2 — Lowest (lowest)
Place each input
file into a separate
band
SEPARATE [boolean]
Default: False
With ‚True‘ you can define that each raster
file goes into a separated stacked band in the
VRT band.
Allow projection
difference
PROJ_DIFFERENCE[boolean]
Default: False
Allows that the output bands have different
projections derived from the projection of
the input raster layers.
Virtual OUTPUT [raster]
Default: [Save
to temporary
file]
Specification of the output raster layer. One
of:
• Save to a Temporary File
• Save to File…
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Advanced parameters
Label Název Type Popis
Add alpha mask
band to VRT when
source raster has
none
ADD_ALPHA [boolean]
Default: False
Adds an alpha mask band to the VRT when
the source raster has none.
Override
projection for
the output file
Optional
ASSIGN_CRS [crs]
Default: None
Overrides the projection for the output file.
No reprojection is done.
Resampling
algorithm
RESAMPLING [enumeration]
Default: 0
The resampling algorithm to be used
Options:
• 0 — Nearest Neighbour (nearest)
• 1 — Bilinear (bilinear)
• 2 — Cubic Convolution (cubic)
• 3 — B-Spline Convolution
(cubicspline)
• 4 — Lanczos Windowed Sinc
(lanczos)
• 5 — Average (average)
• 6 — Mode (mode)
Nodata value(s)
for input bands
(space separated)
Optional
SRC_NODATA [string]
Default: None
Space separated Nodata value(s) for input
band(s)
Additional
command-line
parameters
EXTRA [string]
Default: None
Add extra GDAL command line options
Outputs
Label Název Type Popis
Virtual OUTPUT [raster] Output raster layer
Python code
Algorithm ID: gdal:buildvirtualraster
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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gdal2tiles
Generates a directory with small tiles and metadata, following the OSGeo Tile Map Service Specification. See also the
OpenGIS Web Map Tile Service Implementation Standard. Simple web pages with viewers based on Google Maps,
OpenLayers and Leaflet are generated as well. To explore your maps on-line in the web browser, you only need to
upload the generated directory onto a web server.
This algorithm also creates the necessary metadata for Google Earth (KML SuperOverlay), in case the supplied map
uses EPSG:4326 projection.
ESRI world files and embedded georeferencing is used during tile generation, but you can publish a picture without
proper georeferencing too.
This algorithm is derived from the GDAL gdal2tiles utility.
Parameters
Basic parameters
Label Název Type Popis
Input layer INPUT [raster] GDAL-supported raster layer.
Tile cutting profile PROFILE [enumeration]
Default: 0
One of:
• 0 — Mercator (mercator)
• 1 — Geodetic (geodetic)
• 2 — Raster (raster)
Zoom levels to
render
Optional
ZOOM [string]
Default: ‚‘
Web viewer to
generate
VIEWER [enumerate]
Default: 0
One of:
• 0 — All (all)
• 1 — GoogleMaps (google)
• 2 — OpenLayers (openlayers)
• 3 — Leaflet (leaflet)
• 4 — None (none)
Title of the map
Optional
TITLE [string]
Default: ‚‘
Copyright of the
map
COPYRIGHT [string]
Default: ‚‘
Output directory OUTPUT [folder]
Default: [Save
to temporary
folder]
Specify the output folder for the tiles. One
of:
• Save to a Temporary Directory
• Save to Directory
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Advanced parameters
Label Název Type Popis
Resampling
method
RESAMPLING [enumeration]
Default: 0
The resampling algorithm to be used
Options:
• 0 — Average (average)
• 1 — Nearest neighbour (near)
• 2 — Bilinear (bilinear)
• 3 — Cubic (cubic)
• 4 — Cubic spline (cubicspline)
• 5 — Lanczos Windowed sinc
(lanczos)
• 6 — Antialias (antialias)
The spatial
reference system
used for the
source input data
Optional
SOURCE_CRS [crs]
Default: None
Transparency
value to assign to
the input data
Optional
NODATA [number]
Default: 0.0
URL address
where the
generated tiles
are going to be
published
Optional
URL [string]
Default: ‚‘
Google Maps
API key
(http://code.google.com/apis/maps/signup.html)
Optional
GOOGLE_KEY [string]
Default: ‚‘
Your Google maps API key.
Bing Maps
API key
(https://www.bingmapsportal.com/)
Optional
BING_KEY [string]
Default: ‚‘
Your Bing maps API key.
Generate only
missing files
RESUME [boolean]
Default: False
Generate KML
for Google Earth
KML [boolean]
Default: False
Avoid automatic
generation of
KML files for
EPSG:4326
NO_KML [boolean]
Default: False
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Outputs
Label Název Type Popis
Output directory OUTPUT [folder] The output folder (for the tiles)
Python code
Algorithm ID: gdal:gdal2tiles
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Merge
Merges raster files in a simple way. Here you can use a pseudocolor table from an input raster and define the output
raster type. All the images must be in the same coordinate system.
This algorithm is derived from the GDAL merge utility.
Default menu: Raster ► Miscellaneous
Parameters
Basic parameters
Label Název Type Popis
Input layers INPUT [raster] [list] Input raster layers
Grab pseudocolor
table from first
layer
PCT [boolean]
Default: False
The pseudocolor table from the first layer
will be used for the coloring
Place each input
file into a separate
band
SEPARATE [boolean]
Default: False
Place each input file into a separate band
Output data type DATA_TYPE [enumeration]
Default: 5
Defines the format of the output raster file.
Options:
• 0 — Byte
• 1 — Int16
• 2 — UInt16
• 3 — UInt32
• 4 — Int32
• 5 — Float32
• 6 — Float64
• 7 — CInt16
• 8 — CInt32
• 9 — CFloat32
• 10 — CFloat64
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Label Název Type Popis
Merged OUTPUT [raster]
Default: [Save
to temporary
file]
Specification of the output raster layer. One
of:
• Save to a Temporary File
• Save to File…
Advanced parameters
Label Název Type Popis
Input pixel
value to treat
as „nodata“
Optional
NODATA_INPUT [number]
Default: None
Ignores pixels from files being merged in
with this pixel value
Assign specified
„nodata“ value to
output
Optional
NODATA_OUTPUT [number]
Default: None
Assigns the specified nodata value to output
bands.
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Additional
command-line
parameters
EXTRA [string]
Default: None
Add extra GDAL command line options
Outputs
Label Název Type Popis
Merged OUTPUT [raster] Output raster layer
Python code
Algorithm ID: gdal:merge
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Pansharpening
Performs a pan-sharpening operation. It can create a „classic“ output dataset (such as GeoTIFF), or a VRT dataset
describing the pan-sharpening operation.
See GDAL Pansharpen.
Parameters
Basic parameters
Label Název Type Popis
Spectral dataset SPECTRAL [raster] Input (spectral) raster layer
Panchromatic
dataset
PANCHROMATIC [raster] Input (panchromatic) raster layer
Output OUTPUT [raster]
Default: [Save
to temporary
file]
Specify the output (sharpened) raster layer.
One of:
• Save to a Temporary File
• Save to File…
Advanced parameters
Label Název Type Popis
Resampling
algorithm
RESAMPLING [enumeration]
Default: 2
The resampling algorithm to be used
Options:
• 0 — Nearest Neighbour (nearest)
• 1 — Bilinear (bilinear)
• 2 — Cubic (cubic)
• 3 — Cubic Spline (cubicspline)
• 4 — Lanczos Windowed Sinc
(lanczos)
• 5 — Average (average)
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options
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Outputs
Label Název Type Popis
Output OUTPUT [raster] Output (sharpened) raster layer
Python code
Algorithm ID: gdal:pansharp
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Raster calculator
Command line raster calculator with numpy syntax. Use any basic arithmetic supported by numpy arrays, such as +,
-, *, and / along with logical operators, such as >. Note that all input rasters must have the same dimensions, but no
projection checking is performed.
See the GDAL Raster Calculator utility docs.
Viz také:
Raster calculator
Parameters
Basic parameters
Label Název Type Popis
Input layer A INPUT_A [raster] First input raster layer (mandatory)
Number of raster
band for A
BAND_A [raster band] Band for input layer A (mandatory)
Input layer B
Optional
INPUT_B [raster]
Default: None
Second input raster layer
Number of raster
band for B
Optional
BAND_B [raster band] Band for input layer B
Input layer C
Optional
INPUT_C [raster]
Default: None
Third input raster layer
Number of raster
band for C
Optional
BAND_C [raster band] Band for input layer C
Input layer D
Optional
INPUT_D [raster]
Default: None
Fourth input raster layer
Number of raster
band for D
Optional
BAND_D [raster band] Band for input layer D
Input layer E
Optional
INPUT_E [raster]
Default: None
Fifth input raster layer
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Label Název Type Popis
Number of raster
band for E
Optional
BAND_E [raster band] Band for input layer E
Input layer F
Optional
INPUT_F [raster] Sixth input raster layer
Number of raster
band for F
Optional
BAND_F [raster band]
Default: None
Band for input layer F
Calculation in
gdalnumeric
syntax using +-/*
or any numpy
array functions
(i.e. logical_and())
FORMULA [string]
Default: ‚‘
The calculation formula. Examples:
• A*(A>0) — outputs the value
of the raster A if the value of
A is greater than 0. If not, outputs 0.
• A*(A>0 and A>B)— outputs the
value of A if that value is bigger than
0 and bigger than the value of B. If
not, outputs 0.
• A*logical_or(A<=177,
A>=185) — outputs the value of
A if A <= 177 or A >= 185. If not,
outputs 0.
• sqrt(A*A+B*B) — Outputs the
square root of the sum of the value
of A squared and the value of B
squared.
Set output nodata
value
Optional
NO_DATA [number]
Default: None
Value to use for nodata
Output raster type RTYPE [enumeration]
Default: 5
Defines the format of the output raster file.
Options:
• 0 — Byte
• 1 — Int16
• 2 — UInt16
• 3 — UInt32
• 4 — Int32
• 5 — Float32
• 6 — Float64
Calculated OUTPUT [raster]
Default: [Save
to temporary
file]
Specify the output (calculated) raster layer.
One of:
• Save to a Temporary File
• Save to File…
Advanced parameters
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Label Název Type Popis
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Additional
command-line
parameters
Optional
EXTRA [string]
Default: ‚‘
Add extra GDAL command line options
Outputs
Label Název Type Popis
Calculated OUTPUT [raster] Output (calculated) raster layer
Python code
Algorithm ID: gdal:rastercalculator
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Raster information
The gdalinfo program lists various information about a GDAL supported raster dataset.
This algorithm is derived from the GDAL info utility.
Default menu: Raster ► Miscellaneous
Parameters
Basic parameters
Label Název Type Popis
Input layer INPUT [raster] Input raster layer
Force
computation
of the actual
min/max values
for each band
MIN_MAX [boolean]
Default: False
Forces computation of the actual min/max
values for each band in the dataset
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Label Název Type Popis
Read and
display image
statistics (force
computation if
necessary)
STATS [boolean]
Default: False
Reads and displays image statistics. Forces
computation if no statistics are stored in an
image.
Suppress GCP
info
NO_GCP [boolean]
Default: False
Suppresses ground control points list
printing. It may be useful for datasets
with huge amount of GCPs, such as L1B
AVHRR or HDF4 MODIS which contain
thousands of them.
Suppress
metadata info
NO_METADATA [boolean]
Default: False
Suppresses metadata printing. Some
datasets may contain a lot of metadata
strings.
Layer information OUTPUT [html]
Default: [Save
to temporary
file]
Specify the HTML file for output. One of:
• Save to a Temporary File
• Save to File…
Advanced parameters
Label Název Type Popis
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options
Outputs
Label Název Type Popis
Layer information OUTPUT [html] The HTML file containing information
about the input raster layer
Python code
Algorithm ID: gdal:gdalinfo
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Retile
Retiles a set of input tiles. All the input tiles must be georeferenced in the same coordinate system and have a matching
number of bands. Optionally pyramid levels are generated.
This algorithm is derived from the GDAL Retile utility.
Parameters
Basic parameters
Label Název Type Popis
Input files INPUT [raster] [list] The input raster files
Tile width TILE_SIZE_X [number]
Default: 256
Width of the tiles in pixels (minimum 0)
Tile height TILE_SIZE_Y [number]
Default: 256
Height of the tiles in pixels (minimum 0)
Overlap in
pixels between
consecutive tiles
OVERLAP [number]
Default: 0
Number of
pyramid levels
to build
LEVELS [number]
Default: 1
Minimum: 0
Output directory OUTPUT [folder]
Default: [Save
to temporary
folder]
Specify the output folder for the tiles. One
of:
• Save to a Temporary Directory
• Save to Directory
CSV file
containing
the tile(s)
georeferencing
information
OUTPUT_CSV [file]
Default: [Skip
output]
Specify the output file for the tiles. One of:
• Skip Output
• Save to a Temporary File
• Save to File…
Advanced parameters
Label Název Type Popis
Source coordinate
reference system
Optional
SOURCE_CRS [crs]
Default: None
Resampling
method
RESAMPLING [enumeration]
Default: 0
The resampling algorithm to be used
Options:
• 0 — Nearest Neighbour (nearest)
• 1 — Bilinear (bilinear)
• 2 — Cubic (cubic)
• 3 — Cubic Spline (cubicspline)
• 4 — Lanczos Windowed Sinc
(lanczos)
Column delimiter
used in the CSV
file
Optional
DELIMITER [string]
Default: ‚;‘
Delimiter to use in the CSV file containing
the tile(s) georeferencing information
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Label Název Type Popis
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Additional
command-line
parameters
Optional
EXTRA [string]
Default: ‚‘
Add extra GDAL command line options
Output data type DATA_TYPE [enumeration]
Default: 5
Defines the format of the output raster file.
Options:
• 0 — Byte
• 1 — Int16
• 2 — UInt16
• 3 — UInt32
• 4 — Int32
• 5 — Float32
• 6 — Float64
• 7 — CInt16
• 8 — CInt32
• 9 — CFloat32
• 10 — CFloat64
Build only the
pyramids
ONLY_PYRAMIDS [boolean]
Default: False
Use separate
directory for each
tile row
DIR_FOR_ROW [boolean]
Default: False
Outputs
Label Název Type Popis
Output directory OUTPUT [folder] The output folder for the tiles.
CSV file
containing
the tile(s)
georeferencing
information
OUTPUT_CSV [file] The CSV file with georeferencing
information for the tiles.
Python code
Algorithm ID: gdal:retile
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Tile index
Builds a vector layer with a record for each input raster file, an attribute containing the filename, and a polygon
geometry outlining the raster. This output is suitable for use with MapServer as a raster tileindex.
This algorithm is derived from the GDAL Tile Index utility.
Default menu: Raster ► Miscellaneous
Parameters
Basic parameters
Label Název Type Popis
Input files LAYERS [raster] [list] The input raster files. Can be multiple files.
Field name to hold
the file path to the
indexed rasters
PATH_FIELD_NAME
Optional
[string]
Default: ‚location‘
The output field name to hold the file
path/location to the indexed rasters.
Store absolute
path to the
indexed rasters
ABSOLUTE_PATH [boolean]
Default: False
Set whether the absolute path to the raster
files is stored in the tile index file. By
default the raster filenames will be put in
the file exactly as they are specified in the
command.
Skip files
with different
projection
reference
PROJ_DIFFERENCE[boolean]
Default: False
Only files with same projection as files
already inserted in the tile index will be
inserted. Default does not check projection
and accepts all inputs.
Tile index OUTPUT [vector: polygon]
Default: [Save
to temporary
file]
Specify the polygon vector layer to write the
index to. One of:
• Save to a Temporary File
• Save to File…
Advanced parameters
Label Název Type Popis
Transform
geometries to
the given CRS
Optional
TARGET_CRS [crs] Geometries of input files will be
transformed to the specified target
coordinate reference system. Default
creates simple rectangular polygons in the
same coordinate reference system as the
input rasters.
The name of the
field to store the
SRS of each tile
Optional
CRS_FIELD_NAME [string] The name of the field to store the SRS of
each tile
The format in
which the CRS of
each tile must be
written
CRS_FORMAT [enumeration]
Default: 0
Format for the CRS. One of:
• 0 – Auto (AUTO)
• 1 – Well-known text (WKT)
• 2 – EPSG (EPSG)
• 3 – Proj.4 (PROJ)
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Outputs
Label Název Type Popis
Tile index OUTPUT [vector: polygon] The polygon vector layer with the tile index.
Python code
Algorithm ID: gdal:tileindex
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Viewshed
Calculates a viewshed raster from an input raster DEM using method defined in Wang2000 for a user defined point.
Parameters
Basic parameters
Label Název Type Popis
Input layer INPUT [raster] Input elevation raster layer
Band number BAND [raster band]
Default: 1
The number of the band to use as elevation
Observer location OBSERVER [point] The location of the observer
Observer height OBSERVER_HEIGHT[number]
Default: 1.0
The altitude of the observer, in the DEM
units
Target height TARGET_HEIGHT [number]
Default: 1.0
The altitude of the target element, in the
DEM units
Maximum
distance from
observer to
compute visibility
MAX_DISTANCE [number]
Default: 100.0
Maximum distance from observer to
compute visibility, in the DEM units
Output OUTPUT [raster]
Default: [Save
to temporary
file]
Output raster layer. One of:
• Save to a Temporary File
• Save to File…
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Advanced parameters
Label Název Type Popis
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Additional
command-line
parameters
EXTRA [string]
Default: None
Add extra GDAL command line options
Outputs
Label Název Type Popis
Output OUTPUT [raster] The raster layer displaying the viewshed.
Python code
Algorithm ID: gdal:viewshed
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.2.5 Raster projections
Assign projection
Applies a coordinate system to a raster dataset.
This algorithm is derived from the GDAL edit utility.
Default menu: Raster ► Projections
Parameters
Label Název Type Popis
Input layer INPUT_LAYER [raster] Input raster layer
Desired CRS CRS [crs] The projection (CRS) of the output layer
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Outputs
Label Název Type Popis
Layer with
projection
OUTPUT [raster] The output raster layer (with the new
projection information)
Python code
Algorithm ID: gdal:assignprojection
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Extract projection
Extracts the projection of a raster file and writes it into a world file with extension .wld.
This algorithm is derived from the GDAL srsinfo utility.
Default menu: Raster ► Projections
Parameters
Label Název Type Popis
Input file INPUT_LAYER [raster] Input raster The raster layer has to be file
based, as the algorithm uses the path to the
raster file as the location of the generated .
wld file. Using a non-file raster layer will
lead to an error.
Create also .prj
file
PRJ_FILE_CREATE[boolean]
Default: False
If this is activated a .prj file containing
the projection information is also created.
Outputs
Label Název Type Popis
World file WORLD_FILE [file] Text file with extension .wld containing
transformation parameters for the raster
file.
ESRI Shapefile
prj file
PRJ_FILE [file] Text file with .prj extension that
describes the CRS. Will be None if Create
also .prj file is False.
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Python code
Algorithm ID: gdal:extractprojection
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Warp (reproject)
Reprojects a raster layer into another Coordinate Reference System (CRS). The output file resolution and the
resampling method can be chosen.
This algorithm is derived from the GDAL warp utility.
Default menu: Raster ► Projections
Parameters
Label Název Type Popis
Input layer INPUT [raster] Input raster layer to reproject
Source CRS
Optional
SOURCE_CRS [crs] Defines the CRS of the input raster layer
Target CRS
Optional
TARGET_CRS [crs]
Default:
EPSG:4326
The CRS of the output layer
Resampling
method to use
RESAMPLING [enumeration]
Default: 0
Pixel value resampling method to use.
Options:
• 0 — Nearest neighbour
• 1 — Bilinear
• 2 — Cubic
• 3 — Cubic spline
• 4 — Lanczos windowed sinc
• 5 — Average
• 6 — Mode
• 7 — Maximum
• 8 — Minimum
• 9 — Median
• 10 — First quartile
• 11 — Third quartile
Nodata value for
output bands
Optional
NODATA [number]
Default: None
Sets nodata value for output bands. If not
provided, then nodata values will be copied
from the source dataset.
Output file
resolution
in target
georeferenced
units
Optional
TARGET_RESOLUTION[number]
Default: None
Defines the output file resolution of
reprojection result
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Label Název Type Popis
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
Output data type DATA_TYPE [enumeration]
Default: 0
Defines the format of the output raster file.
Options:
• 0 — Use input layer data type
• 1 — Byte
• 2 — Int16
• 3 — UInt16
• 4 — UInt32
• 5 — Int32
• 6 — Float32
• 7 — Float64
• 8 — CInt16
• 9 — CInt32
• 10 — CFloat32
• 11 — CFloat64
Georeferenced
extents of output
file to be created
Optional
TARGET_EXTENT [extent] Sets the georeferenced extent of the output
file to be created (in the Target CRS by
default. In the CRS of the target raster extent,
if specified).
CRS of the target
raster extent
Optional
TARGET_EXTENT_CRS[crs] Specifies the CRS in which to interpret
the coordinates given for the extent of the
output file. This must not be confused with
the target CRS of the output dataset. It
is instead a convenience e.g. when knowing
the output coordinates in a geodetic long/lat
CRS, but wanting a result in a projected
coordinate system.
Use multithreaded
warping
implementation
MULTITHREADING [boolean]
Default: False
Two threads will be used to process chunks
of the image and perform input/output
operations simultaneously. Note that the
computation itself is not multithreaded.
Additional
command-line
parameters
Optional
EXTRA [string]
Default: None
Add extra GDAL command line options.
Reprojected OUTPUT [raster]
Default: ‚[Save to
temporary file]‘
Specification of the output raster layer. One
of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Reprojected OUTPUT [raster]
Default: [Save
to temporary
file]
Reprojected output raster layer
Python code
Algorithm ID: gdal:warpreproject
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.2.6 Vector conversion
Convert format
Converts any OGR-supported vector layer into another OGR-supported format.
This algorithm is derived from the ogr2ogr utility.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘ (no
additional options)
Additional GDAL creation options.
Converted OUTPUT [same as input] Specification of the output vector layer. One
of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
For Save to File, the output format
has to be specified. All GDAL vector
formats are supported. For Save to
a Temporary File the QGIS default
vector format will be used.
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Outputs
Label Název Type Popis
Converted OUTPUT [same as input] The output vector layer
Python code
Algorithm ID: gdal:convertformat
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Rasterize (overwrite with attribute)
Overwrites a raster layer with values from a vector layer. New values are assigned based on the attribute value of the
overlapping vector feature.
This algorithm is derived from the GDAL rasterize utility.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Input raster layer INPUT_RASTER [raster] Input raster layer
Field to use for
a burn-in value
Optional
FIELD [tablefield:
numeric]
Defines the attribute field to use to set the
pixels values
Add burn in
values to existing
raster values
ADD [boolean]
Default: False
If False, pixels are assigned the selected
field’s value. If True, the selected field’s
value is added to the value of the input
raster layer.
Additional
command-line
parameters
Optional
EXTRA [string]
Default: ‚‘
Add extra GDAL command line options
Outputs
Label Název Type Popis
Rasterized OUTPUT [raster] The overwritten input raster layer
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Python code
Algorithm ID: gdal:rasterize_over
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Rasterize (overwrite with fixed value)
Overwrites parts of a raster layer with a fixed value. The pixels to overwrite are chosen based on the supplied
(overlapping) vector layer.
This algorithm is derived from the GDAL rasterize utility.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Input raster layer INPUT_RASTER [raster] Input raster layer
A fixed value to
burn
BURN [number]
Default: 0.0
The value to burn
Add burn in
values to existing
raster values
ADD [boolean]
Default: False
If False, pixels are assigned the fixed value.
If True, the fixed value is added to the value
of the input raster layer.
Additional
command-line
parameters
Optional
EXTRA [string]
Default: ‚‘
Add extra GDAL command line options
Outputs
Label Název Type Popis
Rasterized OUTPUT [raster] The overwritten input raster layer
Python code
Algorithm ID: gdal:rasterize_over_fixed_value
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Rasterize (vector to raster)
Converts vector geometries (points, lines and polygons) into a raster image.
This algorithm is derived from the GDAL rasterize utility.
Default menu: Raster ► Conversion
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Field to use for
a burn-in value
Optional
FIELD [tablefield:
numeric]
Defines the attribute field from which the
attributes for the pixels should be chosen
A fixed value to
burn
Optional
BURN [number]
Default: 0.0
A fixed value to burn into a band for all
features.
Output raster size
units
UNITS [enumeration]
Default: 0
Units to use when defining the output raster
size/resolution. One of:
• 0 — Pixels
• 1 — Georeferenced units
Width/Horizontal
resolution
WIDTH [number]
Default: 0.0
Sets the width (if size units is „Pixels“)
or horizontal resolution (if size units
is „Georeferenced units“) of the output
raster. Minimum value: 0.0.
Height/Vertical
resolution
HEIGHT [number]
Default: 0.0
Sets the height (if size units is „Pixels“)
or vertical resolution (if size units
is „Georeferenced units“) of the output
raster.
Output extent EXTENT [extent] Extent of the output raster layer. If the
extent is not specified, the minimum extent
that covers the selected reference layer(s)
will be used.
Assign a specified
nodata value to
output bands
Optional
NODATA [number]
Default: 0.0
Assigns a specified nodata value to output
bands
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘
For adding one or more creation options
that control the raster to be created
(colors, block size, file compression…). For
convenience, you can rely on predefined
profiles (see GDAL driver options section).
For Batch Process: separate multiple
options with a pipe character (|).
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Label Název Type Popis
Output data type DATA_TYPE [enumeration]
Default: 5
Defines the format of the output raster file.
Options:
• 0 — Byte
• 1 — Int16
• 2 — UInt16
• 3 — UInt32
• 4 — Int32
• 5 — Float32
• 6 — Float64
• 7 — CInt16
• 8 — CInt32
• 9 — CFloat32
• 10 — CFloat64
Pre-initialize the
output image with
value
Optional
INIT [number] Pre-initializes the output image bands with
this value. Not marked as the nodata value
in the output file. The same value is used in
all the bands.
Invert
rasterization
INVERT [boolean]
Default: False
Burns the fixed burn value, or the burn
value associated with the first feature into
all parts of the image not inside the provided
polygon.
Rasterized OUTPUT [raster]
Default: ‚[Save to
temporary file]‘
Specification of the output raster layer. One
of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed
here For Save to File, the output
format has to be specified. All GDAL raster
formats are supported. For Save to
a Temporary File the QGIS default
raster format will be used.
Outputs
Label Název Type Popis
Rasterized OUTPUT [raster] Output raster layer
Python code
Algorithm ID: gdal:rasterize
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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24.2.7 Vector geoprocessing
Buffer vectors
Create buffers around the features of a vector layer.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] The input vector layer
Geometry column
name
GEOMETRY [string]
Default: ‚geometry‘
The name of the input layer geometry
column to use
Buffer distance DISTANCE [number]
Default: 10.0
Minimum: 0.0
Dissolve by
attribute
Optional
FIELD [tablefield: any]
Default: None
Field to use for dissolving
Dissolve results DISSOLVE [boolean]
Default: False
If set, the result is dissolved. If no field is set
for dissolving, all the buffers are dissolved
into one feature.
Produce one
feature for each
geometry in any
kind of geometry
collection in the
source file
EXPLODE_COLLECTIONS[boolean]
Default: False
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘ (no
additional options)
Additional GDAL creation options.
Buffer OUTPUT [vector: polygon]
Default: [Save
to temporary
file]
Specify the output buffer layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Buffer OUTPUT [vector: polygon] The output buffer layer
Python code
Algorithm ID: gdal:buffervectors
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Clip vector by extent
Clips any OGR-supported vector file to a given extent.
This algorithm is derived from the GDAL ogr2ogr utility.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] The input vector layer
Clip extent EXTENT [extent] Defines the bounding box that should be
used for the output vector file. It has to be
defined in target CRS coordinates.
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘ (no
additional options)
Additional GDAL creation options.
Clipped (extent) OUTPUT [same as input]
Default: [Save
to temporary
file]
Specify the output (clipped) layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Clipped (extent) OUTPUT [same as input] The output (clipped) layer. The default
format is „ESRI Shapefile“.
Python code
Algorithm ID: gdal:clipvectorbyextent
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Clip vector by mask layer
Clips any OGR-supported vector layer by a mask polygon layer.
This algorithm is derived from the GDAL ogr2ogr utility.
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Parameters
Label Název Type Popis
Input layer INPUT [vector: any] The input vector layer
Mask layer MASK [vector: polygon] Layer to be used as clipping extent for the
input vector layer.
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘ (no
additional options)
Additional GDAL creation options.
Clipped (mask) OUTPUT [same as input]
Default: [Save
to temporary
file]
The output (masked) layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Clipped (mask) OUTPUT [same as input] The output (masked) layer. The default
format is „ESRI Shapefile“.
Python code
Algorithm ID: gdal:clipvectorbypolygon
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Dissolve
Dissolve (combine) geometries that have the same value for a given attribute / field. The output geometries are
multipart.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] The input layer to dissolve
Dissolve field
Optional
FIELD [tablefield: any] The field of the input layer to use for
dissolving
Geometry column
name
GEOMETRY [string]
Default: ‚geometry‘
The name of the input layer geometry
column to use for dissolving.
Produce one
feature for each
geometry in any
kind of geometry
collection in the
source file
EXPLODE_COLLECTIONS[boolean]
Default: False
Produce one feature for each geometry in
any kind of geometry collection in the
source file
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Label Název Type Popis
Keep input
attributes
KEEP_ATTRIBUTES[boolean]
Default: False
Keep all attributes from the input layer
Count dissolved
features
COUNT_FEATURES [boolean]
Default: False
Count the dissolved features and include it
in the output layer.
Compute area
and perimeter of
dissolved features
COMPUTE_AREA [boolean]
Default: False
Compute the area and perimeter of
dissolved features and include them in the
output layer
Compute
min/max/sum/mean
for attribute
COMPUTE_STATISTICS[boolean]
Default: False
Calculate statistics (min, max, sum and
mean) for the numeric attribute specified
and include them in the output layer
Numeric attribute
to calculate
statistics on
Optional
STATISTICS_ATTRIBUTE[tablefield:
numeric]
The numeric attribute to calculate statistics
on
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘ (no
additional options)
Additional GDAL creation options.
Dissolved OUTPUT [same as input]
Default: [Save
to temporary
file]
Specify the output layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Dissolved OUTPUT [same as input] The output multipart geometry layer (with
dissolved geometries)
Python code
Algorithm ID: gdal:dissolve
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Offset curve
Offsets lines by a specified distance. Positive distances will offset lines to the left, and negative distances will offset
them to the right.
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Parameters
Label Název Type Popis
Input layer INPUT [vector: line] The input line layer
Geometry column
name
GEOMETRY [string]
Default: ‚geometry‘
The name of the input layer geometry
column to use
Offset distance
(left-sided:
positive, right-sided:
negative)
DISTANCE [number]
Default: 10.0
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘ (no
additional options)
Additional GDAL creation options.
Offset curve OUTPUT [vector: line]
Default: [Save
to temporary
file]
Specify the output line layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Offset curve OUTPUT [vector: line] The output offset curve layer
Python code
Algorithm ID: gdal:offsetcurve
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
One side buffer
Creates a buffer on one side (right or left) of the lines in a line vector layer.
Parameters
Label Název Type Popis
Input layer INPUT [vector: line] The input line layer
Geometry column
name
GEOMETRY [string]
Default: ‚geometry‘
The name of the input layer geometry
column to use
Buffer distance DISTANCE [number]
Default: 10.0
Buffer side BUFFER_SIDE [enumeration]
Default: 0
One of:
• 0 — Right
• 1 — Left
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Label Název Type Popis
Dissolve by
attribute
Optional
FIELD [tablefield: any]
Default: None
Field to use for dissolving
Dissolve all results DISSOLVE [boolean]
Default: False
If set, the result is dissolved. If no field is set
for dissolving, all the buffers are dissolved
into one feature.
Produce one
feature for each
geometry in any
kind of geometry
collection in the
source file
EXPLODE_COLLECTIONS[boolean]
Default: False
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘ (no
additional options)
Additional GDAL creation options.
One-sided buffer OUTPUT [vector: polygon]
Default: [Save
to temporary
file]
Specify the output buffer layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
One-sided buffer OUTPUT [vector: polygon] The output buffer layer
Python code
Algorithm ID: gdal:onesidebuffer
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Points along lines
Generates a point on each line of a line vector layer at a distance from start. The distance is provided as a fraction of
the line length.
Parameters
Label Název Type Popis
Input layer INPUT [vector: line] The input line layer
Geometry column
name
GEOMETRY [string]
Default: ‚geometry‘
The name of the input layer geometry
column to use
Distance from line
start represented
as a fraction of
line length
DISTANCE [number]
Default: 0.5 (middle
of the line)
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘ (no
additional options)
Additional GDAL creation options.
Points along line OUTPUT [vector: point]
Default: [Save
to temporary
file]
Specify the output point layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Points along line OUTPUT [vector: point] The output point layer
Python code
Algorithm ID: gdal:pointsalonglines
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.2.8 Vector miscellaneous
Build virtual vector
Creates a virtual vector layer that contains a set of vector layers. The output virtual vector layer will not be opened in
the current project.
This algorithm is especially useful in case another algorithm needs multiple layers but accept only one vrt in which
the layers are specified.
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Parameters
Label Název Type Popis
Input datasources INPUT [vector: any] [list] Select the vector layers you want to use to
build the virtual vector
Create „unioned“
VRT
UNIONED [boolean]
Default: False
Check if you want to unite all the vectors in
a single vrt file
Virtual vector OUTPUT [same as input]
Default: [Save
to temporary
file]
Specify the output layer containing only the
duplicates. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Virtual vector OUTPUT [vector: any] The output virtual vector made from the
chosen sources
Python code
Algorithm ID: gdal:buildvirtualvector
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Execute SQL
Runs a simple or complex query with SQL syntax on the source layer. The result of the query will be added as a new
layer.
This algorithm is derived from the GDAL ogr2ogr utility.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] OGR-supported input vector layer
SQL expression SQL [string] Defines the SQL query, for example
SELECT * FROM my_table WHERE
name is not null.
SQL dialect DIALECT [enumeration]
Default: 0
SQL dialect to use. One of:
• 0 — None
• 1 — OGR SQL
• 2 — SQLite
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Label Název Type Popis
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘ (no
additional options)
Additional GDAL creation options.
SQL result OUTPUT [vector: any] Specification of the output layer. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
For Save to File, the output format
has to be specified. All GDAL vector
formats are supported. For Save to
a Temporary File the default output
vector layer format will be used.
Outputs
Label Název Type Popis
SQL result OUTPUT [vector: any] Vector layer created by the query
Python code
Algorithm ID: gdal:executesql
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Export to PostgreSQL (available connections)
Imports vector layers inside a PostgreSqL database on the basis of an available connection. The connection has to be
defined properly beforehand. Be aware that the checkboxes ‚Save Username‘ and ‚Save Password‘ are activated. Then
you can use the algorithm.
This algorithm is derived from the GDAL ogr2ogr utility.
Parameters
Label Název Type Popis
Database
(connection name)
DATABASE [string] The PostgreSQL database to connect to
Input layer INPUT [vector: any] OGR-supported vector layer to export to
the database
Shape encoding
Optional
SHAPE_ENCODING [string]
Default: ‚‘
Sets the encoding to apply to the data
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Label Název Type Popis
Output geometry
type
GTYPE [enumeration]
Default: 0
Defines the output geometry type. One of:
• 0 —
• 1 — NONE
• 2 — GEOMETRY
• 3 — POINT
• 4 — LINESTRING
• 5 — POLYGON
• 6 — GEOMETRYCOLLECTION
• 7 — MULTIPOINT
• 8 — MULTIPOLYGON
• 9 — MULTILINESTRING
Assign an output
CRS
Optional
A_SRS [crs]
Default: None
Defines the output CRS of the database
table
Reproject to this
CRS on output
Optional
T_SRS [crs]
Default: None
Reprojects/transforms to this CRS on
output
Override source
CRS
Optional
S_SRS [crs]
Default: None
Overrides the input layer CRS
Schema (schema
name)
Optional
SCHEMA [string]
Default: ‚public‘
Defines the schema for the database table
Table to export to
(leave blank to use
layer name)
Optional
TABLE [string]
Default: ‚‘
Defines a name for the table that will be
imported into the database. By default the
table name is the name of the input vector
file.
Primary Key (new
field)
Optional
PK [string]
Default: ‚id‘
Defines which attribute field will be the
primary key of the database table
Primary Key
(existing field,
used if the above
option is left
empty)
Optional
PRIMARY_KEY [tablefield: any]
Default: None
Defines which attribute field in the exported
layer will be the primary key of the database
table
Geometry column
name
Optional
GEOCOLUMN [string]
Default: ‚geom‘
Defines in which attribute field of the
database there will be the geometry
information
Vector dimensions
Optional
DIM [enumeration]
Default: 0 (2D)
Defines if the vector file to be imported has
2D or 3D data. One of:
• 0 — 2
• 1 — 3
Distance tolerance
for simplification
Optional
SIMPLIFY [string]
Default: ‚‘
Defines a distance tolerance for the
simplification of the vector geometries
to be imported. By default there is no
simplification.
Maximum
distance
between 2 nodes
(densification)
Optional
SEGMENTIZE [string]
Default: ‚‘
The maximum distance between two nodes.
Used to create intermediate points. By
default there is no densification.
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Label Název Type Popis
Select features by
extent (defined in
input layer CRS)
Optional
SPAT [extent]
Default: None
You can select features from a given extent
that will be in the output table.
Clip the input
layer using the
above (rectangle)
extent
Optional
CLIP [boolean]
Default: False
The input layer will be clipped by the extent
you defined before
Select features
using a SQL
„WHERE“
statement (Ex:
column=“value“)
Optional
WHERE [string]
Default: ‚‘
Defines with a SQL „WHERE“ statement
which features should be selected from the
input layer
Group N features
per transaction
(Default: 2000)
Optional
GT [string]
Default: ‚‘
You can group the input features in
transactions where N defines the size. By
default N limits the transaction size to
20000 features.
Overwrite existing
table
Optional
OVERWRITE [boolean]
Default: True
If there is a table with the same name in the
database, and if this option is set to True,
the table will be overwritten.
Append to existing
table
Optional
APPEND [boolean]
Default: False
If checked / True the vector data will be
appended to an existing table. New fields
found in the input layer are ignored. By
default a new table will be created.
Append and add
new fields to
existing table
Optional
ADDFIELDS [boolean]
Default: False
If activated the vector data will be appended
to an existing table, there won’t be a new
table created. New fields found in input
layer are added to the table. By default a new
table will be created.
Do not launder
columns/table
names
Optional
LAUNDER [boolean]
Default: False
With this option checked you can prevent
the default behaviour (converting column
names to lowercase, removing spaces and
other invalid characters).
Do not create
Spatial Index
Optional
INDEX [boolean]
Default: False
Prevents a spatial index for the output table
from being created. By default, a spatial
index is added.
Continue after
a failure, skipping
the failed feature
Optional
SKIPFAILURES [boolean]
Default: False
Promote to
Multipart
Optional
PROMOTETOMULTI [boolean]
Default: True
Casts features geometry type to multipart in
the output table
Keep width and
precision of input
attributes
Optional
PRECISION [boolean]
Default: True
Avoids modifying column attributes to
comply with input data
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘ (no
additional options)
Additional GDAL creation options.
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Outputs
This algorithm has no output.
Python code
Algorithm ID: gdal:importvectorintopostgisdatabaseavailableconnections
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Export to PostgreSQL (new connection)
Imports vector layers inside a PostGreSQL database. A new connection to the PostGIS database must be created.
This algorithm is derived from the GDAL ogr2ogr utility.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] OGR-supported vector layer to export to
the database
Shape encoding
Optional
SHAPE_ENCODING [string]
Default: ‚‘
Sets the encoding to apply to the data
Output geometry
type
GTYPE [enumeration]
Default: 0
Defines the output geometry type. One of:
• 0 —
• 1 — NONE
• 2 — GEOMETRY
• 3 — POINT
• 4 — LINESTRING
• 5 — POLYGON
• 6 — GEOMETRYCOLLECTION
• 7 — MULTIPOINT
• 8 — MULTIPOLYGON
• 9 — MULTILINESTRING
Assign an output
CRS
Optional
A_SRS [crs]
Default: None
Defines the output CRS of the database
table
Reproject to this
CRS on output
Optional
T_SRS [crs]
Default: None
Reprojects/transforms to this CRS on
output
Override source
CRS
Optional
S_SRS [crs]
Default: None
Overrides the input layer CRS
Host
Optional
HOST [string]
Default: ‚localhost‘
Name of the database host
Port
Optional
PORT [string]
Default: ‚5432‘
Port number the PostgreSQL database
server listens on
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Label Název Type Popis
Username
Optional
USER [string]
Default: ‚‘
User name used to log in to the database
Database name
Optional
DBNAME [string]
Default: ‚‘
Name of the database
Password
Optional
PASSWORD [string]
Default: ‚‘
Password used with Username to connect to
the database
Schema (schema
name)
Optional
SCHEMA [string]
Default: ‚public‘
Defines the schema for the database table
Table name, leave
blank to use input
name
Optional
TABLE [string]
Default: ‚‘
Defines a name for the table that will be
imported into the database. By default the
table name is the name of the input vector
file.
Primary Key (new
field)
Optional
PK [string]
Default: ‚id‘
Defines which attribute field will be the
primary key of the database table
Primary Key
(existing field,
used if the above
option is left
empty)
Optional
PRIMARY_KEY [tablefield: any]
Default: None
Defines which attribute field in the exported
layer will be the primary key of the database
table
Geometry column
name
Optional
GEOCOLUMN [string]
Default: ‚geom‘
Defines in which attribute field to store the
geometry information
Vector dimensions
Optional
DIM [enumeration]
Default: 0 (2D)
Defines if the vector file to be imported has
2D or 3D data. One of:
• 0 — 2D
• 1 — 3D
Distance tolerance
for simplification
Optional
SIMPLIFY [string]
Default: ‚‘
Defines a distance tolerance for the
simplification of the vector geometries to
be imported. By default no simplification
there is no simplification.
Maximum
distance
between 2 nodes
(densification)
Optional
SEGMENTIZE [string]
Default: ‚‘
The maximum distance between two nodes.
Used to create intermediate points. By
default there is no densification.
Select features by
extent (defined in
input layer CRS)
Optional
SPAT [extent]
Default: None
You can select features from a given extent
that will be in the output table.
Clip the input
layer using the
above (rectangle)
extent
Optional
CLIP [boolean]
Default: False
The input layer will be clipped by the extent
you defined before
Fields to include
(leave empty to use
all fields)
Optional
FIELDS [string] [list]
Default: []
Defines fields to keep from the imported
vector file. If none is selected, all the fields
are imported.
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Label Název Type Popis
Select features
using a SQL
„WHERE“
statement (Ex:
column=“value“)
Optional
WHERE [string]
Default: ‚‘
Defines with a SQL „WHERE“ statement
which features should be selected for the
output table
Group N features
per transaction
(Default: 2000)
Optional
GT [string]
Default: ‚‘
You can group the input features in
transactions where N defines the size. By
default N limits the transaction size to
20000 features.
Overwrite existing
table
Optional
OVERWRITE [boolean]
Default: True
If there is a table with the same name in the
database, and if this option is set to True,
the table will be overwritten.
Append to existing
table
Optional
APPEND [boolean]
Default: False
If checked / True the vector data will be
appended to an existing table. New fields
found in the input layer are ignored. By
default a new table will be created.
Append and add
new fields to
existing table
Optional
ADDFIELDS [boolean]
Default: False
If activated the vector data will be appended
to an existing table, there won’t be created
a new table. New fields found in input layer
are added to the table. By default a new table
will be created.
Do not launder
columns/table
names
Optional
LAUNDER [boolean]
Default: False
With this option checked you can prevent
the default behaviour (converting column
names to lowercase, removing spaces and
other invalid characters).
Do not create
Spatial Index
Optional
INDEX [boolean]
Default: False
Prevents a spatial index for the output table
from being created. By default, a spatial
index is added.
Continue after
a failure, skipping
the failed feature
Optional
SKIPFAILURES [boolean]
Default: False
Promote to
Multipart
Optional
PROMOTETOMULTI [boolean]
Default: True
Casts features geometry type to multipart in
the output table
Keep width and
precision of input
attributes
Optional
PRECISION [boolean]
Default: True
Avoids modifying column attributes to
comply with input data
Additional
creation options
Optional
OPTIONS [string]
Default: ‚‘ (no
additional options)
Additional GDAL creation options.
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Outputs
This algorithm has no output.
Python code
Algorithm ID: gdal:importvectorintopostgisdatabasenewconnection
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Vector Information
Creates an information file that lists information about an OGR-supported data source. The output will be shown in
a ‚Result‘ window and can be written into a HTML-file. The information includes the geometry type, feature count,
the spatial extent, the projection information and many more.
This algorithm is derived from the GDAL ogrinfo utility.
Parameters
Label Název Type Popis
Input layer INPUT [vector: any] Input vector layer
Summary output
only
Optional
SUMMARY_ONLY [boolean]
Default: True
Suppress
metadata info
Optional
NO_METADATA [boolean]
Default: False
Layer information OUTPUT [html]
Default: [Save
to temporary
file]
Specify the output HTML file that includes
the file information. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
If no HTML-file is defined the output will
be written to a temporary file
Outputs
Label Název Type Popis
Layer information OUTPUT [html] The output HTML-file that includes the file
information.
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Python code
Algorithm ID: gdal:ogrinfo
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.3 LAStools algorithm provider
LAStools is a collection of highly efficient, multicore command line tools for LiDAR data processing.
24.3.1 blast2dem
Popis
Turns points (up to billions) via seamless Delaunay triangulation implemented using streaming into large elevation,
intensity, or RGB rasters.
For more info see the blast2dem page and its online README file.
Parameters
Label Název Type Popis
verbose VERBOSE [boolean]
Default: False
Generates more textual control output to the
console
open LAStools
GUI
GUI [boolean]
Default: False
Starts the GUI of LAStools with pre-populated
input files
input LAS/LAZ
file
INPUT_LASLAZ [file] The file containing the points to be rastered
in LAS/LAZ format.
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Label Název Type Popis
filter (by return,
classification, flag)
FILTER_RETURN_CLASS_FLAGS1[enumeration]
Default: 0
Specifies which points to use to construct
the temporary TIN that is then rasterized.
One of:
• 0 — —
• 1 — keep_last
• 2 — keep_first
• 3 — keep_middle
• 4 — keep_single
• 5 — drop_single
• 6 — keep_double
• 7 — keep_class 2
• 8 — keep_class 2 8
• 9 — keep_class 8
• 10 — keep_class 6
• 11 — keep_class 9
• 12 — keep_class 3 4 5
• 13 — keep_class 2 6
• 14 — drop_class 7
• 15 — drop_withheld
• 16 — drop_synthetic
• 17 — drop_overlap
• 18 — keep_withheld
• 19 — keep_synthetic
• 20 — keep_keypoint
• 21 — keep_overlap
step size / pixel size STEP [number]
Default: 1.0
Specifies the size of the cells of the grid the
TIN is rasterized onto
Attribute ATTRIBUTE [enumeration]
Default: 0
Specifies the attribute that is to be rastered.
One of:
• 0 — elevation
• 1 — slope
• 2 — intensity
• 3 — rgb
Product PRODUCT [enumeration]
Default: 0
Specifies how the attribute is to be turned
into raster values. One of:
• 0 — actual values
• 1 — hillshade
• 2 — gray
• 3 — false
Use tile bounding
box (after tiling
with buffer)
USE_TILE_BB [boolean]
Default: False
Specifies to limit the rastered area to the
tile bounding box (only meaningful for
input LAS/LAZ tiles that were created with
lastile).
additional
command line
parameter(s)
Optional
ADDITIONAL_OPTIONS[string]
Default: ‚‘
Specifies other command-line switches not
available via this menu but known to the
(advanced) LAStools user.
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Label Název Type Popis
Output raster file OUTPUT_RASTER [raster]
Default: [Skip
output]
Specifies where the output raster is stored.
Use image rasters like TIF, PNG, and JPG
for false color, gray ramps, and hillshades.
Use value rasters like TIF, BIL, IMG, ASC,
DTM, FLT, XYZ, and CSV for actual
values. One of:
• Skip Output
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Output raster file OUTPUT_RASTER [raster] The output raster
Python code
Algorithm ID: lastools:blast2dem
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.3.2 blast2iso
Popis
Turns points (up to billions) via seamless Delaunay triangulation implemented using streaming into iso-contour lines.
For more info see the blast2iso page and its online README file.
Parameters
Label Název Type Popis
verbose VERBOSE [boolean]
Default: False
Generates more textual control output to the
console
open LAStools
GUI
GUI [boolean]
Default: False
Starts the GUI of LAStools with pre-populated
input files
input LAS/LAZ
file
INPUT_LASLAZ [file] The file containing the points to be used for
creating iso-contour lines.
smooth
underlying TIN
SMOOTH [number]
Default: 0
Specifies if and with how many passes the
temporary TIN should be smoothed
extract isoline
with a spacing of
ISO_EVERY [number]
Default: 10.0
Specifies spacing at which iso-contour lines
are getting extracted (contour interval)
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Label Název Type Popis
clean isolines
shorter than (0 =
do not clean)
CLEAN [number]
Default: 0.0
Omits iso-contour lines that are shorter than
the specified length
simplify segments
shorter than (0 =
do not simplify)
SIMPLIFY_LENGTH[number]
Default: 0.0
Rudimentary simplification of iso-contour
line segments that are shorter than the
specified length.
simplify segment
pairs with area
less than (0 = do
not simplify)
SIMPLIFY_AREA [number]
Default: 0.0
Rudimentary simplification of bumps
formed by consecutive line segments
whose area is smaller than the specified
size.
additional
command line
parameter(s)
Optional
ADDITIONAL_OPTIONS[string]
Default: ‚‘
Specifies other command-line switches not
available via this menu but known to the
(advanced) LAStools user.
Output vector file OUTPUT_VECTOR [vector: line]
Default: [Skip
output]
Specifies where the output vector
is stored. Use SHP or WKT output
files. If your input LiDAR file is in
geographic coordinates (long/lat) or has
geo-referencing information (but only then)
you can also create a KML output file. One
of:
• Skip Output
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Output vector file OUTPUT_VECTOR [vector: line] The output line vector layer with contours
Python code
Algorithm ID: lastools:blast2iso
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.3.3 las2dem
Popis
Turns points (up to 20 million) via a temporary Delaunay triangulation that is rasterized with a user-defined step size
into an elevation, intensity, or RGB raster.
For more info see the las2dem page and its online README file.
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Parameters
Label Název Type Popis
verbose VERBOSE [boolean]
Default: False
Generates more textual control output to the
console
run new 64 bit
executable
CPU64 [boolean]
Default: False
open LAStools
GUI
GUI [boolean]
Default: False
Starts the GUI of LAStools with pre-populated
input files
input LAS/LAZ
file
INPUT_LASLAZ [file] The file containing the points to be rastered
in LAS/LAZ format.
filter (by return,
classification,
flags)
FILTER_RETURN_CLASS_FLAGS1[enumeration]
Default: 0
Specifies which points to use to construct
the temporary TIN that is then rasterized.
One of:
• 0 — —
• 1 — keep_last
• 2 — keep_first
• 3 — keep_middle
• 4 — keep_single
• 5 — drop_single
• 6 — keep_double
• 7 — keep_class 2
• 8 — keep_class 2 8
• 9 — keep_class 8
• 10 — keep_class 6
• 11 — keep_class 9
• 12 — keep_class 3 4 5
• 13 — keep_class 3
• 14 — keep_class 4
• 15 — keep_class 5
• 16 — keep_class 2 6
• 17 — drop_class 7
• 18 — drop_withheld
• 19 — drop_synthetic
• 20 — drop_overlap
• 21 — keep_withheld
• 22 — keep_synthetic
• 23 — keep_keypoint
• 24 — keep_overlap
step size / pixel size STEP [number]
Default: 1.0
Specifies the size of the cells of the grid the
TIN is rasterized onto
Attribute ATTRIBUTE [enumeration]
Default: 0
Specifies the attribute to rasterise. One of:
• 0 — elevation
• 1 — slope
• 2 — intensity
• 3 — rgb
• 4 — edge_longest
• 5 — edge_shortest
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Label Název Type Popis
Product PRODUCT [enumeration]
Default: 0
Specifies how the attribute is to be turned
into raster values. One of:
• 0 — actual values
• 1 — hillshade
• 2 — gray
• 3 — false
Use tile bounding
box (after tiling
with buffer)
USE_TILE_BB [boolean]
Default: False
Specifies to limit the rastered area to the
tile bounding box (only meaningful for
input LAS/LAZ tiles that were created with
lastile).
additional
command line
parameter(s)
Optional
ADDITIONAL_OPTIONS[string]
Default: ‚‘
Specifies other command-line switches not
available via this menu but known to the
(advanced) LAStools user.
Output raster file OUTPUT_RASTER [raster]
Default: [Skip
output]
Specifies where the output raster is stored.
Use image rasters like TIF, PNG, and JPG
for false color, gray ramps, and hillshades.
Use value rasters like TIF, BIL, IMG, ASC,
DTM, FLT, XYZ, and CSV for actual
values. One of:
• Skip Output
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Output raster file OUTPUT_RASTER [raster] The output raster
Python code
Algorithm ID: lastools:las2dem
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.3.4 las2iso
Popis
Turns point clouds (up to 20 million per file) into iso-contour lines by creating a temporary Delaunay triangulation
on which the contours are then traced.
For more info see the las2iso page and its online README file.
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Parameters
Label Název Type Popis
verbose VERBOSE [boolean]
Default: False
Generates more textual control output to the
console
run new 64 bit
executable
CPU64 [boolean]
Default: False
open LAStools
GUI
GUI [boolean]
Default: False
Starts the GUI of LAStools with pre-populated
input files
input LAS/LAZ
file
INPUT_LASLAZ [file] The file containing the points to be used for
creating iso-contour lines.
smooth
underlying TIN
SMOOTH [number]
Default: 0
Specifies if and with how many passes the
temporary TIN should be smoothed
extract isoline
with a spacing of
ISO_EVERY [number]
Default: 10.0
Specifies spacing at which iso-contour lines
are getting extracted (contour interval)
clean isolines
shorter than (0 =
do not clean)
CLEAN [number]
Default: 0.0
Omits iso-contour lines that are shorter than
the specified length
simplify segments
shorter than (0 =
do not simplify)
SIMPLIFY_LENGTH[number]
Default: 0.0
Rudimentary simplification of iso-contour
line segments that are shorter than the
specified length.
simplify segment
pairs with area
less than (0 = do
not simplify)
SIMPLIFY_AREA [number]
Default: 0.0
Rudimentary simplification of bumps
formed by consecutive line segments
whose area is smaller than the specified
size.
additional
command line
parameter(s)
Optional
ADDITIONAL_OPTIONS[string]
Default: ‚‘
Specifies other command-line switches not
available via this menu but known to the
(advanced) LAStools user.
Output vector file OUTPUT_VECTOR [vector: line]
Default: [Skip
output]
Specifies where the output vector
is stored. Use SHP or WKT output
files. If your input LiDAR file is in
geographic coordinates (long/lat) or has
geo-referencing information (but only then)
you can also create a KML output file. One
of:
• Skip Output
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Output vector file OUTPUT_VECTOR [vector: line] The output line vector layer with contours
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Python code
Algorithm ID: lastools:las2iso
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.3.5 las2las_filter
Popis
Uses las2las to filter LiDAR points based on different attributes and to write the surviving subset of points to a new
LAZ or LAS file.
For more info see the las2las page and its online README file.
Parameters
Label Název Type Popis
verbose VERBOSE [boolean]
Default: False
Generates more textual control output to the
console
run new 64 bit
executable
CPU64 [boolean]
Default: False
open LAStools
GUI
GUI [boolean]
Default: False
Starts the GUI of LAStools with pre-populated
input files
input LAS/LAZ
file
INPUT_LASLAZ [file] The file containing the points to be used for
creating iso-contour lines.
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Label Název Type Popis
filter (by return,
classification,
flags)
FILTER_RETURN_CLASS_FLAGS1[enumeration]
Default: 0
Filters points based on various options such
as return, classification, or flags. One of:
• 0 — —
• 1 — keep_last
• 2 — keep_first
• 3 — keep_middle
• 4 — keep_single
• 5 — drop_single
• 6 — keep_double
• 7 — keep_class 2
• 8 — keep_class 2 8
• 9 — keep_class 8
• 10 — keep_class 6
• 11 — keep_class 9
• 12 — keep_class 3 4 5
• 13 — keep_class 3
• 14 — keep_class 4
• 15 — keep_class 5
• 16 — keep_class 2 6
• 17 — drop_class 7
• 18 — drop_withheld
• 19 — drop_synthetic
• 20 — drop_overlap
• 21 — keep_withheld
• 22 — keep_synthetic
• 23 — keep_keypoint
• 24 — keep_overlap
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Label Název Type Popis
second filter
(by return,
classification,
flags)
FILTER_RETURN_CLASS_FLAGS2[enumeration]
Default: 0
Filters points based on various options such
as return, classification, or flags. One of:
• 0 — —
• 1 — keep_last
• 2 — keep_first
• 3 — keep_middle
• 4 — keep_single
• 5 — drop_single
• 6 — keep_double
• 7 — keep_class 2
• 8 — keep_class 2 8
• 9 — keep_class 8
• 10 — keep_class 6
• 11 — keep_class 9
• 12 — keep_class 3 4 5
• 13 — keep_class 3
• 14 — keep_class 4
• 15 — keep_class 5
• 16 — keep_class 2 6
• 17 — drop_class 7
• 18 — drop_withheld
• 19 — drop_synthetic
• 20 — drop_overlap
• 21 — keep_withheld
• 22 — keep_synthetic
• 23 — keep_keypoint
• 24 — keep_overlap
filter (by
coordinate,
intensity, GPS
time, …)
FILTER_COORDS_INTENSITY1[enumeration]
Default: 0
Filters points based on various other options
(that require a value as argument). One of:
• 0 — —
• 1 — drop_x_above
• 2 — drop_x_below
• 3 — drop_y_above
• 4 — drop_y_below
• 5 — drop_z_above
• 6 — drop_z_below
• 7 — drop_intensity_above
• 8 — drop_intensity_below
• 9 — drop_gps_time_above
• 10 — drop_gps_time_below
• 11 — drop_scan_angle_above
• 12 — drop_scan_angle_below
• 13 — keep_point_source
• 14 — drop_point_source
• 15 — drop_point_source_above
• 16 — drop_point_source_below
• 17 — keep_user_data
• 18 — drop_user_data
• 19 — drop_user_data_above
• 20 — drop_user_data_below
• 21 — keep_every_nth
• 22 — keep_random_fraction
• 23 — thin_with_grid
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Label Název Type Popis
value for filter
(by coordinate,
intensity, GPS
time, …)
FILTER_COORDS_INTENSITY1_ARG[number]
Default: None
The value to use as the argument for the
filter selected above
second filter
(by coordinate,
intensity, GPS
time, …)
FILTER_COORDS_INTENSITY2[enumeration]
Default: 0
Filters points based on various other options
(that require a value as argument). One of:
• 0 — —
• 1 — drop_x_above
• 2 — drop_x_below
• 3 — drop_y_above
• 4 — drop_y_below
• 5 — drop_z_above
• 6 — drop_z_below
• 7 — drop_intensity_above
• 8 — drop_intensity_below
• 9 — drop_gps_time_above
• 10 — drop_gps_time_below
• 11 — drop_scan_angle_above
• 12 — drop_scan_angle_below
• 13 — keep_point_source
• 14 — drop_point_source
• 15 — drop_point_source_above
• 16 — drop_point_source_below
• 17 — keep_user_data
• 18 — drop_user_data
• 19 — drop_user_data_above
• 20 — drop_user_data_below
• 21 — keep_every_nth
• 22 — keep_random_fraction
• 23 — thin_with_grid
value for
second filter
(by coordinate,
intensity, GPS
time, …)
FILTER_COORDS_INTENSITY2_ARG[number]
Default: None
The value to use as the argument for the
filter selected above
additional
command line
parameter(s)
Optional
ADDITIONAL_OPTIONS[string]
Default: ‚‘
Specifies other command-line switches not
available via this menu but known to the
(advanced) LAStools user.
Output LAS/LAZ
file
OUTPUT_LASLAZ [file]
Default: [Skip
output]
Specifies where the output point cloud
is stored. Use LAZ for compressed output,
LAS for uncompressed output, and TXT for
ASCII. One of:
• Skip Output
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Output LAS/LAZ
file
OUTPUT_LASLAZ [file] The output LAS/LAZ format file
Python code
Algorithm ID: lastools:las2las_filter
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.3.6 las2las_project
Transform LAS/LAZ files in a folder to another CRS.
Parameters
Label Název Type Popis
verbose VERBOSE [boolean]
Default: False
Generates more textual control output to the
console
run new 64 bit
executable
CPU64 [boolean]
Default: False
open LAStools
GUI
GUI [boolean]
Default: False
Starts the GUI of LAStools with pre-populated
input files
input LAS/LAZ
file
INPUT_LASLAZ [file] Input LAS/LAZ file
source projection SOURCE_PROJECTION[enumeration]
Default: 0
One of:
• 0 — —
• 1 — epsg
• 2 — utm
• 3 — sp83
• 4 — sp27
• 5 — longlat
• 6 — latlong
• 7 — ecef
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Label Název Type Popis
source utm zone SOURCE_UTM [enumeration]
Default: 0
One of:
• 0 — —
• 1 — 1 (north)
• 2 — 2 (north)
• 3 — 3 (north)
• 4 — 4 (north)
• 5 — 5 (north)
• 6 — 6 (north)
• 7 — 7 (north)
• 8 — 8 (north)
• 9 — 9 (north)
• 10 — 10 (north)
• 11 — 11 (north)
• 12 — 12 (north)
• 13 — 13 (north)
• 14 — 14 (north)
• 15 — 15 (north)
• 16 — 16 (north)
• 17 — 17 (north)
• 18 — 18 (north)
• 19 — 19 (north)
• 20 — 20 (north)
• 21 — 21 (north)
• 22 — 22 (north)
• 23 — 23 (north)
• 24 — 24 (north)
• 25 — 25 (north)
• 26 — 26 (north)
• 27 — 27 (north)
• 28 — 28 (north)
• 29 — 29 (north)
• 30 — 30 (north)
• 31 — 31 (north)
• 32 — 32 (north)
• 33 — 33 (north)
• 34 — 34 (north)
• 35 — 35 (north)
• 36 — 36 (north)
• 37 — 37 (north)
• 38 — 38 (north)
• 39 — 39 (north)
• 40 — 40 (north)
• 41 — 41 (north)
• 42 — 42 (north)
• 43 — 43 (north)
• 44 — 44 (north)
• 45 — 45 (north)
• 46 — 46 (north)
• 47 — 47 (north)
• 48 — 48 (north)
• 49 — 49 (north)
• 50 — 50 (north)
• 51 — 51 (north)
• 52 — 52 (north)
• 53 — 53 (north)
• 54 — 54 (north)
• 55 — 55 (north)
• 56 — 56 (north)
• 57 — 57 (north)
• 58 — 58 (north)
• 59 — 59 (north)
• 60 — 60 (north)
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Label Název Type Popis
source state plane
code
SOURCE_SP [enumeration]
Default: 0
One of:
• 0 — —
• 1 — AK_10
• 2 — AK_2
• 3 — AK_3
• 4 — AK_4
• 5 — AK_5
• 6 — AK_6
• 7 — AK_7
• 8 — AK_8
• 9 — AK_9
• 10 — AL_E
• 11 — AL_W
• 12 — AR_N
• 13 — AR_S
• 14 — AZ_C
• 15 — AZ_E
• 16 — AZ_W
• 17 — CA_I
• 18 — CA_II
• 19 — CA_III
• 20 — CA_IV
• 21 — CA_V
• 22 — CA_VI
• 23 — CA_VII
• 24 — CO_C
• 25 — CO_N
• 26 — CO_S
• 27 — CT
• 28 — DE
• 29 — FL_E
• 30 — FL_N
• 31 — FL_W
• 32 — GA_E
• 33 — GA_W
• 34 — HI_1
• 35 — HI_2
• 36 — HI_3
• 37 — HI_4
• 38 — HI_5
• 39 — IA_N
• 40 — IA_S
• 41 — ID_C
• 42 — ID_E
• 43 — ID_W
• 44 — IL_E
• 45 — IL_W
• 46 — IN_E
• 47 — IN_W
• 48 — KS_N
• 49 — KS_S
• 50 — KY_N
• 51 — KY_S
• 52 — LA_N
• 53 — LA_S
• 54 — MA_I
• 55 — MA_M
• 56 — MD
• 57 — ME_E
• 58 — ME_W
• 59 — MI_C
• 60 — MI_N
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Label Název Type Popis
target projection TARGET_PROJECTION[enumeration]
Default: 0
One of:
• 0 — —
• 1 — epsg
• 2 — utm
• 3 — sp83
• 4 — sp27
• 5 — longlat
• 6 — latlong
• 7 — ecef
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Label Název Type Popis
target utm zone TARGET_UTM [enumeration]
Default: 0
One of:
• 0 — —
• 1 — 1 (north)
• 2 — 2 (north)
• 3 — 3 (north)
• 4 — 4 (north)
• 5 — 5 (north)
• 6 — 6 (north)
• 7 — 7 (north)
• 8 — 8 (north)
• 9 — 9 (north)
• 10 — 10 (north)
• 11 — 11 (north)
• 12 — 12 (north)
• 13 — 13 (north)
• 14 — 14 (north)
• 15 — 15 (north)
• 16 — 16 (north)
• 17 — 17 (north)
• 18 — 18 (north)
• 19 — 19 (north)
• 20 — 20 (north)
• 21 — 21 (north)
• 22 — 22 (north)
• 23 — 23 (north)
• 24 — 24 (north)
• 25 — 25 (north)
• 26 — 26 (north)
• 27 — 27 (north)
• 28 — 28 (north)
• 29 — 29 (north)
• 30 — 30 (north)
• 31 — 31 (north)
• 32 — 32 (north)
• 33 — 33 (north)
• 34 — 34 (north)
• 35 — 35 (north)
• 36 — 36 (north)
• 37 — 37 (north)
• 38 — 38 (north)
• 39 — 39 (north)
• 40 — 40 (north)
• 41 — 41 (north)
• 42 — 42 (north)
• 43 — 43 (north)
• 44 — 44 (north)
• 45 — 45 (north)
• 46 — 46 (north)
• 47 — 47 (north)
• 48 — 48 (north)
• 49 — 49 (north)
• 50 — 50 (north)
• 51 — 51 (north)
• 52 — 52 (north)
• 53 — 53 (north)
• 54 — 54 (north)
• 55 — 55 (north)
• 56 — 56 (north)
• 57 — 57 (north)
• 58 — 58 (north)
• 59 — 59 (north)
• 60 — 60 (north)
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Label Název Type Popis
target state plane
code
TARGET_SP [enumeration]
Default: 0
One of:
• 0 — —
• 1 — AK_10
• 2 — AK_2
• 3 — AK_3
• 4 — AK_4
• 5 — AK_5
• 6 — AK_6
• 7 — AK_7
• 8 — AK_8
• 9 — AK_9
• 10 — AL_E
• 11 — AL_W
• 12 — AR_N
• 13 — AR_S
• 14 — AZ_C
• 15 — AZ_E
• 16 — AZ_W
• 17 — CA_I
• 18 — CA_II
• 19 — CA_III
• 20 — CA_IV
• 21 — CA_V
• 22 — CA_VI
• 23 — CA_VII
• 24 — CO_C
• 25 — CO_N
• 26 — CO_S
• 27 — CT
• 28 — DE
• 29 — FL_E
• 30 — FL_N
• 31 — FL_W
• 32 — GA_E
• 33 — GA_W
• 34 — HI_1
• 35 — HI_2
• 36 — HI_3
• 37 — HI_4
• 38 — HI_5
• 39 — IA_N
• 40 — IA_S
• 41 — ID_C
• 42 — ID_E
• 43 — ID_W
• 44 — IL_E
• 45 — IL_W
• 46 — IN_E
• 47 — IN_W
• 48 — KS_N
• 49 — KS_S
• 50 — KY_N
• 51 — KY_S
• 52 — LA_N
• 53 — LA_S
• 54 — MA_I
• 55 — MA_M
• 56 — MD
• 57 — ME_E
• 58 — ME_W
• 59 — MI_C
• 60 — MI_N
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Label Název Type Popis
additional
command line
parameter(s)
Optional
ADDITIONAL_OPTIONS[string]
Default: ‚‘
Specifies other command-line switches not
available via this menu but known to the
(advanced) LAStools user.
Output LAS/LAZ
file
OUTPUT_LASLAZ [folder]
Default: [Save
to temporary
folder]
Specifies where the folder for the output
point clouds. One of:
• Skip Output
• Save to a Temporary Directory
• Save to Directory…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Output LAS/LAZ
file
OUTPUT_LASLAZ [file] The output LAS/LAZ format file
Python code
Algorithm ID: lastools:las2las_project
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.3.7 las2las_transform
Popis
Uses las2las to filter LiDAR points based on different attributes and to write the surviving subset of points to a new
LAZ or LAS file.
For more info see the las2las page and its online README file.
Parameters
Label Název Type Popis
verbose VERBOSE [boolean]
Default: False
Generates more textual control output to the
console
run new 64 bit
executable
CPU64 [boolean]
Default: False
open LAStools
GUI
GUI [boolean]
Default: False
Starts the GUI of LAStools with pre-populated
input files
input LAS/LAZ
file
INPUT_LASLAZ [file] The first file containing points to be merged
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Label Název Type Popis
transform
(coordinates)
TRANSFORM_COORDINATE1[enumeration]
Default: 0
Either translate, scale, or clamp the X, Y, or
Z coordinate by the value specified below.
One of:
• 0 — —
• 1 — translate_x
• 2 — translate_y
• 3 — translate_z
• 4 — scale_x
• 5 — scale_y
• 6 — scale_z
• 7 — clamp_z_above
• 8 — clamp_z_below
value for
transform
(coordinates)
TRANSFORM_COORDINATE1_ARG[string]
Default: ‚‘
The value that specifies the amount of
translating, scaling, or clamping done by the
transform selected above.
second transform
(coordinates)
TRANSFORM_COORDINATE2[enumeration]
Default: 0
Either translate, scale, or clamp the X, Y, or
Z coordinate by the value specified below.
One of:
• 0 — —
• 1 — translate_x
• 2 — translate_y
• 3 — translate_z
• 4 — scale_x
• 5 — scale_y
• 6 — scale_z
• 7 — clamp_z_above
• 8 — clamp_z_below
value for second
transform
(coordinates)
TRANSFORM_COORDINATE2_ARG[string]
Default: ‚‘
The value that specifies the amount of
translating, scaling, or clamping done by the
transform selected above.
transform
(intensities,
scan angles, GPS
times, …)
TRANSFORM_OTHER1[enumeration]
Default: 0
Either translate, scale, or clamp the X, Y, or
Z coordinate by the value specified below.
One of:
• 0 — —
• 1 — scale_intensity
• 2 — translate_intensity
• 3 — clamp_intensity_above
• 4 — clamp_intensity_below
• 5 — scale_scan_angle
• 6 — translate_scan_angle
• 7 — translate_gps_time
• 8 — set_classification
• 9 — set_user_data
• 10 — set_point_source
• 11 — scale_rgb_up
• 12 — scale_rgb_down
• 13 — repair_zero_returns
value for
transform
(intensities,
scan angles, GPS
times, …)
TRANSFORM_OTHER1_ARG[string]
Default: ‚‘
The value that specifies the amount of
scaling, translating, clamping or setting that
is done by the transform selected above.
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Label Název Type Popis
second transform
(intensities, scan
angles, GPS times,
…)
TRANSFORM_OTHER2[enumeration]
Default: 0
Either translate, scale, or clamp the X, Y, or
Z coordinate by the value specified below.
One of:
• 0 — —
• 1 — scale_intensity
• 2 — translate_intensity
• 3 — clamp_intensity_above
• 4 — clamp_intensity_below
• 5 — scale_scan_angle
• 6 — translate_scan_angle
• 7 — translate_gps_time
• 8 — set_classification
• 9 — set_user_data
• 10 — set_point_source
• 11 — scale_rgb_up
• 12 — scale_rgb_down
• 13 — repair_zero_returns
value for second
transform
(intensities,
scan angles, GPS
times, …)
TRANSFORM_OTHER2_ARG[string]
Default: ‚‘
The value that specifies the amount of
scaling, translating, clamping or setting that
is done by the transform selected above.
operations (first 7
need an argument)
OPERATION [enumeration]
Default: 0
One of:
• 0 — —
• 1 — set_point_type
• 2 — set_point_size
• 3 — set_version_minor
• 4 — set_version_major
• 5 — start_at_point
• 6 — stop_at_point
• 7 — remove_vlr
• 8 — auto_reoffset
• 9 — week_to_adjusted
• 10 — adjusted_to_week
• 11 — auto reoffset
• 12 — scale_rgb_up
• 13 — scale_rgb_down
• 14 — remove_all_vlrs
• 15 — remove_extra
• 16 — clip_to_bounding_box
argument for
operation
OPERATIONARG [string]
Default: ‚‘
The value to use as the argument for the
operation selected above
additional
command line
parameter(s)
Optional
ADDITIONAL_OPTIONS[string]
Default: ‚‘
Specifies other command-line switches not
available via this menu but known to the
(advanced) LAStools user.
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Label Název Type Popis
Output LAS/LAZ
file
OUTPUT_LASLAZ [file]
Default: [Skip
output]
Specifies where the output point cloud
is stored. Use LAZ for compressed output,
LAS for uncompressed output, and TXT for
ASCII. One of:
• Skip Output
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Output LAS/LAZ
file
OUTPUT_LASLAZ [file] The output (merged) LAS/LAZ format file
Python code
Algorithm ID: lastools:las2las_transform
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.3.8 las2txt
Popis
Translates a LAS/LAZ file to a text file.
Parameters
Label Název Type Popis
verbose VERBOSE [boolean]
Default: False
run new 64 bit
executable
CPU64 [boolean]
Default: False
open LAStools
GUI
GUI [boolean]
Default: False
input LAS/LAZ
file
INPUT_LASLAZ [file]
Default: None
parse_string PARSE [string]
Default: ‚xyz‘
additional
command line
parameters
Optional
ADDITIONAL_OPTIONS[string]
Default: ‚‘
Specifies other command-line switches not
available via this menu but known to the
(advanced) LAStools user.
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Label Název Type Popis
Output ASCII file OUTPUT_GENERIC [file]
Default: [Create
temporary
layer]
Specify the output file. One of:
• Create Temporary Layer
(TEMPORARY_OUTPUT)
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Output ASCII file OUTPUT_GENERIC [file] The output file
Python code
Algorithm ID: lastools:las2txt
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.3.9 lasindex
Popis
<put algorithm description here>
Parameters
Label Název Type Popis
verbose VERBOSE [boolean]
Default: False
run new 64 bit
executable
CPU64 [boolean]
Default: False
open LAStools
GUI
GUI [boolean]
Default: False
input LAS/LAZ
file
INPUT_LASLAZ [file]
Default: None
append *.lax file to
*.laz file
APPEND_LAX [boolean]
Default: False
is mobile or
terrestrial LiDAR
(not airborne)
MOBILE_OR_TERRESTRIAL[boolean]
Default: False
additional
command line
parameters
Optional
ADDITIONAL_OPTIONS[string]
Default: ‚‘
Specifies other command-line switches not
available via this menu but known to the
(advanced) LAStools user.
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Outputs
The algorithm has no output.
Python code
Algorithm ID: lastools:lasindex
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.3.10 lasgrid
Grids a selected attribute (e.g. elevation, intensity, classification, scan angle, …) of a large point clouds with a user-defined
step size onto raster using a particular method (e.g. min, max, average).
For more info see the lasgrid page and its online README file.
Parameters
Label Název Type Popis
verbose VERBOSE [boolean]
Default: False
Generates more textual control output to the
console
run new 64 bit
executable
CPU64 [boolean]
Default: False
open LAStools
GUI
GUI [boolean]
Default: False
Starts the GUI of LAStools with pre-populated
input files
input LAS/LAZ
file
INPUT_LASLAZ [file] The file containing the points to be rastered
in LAS/LAZ format.
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Label Název Type Popis
filter (by return,
classification,
flags)
FILTER_RETURN_CLASS_FLAGS1[enumeration]
Default: 0
Specifies the subset of points to use for the
gridding. One of:
• 0 — —
• 1 — keep_last
• 2 — keep_first
• 3 — keep_middle
• 4 — keep_single
• 5 — drop_single
• 6 — keep_double
• 7 — keep_class 2
• 8 — keep_class 2 8
• 9 — keep_class 8
• 10 — keep_class 6
• 11 — keep_class 9
• 12 — keep_class 3 4 5
• 13 — keep_class 3
• 14 — keep_class 4
• 15 — keep_class 5
• 16 — keep_class 2 6
• 17 — drop_class 7
• 18 — drop_withheld
• 19 — drop_synthetic
• 20 — drop_overlap
• 21 — keep_withheld
• 22 — keep_synthetic
• 23 — keep_keypoint
• 24 — keep_overlap
step size / pixel size STEP [number]
Default: 1.0
Specifies the size of the cells of the grid the
TIN is rasterized onto
Attribute ATTRIBUTE [enumeration]
Default: 0
Specifies the attribute to rasterise. One of:
• 0 — elevation
• 1 — intensity
• 2 — rgb
• 3 — classification
Method METHOD [enumeration]
Default: 0
Specifies how the attributes falling into one
cell are turned into a raster value. One of:
• 0 — lowest
• 1 — heighest
• 2 — average
• 3 — stddev
use tile bounding
box (after tiling
with buffer)
USE_TILE_BB [boolean]
Default: False
Specifies to limit the rastered area to the
tile bounding box (only meaningful for
input LAS/LAZ tiles that were created with
lastile).
additional
command line
parameter(s)
Optional
ADDITIONAL_OPTIONS[string]
Default: ‚‘
Specifies other command-line switches not
available via this menu but known to the
(advanced) LAStools user.
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Label Název Type Popis
Output raster file OUTPUT_RASTER [raster]
Default: [Skip
output]
Specifies where the output raster is stored.
Use image rasters like TIF, PNG, and JPG
for false color, gray ramps, and hillshades.
Use value rasters like TIF, BIL, IMG, ASC,
DTM, FLT, XYZ, and CSV for actual
values. One of:
• Skip Output
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Output raster file OUTPUT_RASTER [raster] The output raster
Python code
Algorithm ID: lastools:lasgrid
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.3.11 lasinfo
Parameters
Label Název Type Popis
verbose VERBOSE [boolean]
Default: False
Generates more textual control output to the
console
run new 64 bit
executable
CPU64 [boolean]
Default: False
open LAStools
GUI
GUI [boolean]
Default: False
Starts the GUI of LAStools with pre-populated
input files
input LAS/LAZ
file
INPUT_LASLAZ [file] The file to get information about.
compute density COMPUTE_DENSITY[boolean]
Default: False
repair bounding
box
REPAIR_BB [boolean]
Default: False
repair counters REPAIR_COUNTERS[boolean]
Default: False
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Label Název Type Popis
histogram HISTO1 [enumeration]
Default: 0
First histogram. One of:
• 0 — —
• 1 — x
• 2 — y
• 3 — z
• 4 — intensity
• 5 — classification
• 6 — scan_angle
• 7 — user_data
• 8 — point_source
• 9 — gps_time
• 10 — X
• 11 — Y
• 12 — Z
• 13 — attribute0
• 14 — attribute1
• 15 — attribute2
bin size HISTO1_BIN [number]
Default: 1.0
histogram HISTO2 [enumeration]
Default: 0
Second histogram. One of:
• 0 — —
• 1 — x
• 2 — y
• 3 — z
• 4 — intensity
• 5 — classification
• 6 — scan_angle
• 7 — user_data
• 8 — point_source
• 9 — gps_time
• 10 — X
• 11 — Y
• 12 — Z
• 13 — attribute0
• 14 — attribute1
• 15 — attribute2
bin size HISTO2_BIN [number]
Default: 1.0
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Label Název Type Popis
histogram HISTO3 [enumeration]
Default: 0
Third histogram. One of:
• 0 — —
• 1 — x
• 2 — y
• 3 — z
• 4 — intensity
• 5 — classification
• 6 — scan_angle
• 7 — user_data
• 8 — point_source
• 9 — gps_time
• 10 — X
• 11 — Y
• 12 — Z
• 13 — attribute0
• 14 — attribute1
• 15 — attribute2
bin size HISTO3_BIN [number]
Default: 1.0
additional
command line
parameter(s)
Optional
ADDITIONAL_OPTIONS[string]
Default: ‚‘
Specifies other command-line switches not
available via this menu but known to the
(advanced) LAStools user.
Output ASCII file OUTPUT_GENERIC [file]
Default: [Skip
output]
Specifies where the output is stored. One of:
• Skip Output
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Output ASCII file OUTPUT_GENERIC [file] The file with the output
Python code
Algorithm ID: lastools:lasinfo
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
1226 Kapitola 24. Processing providers and algorithms
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24.3.12 lasmerge
Merge up to seven LAS/LAZ files into one.
Parameters
Label Název Type Popis
verbose VERBOSE [boolean]
Default: False
Generates more textual control output to the
console
run new 64 bit
executable
CPU64 [boolean]
Default: False
open LAStools
GUI
GUI [boolean]
Default: False
Starts the GUI of LAStools with pre-populated
input files
files are flightlines FILES_ARE_FLIGHTLINES[boolean]
Default: False
apply file source
ID
APPLY_FILE_SOURCE_ID[boolean]
Default: False
input LAS/LAZ
file
INPUT_LASLAZ [file] The first file containing points to be merged
2nd file
Optional
FILE2 [file] The second file to merge
3rd file
Optional
FILE3 [file] The third file to merge
4th file
Optional
FILE4 [file] The fourth file to merge
5th file
Optional
FILE5 [file] The fifth file to merge
6th file
Optional
FILE6 [file] The sixth file to merge
7th file
Optional
FILE7 [file] The seventh file to merge
additional
command line
parameter(s)
Optional
ADDITIONAL_OPTIONS[string]
Default: ‚‘
Specifies other command-line switches not
available via this menu but known to the
(advanced) LAStools user.
Output LAS/LAZ
file
OUTPUT_LASLAZ [file]
Default: [Skip
output]
Specifies where the output point cloud
is stored. Use LAZ for compressed output,
LAS for uncompressed output, and TXT for
ASCII. One of:
• Skip Output
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
Output LAS/LAZ
file
OUTPUT_LASLAZ [file] The output (merged) LAS/LAZ format file
Python code
Algorithm ID: lastools:lasmerge
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.3.13 lasprecision
Parameters
Label Název Type Popis
verbose VERBOSE [boolean]
Default: False
Generates more textual control output to the
console
open LAStools
GUI
GUI [boolean]
Default: False
Starts the GUI of LAStools with pre-populated
input files
input LAS/LAZ
file
INPUT_LASLAZ [file] The file the input point cloud
additional
command line
parameter(s)
Optional
ADDITIONAL_OPTIONS[string]
Default: ‚‘
Specifies other command-line switches not
available via this menu but known to the
(advanced) LAStools user.
Output ASCII file OUTPUT_GENERIC [file]
Default: [Skip
output]
Specifies where the output ASCII file
is stored. One of:
• Skip Output
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Output ASCII file OUTPUT_GENERIC [file] The output ASCII file
1228 Kapitola 24. Processing providers and algorithms
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Python code
Algorithm ID: lastools:lasprecision
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.3.14 lasquery
Popis
<put algorithm description here>
Parameters
Label Název Type Popis
verbose VERBOSE [boolean]
Default: False
Generates more textual control output to the
console
open LAStools
GUI
GUI [boolean]
Default: False
Starts the GUI of LAStools with pre-populated
input files
input LAS/LAZ
file
INPUT_LASLAZ [file] The file the input point cloud
area of interest AOI [extent] The extent
additional
command line
parameter(s)
Optional
ADDITIONAL_OPTIONS[string]
Default: ‚‘
Specifies other command-line switches not
available via this menu but known to the
(advanced) LAStools user.
Outputs
Python code
Algorithm ID: lastools:lasquery
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.3. LAStools algorithm provider 1229
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24.3.15 lasvalidate
Parameters
Label Název Type Popis
input LAS/LAZ
file
INPUT_LASLAZ [file] The file the input point cloud
save report to
‚*_LVS.xml‘
ONE_REPORT_PER_FILE[boolean]
additional
command line
parameter(s)
Optional
ADDITIONAL_OPTIONS[string]
Default: ‚‘
Specifies other command-line switches not
available via this menu but known to the
(advanced) LAStools user.
Output XML file OUTPUT_GENERIC [file]
Default: [Skip
output]
Specifies where the output XML file
is stored. One of:
• Skip Output
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Output XML file OUTPUT_GENERIC [file] The output XML file
Python code
Algorithm ID: lastools:lasvalidate
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.3.16 laszip
Parameters
Label Název Type Popis
verbose VERBOSE [boolean]
Default: False
Generates more textual control output to the
console
run new 64 bit
executable
CPU64 [boolean]
Default: False
open LAStools
GUI
GUI [boolean]
Default: False
Starts the GUI of LAStools with pre-populated
input files
input LAS/LAZ
file
INPUT_LASLAZ [file] The file to be zipped
only report size REPORT_SIZE [boolean]
Default: False
continues on next page
1230 Kapitola 24. Processing providers and algorithms
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Tabulka 24.215 – pokračujte na předchozí stránce
Label Název Type Popis
create spatial
indexing file
(*.lax)
CREATE_LAX [boolean]
Default: False
append *.lax into
*.laz file
APPEND_LAX [boolean]
Default: False
additional
command line
parameter(s)
Optional
ADDITIONAL_OPTIONS[string]
Default: ‚‘
Specifies other command-line switches not
available via this menu but known to the
(advanced) LAStools user.
Output LAS/LAZ
file
OUTPUT_LASLAZ [file]
Default: [Skip
output]
Specifies where the output point cloud
is stored. Use LAZ for compressed output,
LAS for uncompressed output, and TXT for
ASCII. One of:
• Skip Output
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Output LAS/LAZ
file
OUTPUT_LASLAZ [file] The output file
Python code
Algorithm ID: lastools:laszip
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.3.17 txt2las
Parameters
Label Název Type Popis
verbose VERBOSE [boolean]
Default: False
Generates more textual control output to the
console
run new 64 bit
executable
CPU64 [boolean]
Default: False
open LAStools
GUI
GUI [boolean]
Default: False
Starts the GUI of LAStools with pre-populated
input files
input LAS/LAZ
file
INPUT_LASLAZ [file] The file to be zipped
parse lines as PARSE [string]
Default: ‚xyz‘
continues on next page
24.3. LAStools algorithm provider 1231
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Tabulka 24.216 – pokračujte na předchozí stránce
Label Název Type Popis
skip the first n
lines
SKIP [number]
Default: 0
resolution of x and
y coordinate
SCALE_FACTOR_XY[number]
Default: 0.01
resolution of
z coordinate
SCALE_FACTOR_Z [number]
Default: 0.01
resolution of
z coordinate
SCALE_FACTOR_Z [number]
Default: 0.01
source projection PROJECTION [enumeration]
Default: 0
One of:
• 0 — —
• 1 — epsg
• 2 — utm
• 3 — sp83
• 4 — sp27
• 5 — longlat
• 6 — latlong
• 7 — ecef
source epsg code EPSG_CODE [number]
continues on next page
1232 Kapitola 24. Processing providers and algorithms
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Tabulka 24.216 – pokračujte na předchozí stránce
Label Název Type Popis
utm zone UTM [enumeration]
Default: 0
One of:
• 0 — —
• 1 — 1 (north)
• 2 — 2 (north)
• 3 — 3 (north)
• 4 — 4 (north)
• 5 — 5 (north)
• 6 — 6 (north)
• 7 — 7 (north)
• 8 — 8 (north)
• 9 — 9 (north)
• 10 — 10 (north)
• 11 — 11 (north)
• 12 — 12 (north)
• 13 — 13 (north)
• 14 — 14 (north)
• 15 — 15 (north)
• 16 — 16 (north)
• 17 — 17 (north)
• 18 — 18 (north)
• 19 — 19 (north)
• 20 — 20 (north)
• 21 — 21 (north)
• 22 — 22 (north)
• 23 — 23 (north)
• 24 — 24 (north)
• 25 — 25 (north)
• 26 — 26 (north)
• 27 — 27 (north)
• 28 — 28 (north)
• 29 — 29 (north)
• 30 — 30 (north)
• 31 — 31 (north)
• 32 — 32 (north)
• 33 — 33 (north)
• 34 — 34 (north)
• 35 — 35 (north)
• 36 — 36 (north)
• 37 — 37 (north)
• 38 — 38 (north)
• 39 — 39 (north)
• 40 — 40 (north)
• 41 — 41 (north)
• 42 — 42 (north)
• 43 — 43 (north)
• 44 — 44 (north)
• 45 — 45 (north)
• 46 — 46 (north)
• 47 — 47 (north)
• 48 — 48 (north)
• 49 — 49 (north)
• 50 — 50 (north)
• 51 — 51 (north)
• 52 — 52 (north)
• 53 — 53 (north)
• 54 — 54 (north)
• 55 — 55 (north)
• 56 — 56 (north)
• 57 — 57 (north)
• 58 — 58 (north)
• 59 — 59 (north)
• 60 — 60 (north)
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Tabulka 24.216 – pokračujte na předchozí stránce
Label Název Type Popis
state plane code SP [enumeration]
Default: 0
One of:
• 0 — —
• 1 — AK_10
• 2 — AK_2
• 3 — AK_3
• 4 — AK_4
• 5 — AK_5
• 6 — AK_6
• 7 — AK_7
• 8 — AK_8
• 9 — AK_9
• 10 — AL_E
• 11 — AL_W
• 12 — AR_N
• 13 — AR_S
• 14 — AZ_C
• 15 — AZ_E
• 16 — AZ_W
• 17 — CA_I
• 18 — CA_II
• 19 — CA_III
• 20 — CA_IV
• 21 — CA_V
• 22 — CA_VI
• 23 — CA_VII
• 24 — CO_C
• 25 — CO_N
• 26 — CO_S
• 27 — CT
• 28 — DE
• 29 — FL_E
• 30 — FL_N
• 31 — FL_W
• 32 — GA_E
• 33 — GA_W
• 34 — HI_1
• 35 — HI_2
• 36 — HI_3
• 37 — HI_4
• 38 — HI_5
• 39 — IA_N
• 40 — IA_S
• 41 — ID_C
• 42 — ID_E
• 43 — ID_W
• 44 — IL_E
• 45 — IL_W
• 46 — IN_E
• 47 — IN_W
• 48 — KS_N
• 49 — KS_S
• 50 — KY_N
• 51 — KY_S
• 52 — LA_N
• 53 — LA_S
• 54 — MA_I
• 55 — MA_M
• 56 — MD
• 57 — ME_E
• 58 — ME_W
• 59 — MI_C
• 60 — MI_N
1234 Kapitola 24. Processing providers and algorithms
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Tabulka 24.216 – pokračujte na předchozí stránce
Label Název Type Popis
additional
command line
parameter(s)
Optional
ADDITIONAL_OPTIONS[string]
Default: ‚‘
Specifies other command-line switches not
available via this menu but known to the
(advanced) LAStools user.
Output LAS/LAZ
file
OUTPUT_LASLAZ [file]
Default: [Skip
output]
Specifies where the output point cloud
is stored. Use LAZ for compressed output,
LAS for uncompressed output, and TXT for
ASCII. One of:
• Skip Output
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
output LAS/LAZ
file
OUTPUT_LASLAZ [file] The output file
Python code
Algorithm ID: lastools:txt2las
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
24.4 TauDEM algorithm provider
TauDEM (Terrain Analysis Using Digital Elevation Models) is a set of Digital Elevation Model (DEM) tools for
the extraction and analysis of hydrologic information from topography as represented by a DEM. This is software
developed at Utah State University (USU) for hydrologic digital elevation model analysis and watershed delineation.
TauDEM is distributed as a set of standalone command line executable programs for a Windows and source code for
compiling and use on other systems.
Poznámka: Please remember that Processing contains only the interface description, so you need to install TauDEM
5.0.6 by yourself and configure Processing properly.
Documentation for TauDEM algorithms derived from official TauDEM documentation
24.4. TauDEM algorithm provider 1235
QGIS Desktop 3.16 User Guide
24.4.1 Basic Grid Analysis
D-Infinity Contributing Area
Calculates a grid of specific catchment area which is the contributing area per unit contour length using the multiple
flow direction D-infinity approach. D-infinity flow direction is defined as steepest downward slope on planar triangular
facets on a block centered grid. The contribution at each grid cell is taken as the grid cell length (or when the optional
weight grid input is used, from the weight grid). The contributing area of each grid cell is then taken as its own
contribution plus the contribution from upslope neighbors that have some fraction draining to it according to the
D-infinity flow model. The flow from each cell either all drains to one neighbor, if the angle falls along a cardinal
(0, π/2, π, 3π/2) or ordinal (π/4, 3π/4, 5π/4, 7π/4) direction, or is on an angle falling between the direct angle to
two adjacent neighbors. In the latter case the flow is proportioned between these two neighbor cells according to how
close the flow direction angle is to the direct angle to those cells. The contour length used here is the grid cell size.
The resulting units of the specific catchment area are length units the same as those of the grid cell size.
When the optional weight grid is not used, the result is reported in terms of specific catchment area, the upslope area
per unit contour length, taken here as the number of cells times grid cell length (cell area divided by cell length). This
assumes that grid cell length is the effective contour length, in the definition of specific catchment area and does not
distinguish any difference in contour length dependent upon the flow direction. When the optional weight grid is used,
the result is reported directly as a summation of weights, without any scaling.
If the optional outlet point shapefile is used, only the outlet cells and the cells upslope (by the D-infinity flow model)
of them are in the domain to be evaluated.
By default, the tool checks for edge contamination. This is defined as the possibility that a contributing area value may
be underestimated due to grid cells outside of the domain not being counted. This occurs when drainage is inwards
from the boundaries or areas with „no data“ values for elevation. The algorithm recognizes this and reports „no data“
for the contributing area. It is common to see streaks of „no data“ values extending inwards from boundaries along
flow paths that enter the domain at a boundary. This is the desired effect and indicates that contributing area for these
grid cells is unknown due to it being dependent on terrain outside of the domain of data available. Edge contamination
1236 Kapitola 24. Processing providers and algorithms
QGIS Desktop 3.16 User Guide
checking may be turned off in cases where you know it is not an issue or want to ignore these problems, if for example,
the DEM has been clipped along a watershed outline.
Parameters
Label Název Type Popis
D-infinity flow
directions
DINF_FLOWDIR [raster] A grid of flow directions based on the
D-infinity flow method using the steepest
slope of a triangular facet. Flow direction
is determined as the direction of the
steepest downward slope on the 8 triangular
facets of a 3x3 block centered grid.
Flow direction is encoded as an angle
in radians, counter-clockwise from east
as a continuous (floating point) quantity
between 0 and 2π. The resulting flow in
a grid is then usually interpreted as being
proportioned between the two neighboring
cells that define the triangular facet with the
steepest downward slope.
Outlets
Optional
OUTLETS [vector: point] A point shapefile defining the outlets of
interest. If this input file is used, only
the cells upslope of these outlet cells are
considered to be within the domain being
evaluated.
Weight grid
Optional
WEIGHT_GRID [raster] A grid giving contribution to flow for each
cell. These contributions (also sometimes
referred to as weights or loadings) are
used in the contributing area accumulation.
If this input file is not used, the result
is reported in terms of specific catchment
area (the upslope area per unit contour
length) taken as the number of cells times
grid cell length (cell area divided by cell
length).
continues on next page
24.4. TauDEM algorithm provider 1237
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Tabulka 24.217 – pokračujte na předchozí stránce
Label Název Type Popis
Check for edge
contamination
EDGE_CONTAMINATION[boolean]
Default: True
A flag that indicates whether the tool
should check for edge contamination. Edge
contamination is defined as the possibility
that a contributing area value may be
underestimated due to the fact that grid
cells outside of the domain have not been
evaluated. This occurs when drainage
is inwards from the boundaries or areas
with NODATA values for elevation. The
algorithm recognizes this and reports
NODATA for the impated cells. It
is common to see streaks of NODATA
values extending inwards from boundaries
along flow paths that enter the domain
at a boundary. This is the desired effect
and indicates that contributing area for
these grid cells is unknown due to it being
dependent on terrain outside of the domain
of available data. Edge contamination
checking may be turned off in cases where
you know this is not an issue, or want to
ignore these problems, if for example, the
DEM has been clipped along a watershed
outline.
D-infinity specific
catchment area
DINF_CONTRIB_AREA[raster]
Default: [Save
to temporary
file]
Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
D-infinity specific
catchment area
DINF_CONTRIB_AREA[raster] A grid of specific catchment area which
is the contributing area per unit contour
length using the multiple flow direction D-infinity
approach. The contributing area
of each grid cell is then taken as its
own contribution plus the contribution from
upslope neighbors that have some fraction
draining to it according to the D-infinity
flow model.
Algorithm ID: taudem:areadinf
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
1238 Kapitola 24. Processing providers and algorithms
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D-Infinity Flow Directions
Assigns a flow direction based on the D-infinity flow method using the steepest slope of a triangular facet (Tarboton,
1997, „A New Method for the Determination of Flow Directions and Contributing Areas in Grid Digital Elevation
Models“, Water Resources Research, 33(2): 309-319). Flow direction is defined as steepest downward slope on planar
triangular facets on a block centered grid. Flow direction is encoded as an angle in radians counter-clockwise from east
as a continuous (floating point) quantity between 0 and 2π. The flow direction angle is determined as the direction of
the steepest downward slope on the eight triangular facets formed in a 3 x 3 grid cell window centered on the grid cell
of interest. The resulting flow in a grid is then usually interpreted as being proportioned between the two neighboring
cells that define the triangular facet with the steepest downward slope.
A block-centered representation is used with each elevation value taken to represent the elevation of the center of
the corresponding grid cell. Eight planar triangular facets are formed between each grid cell and its eight neighbors.
Each of these has a downslope vector which when drawn outwards from the center may be at an angle that lies within
or outside the 45 degree (π/4 radian) angle range of the facet at the center point. If the slope vector angle is within
the facet angle, it represents the steepest flow direction on that facet. If the slope vector angle is outside a facet,
the steepest flow direction associated with that facet is taken along the steepest edge. The slope and flow direction
associated with the grid cell is taken as the magnitude and direction of the steepest downslope vector from all eight
facets. Slope is measured as drop/distance, i.e. tan of the slope angle.
In the case where no slope vectors are positive (downslope), the flow direction is set using the method of Garbrecht
and Martz (1997) for the determination of flow across flat areas. This makes flat areas drain away from high ground
and towards low ground. The flow path grid to enforce drainage along existing streams is an optional input, and if
used, takes precedence over elevations for the setting of flow directions.
The D-infinity flow direction algorithm may be applied to a DEM that has not had its pits filled, but it will then result
in „no data“ values for the D-infinity flow direction and slope associated with the lowest point of the pit.
24.4. TauDEM algorithm provider 1239
QGIS Desktop 3.16 User Guide
Parameters
Label Název Type Popis
Pit filled elevation PIT_FILLED [raster] A grid of elevation values. This is usually
the output of the „Pit Remove“ tool,
in which case it is elevations with pits
removed. Pits are low elevation areas in
digital elevation models (DEMs) that are
completely surrounded by higher terrain.
They are generally taken to be artifacts of
the digitation process that interfere with the
processing of flow across DEMs. So they
are removed by raising their elevation to
the point where they just drain off the
domain. This step is not essential if you
have reason to believe that the pits in your
DEM are real. If a few pits actually exist and
so should not be removed, while at the same
time others are believed to be artifacts that
need to be removed, the actual pits should
have NODATA elevation values inserted at
their lowest point. NODATA values serve
to define edges of the domain in the flow
field, and elevations are only raised to where
flow is off an edge, so an internal NODATA
value will stop a pit from being removed, if
necessary.
D-infinity flow
directions
DINF_FLOWDIR [raster]
Default: [Save
to temporary
file]
Specification of the output flow direction
raster. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
D-infinity slope DINF_SLOPE [raster]
Default: [Save
to temporary
file]
Specification of the output slope raster. One
of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
1240 Kapitola 24. Processing providers and algorithms
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Label Název Type Popis
D-infinity flow
directions
DINF_FLOWDIR [raster] A grid of flow directions based on the
D-infinity flow method using the steepest
slope of a triangular facet. Flow direction
is determined as the direction of the
steepest downward slope on the 8 triangular
facets of a 3x3 block centered grid.
Flow direction is encoded as an angle
in radians, counter-clockwise from east
as a continuous (floating point) quantity
between 0 and 2π. The resulting flow in
a grid is then usually interpreted as being
proportioned between the two neighboring
cells that define the triangular facet with the
steepest downward slope.
D-infinity slope DINF_SLOPE [raster] A grid of slope evaluated using the D-infinity
method described in Tarboton,
D. G., (1997), „A New Method for
the Determination of Flow Directions
and Contributing Areas in Grid Digital
Elevation Models“, Water Resources
Research, 33(2): 309-319. This is the
steepest outwards slope on one of eight
triangular facets centered at each grid cell,
measured as drop/distance, i.e. tan of the
slope angle.
Algorithm ID: taudem:dinfflowdir
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
D8 Contributing Area
Calculates a grid of contributing areas using the single direction D8 flow model. The contribution of each grid cell
is taken as one (or when the optional weight grid is used, the value from the weight grid). The contributing area for
each grid cell is taken as its own contribution plus the contribution from upslope neighbors that drain in to it according
to the D8 flow model.
If the optional outlet point shapefile is used, only the outlet cells and the cells upslope (by the D8 flow model) of them
are in the domain to be evaluated.
By default, the tool checks for edge contamination. This is defined as the possibility that a contributing area value may
be underestimated due to grid cells outside of the domain not being counted. This occurs when drainage is inwards
from the boundaries or areas with „no data“ values for elevation. The algorithm recognizes this and reports „no data“
for the contributing area. It is common to see streaks of „no data“ values extending inwards from boundaries along flow
paths that enter the domain at a boundary. This is the desired effect and indicates that contributing area for these grid
cells is unknown due to it being dependent on terrain outside of the domain of data available. Edge contamination
checking may be turned off in cases where you know this is not an issue or want to ignore these problems, if for
example, the DEM has been clipped along a watershed outline.
24.4. TauDEM algorithm provider 1241
QGIS Desktop 3.16 User Guide
Parameters
Label Název Type Popis
D8 flow directions D8_FLOWDIR [raster] A grid of D8 flow directions which are
defined, for each cell, as the direction of
the one of its eight adjacent or diagonal
neighbors with the steepest downward
slope. This grid can be obtained as the
output of the „D8 Flow Directions“ tool.
Outlets
Optional
OUTLETS [vector: point] A point shapefile defining the outlets of
interest. If this input file is used, only
the cells upslope of these outlet cells are
considered to be within the domain being
evaluated.
Weight grid
Optional
WEIGHT_GRID [raster] A grid giving contribution to flow for each
cell. These contributions (also sometimes
referred to as weights or loadings) are used
in the contributing area accumulation. If
this input file is not used, the contribution
to flow will assumed to be one for each grid
cell.
Check for edge
contamination
EDGE_CONTAMINATION[boolean]
Default: True
A flag that indicates whether the tool
should check for edge contamination. Edge
contamination is defined as the possibility
that a contributing area value may be
underestimated due to the fact that grid
cells outside of the domain have not been
evaluated. This occurs when drainage
is inwards from the boundaries or areas
with NODATA values for elevation. The
algorithm recognizes this and reports
NODATA for the impated cells. It
is common to see streaks of NODATA
values extending inwards from boundaries
along flow paths that enter the domain
at a boundary. This is the desired effect
and indicates that contributing area for
these grid cells is unknown due to it being
dependent on terrain outside of the domain
of available data. Edge contamination
checking may be turned off in cases where
you know this is not an issue, or want to
ignore these problems, if for example, the
DEM has been clipped along a watershed
outline.
D8 specific
catchment area
D8_CONTRIB_AREA[raster]
Default: [Save
to temporary
file]
Specification of the output raster. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
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Outputs
Label Název Type Popis
D8 specific
catchment area
D8_CONTRIB_AREA[raster] A grid of contributing area values
calculated as the cells own contribution plus
the contribution from upslope neighbors
that drain in to it according to the D8 flow
model.
Algorithm ID: taudem:aread8
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
D8 Flow Directions
Creates 2 grids. The first contains the flow direction from each grid cell to one of its adjacent or diagonal neighbors,
calculated using the direction of steepest descent. The second contain the slope, as evaluated in the direction of
steepest descent, and is reported as drop/distance, i.e. tan of the angle. Flow direction is reported as NODATA for
any grid cell adjacent to the edge of the DEM domain, or adjacent to a NODATA value in the DEM. In flat areas,
flow directions are assigned away from higher ground and towards lower ground using the method of Garbrecht and
Martz (1997). The D8 flow direction algorithm may be applied to a DEM that has not had its pits filled, but it will
then result in NODATA values for flow direction and slope at the lowest point of each pit.
D8 Flow Direction Coding:
• 1 — East
• 2 — Northeast
• 3 — North
• 4 — Northwest
• 5 — West
• 6 — Southwest
• 7 — South
• 8 — Southeast
The flow direction routing across flat areas is performed according to the method described by Garbrecht, J. and L.
W. Martz, (1997), „The Assignment of Drainage Direction Over Flat Surfaces in Raster Digital Elevation Models“,
Journal of Hydrology, 193: 204-213.
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Parameters
Label Název Type Popis
Pit filled elevation PIT_FILLED [raster] A grid of elevation values. This is usually
the output of the „Pit Remove“ tool,
in which case it is elevations with pits
removed. Pits are low elevation areas in
digital elevation models (DEMs) that are
completely surrounded by higher terrain.
They are generally taken to be artifacts of
the digitation process that interfere with the
processing of flow across DEMs. So they
are removed by raising their elevation to
the point where they just drain off the
domain. This step is not essential if you
have reason to believe that the pits in your
DEM are real. If a few pits actually exist and
so should not be removed, while at the same
time others are believed to be artifacts that
need to be removed, the actual pits should
have NODATA elevation values inserted at
their lowest point. NODATA values serve
to define edges of the domain in the flow
field, and elevations are only raised to where
flow is off an edge, so an internal NODATA
value will stop a pit from being removed, if
necessary.
D8 flow directions D8_FLOWDIR [raster]
Default: [Save
to temporary
file]
Specification of the output flow direction
raster. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
D8 slope D8_SLOPE [raster]
Default: [Save
to temporary
file]
Specification of the output slope raster. One
of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
D8 flow directions D8_FLOWDIR [raster] A grid of D8 flow directions which are
defined, for each cell, as the direction of
the one of its eight adjacent or diagonal
neighbors with the steepest downward
slope.
D8 slope D8_SLOPE [raster] A grid giving slope in the D8 flow direction.
This is measured as drop/distance.
Algorithm ID: taudem:d8flowdir
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
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provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Grid Network
Creates 3 grids that contain for each grid cell: 1) the longest path, 2) the total path, and 3) the Strahler order number.
These values are derived from the network defined by the D8 flow model.
The longest upslope length is the length of the flow path from the furthest cell that drains to each cell. The total
upslope path length is the length of the entire grid network upslope of each grid cell. Lengths are measured between
cell centers taking into account cell size and whether the direction is adjacent or diagonal.
Strahler order is defined as follows: A network of flow paths is defined by the D8 Flow Direction grid. Source flow
paths have a Strahler order number of one. When two flow paths of different order join the order of the downstream
flow path is the order of the highest incoming flow path. When two flow paths of equal order join the downstream
flow path order is increased by 1. When more than two flow paths join the downstream flow path order is calculated
as the maximum of the highest incoming flow path order or the second highest incoming flow path order + 1. This
generalizes the common definition to cases where more than two flow paths join at a point.
Where the optional mask grid and threshold value are input, the function is evaluated only considering grid cells that
lie in the domain with mask grid value greater than or equal to the threshold value. Source (first order) grid cells are
taken as those that do not have any other grid cells from inside the domain draining in to them, and only when two
of these flow paths join is order propagated according to the ordering rules. Lengths are also only evaluated counting
paths within the domain greater than or equal to the threshold.
If the optional outlet point shapefile is used, only the outlet cells and the cells upslope (by the D8 flow model) of them
are in the domain to be evaluated.
Parameters
Label Název Type Popis
D8 flow directions D8_FLOWDIR [raster] A grid of D8 flow directions which are
defined, for each cell, as the direction of
the one of its eight adjacent or diagonal
neighbors with the steepest downward
slope. This grid can be obtained as the
output of the „D8 Flow Directions“ tool.
Mask Grid
Optional
MASK_GRID [raster] A grid that is used to determine the
domain do be analyzed. If the mask grid
value >= mask threshold (see below), then
the cell will be included in the domain.
While this tool does not have an edge
contamination flag, if edge contamination
analysis is needed, then a mask grid from
a function like „D8 Contributing Area“
that does support edge contamination can
be used to achieve the same result.
Mask threshold
Optional
THRESHOLD [number]
Default: 100.0
This input parameter is used in the
calculation mask grid value >= mask
threshold to determine if the grid cell is in
the domain to be analyzed.
Outlets
Optional
OUTLETS [vector: point] A point shapefile defining the outlets of
interest. If this input file is used, only
the cells upslope of these outlet cells are
considered to be within the domain being
evaluated.
continues on next page
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Tabulka 24.222 – pokračujte na předchozí stránce
Label Název Type Popis
Longest upslope
length
LONGEST_PATH [raster]
Default: [Save
to temporary
file]
Specification of the output raster with total
upslope lengths. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Total upslope
length
TOTAL_PATH [raster]
Default: [Save
to temporary
file]
Specification of the output raster with
upslope lengths. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Strahler network
order
STRAHLER_ORDER [raster]
Default: [Save
to temporary
file]
Specification of the output raster with
Strahler network order. One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Longest upslope
length
LONGEST_PATH [raster] A grid that gives the length of the longest
upslope D8 flow path terminating at each
grid cell. Lengths are measured between
cell centers taking into account cell size
and whether the direction is adjacent or
diagonal.
Total upslope
length
TOTAL_PATH [raster] The total upslope path length is the length
of the entire D8 flow grid network upslope
of each grid cell. Lengths are measured
between cell centers taking into account cell
size and whether the direction is adjacent or
diagonal.
Strahler network
order
STRAHLER_ORDER [raster] A grid giving the Strahler order number for
each cell. A network of flow paths is defined
by the D8 Flow Direction grid. Source
flow paths have a Strahler order number
of one. When two flow paths of different
order join the order of the downstream flow
path is the order of the highest incoming
flow path. When two flow paths of equal
order join the downstream flow path order
is increased by 1. When more than two
flow paths join the downstream flow path
order is calculated as the maximum of the
highest incoming flow path order or the
second highest incoming flow path order +
1. This generalizes the common definition
to cases where more than two flow paths
join at a point.
Algorithm ID: taudem:gridnet
import processing
processing.run("algorithm_id", {parameter_dictionary})
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The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Pit Remove
Identifies all pits in the DEM and raises their elevation to the level of the lowest pour point around their edge. Pits
are low elevation areas in digital elevation models (DEMs) that are completely surrounded by higher terrain. They are
generally taken to be artifacts that interfere with the routing of flow across DEMs, so are removed by raising their
elevation to the point where they drain off the edge of the domain. The pour point is the lowest point on the boundary
of the „watershed“ draining to the pit. This step is not essential if you have reason to believe that the pits in your
DEM are real. If a few pits actually exist and so should not be removed, while at the same time others are believed
to be artifacts that need to be removed, the actual pits should have NODATA elevation values inserted at their lowest
point. NODATA values serve to define edges in the domain, and elevations are only raised to where flow is off an
edge, so an internal NODATA value will stop a pit from being removed, if necessary.
Parameters
Label Název Type Popis
Elevation ELEVATION [raster] A digital elevation model (DEM) grid to
serve as the base input for the terrain
analysis and stream delineation.
Depression mask
Optional
DEPRESSION_MASK[raster]
Consider only 4
way neighbors
FOUR_NEIGHBOURS[boolean]
Default: False
Pit removed
elevation
PIT_FILLED [raster]
Default: [Save
to temporary
file]
Specification of the (pit filled) output raster.
One of:
• Save to a Temporary File
• Save to File…
The file encoding can also be changed here.
Outputs
Label Název Type Popis
Pit removed
elevation
PIT_FILLED [raster] A grid of elevation values with pits removed
so that flow is routed off of the domain.
Algorithm ID: taudem:pitremove
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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24.4.2 Specialized Grid Analysis
D8 Distance To Streams
Computes the horizontal distance to stream for each grid cell, moving downslope according to the D8 flow model,
until a stream grid cell is encountered.
Parameters
Label Name Type Popis
D8 Flow Direction
Grid
[raster] This input is a grid of flow directions that are encoded
using the D8 method where all flow from a cells goes
to a single neighboring cell in the direction of steepest
descent. This grid can be obtained as the output of the
„D8 Flow Directions“ tool.
Stream Raster
Grid
[raster] A grid indicating streams. Such a grid can be created by
several of the tools in the „Stream Network Analysis“
toolset. However, the tools in the „Stream Network
Analysis“ toolset only create grids with a value of
0 for no stream, or 1 for stream cells. This tool can
also accept grids with values greater than 1, which
can be used in conjunction with the Threshold
parameter to determine the location of streams. This
allows Contributing Area grids to be used to define
streams as well as the normal Stream Raster grids. This
grid expects integer (long integer) values and any non-integer
values will be truncated to an integer before
being evaluated.
Threshold [number]
Default: 50
This value acts as threshold on the Stream Raster
Grid to determine the location of streams. Cells with
a Stream Raster Grid value greater than or equal
to the Threshold value are interpreted as streams.
Outputs
Label Name Type Popis
Output Distance
to Streams
[raster] A grid giving the horizontal distance along the flow
path as defined by the D8 Flow Directions Grid to the
streams in the Stream Raster Grid.
Python code
Algorithm ID: taudem:d8hdisttostrm
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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D-Infinity Avalanche Runout
Identifies an avalanche’s affected area and the flow path length to each cell in that affacted area. All cells downslope
from each source area cell, up to the point where the slope from the source to the affected area is less than a threshold
angle called the Alpha Angle can be in the affected area. This tool uses the D-infinity multiple flow direction method
for determining flow direction. This will likely cause very small amounts of flow to be dispersed to some downslope
cells that might overstate the affected area, so a threshold proportion can be set to avoid this excess dispersion. The
flow path length is the distance from the cell in question to the source cell that has the highest angle.
All points downslope from the source area are potentially in the affected area, but not beyond a point where the slope
from the source to the affected area is less than a threshold angle called the Alpha Angle.
Slope is to be measured using the straight line distance from source point to evaluation point.
It makes more physical sense to me for the angle to be measured along the flow path. Nevertheless it is equally easy to
code straight line angles as angles along the flow path, so an option that allows switching will be provided. The most
practical way to evaluate avalanche runout is to keep track of the source point with the greatest angle to each point.
Then the recursive upslope flow algebra approach will look at a grid cell and all its upslope neighbors that flow to it.
Information from the upslope neighbors will be used to calculate the angle to the grid cell in question and retain it in
the runout zone if the angle exceeds the alpha angle. This procedure makes the assumption that the maximum angle
at a grid cell will be from the set of cells that have maximum angles to the inflowing neighbors. This will always be
true of angle is calculated along a flow path, but I can conceive of cases where flow paths bend back on themselves
where this would not be the case for straight line angles.
The D-infinity multiple flow direction field assigns flow from each grid cell to multiple downslope neighbors using
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proportions (Pik) that vary between 0 and 1 and sum to 1 for all flows out of a grid cell. It may be desirable to specify
a threshold T that this proportion has to exceed before a grid cell is counted as flowing to a downslope grid cell, e.g.
Pik > T (=0.2 say) to avoid dispersion to grid cells that get very little flow. T will be specified as a user input. If all
upslope grid cells are to be used T may be input as 0.
Avalanche source sites are to be input as a short integer grid (name suffix *ass, e.g. demass) comprised of positive
values where avalanches may be triggered and 0 values elsewhere.
The following grids are output:
• rz — A runout zone indicator with value 0 to indicate that this grid cell is not in the runout zone and value > 0
to indicate that this grid cell is in the runout zone. Since there may be information in the angle to the associated
source site, this variable will be assigned the angle to the source site (in degrees)
• dm — Along flow distance from the source site that has the highest angle to the point in question
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Parameters
Label Name Type Popis
D-Infinity Flow
Direction Grid
[raster] A grid giving flow direction by the D-infinity method.
Flow direction is measured in radians, counter
clockwise from east. This can be created by the tool
„D-Infinity Flow Directions“.
Pit Filled
Elevation Grid
[raster] This input is a grid of elevation values. As a general
rule, it is recommended that you use a grid of elevation
values that have had the pits removed for this input. Pits
are generally taken to be artifacts that interfere with the
analysis of flow across them. This grid can be obtained
as the output of the „Pit Remove“ tool, in which case it
contains elevation values where the pits have been filled
to the point where they just drain.
Avalanche Source
Site Grid
[raster] This is a grid of source areas for snow avalanches
that are commonly identified manually using a mix
of experience and visual interpretation of maps.
Avalanche source sites are to be input as a short integer
grid (name suffix *ass, e.g. demass) comprised of
positive values where avalanches may be triggered and
0 values elsewhere.
Proportion
Threshold
[number]
Default: 0.2
This value is a threshold proportion that is used to
limit the dispersion of flow caused by using the D-infinity
multiple flow direction method for determining
flow direction. The D-infinity multiple flow direction
method often causes very small amounts of flow to be
dispersed to some downslope cells that might overstate
the affected area, so a threshold proportion can be set
to avoid this excess dispersion.
Alpha Angle
Threshold
[number]
Default: 18
This value is the threshold angle, called the Alpha
Angle, that is used to determine which of the cells
downslope from the source cells are in the affected area.
Only the cells downslope from each source area cell,
up to the point where the slope from the source to the
affected area is less than a threshold angle are in the
affected area.
Measure distance
along flow path
[boolean]
Default: True
This option selects the method used to measure the
distance used to calculate the slope angle. If option
is True then measure it along the flow path, where
the False option causes the slope to be measure along
the straight line distance from the source cell to the
evaluation cell.
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Outputs
Label Name Type Popis
Runout Zone Grid [raster] This grid Identifies the avalanche’s runout zone
(affected area) using a runout zone indicator with value
0 to indicate that this grid cell is not in the runout
zone and value > 0 to indicate that this grid cell is in
the runout zone. Since there may be information in the
angle to the associated source site, this variable will be
assigned the angle to the source site (in degrees).
Path Distance
Grid
[raster] This is a grid of the flow distance from the source site
that has the highest angle to each cell.
Python code
Algorithm ID: taudem:dinfavalanche
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
D-Infinity Concentration Limited Accumulation
This function applies to the situation where an unlimited supply of a substance is loaded into flow at a concentration or
solubility threshold Csol over a region indicated by an indicator grid (dg). It a grid of the concentration of a substance at
each location in the domain, where the supply of substance from a supply area is loaded into the flow at a concentration
or solubility threshold. The flow is first calculated as a D-infinity weighted contributing area of an input Effective
Runoff Weight Grid (notionally excess precipitation). The concentration of substance over the supply area (indicator
grid) is at the concentration threshold. As the substance moves downslope with the D-infinity flow field, it is subject
to first order decay in moving from cell to cell as well as dilution due to changes in flow. The decay multiplier grid
gives the fractional (first order) reduction in quantity in moving from grid cell x to the next downslope cell. If the
outlets shapefile is used, the tool only evaluates the part of the domain that contributes flow to the locations given by
the shapefile. This is useful for a tracking a contaminant or compound from an area with unlimited supply of that
compound that is loaded into a flow at a concentration or solubility threshold over a zone and flow from the zone may
be subject to decay or attenuation.
The indicator grid (dg) is used to delineate the area of the substance supply using the (0, 1) indicator function i(x).
A[] denotes the weighted accumulation operator evaluated using the D-Infinity Contributing Area function. The
Effective Runoff Weight Grid gives the supply to the flow (e.g. the excess rainfall if this is overland flow) denoted
as w(x). The specific discharge is then given by:
Q(x)=A[w(x)]
This weighted accumulation Q(x) is output as the Overland Flow Specific Discharge Grid. Over the substance supply
area concentration is at the threshold (the threshold is a saturation or solubility limit). If i(x) = 1, then
C(x) = Csol, and L(x) = Csol Q(x),
where L(x) denotes the load being carried by the flow. At remaining locations, the load is determined by load
accumulation and the concentration by dilution:
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Here d(x) = d(i, j) is a decay multiplier giving the fractional (first order) reduction in mass in moving from
grid cell x to the next downslope cell. If travel (or residence) times t(x) associated with flow between cells are
available d(x) may be evaluated as exp(-k t(x)) where k is a first order decay parameter. The Concentration
grid output is C(x). If the outlets shapefile is used, the tool only evaluates the part of the domain that contributes
flow to the locations given by the shapefile.
Useful for a tracking a contaminant released or partitioned to flow at a fixed threshold concentration.
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Parameters
Label Name Type Popis
D-Infinity Flow
Direction Grid
[raster] A grid giving flow direction by the D-infinity method.
Flow direction is measured in radians, counter
clockwise from east. This grid can be created by the
function „D-Infinity Flow Directions“.
Disturbance
Indicator Grid
[raster] A grid that indicates the source zone of the area of
substance supply and must be 1 inside the zone and 0
or NODATA over the rest of the domain.
Decay Multiplier
Grid
[raster] A grid giving the factor by which flow leaving
each grid cell is multiplied before accumulation on
downslope grid cells. This may be used to simulate the
movement of an attenuating or decaying substance. If
travel (or residence) times t(x) associated with flow
between cells are available d(x) may be evaluated
as exp(-k t(x)) where k is a first order decay
parameter.
Effective Runoff
Weight Grid
[raster] A grid giving the input quantity (notionally effective
runoff or excess precipitation) to be used in the
D-infinity weighted contributing area evaluation of
Overland Flow Specific Discharge.
Outlets shapefile
Optional
[vector: point] This optional input is a point shapefile defining outlets
of interest. If this file is used, the tool will only evaluate
the area upslope of these outlets.
Concentration
Threshold
[number]
Default: 1.0
The concentration or solubility threshold. Over the
substance supply area, concentration is at this threshold.
Check for edge
contamination
[boolean]
Default: True
This option determines whether the tool should check
for edge contamination. Edge contamination is defined
as the possibility that a value may be underestimated
due to grid cells outside of the domain not being
considered when determining contributing area.
Outputs
Label Name Type Popis
Concentration
Grid
[raster] A grid giving the resulting concentration of the
compound of interest in the flow.
Python code
Algorithm ID: taudem:dinfconclimaccum
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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D-Infinity Decaying Accumulation
The D-Infinity Decaying Accumulation tool creates a grid of the accumulated quantity at each location in the domain
where the quantity accumulates with the D-infinity flow field, but is subject to first order decay in moving from cell to
cell. By default, the quantity contribution of each grid cell is the cell length to give a per unit width accumulation, but
can optionally be expressed with a weight grid. The decay multiplier grid gives the fractional (first order) reduction
in quantity in accumulating from grid cell x to the next downslope cell.
A decayed accumulation operator DA[.] takes as input a mass loading field m(x) expressed at each grid location
as m(i, j) that is assumed to move with the flow field but is subject to first order decay in moving from cell to
cell. The output is the accumulated mass at each location DA(x). The accumulation of m at each grid cell can be
numerically evaluated.
Here d(x) = d(i ,j) is a decay multiplier giving the fractional (first order) reduction in mass in moving from
grid cell x to the next downslope cell. If travel (or residence) times t(x) associated with flow between cells are
available d(x) may be evaluated as exp(-k t(x)) where k is a first order decay parameter. The weight grid
is used to represent the mass loading m(x). If not specified this is taken as 1. If the outlets shapefile is used the
function is only evaluated on that part of the domain that contributes flow to the locations given by the shapefile.
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Useful for a tracking contaminant or compound subject to decay or attenuation.
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Parameters
Label Name Type Popis
D-Infinity Flow
Direction Grid
[raster] A grid giving flow direction by the D-infinity method.
Flow direction is measured in radians, counter
clockwise from east. This grid can be created by the
function „D-Infinity Flow Directions“.
Decay Multiplier
Grid
[raster] A grid giving the factor by which flow leaving each grid
cell is multiplied before accumulation on downslope
grid cells. This may be used to simulate the movement
of an attenuating substance.
Weight Grid
Optional
[raster] A grid giving weights (loadings) to be used in the
accumulation. If this optional grid is not specified,
weights are taken as the linear grid cell size to give a per
unit width accumulation.
Outlets Shapefile
Optional
[vector: point] This optional input is a point shapefile defining outlets
of interest. If this file is used, the tool will only evaluate
the area upslope of these outlets.
Check for edge
contamination
[boolean]
Default: True
This option determines whether the tool should check
for edge contamination. Edge contamination is defined
as the possibility that a value may be underestimated
due to grid cells outside of the domain not being
considered when determining contributing area.
Outputs
Label Name Type Popis
Decayed Specific
Catchment Area
Grid
[raster] The D-Infinity Decaying Accumulation tool creates
a grid of the accumulated mass at each location in
the domain where mass moves with the D-infinity flow
field, but is subject to first order decay in moving from
cell to cell.
Python code
Algorithm ID: taudem:dinfdecayaccum
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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D-Infinity Distance Down
Calculates the distance downslope to a stream using the D-infinity flow model. The D-infinity flow model is a multiple
flow direction model, because the outflow from each grid cell is proportioned between up to 2 downslope grid cells.
As such, the distance from any grid cell to a stream is not uniquely defined. Flow that originates at a particular grid
cell may enter the stream at a number of different cells. The statistical method may be selected as the longest, shortest
or weighted average of the flow path distance to the stream. Also one of several ways of measuring distance may
be selected: the total straight line path (Pythagoras), the horizontal component of the straight line path, the vertical
component of the straight line path, or the total surface flow path.
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Parameters
Label Name Type Popis
D-Infinity Flow
Direction Grid
[raster] A grid giving flow direction by the D-infinity method.
Flow direction is measured in radians, counter
clockwise from east. This can be created by the tool
„D-Infinity Flow Directions“.
Pit Filled
Elevation Grid
[raster] This input is a grid of elevation values. As a general
rule, it is recommended that you use a grid of elevation
values that have had the pits removed for this input. Pits
are generally taken to be artifacts that interfere with the
analysis of flow across them. This grid can be obtained
as the output of the „Pit Remove“ tool, in which case it
contains elevation values where the pits have been filled
to the point where they just drain.
Stream Raster
Grid
[raster] A grid indicating streams, by using a grid cell value of 1
on streams and 0 off streams. This is usually the output
of one of the tools in the „Stream Network Analysis“
toolset.
Weight Path Grid
Optional
[raster] A grid giving weights (loadings) to be used in the
distance calculation. This might be used for example
where only flow distance through a buffer is to be
calculated. The weight is then 1 in the buffer and 0
outside it. Alternatively the weight may reflect some
sort of cost function for travel over the surface, perhaps
representing travel time or attenuation of a process. If
this input file is not used, the loadings will assumed to
be one for each grid cell.
Statistical Method [enumeration]
Default: 2
Statistical method used to calculate the distance down
to the stream. In the D-Infinity flow model, the outflow
from each grid cell is proportioned between two
downslope grid cells. Therefore, the distance from any
grid cell to a stream is not uniquely defined. Flow that
originates at a particular grid cell may enter the stream
at a number of cells. The distance to the stream may be
defined as the longest (maximum), shortest (minimum)
or weighted average of the distance down to the stream.
Options:
• 0 — Minimum
• 1 — Maximum
• 2 — Average
Distance Method [enumeration]
Default: 1
Distance method used to calculate the distance down
to the stream. One of several ways of measuring
distance may be selected: the total straight line path
(Pythagoras), the horizontal component of the straight
line path (horizontal), the vertical component of the
straight line path (vertical), or the total surface flow path
(surface).
Options:
• 0 — Pythagoras
• 1 — Horizontal
• 2 — Vertical
• 3 — Surface
Check for edge
contamination
[boolean]
Default: True
A flag that determines whether the tool should check for
edge contamination. This is defined as the possibility
that a value may be underestimated due to grid cells
outside of the domain not being counted. In the context
of Distance Down this occurs when part of a flow
path traced downslope from a grid cell leaves the
domain without reaching a stream grid cell. With
edge contamination checking selected, the algorithm
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Outputs
Label Name Type Popis
D-Infinity Drop to
Stream Grid
[raster] Grid containing the distance to stream calculated using
the D-infinity flow model and the statistical and path
methods chosen.
Python code
Algorithm ID: taudem:dinfdistdown
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
D-Infinity Distance Up
This tool calculates the distance from each grid cell up to the ridge cells along the reverse D-infinity flow directions.
Ridge cells are defined to be grid cells that have no contribution from grid cells further upslope. Given the convergence
of multiple flow paths at any grid cell, any given grid cell can have multiple upslope ridge cells. There are three
statistical methods that this tool can use: maximum distance, minimum distance and waited flow average over these
flow paths. A variant on the above is to consider only grid cells that contribute flow with a proportion greater than
a user specified threshold (t) to be considered as upslope of any given grid cell. Setting t=0.5 would result in only
one flow path from any grid cell and would give the result equivalent to a D8 flow model, rather than D-infinity flow
model, where flow is proportioned between two downslope grid cells. Finally there are several different optional paths
that can be measured: the total straight line path (Pythagoras), the horizontal component of the straight line path, the
vertical component of the straight line path, or the total surface flow path.
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Parameters
Label Name Type Popis
D-Infinity Flow
Direction Grid
[raster] A grid giving flow direction by the D-infinity method.
Flow direction is measured in radians, counter
clockwise from east. This can be created by the tool
„D-Infinity Flow Directions“.
Pit Filled
Elevation Grid
[raster] This input is a grid of elevation values. As a general
rule, it is recommended that you use a grid of elevation
values that have had the pits removed for this input. Pits
are generally taken to be artifacts that interfere with the
analysis of flow across them. This grid can be obtained
as the output of the „Pit Remove“ tool, in which case it
contains elevation values where the pits have been filled
to the point where they just drain.
Slope Grid [raster] This input is a grid of slope values. This is measured
as drop/distance and it is most often obtained as the
output of the „D-Infinity Flow Directions“ tool.
Statistical Method [enumeration]
Default: 2
Statistical method used to calculate the distance down
to the stream. In the D-Infinity flow model, the outflow
from each grid cell is proportioned between two
downslope grid cells. Therefore, the distance from any
grid cell to a stream is not uniquely defined. Flow that
originates at a particular grid cell may enter the stream
at a number of cells. The distance to the stream may be
defined as the longest (maximum), shortest (minimum)
or weighted average of the distance down to the stream.
Options:
• 0 — Minimum
• 1 — Maximum
• 2 — Average
Distance Method [enumeration]
Default: 1
Distance method used to calculate the distance down
to the stream. One of several ways of measuring
distance may be selected: the total straight line path
(Pythagoras), the horizontal component of the straight
line path (horizontal), the vertical component of the
straight line path (vertical), or the total surface flow path
(surface).
Options:
• 0 — Pythagoras
• 1 — Horizontal
• 2 — Vertical
• 3 — Surface
Proportion
Threshold
[number]
Default: 0.5
The proportion threshold parameter where only grid
cells that contribute flow with a proportion greater than
this user specified threshold (t) is considered to be
upslope of any given grid cell. Setting t=0.5 would
result in only one flow path from any grid cell and would
give the result equivalent to a D8 flow model, rather
than D-Infinity flow model, where flow is proportioned
between two downslope grid cells.
Check for edge
contamination
[boolean]
Default: True
A flag that determines whether the tool should check for
edge contamination. This is defined as the possibility
that a value may be underestimated due to grid cells
outside of the domain not being counted.
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Outputs
Label Name Type Popis
D-Infinity
Distance Up
[raster] Grid containing the distances up to the ridge calculated
using the D-Infinity flow model and the statistical and
path methods chosen.
Python code
Algorithm ID: taudem:dinfdistup
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
D-Infinity Reverse Accumulation
This works in a similar way to evaluation of weighted Contributing area, except that the accumulation is by propagating
the weight loadings upslope along the reverse of the flow directions to accumulate the quantity of weight loading
downslope from each grid cell. The function also reports the maximum value of the weight loading downslope from
each grid cell in the Maximum Downslope grid.
This function is designed to evaluate and map the hazard due to activities that may have an effect downslope. The
example is land management activities that increase runoff. Runoff is sometimes a trigger for landslides or debris
flows, so the weight grid here could be taken as a terrain stability map. Then the reverse accumulation provides
a measure of the amount of unstable terrain downslope from each grid cell, as an indicator of the danger of activities
that may increase runoff, even though there may be no potential for any local impact.
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Parameters
Label Name Type Popis
D-Infinity Flow
Direction Grid
[raster] A grid giving flow direction by the D-infinity method.
Flow direction is measured in radians, counter
clockwise from east. This can be created by the tool
„D-Infinity Flow Directions“.
Weight Grid [raster] A grid giving weights (loadings) to be used in the
accumulation.
Outputs
Label Name Type Popis
Reverse
Accumulation
Grid
[raster] The grid giving the result of the „Reverse
Accumulation“ function. This works in a similar
way to evaluation of weighted Contributing area,
except that the accumulation is by propagating the
weight loadings upslope along the reverse of the
flow directions to accumulate the quantity of loading
downslope from each grid cell.
Maximum
Downslope Grid
[raster] The grid giving the maximum of the weight loading grid
downslope from each grid cell.
Python code
Algorithm ID: taudem:dinfrevaccum
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
D-Infinity Transport Limited Accumulation - 2
This function is designed to calculate the transport and deposition of a substance (e.g. sediment) that may be limited
by both supply and the capacity of the flow field to transport it. This function accumulates substance flux (e.g. sediment
transport) subject to the rule that transport out of any grid cell is the minimum between supply and transport capacity,
Tcap. The total supply at a grid cell is calculated as the sum of the transport in from upslope grid cells, Tin, plus the
local supply contribution, E (e.g. erosion). This function also outputs deposition, D, calculated as total supply minus
actual transport.
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Here E is the supply. Tout at each grid cell becomes Tin for downslope grid cells and is reported as Transport
limited accumulation (tla). D is deposition (tdep). The function provides the option to evaluate concentration of
a compound (contaminant) adhered to the transported substance. This is evaluated as follows:
Where Lin is the total incoming compound loading and Cin and Tin refer to the Concentration and Transport
entering from each upslope grid cell.
If
else
where Cs is the concentration supplied locally and the difference in the second term on the right represents the
additional supply from the local grid cell. Then,
Cout at each grid cell comprises is the concentration grid output from this function.
If the outlets shapefile is used the tool only evaluates that part of the domain that contributes flow to the locations
given by the shapefile.
Transport limited accumulation is useful for modeling erosion and sediment delivery, including the spatial dependence
of sediment delivery ratio and contaminant that adheres to sediment.
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Parameters
Label Name Type Popis
D-Infinity Flow
Direction Grid
[raster] A grid giving flow direction by the D-infinity method.
Flow direction is measured in radians, counter
clockwise from east. This can be created by the tool
„D-Infinity Flow Directions“.
Supply Grid [raster] A grid giving the supply (loading) of material to
a transport limited accumulation function. In the
application to erosion, this grid would give the erosion
detachment, or sediment supplied at each grid cell.
Transport
Capacity Grid
[raster] A grid giving the transport capacity at each grid cell
for the transport limited accumulation function. In the
application to erosion this grid would give the transport
capacity of the carrying flow.
Input
Concentration
Grid
[raster] A grid giving the concentration of a compound
of interest in the supply to the transport limited
accumulation function. In the application to
erosion, this grid would give the concentration of
say phosphorous adhered to the eroded sediment.
Outlets Shapefile
Optional
[vector: point] This optional input is a point shapefile defining outlets
of interest. If this file is used, the tool will only evaluate
the area upslope of these outlets.
Check for edge
contamination
[boolean]
Default: True
This option determines whether the tool should check
for edge contamination. Edge contamination is defined
as the possibility that a value may be underestimated
due to grid cells outside of the domain not being
considered when determining the result.
Outputs
Label Name Type Popis
Transport
Limited
Accumulation
Grid
[raster] This grid is the weighted accumulation of supply
accumulated respecting the limitations in transport
capacity and reports the transport rate calculated by
accumulating the substance flux subject to the rule that
the transport out of any grid cell is the minimum of the
total supply (local supply plus transport in) to that grid
cell and the transport capacity.
Deposition Grid [raster] A grid giving the deposition resulting from the transport
limited accumulation. This is the residual from the
transport in to each grid cell minus the transport
capacity out of the grid cell. The deposition grid
is calculated as the transport in + the local supply - the
transport out.
Output
Concentration
Grid
[raster] If an input concentration in supply grid is given, then
this grid is also output and gives the concentration of
a compound (contaminant) adhered or bound to the
transported substance (e.g. sediment) is calculated.
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Python code
Algorithm ID: unknown
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
D-Infinity Transport Limited Accumulation
This function is designed to calculate the transport and deposition of a substance (e.g. sediment) that may be limited
by both supply and the capacity of the flow field to transport it. This function accumulates substance flux (e.g. sediment
transport) subject to the rule that transport out of any grid cell is the minimum between supply and transport capacity,
Tcap. The total supply at a grid cell is calculated as the sum of the transport in from upslope grid cells, Tin, plus the
local supply contribution, E (e.g. erosion). This function also outputs deposition, D, calculated as total supply minus
actual transport.
Here E is the supply. Tout at each grid cell becomes Tin for downslope grid cells and is reported as Transport
limited accumulation (tla). D is deposition (tdep). The function provides the option to evaluate concentration of
a compound (contaminant) adhered to the transported substance. This is evaluated as follows:
Where Lin is the total incoming compound loading and Cin and Tin refer to the Concentration and Transport
entering from each upslope grid cell.
If
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else
where Cs is the concentration supplied locally and the difference in the second term on the right represents the
additional supply from the local grid cell. Then,
Cout at each grid cell comprises is the concentration grid output from this function.
If the outlets shapefile is used the tool only evaluates that part of the domain that contributes flow to the locations
given by the shapefile.
Transport limited accumulation is useful for modeling erosion and sediment delivery, including the spatial dependence
of sediment delivery ratio and contaminant that adheres to sediment.
Parameters
Label Name Type Popis
D-Infinity Flow
Direction Grid
[raster] A grid giving flow direction by the D-infinity method.
Flow direction is measured in radians, counter
clockwise from east. This can be created by the tool
„D-Infinity Flow Directions“.
Supply Grid [raster] A grid giving the supply (loading) of material to
a transport limited accumulation function. In the
application to erosion, this grid would give the erosion
detachment, or sediment supplied at each grid cell.
Transport
Capacity Grid
[raster] A grid giving the transport capacity at each grid cell
for the transport limited accumulation function. In the
application to erosion this grid would give the transport
capacity of the carrying flow.
Outlets Shapefile
Optional
[vector: point] This optional input is a point shapefile defining outlets
of interest. If this file is used, the tool will only evaluate
the area upslope of these outlets.
Check for edge
contamination
[boolean]
Default: True
This option determines whether the tool should check
for edge contamination. Edge contamination is defined
as the possibility that a value may be underestimated
due to grid cells outside of the domain not being
considered when determining the result.
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Outputs
Label Name Type Popis
Transport
Limited
Accumulation
Grid
[raster] This grid is the weighted accumulation of supply
accumulated respecting the limitations in transport
capacity and reports the transport rate calculated by
accumulating the substance flux subject to the rule that
the transport out of any grid cell is the minimum of the
total supply (local supply plus transport in) to that grid
cell and the transport capacity.
Deposition Grid [raster] A grid giving the deposition resulting from the transport
limited accumulation. This is the residual from the
transport in to each grid cell minus the transport
capacity out of the grid cell. The deposition grid
is calculated as the transport in + the local supply - the
tranport out.
Python code
Algorithm ID: taudem:dinftranslimaccum
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
D-Infinity Upslope Dependence
The D-Infinity Upslope Dependence tool quantifies the amount each grid cell in the domain contributes to a destination
set of grid cells. D-Infinity flow directions proportion flow from each grid cell between multiple downslope grid cells.
Following this flow field downslope the amount of flow originating at each grid cell that reaches the destination zone
is defined. Upslope influence is evaluated using a downslope recursion, examining grid cells downslope from each
grid cell, so that the map produced identifies the area upslope where flow through the destination zone originates, or
the area it depends on, for its flow.
The figures below illustrate the amount each source point in the domain x (blue) contributes to the destination point
or zone y (red). If the indicator weighted contributing area function is denoted I(y; x) giving the weighted
contribution using a unit value (1) from specific grid cells y to grid cells x, then the upslope dependence is: D(x;
y) = I(y; x).
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This is useful for example to track where flow or a flow related substance or contaminant that enters a destination area
may come from.
Parameters
Label Name Type Popis
D-Infinity Flow
Direction Grid
[raster] A grid giving flow direction by the D-Infinity method
where the flow direction angle is determined as the
direction of the steepest downward slope on the eight
triangular facets formed in a 3x3 grid cell window
centered on the grid cell of interest. This grid can be
produced using the „D-Infinity Flow Direction“ tool.
Destination Grid [raster] A grid that encodes the destination zone that may
receive flow from upslope. This grid must be 1 inside
the zone y and 0 over the rest of the domain.
Outputs
Label Name Type Popis
Output Upslope
Dependence Grid
[raster] A grid quantifing the amount each source point in
the domain contributes to the zone defined by the
destination grid.
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Python code
Algorithm ID: taudem:dinfupdependence
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Slope Average Down
This tool computes slope in a D8 downslope direction averaged over a user selected distance. Distance should be
specified in horizontal map units.
Parameters
Label Name Type Popis
D8 Flow Direction
Grid
[raster] This input is a grid of flow directions that are encoded
using the D8 method where all flow from a cells goes
to a single neighboring cell in the direction of steepest
descent. This grid can be obtained as the output of the
„D8 Flow Directions“ tool.
Pit Filled
Elevation Grid
[raster] This input is a grid of elevation values. As a general
rule, it is recommended that you use a grid of elevation
values that have had the pits removed for this input. Pits
are generally taken to be artifacts that interfere with the
analysis of flow across them. This grid can be obtained
as the output of the „Pit Remove“ tool, in which case it
contains elevation values where the pits have been filled
to the point where they just drain.
Downslope
Distance
[number]
Default: 50
Input parameter of downslope distance over which to
calculate the slope (in horizontal map units).
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Outputs
Label Name Type Popis
Slope Average
Down Grid
[raster] This output is a grid of slopes calculated in the
D8 downslope direction, averaged over the selected
distance.
Python code
Algorithm ID: taudem:slopeavedown
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Slope Over Area Ratio
Calculates the ratio of the slope to the specific catchment area (contributing area). This is algebraically related to the
more common ln(a/tan beta) wetness index, but contributing area is in the denominator to avoid divide by 0 errors
when slope is 0.
Parameters
Label Name Type Popis
Slope Grid [raster] A grid of slope. This grid can be generated using ether
the „D8 Flow Directions“ tool or the „D-Infinity
Flow Directions“ tool.
Specific
Catchment Area
Grid
[raster] A grid giving the contributing area value for each cell
taken as its own contribution plus the contribution from
upslope neighbors that drain in to it. Contributing area
is counted in terms of the number of grid cells (or
summation of weights). This grid can be generated
using either the „D8 Contributing Area“ tool or the
„D-Infinity Contributing Area“ tool.
Outputs
Label Name Type Popis
Slope Divided By
Area Ratio Grid
[raster] A grid of the ratio of slope to specific catchment area
(contributing area). This is algebraically related to the
more common ln(a/tan beta) wetness index, but
contributing area is in the denominator to avoid divide
by 0 errors when slope is 0.
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Python code
Algorithm ID: taudem:slopearearatio
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Topographic wetness index
Calculates the topographic wetness index (TWI).
Parameters
Label Name Type Popis
Slope [raster] A grid of slope. This grid can be generated using ether
the „D8 Flow Directions“ tool or the „D-Infinity
Flow Directions“ tool.
Specific catchment
area
[raster] A grid giving the contributing area value for each cell
taken as its own contribution plus the contribution from
upslope neighbors that drain in to it. Contributing area
is counted in terms of the number of grid cells (or
summation of weights). This grid can be generated
using either the „D8 Contributing Area“ tool or the
„D-Infinity Contributing Area“ tool.
Outputs
Label Name Type Popis
Wetness index [raster] A grid of the wetness index (TWI).
Python code
Algorithm ID: taudem:twi
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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24.4.3 Stream Network Analysis
Connect down
For each zone in a raster entered (e.g. HUC converted to grid) it identifies the point with largest AreaD8. This is taken
to be the outlet. A OGR file is created. Using flow directions each outlet is moved downflow a specified number of
grid cells which is user controllable (Default is 1). The ID of the location the point has moved to is taken as iddown.
Two OGR files are created one with the initial points and one with the moved points. Both contain id, iddown and
AreaD8.
Parameters
Label Name Type Popis
D8 flow directions [raster] A grid of flow directions that are encoded using the
D8 method where all flow from a cells goes to a single
neighboring cell in the direction of steepest descent
D8 contribution
area
[raster] A grid giving the contributing area value in terms of
the number of grid cells (or the summation of weights)
for each cell taken as its own contribution plus the
contribution from upslope neighbors that drain in to it
using the D8 algorithm. This is usually the output of the
„D8 Contributing Area“ tool.
Watershed [raster] Watershed grid delineated from gage watershed
function or streamreachwatershed function. Other
watershed (e.g. HUC) raster also can be used
as watershed grid.
Grid cells move to
downstream
[number] Number of grid cells move to downstream based on
flow directions.
Outputs
Label Name Type Popis
Outlets [vector: point] A point OGR file where each point is created from
watershed grid having the largest contributing area for
each zone.
Moved Outlets [vector: point] A point OGR file defining moved outlets of interest.
where each outlet is moved downflow a specified
number of grid cells using flow directions.
Python code
Algorithm ID: taudem:connectdown
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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D8 Extreme Upslope Value
Evaluates the extreme (either maximum or minimum) upslope value from an input grid based on the D8 flow model.
This is intended initially for use in stream raster generation to identify a threshold of the slope times area product that
results in an optimum (according to drop analysis) stream network.
If the optional outlet point shapefile is used, only the outlet cells and the cells upslope (by the D8 flow model) of them
are in the domain to be evaluated.
By default, the tool checks for edge contamination. This is defined as the possibility that a result may be underestimated
due to grid cells outside of the domain not being counted. This occurs when drainage is inwards from the boundaries
or areas with „no data“ values for elevation. The algorithm recognizes this and reports „no data“ for the result for these
grid cells. It is common to see streaks of „no data“ values extending inwards from boundaries along flow paths that
enter the domain at a boundary. This is the desired effect and indicates that the result for these grid cells is unknown
due to it being dependent on terrain outside of the domain of data available. Edge contamination checking may be
turned off in cases where you know this is not an issue or want to ignore these problems, if for example, the DEM
has been clipped along a watershed outline.
Parameters
Label Name Type Popis
D8 Flow
Directions Grid
[raster] A grid of D8 flow directions which are defined, for each
cell, as the direction of the one of its eight adjacent or
diagonal neighbors with the steepest downward slope.
This grid can be obtained as the output of the „D8 Flow
Directions“ tool.
Upslope Values
Grid
[raster] This is the grid of values of which the maximum
or minimum upslope value is selected. The values
most commonly used are the slope times area product
needed when generating stream rasters according to
drop analysis.
Outlets Shapefile
Optional
[vector: point] A point shape file defining outlets of interest. If this
input file is used, only the area upslope of these outlets
will be evaluated by the tool.
Check for edge
contamination
[boolean]
Default: True
A flag that indicates whether the tool should check for
edge contamination.
Use max upslope
value
[boolean]
Default: True
A flag to indicate whether the maximum or minimum
upslope value is to be calculated.
Outputs
Label Name Type Popis
Extreme Upslope
Values Grid
[raster] A grid of the maximum/minimum upslope values.
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Python code
Algorithm ID: taudem:d8flowpathextremeup
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Gage Watershed
Calculates Gage Watersheds Grid. Each grid cell is labeled with the identifier (from column id) of the gage to which
it drains directly without passing through any other gages.
Parameters
Label Name Type Popis
A suppr D-infinity
flow directions
DINF_FLOWDIR[raster] A grid of flow directions based on the D-infinity flow
method
D8 Flow
Directions Grid
[raster] A grid of D8 flow directions which are defined, for each
cell, as the direction of the one of its eight adjacent or
diagonal neighbors with the steepest downward slope.
This grid can be obtained as the output of the „D8 Flow
Directions“ tool.
Gages Shapefile [vector: point] A point shapefile defining the gages to which watersheds
will be delineated. This shapefile should have a colmun
id. Grid cells draining directly to each point in this
shapefile will be labeled with this id.
Outputs
Label Name Type Popis
Gage Watershed
Grid
[raster] A grid identifies each gage watershed. Each grid cell
is labeled with the identifier (from column id) of the
gage to which it drains directly without passing through
any other gages.
Downstream
Identifiers File
[file] Text file giving watershed downslope connectivity
Python code
Algorithm ID: taudem:gagewatershed
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Length Area Stream Source
Creates an indicator grid (1, 0) that evaluates A >= (M)(Ly) based on upslope path length, D8 contributing
area grid inputs, and parameters M and y. This grid indicates likely stream source grid cells. This is an experimental
method with theoretical basis in Hack’s law which states that for streams L ~ A 0.6. However for hillslopes with
parallel flow L ~ A. So a transition from hillslopes to streams may be represented by L ~ A 0.8 suggesting
identifying grid cells as stream cells if A > M (L (1/0.8)).
Parameters
Label Name Type Popis
Length Grid [raster] A grid of the maximum upslope length for each cell.
This is calculated as the length of the flow path from the
furthest cell that drains to each cell. Length is measured
between cell centers taking into account cell size and
whether the direction is adjacent or diagonal. It is this
length (L) that is used in the formula, A >(M)(Ly),
to determine which cells are considered stream cells.
This grid can be obtained as an output from the „Grid
Network“ tool.
Contributing Area
Grid
[raster] A grid of contributing area values for each cell that were
calculated using the D8 algorithm. The contributing
area for a cell is the sum of its own contribution plus
the contribution from all upslope neighbors that drain to
it, measured as a number of cells. This grid is typically
obtained as the output of the „D8 Contributing Area“
tool. In this tool, it is the contributing area (A) that
is compared in the formula A > (M)(Ly) to
determine the transition to a stream.
Threshold [number]
Default: 0.03
The multiplier threshold (M) parameter which is used in
the formula: A > (M)(Ly), to identify the beginning
of streams.
Exponent [number]
Default: 1.3
The exponent (y) parameter which is used in the
formula: A > (M)(Ly), to identify the beginning
of streams. In branching systems, Hack’s law suggests
that L = 1/M A(1/y) with 1/y = 0.6 (or 0.56)
(y about 1.7). In parallel flow systems L is proportional
to A (y about 1). This method tries to identify the
transition between these two paradigms by using an
exponent y somewhere in between (y about 1.3).
Outputs
Label Name Type Popis
Stream Source
Grid
[raster] An indicator grid (1,0) that evaluates A >= (M)(L^y),
based on the maximum upslope path length, the D8
contributing area grid inputs, and parameters M and y.
This grid indicates likely stream source grid cells.
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Python code
Algorithm ID: taudem:lengtharea
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Move Outlets To Streams
Moves outlet points that are not aligned with a stream cell from a stream raster grid, downslope along the D8 flow
direction until a stream raster cell is encountered, the „max_dist“ number of grid cells are examined, or the flow path
exits the domain (i.e. a „no data“ value is encountered for the D8 flow direction). The output file is a new outlets
shapefile where each point has been moved to coincide with the stream raster grid, if possible. A field „dist_moved“
is added to the new outlets shapefile to indicate the changes made to each point. Points that are already on a stream
cell are not moved and their „dist_moved“ field is assigned a value 0. Points that are initially not on a stream cell are
moved by sliding them downslope along the D8 flow direction until one of the following occurs: a) A stream raster
grid cell is encountered before traversing the „max_dist“ number of grid cells. In which case, the point is moved and
the „dist_moved“ field is assigned a value indicating how many grid cells the point was moved. b) More than the
„max_number“ of grid cells are traversed, or c) the traversal ends up going out of the domain (i.e., a „no data“ D8
flow direction value is encountered). In which case, the point is not moved and the „dist_moved“ field is assigned
a value of -1.
Parameters
Label Name Type Popis
D8 Flow Direction
Grid
[raster] A grid of D8 flow directions which are defined, for each
cell, as the direction of the one of its eight adjacent or
diagonal neighbors with the steepest downward slope.
This grid can be obtained as the output of the „D8 Flow
Directions“ tool.
Stream Raster
Grid
[raster] This output is an indicator grid (1, 0) that indicates the
location of streams, with a value of 1 for each of the
stream cells and 0 for the remainder of the cells. This
file is produced by several different tools in the „Stream
Network Analysis“ toolset.
Outlets Shapefile [vector: point] A point shape file defining points of interest or outlets
that should ideally be located on a stream, but may not
be exactly on the stream due to the fact that the shapefile
point locations may not have been accurately registered
with respect to the stream raster grid.
Maximum
Number of Grid
Cells to traverse
[number]
Default: 50
This input parameter is the maximum number of grid
cells that the points in the input outlet shapefile will
be moved before they are saved to the output outlet
shapefile.
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Outputs
Label Name Type Popis
Output Outlet
Shapefile
[vector: point] A point shape file defining points of interest or outlets.
This file has one point in it for each point in the
input outlet shapefile. If the original point was located
on a stream, then the point was not moved. If the
original point was not on a stream, the point was moved
downslope according to the D8 flow direction until it
reached a stream or the maximum distance had been
reached. This file has an additional field „dist_moved“
added to it which is the number of cells that the point
was moved. This field is 0 if the cell was originally on
a stream, -1 if it was not moved because there was
not a stream within the maximum distance, or some
positive value if it was moved.
Python code
Algorithm ID: taudem:moveoutletstostreams
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Peuker Douglas
Creates an indicator grid (1, 0) of upward curved grid cells according to the Peuker and Douglas algorithm.
With this tool, the DEM is first smoothed by a kernel with weights at the center, sides, and diagonals. The Peuker
and Douglas (1975) method (also explained in Band, 1986), is then used to identify upwardly curving grid cells.
This technique flags the entire grid, then examines in a single pass each quadrant of 4 grid cells, and unflags the
highest. The remaining flagged cells are deemed „upwardly curved“, and when viewed, resemble a channel network.
This proto-channel network generally lacks connectivity and requires thinning, issues that were discussed in detail by
Band (1986).
Parameters
Label Name Type Popis
Elevation Grid [raster] A grid of elevation values. This is usually the output of
the „Pit Remove“ tool, in which case it is elevations
with pits removed.
Center Smoothing
Weight
[number]
Default: 0.4
The center weight parameter used by a kernel to smooth
the DEM before the tool identifies upwardly curved grid
cells.
Side Smoothing
Weight
[number]
Default: 0.1
The side weight parameter used by a kernel to smooth
the DEM before the tool identifies upwardly curved grid
cells.
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Diagonal
Smoothing Weight
[number]
Default: 0.05
The diagonal weight parameter used by a kernel to
smooth the DEM before the tool identifies upwardly
curved grid cells.
Outputs
Label Name Type Popis
Stream Source
Grid
[raster] An indicator grid (1, 0) of upward curved grid cells
according to the Peuker and Douglas algorithm, and
if viewed, resembles a channel network. This proto-channel
network generally lacks connectivity and
requires thinning, issues that were discussed in detail
by Band (1986).
Python code
Algorithm ID: taudem:peukerdouglas
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
See also
• Band, L. E., (1986), „Topographic partition of watersheds with digital elevation models“, Water Resources
Research, 22(1): 15-24.
• Peuker, T. K. and D. H. Douglas, (1975), „Detection of surface-specific points by local parallel processing of
discrete terrain elevation data“, Comput. Graphics Image Process., 4: 375-387.
Peuker Douglas stream
Combines the functionality of the „Peuker Douglas“, „D8 Contributing Area“, „Stream Drop Analysis“ and „Stream
Definition by Threshold“ tools in order to generate a stream indicator grid (1,0) where the streams are located using
a DEM curvature-based method. With this method, the DEM is first smoothed by a kernel with weights at the center,
sides, and diagonals. The Peuker and Douglas (1975) method (also explained in Band, 1986), is then used to identify
upwardly curving grid cells. This technique flags the entire grid, then examines in a single pass each quadrant of
4 grid cells, and unflags the highest. The remaining flagged cells are deemed ‚upwardly curved‘, and when viewed,
resemble a channel network. This proto-channel network sometimes lacks connectivity, and/or requires thinning,
issues that were discussed in detail by Band (1986). The thinning and connecting of these grid cells is achieved here
by computing the D8 contributing area using only these upwardly curving cells. An accumulation threshold on the
number of these cells is then used to map the channel network where this threshold is optionally set by the user, or
determined via drop analysis.
If drop analysis is used, then instead of providing a value for the accumulation threshold, the accumulation threshold
value is determined by searching the range between the Drop Analysis Parameters „Lowest“ and „Highest“, using the
number of steps in the parameter „Number“. For the science behind drop analysis, see Tarboton, et al. (1991, 1992),
and Tarboton and Ames (2001). The value of accumulation threshold that is selected is the smallest value where the
absolute value of the t-statistic is less than 2. This is written to the drop analysis table text file. Drop analysis is only
possible when outlets have been specified, because if an entire grid domain is analyzed, as the threshold varies, shorter
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streams draining off the edge may not meet the threshold criterion and be excluded from the analysis. This makes
defining drainage density problematic and it is somewhat inconsistent to compare statistics evaluated over differing
domains.
Parameters
Outputs
Label Name Type Popis
Stream source [raster] An indicator grid (1, 0) of upward curved grid cells
according to the Peuker and Douglas algorithm, and
if viewed, resembles a channel network. This proto-channel
network generally lacks connectivity and
requires thinning, issues that were discussed in detail
by Band (1986).
Python code
Algorithm ID: taudem:peukerdouglasstreamdef
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Slope Area Combination
Creates a grid of slope-area values = (Sm) (An) based on slope and specific catchment area grid inputs, and
parameters m and n. This tool is intended for use as part of the slope-area stream raster delineation method.
Parameters
Label Name Type Popis
Slope Grid [raster] This input is a grid of slope values. This grid can be
obtained from the „D-Infinity Flow Directions“ tool.
Contributing Area
Grid
[raster] A grid giving the specific catchment area for each
cell taken as its own contribution (grid cell length
or summation of weights) plus the proportional
contribution from upslope neighbors that drain in to
it. This grid is typically obtained from the „D-Infinity
Contributing Area“ tool.
Slope Exponent [number]
Default: 2
The slope exponent (m) parameter which will be used
in the formula: (Sm)(An), that is used to create the
slope-area grid.
Area Exponent [number]
Default: 1
The area exponent (n) parameter which will be used
in the formula: (Sm)(An), that is used to create the
slope-area grid.
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Outputs
Label Name Type Popis
Slope Area Grid [raster] A grid of slope-area values = (Sm)(An) calculated
from the slope grid, specific catchment area grid,
m slope exponent parameter, and n area exponent
parameter.
Python code
Algorithm ID: taudem:slopearea
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Slope area stream definition
Creates a grid of slope-area values = (Sm) (An) based on slope and specific catchment area grid inputs, and
parameters m and n. This tool is intended for use as part of the slope-area stream raster delineation method.
Parameters
Label Name Type Popis
D8 flow directions [raster]
D-infinity
Contributing
Area
[raster] A grid giving the specific catchment area for each
cell taken as its own contribution (grid cell length
or summation of weights) plus the proportional
contribution from upslope neighbors that drain in to
it. This grid is typically obtained from the „D-Infinity
Contributing Area“ tool.
Slope [raster] This input is a grid of slope values. This grid can be
obtained from the „D-Infinity Flow Directions“ tool.
Mask grid [raster]
Outlets [vector: point]
Pit-filled grid for
drop analysis
[raster]
D8 contributing
area for drop
analysis
[raster]
Slope Exponent [number]
Default: 2
The slope exponent (m) parameter which will be used
in the formula: (Sm)(An), that is used to create the
slope-area grid.
Area Exponent [number]
Default: 1
The area exponent (n) parameter which will be used
in the formula: (Sm)(An), that is used to create the
slope-area grid.
Accumulation
threshold
[number]
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Minimum
threshold
[number]
Maximum
threshold
[number]
Number of drop
thresholds
[number]
Type of threshold
step
[enumeration]
Default: 0
Options:
• 0 — Logarithmic
• 1 — Linear
Check for edge
contamination
[boolean]
Select threshold by
drop analysis
[boolean]
Outputs
Label Name Type Popis
Stream raster [raster]
Slope area [raster] A grid of slope-area values = (Sm)(An) calculated
from the slope grid, specific catchment area grid,
m slope exponent parameter, and n area exponent
parameter.
Maximum
upslope
[raster]
Drop analysis [file]
Python code
Algorithm ID: taudem:slopeareastreamdef
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Stream Definition By Threshold
Operates on any grid and outputs an indicator (1, 0) grid identifying cells with input values >= the threshold value.
The standard use is to use an accumulated source area grid to as the input grid to generate a stream raster grid as the
output. If you use the optional input mask grid, it limits the domain being evaluated to cells with mask values >=
0. When you use a D-infinity contributing area grid (*sca) as the mask grid, it functions as an edge contamination
mask. The threshold logic is:
src = ((ssa >= thresh) & (mask >= s0)) ? 1:0
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Parameters
Label Name Type Popis
Accumulated
Stream Source
Grid
[raster] This grid nominally accumulates some characteristic or
combination of characteristics of the watershed. The
exact characteristic(s) varies depending on the stream
network raster algorithm being used. This grid needs to
have the property that grid cell values are monotonically
increasing downslope along D8 flow directions, so that
the resulting stream network is continuous. While this
grid is often from an accumulation, other sources such
as a maximum upslope function will also produce
a suitable grid.
Threshold [number]
Default: 100
This parameter is compared to the value in the
Accumulated Stream Source grid (*ssa) to determine
if the cell should be considered a stream cell. Streams
are identified as grid cells for which ssa value is >= this
threshold.
Mask Grid
Optional
[raster] This optional input is a grid that is used to mask the
domain of interest and output is only provided where
this grid is >= 0. A common use of this input is to
use a D-Infinity contributing area grid as the mask
so that the delineated stream network is constrained
to areas where D-infinity contributing area is available,
replicating the functionality of an edge contamination
mask.
Outputs
Label Name Type Popis
Stream Raster
Grid
[raster] This is an indicator grid (1, 0) that indicates the location
of streams, with a value of 1 for each of the stream cells
and 0 for the remainder of the cells.
Python code
Algorithm ID: taudem:threshold
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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Stream definition with drop analysis
Combines the function of the „Stream Drop Analysis“ tool and the „Stream Definition by Threshold“ tools. It applies
a series of thresholds (determined from the input parameters) to the input accumulated stream source grid (ssa)
grid and outputs the results in the stream drop statistics table (drp.txt). Then it outputs a stream raster grid, which
is an indicator (1,0) grid of stream cells. Stream cells are defined as those cells where the accumulated stream source
value is >= the optimal threshold as determined from the stream drop statistics. There is an option to include a mask
input to replicate the functionality for using the *sca file as an edge contamination mask. The threshold logic should
be: src = ((ssa >= thresh) & (mask >=0)) ? 1:0
Parameters
Outputs
Python code
Algorithm ID: taudem:streamdefdropanalysis
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
Stream Drop Analysis
Applies a series of thresholds (determined from the input parameters) to the input accumulated stream source grid
(*ssa) grid and outputs the results in the *drp.txt file the stream drop statistics table. This function is designed to
aid in the determination of a geomorphologically objective threshold to be used to delineate streams. Drop Analysis
attempts to select the right threshold automatically by evaluating a stream network for a range of thresholds and
examining the constant drop property of the resulting Strahler streams. Basically it asks the question: Is the mean
stream drop for first order streams statistically different from the mean stream drop for higher order streams, using
a T-test. Stream drop is the difference in elevation from the beginning to the end of a stream defined as the sequence of
links of the same stream order. If the T-test shows a significant difference then the stream network does not obey this
„law“ so a larger threshold needs to be chosen. The smallest threshold for which the T-test does not show a significant
difference gives the highest resolution stream network that obeys the constant stream drop „law“ from geomorphology,
and is the threshold chosen for the „objective“ or automatic mapping of streams from the DEM. This function can be
used in the development of stream network rasters, where the exact watershed characteristic(s) that were accumulated
in the accumulated stream source grid vary based on the method being used to determine the stream network raster.
The constant stream drop „law“ was identified by Broscoe (1959). For the science behind using this to determine
a stream delineation threshold, see Tarboton et al. (1991, 1992), Tarboton and Ames (2001).
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Parameters
Label Name Type Popis
D8 Contributing
Area Grid
[raster] A grid of contributing area values for each cell that were
calculated using the D8 algorithm. The contributing
area for a cell is the sum of its own contribution plus
the contribution from all upslope neighbors that drain to
it, measured as a number of cells or the sum of weight
loadings. This grid can be obtained as the output of the
„D8 Contributing Area“ tool. This grid is used in the
evaluation of drainage density reported in the stream
drop table.
D8 Flow Direction
Grid
[raster] A grid of D8 flow directions which are defined, for each
cell, as the direction of the one of its eight adjacent or
diagonal neighbors with the steepest downward slope.
This grid can be obtained as the output of the „D8 Flow
Directions“ tool.
Pit Filled
Elevation Grid
[raster] A grid of elevation values. This is usually the output of
the „Pit Remove“ tool, in which case it is elevations
with pits removed.
Accumulated
Stream Source
Grid
[raster] This grid must be monotonically increasing along
the downslope D8 flow directions. It it compared to
a series of thresholds to determine the beginning of
the streams. It is often generated by accumulating some
characteristic or combination of characteristics of the
watershed with the „D8 Contributing Area“ tool, or
using the maximum option of the „D8 Flow Path
Extreme“ tool. The exact method varies depending on
the algorithm being used.
Outlets Shapefile [vector: point] A point shapefile defining the outlets upstream of which
drop analysis is performed.
Minimum
Threshold
[number]
Default: 5
This parameter is the lowest end of the range searched
for possible threshold values using drop analysis. This
technique looks for the smallest threshold in the range
where the absolute value of the t-statistic is less than 2.
For the science behind the drop analysis see Tarboton
et al. (1991, 1992), Tarboton and Ames (2001).
Maximum
Threshold
[number]
Default: 500
This parameter is the highest end of the range searched
for possible threshold values using drop analysis. This
technique looks for the smallest threshold in the range
where the absolute value of the t-statistic is less than 2.
For the science behind the drop analysis see Tarboton
et al. (1991, 1992), Tarboton and Ames (2001).
Number of
Threshold Values
[number]
Default: 10
The parameter is the number of steps to divide the
search range into when looking for possible threshold
values using drop analysis. This technique looks for the
smallest threshold in the range where the absolute value
of the t-statistic is less than 2. For the science behind
the drop analysis see Tarboton et al. (1991, 1992),
Tarboton and Ames (2001).
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Spacing for
Threshold Values
[enumeration]
Default: 0
This parameter indicates whether logarithmic or linear
spacing should be used when looking for possible
threshold values using drop analysis.
Options:
• 0 — Logarithmic
• 1 — Linear
Outputs
Label Name Type Popis
D-Infinity Drop to
Stream Grid
[file] This is a comma delimited text file with the following
header line:
Threshold,DrainDen,NoFirstOrd,
→NoHighOrd,MeanDFirstOrd,MeanDHighOrd,
→StdDevFirstOrd,StdDevHighOrd,T
The file then contains one line of data for each threshold
value examined, and then a summary line that indicates
the optimum threshold value. This technique looks for
the smallest threshold in the range where the absolute
value of the t-statistic is less than 2. For the science
behind the drop analysis, see Tarboton et al. (1991,
1992), Tarboton and Ames (2001).
Python code
Algorithm ID: taudem:dropanalysis
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
See also
• Broscoe, A. J., (1959), „Quantitative analysis of longitudinal stream profiles of small watersheds“, Office of
Naval Research, Project NR 389-042, Technical Report No. 18, Department of Geology, Columbia University,
New York.
• Tarboton, D. G., R. L. Bras and I. Rodriguez-Iturbe, (1991), „On the Extraction of Channel Networks from
Digital Elevation Data“, Hydrologic Processes, 5(1): 81-100.
• Tarboton, D. G., R. L. Bras and I. Rodriguez-Iturbe, (1992), „A Physical Basis for Drainage Density“,
Geomorphology, 5(1/2): 59-76.
• Tarboton, D. G. and D. P. Ames, (2001), „Advances in the mapping of flow networks from digital
elevation data“, World Water and Environmental Resources Congress, Orlando, Florida, May 20-24, ASCE,
https://www.researchgate.net/publication/2329568_Advances_in_the_Mapping_of_Flow_Networks_
From_Digital_Elevation_Data.
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Stream Reach and Watershed
This tool produces a vector network and shapefile from the stream raster grid. The flow direction grid is used to connect
flow paths along the stream raster. The Strahler order of each stream segment is computed. The subwatershed draining
to each stream segment (reach) is also delineated and labeled with the value identifier that corresponds to the WSNO
(watershed number) attribute in the Stream Reach Shapefile.
This tool orders the stream network according to the Strahler ordering system. Streams that don’t have any other
streams draining in to them are order 1. When two stream reaches of different order join the order of the downstream
reach is the order of the highest incoming reach. When two reaches of equal order join the downstream reach order
is increased by 1. When more than two reaches join the downstream reach order is calculated as the maximum of the
highest incoming reach order or the second highest incoming reach order + 1. This generalizes the common definition
to cases where more than two reaches join at a point. The network topological connectivity is stored in the Stream
Network Tree file, and coordinates and attributes from each grid cell along the network are stored in the Network
Coordinates file.
The stream raster grid is used as the source for the stream network, and the flow direction grid is used to trace
connections within the stream network. Elevations and contributing area are used to determine the elevation and
contributing area attributes in the network coordinate file. Points in the outlets shapefile are used to logically split
stream reaches to facilitate representing watersheds upstream and downstream of monitoring points. The program
uses the attribute field „id“ in the outlets shapefile as identifiers in the Network Tree file. This tool then translates the
text file vector network representation in the Network Tree and Coordinates files into a shapefile. Further attributes
are also evaluated. The program has an option to delineate a single watershed by representing the entire area draining
to the Stream Network as a single value in the output watershed grid.
Parameters
Label Name Type Popis
Pit Filled
Elevation Grid
[raster] A grid of elevation values. This is usually the output of
the „Pit Remove“ tool, in which case it is elevations
with pits removed.
D8 Flow Direction
Grid
[raster] A grid of D8 flow directions which are defined, for each
cell, as the direction of the one of its eight adjacent or
diagonal neighbors with the steepest downward slope.
This grid can be obtained as the output of the „D8 Flow
Directions“ tool.
D8 Drainage Area [raster] A grid giving the contributing area value in terms of
the number of grid cells (or the summation of weights)
for each cell taken as its own contribution plus the
contribution from upslope neighbors that drain in to
it using the D8 algorithm. This is usually the output
of the „D8 Contributing Area“ tool and is used
to determine the contributing area attribute in the
Network Coordinate file.
Stream Raster
Grid
[raster] An indicator grid indicating streams, by using a grid cell
value of 1 on streams and 0 off streams. Several of the
„Stream Network Analysis“ tools produce this type
of grid. The Stream Raster Grid is used as the source
for the stream network.
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Tabulka 24.245 – pokračujte na předchozí stránce
Outlets Shapefile
as Network Nodes
Optional
[vector: point] A point shape file defining points of interest. If this
file is used, the tool will only deliniate the stream
network upstream of these outlets. Additionally, points
in the Outlets Shapefile are used to logically split stream
reaches to facilitate representing watersheds upstream
and downstream of monitoring points. This tool
REQUIRES THAT THERE BE an integer attribute
field „id“ in the Outlets Shapefile, because the „id“
values are used as identifiers in the Network Tree file.
Delineate Single
Watershed
[boolean]
Default: True
This option causes the tool to delineate a single
watershed by representing the entire area draining
to the Stream Network as a single value in the
output watershed grid. Otherwise a seperate watershed
is delineated for each stream reach. Default is False
(seperate watershed).
Outputs
Label Name Type Popis
Stream Order
Grid
[raster] The Stream Order Grid has cells values of streams
ordered according to the Strahler order system. The
Strahler ordering system defines order 1 streams
as stream reaches that don’t have any other reaches
draining in to them. When two stream reaches of
different order join the order of the downstream reach
is the order of the highest incoming reach. When two
reaches of equal order join the downstream reach order
is increased by 1. When more than two reaches join the
downstream reach order is calculated as the maximum
of the highest incoming reach order or the second
highest incoming reach order + 1. This generalizes the
common definition to cases where more than two flow
paths reaches join at a point.
Watershed Grid [raster] This output grid identified each reach watershed with
a unique ID number, or in the case where the delineate
single watershed option was checked, the entire area
draining to the stream network is identified with a single
ID.
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Tabulka 24.246 – pokračujte na předchozí stránce
Stream Reach
Shapefile
[vector: line] This output is a polyline shapefile giving the links in
a stream network. The columns in the attribute table
are:
• LINKNO — Link Number. A unique number
associated with each link (segment of channel
between junctions). This is arbitrary and will
vary depending on number of processes used
• DSLINKNO — Link Number of the
downstream link. -1 indicates that this does
not exist
• USLINKNO1 — Link Number of first upstream
link. (-1 indicates no link upstream, i.e. for
a source link)
• USLINKNO2 — Link Number of second
upstream link. (-1 indicates no second link
upstream, i.e. for a source link or an internal
monitoring point where the reach is logically split
but the network does not bifurcate)
• DSNODEID — Node identifier for node at
downstream end of stream reach. This identifier
corresponds to the „id“ attribute from the Outlets
shapefile used to designate nodes
• Order — Strahler Stream Order
• Length — Length of the link. The units are the
horizontal map units of the underlying DEM grid
• Magnitude — Shreve Magnitude of the link. This
is the total number of sources upstream
• DS_Cont_Ar — Drainage area at the
downstream end of the link. Generally this
is one grid cell upstream of the downstream end
because the drainage area at the downstream end
grid cell includes the area of the stream being
joined
• Drop — Drop in elevation from the start to the
end of the link
• Slope — Average slope of the link (computed
as drop/length)
• Straight_L — Straight line distance from the start
to the end of the link
• US_Cont_Ar — Drainage area at the upstream
end of the link
• WSNO — Watershed number. Cross reference
to the *w.shp and *w grid files giving the
identification number of the watershed draining
directly to the link
• DOUT_END — Distance to the eventual outlet
(i.e. the most downstream point in the stream
network) from the downstream end of the link
• DOUT_START — Distance to the eventual
outlet from the upstream end of the link
• DOUT_MID — Distance to the eventual outlet
from the midpoint of the link
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Tabulka 24.246 – pokračujte na předchozí stránce
Network
Connectivity
Tree
[file] This output is a text file that details the network
topological connectivity is stored in the Stream
Network Tree file. Columns are as follows:
• Link Number (Arbitrary — will vary depending
on number of processes used)
• Start Point Number in Network coordinates
(*coord.dat) file (Indexed from 0)
• End Point Number in Network coordinates
(*coord.dat) file (Indexed from 0)
• Next (Downstream) Link Number. Points to
Link Number. -1 indicates no links downstream,
i.e. a terminal link
• First Previous (Upstream) Link Number. Points
to Link Number. -1 indicates no upstream links
• Second Previous (Upstream) Link Numbers.
Points to Link Number. -1 indicates no upstream
links. Where only one previous link is -1, it
indicates an internal monitoring point where the
reach is logically split, but the network does not
bifurcate
• Strahler Order of Link
• Monitoring point identifier at downstream end
of link. -1 indicates downstream end is not
a monitoring point
• Network magnitude of the link, calculated as the
number of upstream sources (following Shreve)
Network
Coordinates
[file] This output is a text file that contains the coordinates
and attributes of points along the stream network.
Columns are as follows:
• X coordinate
• Y Coordinate
• Distance along channels to the downstream end
of a terminal link
• Elevation
• Contributing area
Python code
Algorithm ID: taudem:streamnet
import processing
processing.run("algorithm_id", {parameter_dictionary})
The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary
provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to
run processing algorithms from the Python console.
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24.5 OTB applications provider
OTB (Orfeo ToolBox) is an image processing library for remote sensing data. It also provides applications that provide
image processing functionalities. The list of applications and their documentation are available in OTB CookBook
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KAPITOLA 25
Zásuvné moduly
25.1 QGIS Plugins
QGIS has been designed with a plugin architecture. This allows many new features and functions to be easily added
to the application. Some of the features in QGIS are actually implemented as plugins.
25.1.1 Core and External plugins
QGIS plugins are implemented either as Core Plugins or External Plugins.
Core Plugins are maintained by the QGIS Development Team and are automatically part of every QGIS distribution.
They are written in one of two languages: C++ or Python.
Most of External Plugins are currently written in Python. They are stored either in the ‚Official‘ QGIS Repository
at https://plugins.qgis.org/plugins/ or in external repositories and are maintained by the individual authors. Detailed
documentation about the usage, minimum QGIS version, home page, authors,and other important information are
provided for the plugins in the Official repository. For other external repositories, documentation might be available
with the external plugins themselves. External plugins documentation is not included in this manual.
To install or activate a plugin, go to Plugins menu and select Manage and install plugins…. Installed external
python plugins are placed under the python/plugins folder of the active user profile path.
Paths to Custom C++ plugins libraries can also be added under Settings ► Options ► System.
Poznámka: According to the plugin manager settings, QGIS main interface can display an icon on the right of the
status bar to inform you that there are updates for your installed plugins or new plugins available.
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25.1.2 The Plugins Dialog
The tabs in the Plugins dialog allow the user to install, uninstall and upgrade plugins in different ways. Each plugin
has some metadata displayed in the right panel:
• information on whether the plugin is experimental
• description
• rating vote(s) (you can vote for your preferred plugin!)
• tags
• some useful links to the home page, tracker and code repository
• author(s)
• version available
At the top of the dialog, a Search function helps you find any plugin using metadata information (author, name,
description…). It is available in nearly every tab (except Settings).
The Settings tab
The Settings tab is the main place you can configure which plugins can be displayed in your application. You can
use the following options:
• Check for updates on startup. Whenever a new plugin or a plugin update is available, QGIS will inform you
‚every time QGIS starts‘, ‚once a day‘, ‚every 3 days‘, ‚every week‘, ‚every 2 weeks‘ or ‚every month‘.
• Show also experimental plugins. QGIS will show you plugins in early stages of development, which are
generally unsuitable for production use.
• Show also deprecated plugins. Because they use functions that are no longer available in QGIS, these plugins
are set deprecated and generally unsuitable for production use. They appear among invalid plugins list.
By default, QGIS provides you with its official plugin repository with the URL https://plugins.qgis.org/plugins/
plugins.xml?qgis=3.0 (in case of QGIS 3.0) in the Plugin repositories section. To add external author repositories,
click Add… and fill in the Repository Details form with a name and the URL. The URL can be of http:// or
file:// protocol type.
The default QGIS repository is an open repository and you don’t need any authentication to access it. You can
however deploy your own plugin repository and require an authentication (basic authentication, PKI). You can get
more information on QGIS authentication support in Authentication chapter.
If you do not want one or more of the added repositories, they can be disabled from the Settings tab via the Edit…
button, or completely removed with the Delete button.
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Obr. 25.1: The Settings tab
The All tab
In the All tab, all the available plugins are listed, including both core and external plugins. Use Upgrade All to
look for new versions of the plugins. Furthermore, you can use Install Plugin if a plugin is listed but not installed,
Uninstall Plugin as well as Reinstall Plugin if a plugin is installed. An installed plugin can be temporarily de/activated
using the checkbox.
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Obr. 25.2: The All tab
The Installed tab
In the Installed tab, you’ll find listed the Core plugins, that you can not uninstall. You can extend this list with
external plugins that can be uninstalled and reinstalled any time, using the Uninstall Plugin and Reinstall Plugin buttons.
You can Upgrade All the plugins here as well.
Obr. 25.3: The Installed tab
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The Not installed tab
The Not installed tab lists all plugins available that are not installed. You can use the Install Plugin button to
implement a plugin into QGIS.
Obr. 25.4: The Not installed tab
The Upgradeable and New tabs
The Upgradeable and New tabs are enabled when new plugins are added to the repository or a new version
of an installed plugin is released. If you activated Show also experimental plugins in the Settings menu, those
also appear in the list giving you opportunity to early test upcoming tools.
Installation can be done with the Install Plugin, Upgrade Plugin or Upgrade All buttons.
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Obr. 25.5: The Upgradeable tab
The Invalid tab
The Invalid tab lists all installed plugins that are currently broken for any reason (missing dependency, errors while
loading, incompatible functions with QGIS version…). You can try the Reinstall Plugin button to fix an invalidated
plugin but most of the times the fix will be elsewhere (install some libraries, look for another compatible plugin or
help to upgrade the broken one).
Obr. 25.6: The Invalid tab
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The Install from ZIP tab
The Install from ZIP tab provides a file selector widget to import plugins in a zipped format, e.g. plugins
downloaded directly from their repository.
Obr. 25.7: The Install from zip tab
25.2 Using QGIS Core Plugins
25.2.1 DB Manager Plugin
The DB Manager Plugin is intended to be the main tool to integrate and manage spatial database formats supported
by QGIS (PostGIS, SpatiaLite, GeoPackage, Oracle Spatial, Virtual layers) in one user interface. The DB Manager
Plugin provides several features. You can drag layers from the QGIS Browser into the DB Manager, and it will
import your layer into your spatial database. You can drag and drop tables between spatial databases and they will get
imported.
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Obr. 25.8: DB Manager dialog
The Database menu allows you to connect to an existing database, to start the SQL window and to exit the DB
Manager Plugin. Once you are connected to an existing database, the menus Schema (relevant for DBMSs, such
as PostGIS / PostgreSQL) and Table will appear.
The Schema menu includes tools to create and delete (only if empty) schemas and, if topology is available (e.g. with
PostGIS topology), to start a TopoViewer.
The Table menu allows you to create and edit tables and to delete tables and views. It is also possible to empty tables
and to move tables between schemas. You can Run Vacuum Analyze for the selected table. Vacuum reclaims space and
makes it available for reuse, and analyze updates statistics that is used to determine the most efficient way to execute
a query. Change Logging… allows you to add change logging support to a table. Finally, you can Import Layer/File…
and Export to File….
The Providers window lists all existing databases supported by QGIS. With a double-click, you can connect to the
database. With the right mouse button, you can rename and delete existing schemas and tables. Tables can also be
added to the QGIS canvas with the context menu.
If connected to a database, the main window of the DB Manager offers four tabs. The Info tab provides information
about the table and its geometry, as well as about existing fields, constraints and indexes. It allows you to create
a spatial index on a the selected table. The Table tab shows the table, and the Preview tab renders the geometries
as preview. When you open an SQL Window, it will be placed in a new tab.
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Working with the SQL Window
You can use the DB Manager to execute SQL queries against your spatial database. Queries can be saved and loaded,
and there the SQL Query Builder will help you formulate your queries. You can even view spatial output by checking
Load as new layer and specifying Column(s) with unique values (IDs), Geometry column and Layer name (prefix).
It is possible to highlight a portion of the SQL to only execute that portion when pressing Ctrl+R or clicking the
Execute button.
The Query History button stores the last 20 queries of each database and provider.
Double clicking on an entry will add the string to the SQL window.
Obr. 25.9: Executing SQL queries in the DB Manager SQL window
Poznámka: The SQL Window can also be used to create Virtual Layers. In that case, instead of selecting a database,
select QGIS Layers under Virtual Layers before opening the SQL Window. See Creating virtual layers for
instructions on the SQL syntax to use.
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25.2.2 Geometry Checker Plugin
Geometry Checker is a powerful core plugin to check and fix the geometry validity of a layer. It is available from the
Vector menu ( Check Geometries…).
Configuring the checks
The Check Geometries dialog shows different grouped settings in the first tab (Setup):
• Input vector layers: to select the layers to check. A Only selected features checkbox can be used to restrict
the checking to the geometries of the selected features.
• Allowed geometry types gives the chance to restrict the geometry type of the input layer(s) to:
– Point
– Multipoint
– Line
– Multiline
– Polygon
– Multipolygon
• Geometry validity. Depending on geometry types you can choose between:
– Self intersections
– Duplicate nodes
– Self contacts
– Polygon with less than 3 nodes.
• Geometry properties. Depending on geometry types, different options are available:
– Polygons and multipolygons may not contain any holes
– Multipart objects must consist of more than one part
– Lines must not have dangles
• Geometry conditions. Allows you to add some condition to validate the geometries with:
– Minimal segment length (map units)
– Minimum angle between segment (deg)
– Minimal polygon area (map units sqr.)
– No sliver polygons with a Maximum thinness and a Max. area (map units sqr.)
• Topology checks. Depending on geometry types, many different options are available:
– Checks for duplicates
– Checks for features within other features
– Checks for overlaps smaller than
– Checks for gaps smaller than
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– Points must be covered by lines
– Points must properly lie inside a polygon
– Lines must not intersect any other lines
– Lines must not intersect with features of layer
– Polygons must follow boundaries of layer
• Tolerance. You can define the tolerance of the check in map layer units.
• Output vector layer gives the choice to:
– Modify input layer
– Create new layers
When you are happy with the configuration, you can click on the Run button.
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Obr. 25.10: The Geometry Checker Plugin
The Geometry Checker Plugin can find the following errors:
• Self intersections: a polygon with a self intersection
• Duplicate nodes: two duplicates nodes in a segment
• Holes: hole in a polygon
• Segment length: a segment length lower than a threshold
• Minimum angle: two segments with an angle lower than a threshold
• Minimum area: polygon area lower than a threshold
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• Silver polygon: this error come from very small polygon (with small area) with a large perimeter
• Duplicates features
• Feature within feature
• Overlaps: polygon overlapping
• Gaps: gaps between polygons
The following figure shows the different checks made by the plugin.
Obr. 25.11: Some checks supported by the plugin
Analysing the results
The results appear in the second tab (Result) and as an overview layer of the errors in the canvas (its name has the
default prefix checked_). A table lists the Geometry check result with one error per row and columns containing:
the layer name, an ID, the error type, then the coordinates of the error, a value (depending on the type of the error)
and finally the resolution column which indicates the resolution of the error. At the bottom of this table, you can
Export the error into different file formats. You also have a counter with the number of total errors and fixed ones.
You can select a row to see the location of the error. You can change this behavior by selecting another action between
Error (default), Feature, Don’t move, and Highlight contour of selected features.
Below the zoom action when clicking on the table row, you can:
• Show selected features in attribute table
• Fix selected errors using default resolution
• Fix selected errors, prompt for resolution method You will see a window to choose the resolution’s method
among which:
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– Merge with neighboring polygon with longest shared edge
– Merge with neighboring polygon with largest area
– Merge with neighboring polygon with identical attribute value, if any, or leave as is
– Delete feature
– No action
• Error resolution settings allows you to change the default resolution method depending on the error type
Tip: Fix multiple errors
You can fix multiple errors by selecting more than one row in the table with the CTRL + click action.
Finally, you can choose which Attribute to use when merging features by attribute value.
25.2.3 MetaSearch Catalog Client
Úvod
MetaSearch is a QGIS plugin to interact with metadata catalog services, supporting the OGC Catalog Service for the
Web (CSW) standard.
MetaSearch provides an easy and intuitive approach and user-friendly interface to searching metadata catalogs within
QGIS.
Obr. 25.12: Search and results of Services in MetaSearch
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Working with Metadata Catalogs in QGIS
MetaSearch is included by default in QGIS, with all of its dependencies, and can be enabled from the QGIS Plugin
Manager.
CSW (Catalog Service for the Web)
CSW (Catalog Service for the Web) is an OGC (Open Geospatial Consortium) specification that defines common
interfaces to discover, browse and query metadata about data, services, and other potential resources.
Startup
To start MetaSearch, click the icon or select Web ► MetaSearch ► MetaSearch via the QGIS main menu. The
MetaSearch dialog will appear. The main GUI consists of three tabs: Services, Search and Settings.
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Managing Catalog Services
Obr. 25.13: Managing Catalog Services
The Services tab allows the user to manage all available catalog services. MetaSearch provides a default list of Catalog
Services, which can be added by pressing the Add Default Services button.
To find all listed Catalog Service entries, click the dropdown select box.
To add a Catalog Service entry:
1. Click the New button
2. Enter a Name for the service, as well as the URL (endpoint). Note that only the base URL is required (not a full
GetCapabilities URL).
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3. If the CSW requires authentication, enter the appropriate User name and Password credentials.
4. Click OK to add the service to the list of entries.
To edit an existing Catalog Service entry:
1. Select the entry you would like to edit
2. Click the Edit button
3. And modify the Name or URL values
4. Kliknout OK.
To delete a Catalog Service entry, select the entry you would like to delete and click the Delete button. You will be
asked to confirm deleting the entry.
MetaSearch allows loading and saving connections to an XML file. This is useful when you need to share settings
between applications. Below is an example of the XML file format.
<?xml version="1.0" encoding="UTF-8"?>
<qgsCSWConnections version="1.0">
<csw name="Data.gov CSW" url="https://catalog.data.gov/csw-all"/>
<csw name="Geonorge - National CSW service for Norway" url="https://www.
→geonorge.no/geonetwork/srv/eng/csw"/>
<csw name="Geoportale Nazionale - Servizio di ricerca Italiano" url="http://
→www.pcn.minambiente.it/geoportal/csw"/>
<csw name="LINZ Data Service" url="http://data.linz.govt.nz/feeds/csw"/>
<csw name="Nationaal Georegister (Nederland)" url="http://www.
→nationaalgeoregister.nl/geonetwork/srv/eng/csw"/>
<csw name="RNDT - Repertorio Nazionale dei Dati Territoriali - Servizio di␣
→ricerca" url="http://www.rndt.gov.it/RNDT/CSW"/>
<csw name="UK Location Catalogue Publishing Service" url="http://csw.data.gov.
→uk/geonetwork/srv/en/csw"/>
<csw name="UNEP/GRID-Geneva Metadata Catalog" url="http://metadata.grid.unep.
→ch:8080/geonetwork/srv/eng/csw"/>
</qgsCSWConnections>
To load a list of entries:
1. Click the Load button. A new window will appear.
2. Click the Browse button and navigate to the XML file of entries you wish to load.
3. Click Open. The list of entries will be displayed.
4. Select the entries you wish to add from the list and click Load.
Click the Service Info button to display information about the selected Catalog Service such as service identification,
service provider and contact information. If you would like to view the raw XML response, click the GetCapabilities
Response button. A separate window will open displaying the Capabilities XML.
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Searching Catalog Services
Obr. 25.14: Searching catalog services
The Search tab allows the user to query Catalog Services for data and services, set various search parameters and
view results.
The following search parameters are available:
• Keywords: free text search keywords;
• From: the Catalog Service to perform the query against;
• Bounding box: the spatial area of interest to filter, defined by Xmax, Xmin, Ymax, and Ymin. Click Set Global
to do a global search, click Map Extent to do a search in the visible area, or enter values manually.
Clicking the Search button will search the selected Metadata Catalog. Search results are displayed in a list, and can be
sorted by clicking on the column header. You can navigate through search results with the directional buttons below
the search results.
Select a result and:
• Click the View Search Results as XML button to open a window with the service response in raw XML format.
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• If the metadata record has an associated bounding box, a footprint of the bounding box will be displayed on
the map.
• Double-click the record to display the record metadata with any associated access links. Clicking a link opens
the link in the user’s web browser.
• If the record is a supported web service (WMS/WMTS, WFS, WCS, ArcGIS Map Service, ArcGIS Feature
Service, etc.), the Add Data button will be enabled. When clicking this button, MetaSearch will verify if this
is a valid OWS. The service will then be added to the appropriate QGIS connection list, and the appropriate
connection dialog will appear.
Obr. 25.15: Metadata record display
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Nastavení
Obr. 25.16: MetaSearch settings
You can fine tune MetaSearch with the following Settings:
• Server Timeout: when searching metadata catalogs, the number of seconds for blocking connection attempt.
Default value is 10.
• Results paging: when searching metadata catalogs, the number of results to show per page. Default value is 10.
CSW Server Errors
In some cases, the CSW will work in a web browser, but not in MetaSearch. This may be due to the CSW server’s
configuration/setup. CSW server providers should ensure URLs are consistent and up to date in their configuration
(this is common in HTTP -> HTTPS redirection scenarios). Please see the pycsw FAQ item for a deeper explanation
of the issue and fix. Although the FAQ item is pycsw specific it can also apply in general to other CSW servers.
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25.2.4 Offline Editing Plugin
For data collection, it is a common situation to work with a laptop or a cell phone offline in the field. Upon returning
to the network, the changes need to be synchronized with the master datasource (e.g., a PostGIS database). If several
persons are working simultaneously on the same datasets, it is difficult to merge the edits by hand, even if people
don’t change the same features.
The Offline Editing
Plugin automates the synchronisation by copying the content of a datasource (usually PostGIS
or WFS-T) to a SpatiaLite or GeoPackage database and storing the offline edits to dedicated tables. After being
connected to the network again, it is possible to apply the offline edits to the master dataset.
To use the plugin:
1. Open a project with some vector layers (e.g., from a PostGIS or WFS-T datasource).
2. Assuming you have already enabled the plugin (see Core and External plugins) go to Database ► Offline Editing
► Convert to offline project. The eponym dialog opens.
3. Select the Storage type. It can be of GeoPackage or SpatiaLite database type.
4. Use the Browse button to indicate the location of the database in which to store the Offline data. It can be an
existing file or one to create.
5. In the Select remote layers section, check the layers you’d like to save. The content of the layers is saved to
database tables.
6. You can check Only synchronize selected features if a selection is present allowing to only save and work on
a subset. It can be invaluable in case of large layers.
This is all!
7. Save your project and bring it on the field.
8. Edit the layers offline.
9. After being connected again, upload the changes using Database ► Offline Editing ► Synchronize.
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Obr. 25.17: Create an offline project
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25.2.5 Topology Checker Plugin
Obr. 25.18: The Topology Checker Plugin
Topology describes the relationships between points, lines and polygons that represent the features of a geographic
region. With the Topology Checker plugin, you can look over your vector files and check the topology with
several topology rules. These rules check with spatial relations whether your features ‚Equal‘, ‚Contain‘, ‚Cover‘,
are ‚CoveredBy‘, ‚Cross‘, are ‚Disjoint‘, ‚Intersect‘, ‚Overlap‘, ‚Touch‘ or are ‚Within‘ each other. It depends on your
individual questions which topology rules you apply to your vector data (e.g., normally you won’t accept overshoots
in line layers, but if they depict dead-end streets you won’t remove them from your vector layer).
QGIS has a built-in topological editing feature, which is great for creating new features without errors. But existing
data errors and user-induced errors are hard to find. This plugin helps you find such errors through a list of rules.
It is very simple to create topology rules with the Topology Checker plugin.
On point layers the following rules are available:
• Must be covered by: Here you can choose a vector layer from your project. Points that aren’t covered by the
given vector layer occur in the ‚Error‘ field.
• Must be covered by endpoints of: Here you can choose a line layer from your project.
• Must be inside: Here you can choose a polygon layer from your project. The points must be inside a polygon.
Otherwise, QGIS writes an ‚Error‘ for the point.
• Must not have duplicates: Whenever a point is represented twice or more, it will occur in the ‚Error‘ field.
• Must not have invalid geometries: Checks whether the geometries are valid.
• Must not have multi-part-geometries: All multi-part points are written into the ‚Error‘ field.
On line layers, the following rules are available:
• End points must be covered by: Here you can select a point layer from your project.
• Must not have dangles: This will show the overshoots in the line layer.
25.2. Using QGIS Core Plugins 1315
QGIS Desktop 3.16 User Guide
• Must not have duplicates: Whenever a line feature is represented twice or more, it will occur in the ‚Error‘
field.
• Must not have invalid geometries: Checks whether the geometries are valid.
• Must not have multi-part geometries: Sometimes, a geometry is actually a collection of simple (single-part)
geometries. Such a geometry is called multi-part geometry. If it contains just one type of simple geometry, we
call it multi-point, multi-linestring or multi-polygon. All multi-part lines are written into the ‚Error‘ field.
• Must not have pseudos: A line geometry’s endpoint should be connected to the endpoints of two other
geometries. If the endpoint is connected to only one other geometry’s endpoint, the endpoint is called a pseudo
node.
On polygon layers, the following rules are available:
• Must contain: Polygon layer must contain at least one point geometry from the second layer.
• Must not have duplicates: Polygons from the same layer must not have identical geometries. Whenever
a polygon feature is represented twice or more it will occur in the ‚Error‘ field.
• Must not have gaps: Adjacent polygons should not form gaps between them. Administrative boundaries could
be mentioned as an example (US state polygons do not have any gaps between them…).
• Must not have invalid geometries: Checks whether the geometries are valid. Some of the rules that define
a valid geometry are:
– Polygon rings must close.
– Rings that define holes should be inside rings that define exterior boundaries.
– Rings may not self-intersect (they may neither touch nor cross one another).
– Rings may not touch other rings, except at a point.
• Must not have multi-part geometries: Sometimes, a geometry is actually a collection of simple (single-part)
geometries. Such a geometry is called multi-part geometry. If it contains just one type of simple geometry, we
call it multi-point, multi-linestring or multi-polygon. For example, a country consisting of multiple islands can
be represented as a multi-polygon.
• Must not overlap: Adjacent polygons should not share common area.
• Must not overlap with: Adjacent polygons from one layer should not share common area with polygons from
another layer.
Below is the list of Core plugins provided with QGIS. They are not necessarily enabled by default.
Ikona Plugin Popis Manual Reference
Správce databází Manage your databases within QGIS DB Manager Plugin
Geometry Checker Check and repair errors in vector geometries Geometry Checker Plugin
GPS Tools Tools for loading and importing GPS data GPS Plugin
GRASS GRASS functionality GRASS GIS Integration
MetaSearch Catalog
Client
Interact with metadata catalog services
(CSW)
MetaSearch Catalog Client
Offline Editing Offline editing and synchronizing with
database
Offline Editing Plugin
Zpracování Spatial data processing framework QGIS processing
framework
Topology Checker Find topological errors in vector layers Topology Checker Plugin
1316 Kapitola 25. Zásuvné moduly
QGIS Desktop 3.16 User Guide
25.3 QGIS Python console
As you will see later in this chapter, QGIS has been designed with a plugin architecture. Plugins can be written in
Python, a very famous language in the geospatial world.
QGIS brings a Python API (see PyQGIS Developer Cookbook for some code sample) to let the user interact with its
objects (layers, feature or interface). QGIS also has a Python console.
The QGIS Python Console is an interactive shell for the python command executions. It also has a python file editor
that allows you to edit and save your python scripts. Both console and editor are based on PyQScintilla2 package. To
open the console go to Plugins ► Python Console (Ctrl+Alt+P).
25.3.1 The Interactive Console
The interactive console is composed of a toolbar, an input area and an output one.
Panel nástrojů
The toolbar proposes the following tools:
• Clear Console
to wipe the output area;
• Run Command
available in the input area: same as pressing Enter;
• Show Editor
: toggles The Code Editor visibility;
• Options…
: opens a dialog to configure console properties (see Python Console Settings);
• Help…
: browses the current documentation.
Console
The console main features are:
• Code completion, highlighting syntax and calltips for the following APIs:
– Python
– PyQGIS
– PyQt5
– QScintilla2
– osgeo-gdal-ogr
• Ctrl+Alt+Space to view the auto-completion list if enabled in the Python Console Settings;
• Execute code snippets from the input area by typing and pressing Enter or Run Command;
• Execute code snippets from the output area using the Enter Selected from the contextual menu or pressing
Ctrl+E;
• Browse the command history from the input area using the Up and Down arrow keys and execute the command
you want;
• Ctrl+Shift+Space to view the command history: double-clicking a row will execute the command. The
Command History dialog can also be accessed from context menu of input area;
• Save and clear the command history. The history will be saved into the console_history.txt file under
the active user profile folder;
• Open QGIS C++ API documentation by typing _api;
25.3. QGIS Python console 1317
QGIS Desktop 3.16 User Guide
• Open QGIS Python API documentation by typing _pyqgis.
• Open PyQGIS Cookbook by typing _cookbook.
Tip: Reuse executed commands from the output panel
You can execute code snippets from the output panel by selecting some text and pressing Ctrl+E. No matter if
selected text contains the interpreter prompt (>>>, ...).
Obr. 25.19: The Python Console
25.3.2 The Code Editor
Use the Show Editor
button to enable the editor widget. It allows editing and saving Python files and offers advanced
functionalities to manage your code (comment and uncomment code, check syntax, share the code via codepad.org
and much more). Main features are:
• Code completion, highlighting syntax and calltips for the following APIs:
– Python
– PyQGIS
– PyQt5
– QScintilla2
– osgeo-gdal-ogr
• Ctrl+Space to view the auto-completion list.
• Sharing code snippets via codepad.org.
• Ctrl+4 Syntax check.
• Search bar (open it with the default Desktop Environment shortcut, usually Ctrl+F):
– Use the default Desktop Environment shortcut to find next/previous (Ctrl+G and Shift+Ctrl+G);
– Automatically find first match when typing in find box;
– Set initial find string to selection when opening find;
– Pressing Esc closes the find bar.
• Object inspector: a class and function browser;
• Go to an object definition with a mouse click (from Object inspector);
1318 Kapitola 25. Zásuvné moduly
QGIS Desktop 3.16 User Guide
• Execute code snippets with the Run Selected command in contextual menu;
• Execute the whole script with the Run Script command (this creates a byte-compiled file with the extension
.pyc).
Poznámka: Running partially or totally a script from the Code Editor outputs the result in the Console output area.
Obr. 25.20: The Python Console editor
Tip: Save the options
To save the state of console’s widgets you have to close the Python Console from the close button. This allows you to
save the geometry to be restored to the next start.
25.3. QGIS Python console 1319
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1320 Kapitola 25. Zásuvné moduly
KAPITOLA 26
Pomoc a podpora
26.1 Mailing list
QGIS je v aktivním vývoji a jako takový nebude vždy fungovat tak, jak jste očekávali. Preferovaný způsob, jak získat
pomoc, je připojení se k mailing listu uživatelů qgis. Vaše dotazy se dostanou k širšímu publiku a odpovědi budou
prospěšné ostatním.
26.1.1 Uživatelé QGIS
This mailing list is used for discussion about QGIS in general, as well as specific questions regarding its installation and
use. You can subscribe to the qgis-users mailing list by visiting the following URL: https://lists.osgeo.org/mailman/
listinfo/qgis-user
26.1.2 Vývojáři QGIS
If you are a developer facing problems of a more technical nature, you may want to join the qgis-developer mailing
list. This list is also a place where people can chime in and collect and discuss QGIS related UX (User Experience) /
usability issues. It’s here: https://lists.osgeo.org/mailman/listinfo/qgis-developer
26.1.3 Komunitní tým QGIS
This list deals with topics like documentation, context help, user guide, web sites, blog, mailing lists, forums, and
translation efforts. If you would like to work on the user guide as well, this list is a good starting point to ask your
questions. You can subscribe to this list at: https://lists.osgeo.org/mailman/listinfo/qgis-community-team
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QGIS Desktop 3.16 User Guide
26.1.4 Překlady QGIS
This list deals with the translation efforts. If you like to work on the translation of the website, manuals or the graphical
user interface (GUI), this list is a good starting point to ask your questions. You can subscribe to this list at: https:
//lists.osgeo.org/mailman/listinfo/qgis-tr
26.1.5 Řídící výbor projektu QGIS (PSC)
This list is used to discuss Steering Committee issues related to overall management and direction of QGIS. You can
subscribe to this list at: https://lists.osgeo.org/mailman/listinfo/qgis-psc
26.1.6 Uživatelské skupiny QGIS
In order to locally promote QGIS and contribute to its development, some QGIS communities are organized into QGIS
User Groups. These groups are places to discuss local topics, organize regional or national user meetings, organize
sponsoring of features… The list of current user groups is available at https://qgis.org/en/site/forusers/usergroups.
html
Jste vítáni k zapsání se k jakémukoliv z těchto seznamů. Prosíme nezapomeňte přispět do seznamů zodpovězením
otázek a sdílením Vašich zkušeností.
26.2 IRC
We also maintain a presence on IRC - visit us by joining the #qgis channel on irc.freenode.net. Please wait for
a response to your question, as many folks on the channel are doing other things and it may take a while for them to
notice your question. If you missed a discussion on IRC, not a problem! We log all discussion, so you can easily catch
up. Just go to http://irclogs.geoapt.com/qgis/ and read the IRC-logs.
26.3 Commercial support
Commercial support for QGIS is also available. Check the website https://qgis.org/en/site/forusers/commercial_
support.html for more information.
26.4 BugTracker
While the qgis-users mailing list is useful for general ‚How do I do XYZ in QGIS?‘-type questions, you may wish to
notify us about bugs in QGIS. You can submit bug reports using the QGIS bug tracker.
Mějte na paměti, že vaše chyba nemusí mít vždy přednost, ve kterou můžete doufat (v závislosti na její závažnosti).
Některé chyby mohou vyžadovat větší úsilí vývojářů k nápravě a pracovní síla nemusí být vždy k dispozici.
Feature requests can be submitted as well using the same ticket system as for bugs. Please make sure to select the
type Feature request.
If you have found a bug and fixed it yourself, you can submit a Pull Request on the Github QGIS Project.
Read Bugs, Features and Issues and submit_patch for more details.
1322 Kapitola 26. Pomoc a podpora
QGIS Desktop 3.16 User Guide
26.5 Blog
The QGIS community also runs a weblog at https://plugins.qgis.org/planet/, which has some interesting articles for
users and developers. Many other QGIS blogs exist, and you are invited to contribute with your own QGIS blog!
26.6 Zásuvné moduly
The website https://plugins.qgis.org is the official QGIS plugins web portal. Here, you find a list of all stable and
experimental QGIS plugins available via the ‚Official QGIS Plugin Repository‘.
26.7 Wiki
Lastly, we maintain a WIKI web site at https://github.com/qgis/QGIS/wiki where you can find a variety of useful
information relating to QGIS development, release plans, links to download sites, message-translation hints and more.
Check it out, there are some goodies inside!
26.5. Blog 1323
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1324 Kapitola 26. Pomoc a podpora
KAPITOLA 27
Contributors
QGIS is an open source project developed by a team of dedicated volunteers and organisations. We strive to be
a welcoming community for people of all race, creed, gender and walks of life. At any moment, you can get involved.
27.1 Authors
Below are listed people who dedicate their time and energy to write, review, and update the whole QGIS
documentation.
Tim Sutton Yves Jacolin Jacob Lanstorp Gary E. Sherman Richard Duivenvoorde
Tara Athan Anita Graser Arnaud Morvan Gavin Macaulay Luca Casagrande
K. Koy Hugo Mercier Akbar Gumbira Marie Silvestre Jürgen E. Fischer
Fran Raga Eric Goddard Martin Dobias Diethard Jansen Saber Razmjooei
Ko Nagase Nyall Dawson Matthias Kuhn Andreas Neumann Harrissou Sant-anna
Manel Clos David Willis Larissa Junek Paul Blottière Sebastian Dietrich
Chris Mayo Stephan Holl Magnus Homann Bernhard Ströbl Alessandro Pasotti
N. Horning Radim Blazek Joshua Arnott Luca Manganelli Marco Hugentobler
Andre Mano Mie Winstrup Frank Sokolic Vincent Picavet Jean-Roc Morreale
Andy Allan Victor Olaya Tyler Mitchell René-Luc D’Hont Marco Bernasocchi
Ilkka Rinne Werner Macho Chris Berkhout Nicholas Duggan Jonathan Willitts
David Adler Lars Luthman Brendan Morely Raymond Nijssen Carson J.Q. Farmer
Jaka Kranjc Mezene Worku Patrick Sunter Steven Cordwell Stefan Blumentrath
Andy Schmid Vincent Mora Alexandre Neto Hien Tran-Quang Alexandre Busquets
João Gaspar Tom Kralidis Alexander Bruy Paolo Cavallini Milo Van der Linden
Peter Ersts Ujaval Gandhi Dominic Keller Giovanni Manghi Maximilian Krambach
Anne Ghisla Dick Groskamp Uros Preloznik Stéphane Brunner QGIS Korean Translator
Zoltan Siki Håvard Tveite Mattheo Ghetta Salvatore Larosa Konstantinos Nikolaou
Tom Chadwin Larry Shaffer Nathan Woodrow Martina Savarese Godofredo Contreras
Astrid Emde Luigi Pirelli Thomas Gratier Giovanni Allegri GiordanoPezzola
Paolo Corti Tudor Bărăscu Maning Sambale Claudia A. Engel Yoichi Kayama
Otto Dassau Denis Rouzaud Nick Bearman embelding ajazepk
Ramon Andrei zstadler icephale Rosa Aguilar
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27.2 Translators
QGIS is a multi-language application and as is, also publishes a documentation translated into several languages.
Many other languages are being translated and would be released as soon as they reach a reasonable percentage
of translation. If you wish to help improving a language or request a new one, please see https://qgis.org/en/site/
getinvolved/index.html.
The current translations are made possible thanks to:
Language Contributors
Bahasa
Indonesia
Emir Hartato, I Made Anombawa, Januar V. Simarmata, Muhammad Iqnaul Haq Siregar, Trias
Aditya
Chinese
(Traditional)
Calvin Ngei, Zhang Jun, Richard Xie
Dutch Carlo van Rijswijk, Dick Groskamp, Diethard Jansen, Raymond Nijssen, Richard
Duivenvoorde, Willem Hoffman
Finnish Matti Mäntynen, Kari Mikkonen
French Arnaud Morvan, Augustin Roche, Didier Vanden Berghe, Dofabien, Etienne Trimaille, Francis
Gasc, Harrissou Sant-anna, Jean-Roc Morreale, Jérémy Garniaux, Loïc Buscoz, Lsam, Marc-André
Saia, Marie Silvestre, Mathieu Bossaert, Mathieu Lattes, Mayeul Kauffmann, Médéric
Ribreux, Mehdi Semchaoui, Michael Douchin, Nicolas Boisteault, Nicolas Rochard, Pascal
Obstetar, Robin Prest, Rod Bera, Stéphane Henriod, Stéphane Possamai, sylther, Sylvain Badey,
Sylvain Maillard, Vincent Picavet, Xavier Tardieu, Yann Leveille-Menez, yoda89
Galician Xan Vieiro
German Jürgen E. Fischer, Otto Dassau, Stephan Holl, Werner Macho
Hindi Harish Kumar Solanki
Italian Alessandro Fanna, Anne Ghisla, Flavio Rigolon, Giuliano Curti, Luca Casagrande, Luca
Delucchi, Marco Braida, Matteo Ghetta, Maurizio Napolitano, Michele Beneventi, Michele
Ferretti, Roberto Angeletti, Paolo Cavallini, Stefano Campus
Japanese Baba Yoshihiko, Minoru Akagi, Norihiro Yamate, Takayuki Mizutani, Takayuki Nuimura,
Yoichi Kayama
Korean OSGeo Korean Chapter
Polish Andrzej Świąder, Borys Jurgiel, Ewelina Krawczak, Jakub Bobrowski, Mateusz Łoskot, Michał
Kułach, Michał Smoczyk, Milena Nowotarska, Radosław Pasiok, Robert Szczepanek, Tomasz
Paul
Portuguese Alexandre Neto, Duarte Carreira, Giovanni Manghi, João Gaspar, Joana Simões, Leandro
Infantini, Nelson Silva, Pedro Palheiro, Pedro Pereira, Ricardo Sena
Portuguese
(Brasil)
Arthur Nanni, Felipe Sodré Barros, Leônidas Descovi Filho, Marcelo Soares Souza, Narcélio
de Sá Pereira Filho, Sidney Schaberle Goveia
Romanian Alex Bădescu, Bogdan Pacurar, Georgiana Ioanovici, Lonut Losifescu-Enescu, Sorin Călinică,
Tudor Bărăscu
Russian Alexander Bruy, Artem Popov
Spanish Carlos Dávila, Diana Galindo, Edwin Amado, Gabriela Awad, Javier César Aldariz, Mayeul
Kauffmann, Fran Raga
Ukrainian Alexander Bruy
1326 Kapitola 27. Contributors
QGIS Desktop 3.16 User Guide
27.3 Statistics of translation
Efforts of translation for QGIS 3.16 Long Term Release are provided below.
(last update: 2022-03-11)
Number of strings Number of target languages Overall Translation ratio
32361 59 12.3%
Language Translation ratio
(%)
Language Translation ratio
(%)
Language Translation ratio
(%)
Albanian 0.23 Arabic 4.02 Azerbaijani 0.02
Basque 1.42 Bengali 0.19 Bulgarian 2.59
Burmese 0.1 Catalan 1.51 Chinese
Simplified
8.53
Chinese
Traditional
0.69 Croatian 0.12 Czech 6.0
Danish 0.66 Dutch 100.0 Estonian 1.3
Finnish 1.81 French 98.49 Galician 0.59
Georgian 0.11 German 21.73 Greek 0.37
Hebrew 0.74 Hindi 0.31 Hungarian 9.3
Igbo 0.01 Indonesian 2.77 Italian 88.87
Japanese 71.07 Kabyle 0.11 Korean 88.58
Lao 0.0 Lithuanian 6.06 Macedonian 0.13
Malay 0.05 Malayalam 0.1 Marathi 0.19
Mongolian 0.11 N’ko 1.82 Norwegian
Bokmål
3.32
Panjabi
(Punjabi)
0.0 Persian 0.48 Polish 1.85
Portuguese
(Brazil)
37.01 Portuguese
(Portugal)
8.5 Romanian 30.61
Russian 14.94 Serbian 0.11 Slovak 1.55
Slovenian 3.2 Spanish 96.0 Swedish 1.19
Tagalog 0.1 Tamil 0.52 Telugu 0.03
Thai 0.11 Turkish 2.82 Ukrainian 2.37
Urdu 0.0 Vietnamese 0.33
27.3. Statistics of translation 1327
QGIS Desktop 3.16 User Guide
1328 Kapitola 27. Contributors
KAPITOLA 28
Dodatky
28.1 Appendix A: GNU General Public License
Version 2, June 1991
Copyright (C) 1989, 1991 Free Software Foundation, Inc. 59 Temple Place - Suite 330, Boston, MA 02111-1307,
USA
Každému je povoleno kopírovat a šířit doslovné kopie tohoto licenčního dokumentu, ale není povoleno je měnit.
Úvod
The licenses for most software are designed to take away your freedom to share and change it. By contrast, the
GNU General Public License is intended to guarantee your freedom to share and change free software–to make sure
the software is free for all its users. This General Public License applies to most of the Free Software Foundation’s
software and to any other program whose authors commit to using it. (Some other Free Software Foundation software
is covered by the GNU Library General Public License instead.) You can apply it to your programs, too.
When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed
to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish),
that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new
free programs; and that you know you can do these things.
To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to
surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the
software, or if you modify it.
For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all
the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show
them these terms so they know their rights.
We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal
permission to copy, distribute and/or modify the software.
Also, for each author’s protection and ours, we want to make certain that everyone understands that there is no
warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to
know that what they have is not the original, so that any problems introduced by others will not reflect on the original
authors‘ reputations.
Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors
of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this,
1329
QGIS Desktop 3.16 User Guide
we have made it clear that any patent must be licensed for everyone’s free use or not licensed at all.
The precise terms and conditions for copying, distribution and modification follow. TERMS AND CONDITIONS
FOR COPYING, DISTRIBUTION AND MODIFICATION
0. This License applies to any program or other work which contains a notice placed by the copyright holder
saying it may be distributed under the terms of this General Public License. The „Program“, below, refers to
any such program or work, and a „work based on the Program“ means either the Program or any derivative work
under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim or with
modifications and/or translated into another language. (Hereinafter, translation is included without limitation
in the term „modification“.) Each licensee is addressed as „you“.
Activities other than copying, distribution and modification are not covered by this License; they are outside its
scope. The act of running the Program is not restricted, and the output from the Program is covered only if its
contents constitute a work based on the Program (independent of having been made by running the Program).
Whether that is true depends on what the Program does.
1. You may copy and distribute verbatim copies of the Program’s source code as you receive it, in any medium,
provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and
disclaimer of warranty; keep intact all the notices that refer to this License and to the absence of any warranty;
and give any other recipients of the Program a copy of this License along with the Program.
You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty
protection in exchange for a fee.
2. You may modify your copy or copies of the Program or any portion of it, thus forming a work based on the
Program, and copy and distribute such modifications or work under the terms of Section 1 above, provided that
you also meet all of these conditions:
a) You must cause the modified files to carry prominent notices stating that you changed the files and the
date of any change.
b) You must cause any work that you distribute or publish, that in whole or in part contains or is derived
from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under the
terms of this License.
c) If the modified program normally reads commands interactively when run, you must cause it, when started
running for such interactive use in the most ordinary way, to print or display an announcement including
an appropriate copyright notice and a notice that there is no warranty (or else, saying that you provide
a warranty) and that users may redistribute the program under these conditions, and telling the user how
to view a copy of this License. (Exception: if the Program itself is interactive but does not normally print
such an announcement, your work based on the Program is not required to print an announcement.)
These requirements apply to the modified work as a whole. If identifiable sections of that work are not derived
from the Program, and can be reasonably considered independent and separate works in themselves, then this
License, and its terms, do not apply to those sections when you distribute them as separate works. But when
you distribute the same sections as part of a whole which is a work based on the Program, the distribution
of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire
whole, and thus to each and every part regardless of who wrote it.
Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you;
rather, the intent is to exercise the right to control the distribution of derivative or collective works based on
the Program.
In addition, mere aggregation of another work not based on the Program with the Program (or with a work
based on the Program) on a volume of a storage or distribution medium does not bring the other work under
the scope of this License.
3. You may copy and distribute the Program (or a work based on it, under Section 2) in object code or executable
form under the terms of Sections 1 and 2 above provided that you also do one of the following:
a) Accompany it with the complete corresponding machine-readable source code, which must be distributed
under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,
b) Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no
more than your cost of physically performing source distribution, a complete machine-readable copy of
1330 Kapitola 28. Dodatky
QGIS Desktop 3.16 User Guide
the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium
customarily used for software interchange; or,
c) Accompany it with the information you received as to the offer to distribute corresponding source code.
(This alternative is allowed only for noncommercial distribution and only if you received the program in
object code or executable form with such an offer, in accord with Subsection b above.)
The source code for a work means the preferred form of the work for making modifications to it. For an
executable work, complete source code means all the source code for all modules it contains, plus any associated
interface definition files, plus the scripts used to control compilation and installation of the executable. However,
as a special exception, the source code distributed need not include anything that is normally distributed (in
either source or binary form) with the major components (compiler, kernel, and so on) of the operating system
on which the executable runs, unless that component itself accompanies the executable.
If distribution of executable or object code is made by offering access to copy from a designated place, then
offering equivalent access to copy the source code from the same place counts as distribution of the source
code, even though third parties are not compelled to copy the source along with the object code.
4. You may not copy, modify, sublicense, or distribute the Program except as expressly provided under this
License. Any attempt otherwise to copy, modify, sublicense or distribute the Program is void, and will
automatically terminate your rights under this License. However, parties who have received copies, or rights,
from you under this License will not have their licenses terminated so long as such parties remain in full
compliance.
5. You are not required to accept this License, since you have not signed it. However, nothing else grants you
permission to modify or distribute the Program or its derivative works. These actions are prohibited by law if
you do not accept this License. Therefore, by modifying or distributing the Program (or any work based on the
Program), you indicate your acceptance of this License to do so, and all its terms and conditions for copying,
distributing or modifying the Program or works based on it.
6. Each time you redistribute the Program (or any work based on the Program), the recipient automatically
receives a license from the original licensor to copy, distribute or modify the Program subject to these terms
and conditions. You may not impose any further restrictions on the recipients‘ exercise of the rights granted
herein. You are not responsible for enforcing compliance by third parties to this License.
7. If, as a consequence of a court judgment or allegation of patent infringement or for any other reason (not
limited to patent issues), conditions are imposed on you (whether by court order, agreement or otherwise) that
contradict the conditions of this License, they do not excuse you from the conditions of this License. If you
cannot distribute so as to satisfy simultaneously your obligations under this License and any other pertinent
obligations, then as a consequence you may not distribute the Program at all. For example, if a patent license
would not permit royalty-free redistribution of the Program by all those who receive copies directly or indirectly
through you, then the only way you could satisfy both it and this License would be to refrain entirely from
distribution of the Program.
If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of
the section is intended to apply and the section as a whole is intended to apply in other circumstances.
It is not the purpose of this section to induce you to infringe any patents or other property right claims or
to contest validity of any such claims; this section has the sole purpose of protecting the integrity of the
free software distribution system, which is implemented by public license practices. Many people have made
generous contributions to the wide range of software distributed through that system in reliance on consistent
application of that system; it is up to the author/donor to decide if he or she is willing to distribute software
through any other system and a licensee cannot impose that choice.
This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this
License.
8. If the distribution and/or use of the Program is restricted in certain countries either by patents or by copyrighted
interfaces, the original copyright holder who places the Program under this License may add an explicit
geographical distribution limitation excluding those countries, so that distribution is permitted only in or among
countries not thus excluded. In such case, this License incorporates the limitation as if written in the body of
this License.
28.1. Appendix A: GNU General Public License 1331
QGIS Desktop 3.16 User Guide
9. The Free Software Foundation may publish revised and/or new versions of the General Public License from
time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address
new problems or concerns.
Each version is given a distinguishing version number. If the Program specifies a version number of this License
which applies to it and „any later version“, you have the option of following the terms and conditions either of
that version or of any later version published by the Free Software Foundation. If the Program does not specify
a version number of this License, you may choose any version ever published by the Free Software Foundation.
10. If you wish to incorporate parts of the Program into other free programs whose distribution conditions are
different, write to the author to ask for permission. For software which is copyrighted by the Free Software
Foundation, write to the Free Software Foundation; we sometimes make exceptions for this. Our decision will
be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting
the sharing and reuse of software generally.
NO WARRANTY
11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE
PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE
STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE
PROGRAM „AS IS“ WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY
AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE
DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR
CORRECTION.
12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES
ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT
NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES
SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH
ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF
THE POSSIBILITY OF SUCH DAMAGES.
QGIS Qt exception for GPL
In addition, as a special exception, the QGIS Development Team gives permission to link the code of this program with
the Qt library, including but not limited to the following versions (both free and commercial): Qt/Non-commercial
Windows, Qt/Windows, Qt/X11, Qt/Mac, and Qt/Embedded (or with modified versions of Qt that use the same
license as Qt), and distribute linked combinations including the two. You must obey the GNU General Public License
in all respects for all of the code used other than Qt. If you modify this file, you may extend this exception to your
version of the file, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from
your version.
28.2 Appendix B: GNU Free Documentation License
Verze 1.3, 3. listopad 2008
Copyright 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc
http://fsf.org/
Každému je povoleno kopírovat a šířit doslovné kopie tohoto licenčního dokumentu, ale není povoleno je měnit.
Úvod
Smyslem této licence je učinit manuál, učebnici nebo jiný funkční a užitečný dokument „svobodným“ v tomto smyslu
svobody: zaručit každému skutečnou svobodu pro kopírování a šíření, s úpravami či bez úprav, ať už komerčně nebo
1332 Kapitola 28. Dodatky
QGIS Desktop 3.16 User Guide
nekomerčně. Za druhé, tato licence zajišťuje pro autora i vydavatele možnost zásluh za jejich práci, aniž by byl
odpovědným za úpravy, které udělali jiní.
Tato licence je druh „copyleftu“, což znamená, že odvozená díla od daného dokumentu musí být sama taktéž
svobodná. Doplňuje GNU všeobecnou veřejnou licenci, což je copyleftová licence určená pro svobodný software.
Navrhli jsme tuto licenci, k použití pro manuály ke svobodnému softwaru, protože svobodný software vyžaduje
svobodnou dokumentaci: Svobodný program by měl přijít s manuály poskytujícími stejné svobody, jako software.
Avašak tato licence není omezena softwarovými manuály; může být použita pro jakékoli textové dílo, nehledě na
téma nebo zda je vydáno jako tištěná kniha. Doporučujeme tuto licenci zejména pro díla, jejichž účelem je výuka
nebo poskytování informací.
1. POUŽITELNOST A DEFINICE
Tato licence platí pro jakýkoli manuál nebo jiné dílo, v jakémkoliv médiu, které obsahuje oznámení, umístěné
držitelem autorských práv, které říká, že dílo může být šířeno za podmínek této licence. Toto oznámení uděluje
celosvětovou, bezplatnou licenci, neomezenou v trvání, pro použití daného díla za podmínek stanovených zde. Tento
dokument, níže, odkazuje na další takový manuál nebo dílo. Každý člen veřejnosti je držitelem licence, a je označován
jako „vy“. Licenci přijímáte, pokud kopírujete, upravujete nebo distribujete dílo takovým způsobem, který vyžaduje
povolení podléhající autorskému zákonu.
„Upravená verze“ dokumentu znamená jakékoli dílo obsahující dokument nebo jeho část, ať už zkopírovaný
doslovně, nebo s úpravami a/nebo přeložený do jiného jazyka.
„Druhotný oddíl“ je pojmenovaný jako dodatek nebo vstupní díl dokumentační části, který se zabývá výhradně
vztahem vydavatelů nebo autorů dokumentu k celkovému tématu dokumentu (nebo souvisejících záležitostí)
a neobsahuje nic, co by mohlo přímo spadat do rámce tohoto celkového tému. (Je-li tedy dokument částí učebnice
matematiky, druhotný oddíl nesmí vysvětlovat cokoli z matematiky.) Tento vztah by mohl být otázkou historického
spojení s tématem či souvisejícími záležitostmi nebo s právním, obchodním, filozofickým, etickým či politickým
postojem k nim.
„Neměnné oddíly“ jsou z jisté čísti druhotnými oddíly, jejichž názvy jsou označeny tak, jako názvy neměnných
oddílů s poznámkou, kde stojí, že se dokument zveřejňuje pod touto licencí. Pokud se oddíl nepřizpůsobí výše uvedené
definici druhotného oddílu, pak není povoleno, aby byl označen za neměnný. Dokument může obsahovat prázdné
neměnné oddíly. V případě, že dokument neurčí žádné neměnné oddíly, pak v něm žádné nejsou.
The „Cover Texts“ are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in
the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words,
and a Back-Cover Text may be at most 25 words.
A „Transparent“ copy of the Document means a machine-readable copy, represented in a format whose specification
is available to the general public, that is suitable for revising the document straightforwardly with generic text editors
or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor,
and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input
to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has
been arranged to thwart or discourage subsequent modification by readers is not Transparent. An image format is not
Transparent if used for any substantial amount of text. A copy that is not „Transparent“ is called Opaque.
Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format,
LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML,
PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and
JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word processors,
SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated
HTML, PostScript or PDF produced by some word processors for output purposes only.
„** Titulní stránka **“ znamená u tištěné knihy samotnou titulní stránku a také následující stránky, které jsou čitelně
potřebné k uchovávání materiálu, který tato licence vyžaduje, aby se objevil na titulní stránce. U děl ve formátech,
které nemají žádnou titulní stránku jako takovou, znamená „titulní stránka“ text v blízkosti nejvýznamnějšího vzhledu
názvu díla, který předchází začátek textu.
The „publisher“ means any person or entity that distributes copies of the Document to the public.
A section „Entitled XYZ“ means a named subunit of the Document whose title either is precisely XYZ or contains
XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific
section name mentioned below, such as „Acknowledgements“, „Dedications“, „Endorsements“, or „History“.)
28.2. Appendix B: GNU Free Documentation License 1333
QGIS Desktop 3.16 User Guide
To „Preserve the Title“ of such a section when you modify the Document means that it remains a section „Entitled
XYZ“ according to this definition.
The Document may include Warranty Disclaimers next to the notice which states that this License applies to the
Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards
disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on
the meaning of this License.
2. VERBATIM COPYING
Můžete kopírovat a distribuovat dokument na jakémkoli médiu, ať už komerčně nebo nekomerčně, za předpokladu,
že tato licence, upozornění na autorská práva a upozornění na licenci uvádějící, že tato licence se vztahuje na
dokument, jsou reprodukovány ve všech kopiích a že nepřidáte žádné další podmínky k těm z této licence. Nesmíte
používat technická opatření, která by bránila nebo kontrolovala čtení nebo další kopírování kopií, které vytváříte nebo
distribuujete. Výměnou za kopie však můžete přijmout náhradu. Pokud distribuujete dostatečně velký počet kopií,
musíte rovněž dodržet podmínky v části 3.
You may also lend copies, under the same conditions stated above, and you may publicly display copies.
3. COPYING IN QUANTITY
If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering
more than 100, and the Document’s license notice requires Cover Texts, you must enclose the copies in covers that
carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the
back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover
must present the full title with all words of the title equally prominent and visible. You may add other material on the
covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and
satisfy these conditions, can be treated as verbatim copying in other respects.
If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many
as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.
If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include
a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network
location from which the general network-using public has access to download using public-standard network
protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you
must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this
Transparent copy will remain thus accessible at the stated location until at least one year after the last time you
distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.
It is requested, but not required, that you contact the authors of the Document well before redistributing any large
number of copies, to give them a chance to provide you with an updated version of the Document.
4. MODIFICATIONS
You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above,
provided that you release the Modified Version under precisely this License, with the Modified Version filling the role
of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy
of it. In addition, you must do these things in the Modified Version:
A. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of
previous versions (which should, if there were any, be listed in the History section of the Document). You may
use the same title as a previous version if the original publisher of that version gives permission.
B. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications
in the Modified Version, together with at least five of the principal authors of the Document (all of its principal
authors, if it has fewer than five), unless they release you from this requirement.
C. State on the Title page the name of the publisher of the Modified Version, as the publisher.
D. Preserve all the copyright notices of the Document.
E. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
F. Include, immediately after the copyright notices, a license notice giving the public permission to use the
Modified Version under the terms of this License, in the form shown in the Addendum below.
1334 Kapitola 28. Dodatky
QGIS Desktop 3.16 User Guide
G. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the
Document’s license notice.
H. Include an unaltered copy of this License.
I. Preserve the section Entitled „History“, Preserve its Title, and add to it an item stating at least the title, year,
new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled
„History“ in the Document, create one stating the title, year, authors, and publisher of the Document as given
on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.
J. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the
Document, and likewise the network locations given in the Document for previous versions it was based on.
These may be placed in the „History“ section. You may omit a network location for a work that was published
at least four years before the Document itself, or if the original publisher of the version it refers to gives
permission.
K. U jakékoli části s názvem „Poděkování“ nebo „Věnování“ zachovejte název sekce a v této části uchovejte
veškerou podstatu a tón každého z uznání a / nebo věnování uvedených přispěvatelů.
L. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers
or the equivalent are not considered part of the section titles.
M. Delete any section Entitled „Endorsements“. Such a section may not be included in the Modified Version.
N. Do not retitle any existing section to be Entitled „Endorsements“ or to conflict in title with any Invariant Section.
O. Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and
contain no material copied from the Document, you may at your option designate some or all of these sections
as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version’s license notice. These
titles must be distinct from any other section titles.
You may add a section Entitled „Endorsements“, provided it contains nothing but endorsements of your Modified
Version by various parties—for example, statements of peer review or that the text has been approved by an
organization as the authoritative definition of a standard.
You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover
Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one
of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already
includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you
are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the
previous publisher that added the old one.
The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity
for or to assert or imply endorsement of any Modified Version.
5. COMBINING DOCUMENTS
You may combine the Document with other documents released under this License, under the terms defined in section
4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the
original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice,
and that you preserve all their Warranty Disclaimers.
The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be
replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make
the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or
publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list
of Invariant Sections in the license notice of the combined work.
In the combination, you must combine any sections Entitled „History“ in the various original documents, forming one
section Entitled „History“; likewise combine any sections Entitled „Acknowledgements“, and any sections Entitled
„Dedications“. You must delete all sections Entitled „Endorsements“.
6. COLLECTIONS OF DOCUMENTS
28.2. Appendix B: GNU Free Documentation License 1335
QGIS Desktop 3.16 User Guide
You may make a collection consisting of the Document and other documents released under this License, and replace
the individual copies of this License in the various documents with a single copy that is included in the collection,
provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.
You may extract a single document from such a collection, and distribute it individually under this License, provided
you insert a copy of this License into the extracted document, and follow this License in all other respects regarding
verbatim copying of that document.
7. AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other separate and independent documents or works, in or on
a volume of a storage or distribution medium, is called an „aggregate“ if the copyright resulting from the compilation
is not used to limit the legal rights of the compilation’s users beyond what the individual works permit. When the
Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not
themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less
than one half of the entire aggregate, the Document’s Cover Texts may be placed on covers that bracket the Document
within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must
appear on printed covers that bracket the whole aggregate.
8. TRANSLATION
Překlad je považován za druh úpravy, takže překlady Dokumentu můžete distribuovat za podmínek uvedených v části
4. Nahrazení Invariantních sekcí překlady vyžaduje zvláštní povolení jejich držitelů autorských práv, ale kromě
některých můžete zahrnout i překlady některých nebo všech Invariantních sekcí. původní verze těchto Invariantních
sekcí. Můžete zahrnout překlad této licence a všech licenčních oznámení v dokumentu a veškerá zřeknutí se záruky
za předpokladu, že uvedete také původní anglickou verzi této licence a původní verze těchto oznámení a zřeknutí
se odpovědnosti. V případě neshody mezi překladem a původní verzí této licence nebo oznámením či zřeknutím se
odpovědnosti bude mít přednost původní verze.
If a section in the Document is Entitled „Acknowledgements“, „Dedications“, or „History“, the requirement (section
4) to Preserve its Title (section 1) will typically require changing the actual title.
9. TERMINATION
You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License.
Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your
rights under this License.
However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a)
provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently,
if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.
Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies
you of the violation by some reasonable means, this is the first time you have received notice of violation of this
License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of
the notice.
Termination of your rights under this section does not terminate the licenses of parties who have received copies or
rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of
a copy of some or all of the same material does not give you any rights to use it.
10. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from
time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new
problems or concerns. See http://www.gnu.org/copyleft/.
Each version of the License is given a distinguishing version number. If the Document specifies that a particular
numbered version of this License „or any later version“ applies to it, you have the option of following the terms
and conditions either of that specified version or of any later version that has been published (not as a draft) by the
Free Software Foundation. If the Document does not specify a version number of this License, you may choose any
version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a proxy can
decide which future versions of this License can be used, that proxy’s public statement of acceptance of a version
permanently authorizes you to choose that version for the Document.
1336 Kapitola 28. Dodatky
QGIS Desktop 3.16 User Guide
11. RELICENSING
„Massive Multiauthor Collaboration Site“ (or „MMC Site“) means any World Wide Web server that publishes
copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody
can edit is an example of such a server. A „Massive Multiauthor Collaboration“ (or „MMC“) contained in the site
means any set of copyrightable works thus published on the MMC site.
„CC-BY-SA“ means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons
Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well
as future copyleft versions of that license published by that same organization.
„Incorporate“ means to publish or republish a Document, in whole or in part, as part of another Document.
An MMC is „eligible for relicensing“ if it is licensed under this License, and if all works that were first published under
this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1)
had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.
The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any
time before August 1, 2009, provided the MMC is eligible for relicensing.
ADDENDUM: How to use this License for your documents
To use this License in a document you have written, include a copy of the License in the document and put the
following copyright and license notices just after the title page:
Copyright © YEAR YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
A copy of the license is included in the section entitled "GNU
Free Documentation License".
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the „with … Texts.“ line with this:
with the Invariant Sections being LIST THEIR TITLES, with the
Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two
alternatives to suit the situation.
Pokud váš dokument obsahuje netriviální příklady programového kódu, doporučujeme tyto příklady uvolnit paralelně
pod vaší volnou licencí svobodného softwaru, jako je GNU General Public License, aby bylo povoleno jejich použití
ve svobodném softwaru.
28.3 Appendix C: QGIS File Formats
28.3.1 QGS/QGZ - The QGIS Project File Format
The QGS format is an XML format for storing QGIS projects. The QGZ format is a compressed (zip) archive
containing a QGS file and a QGD file. The QGD file is the associated sqlite database of the qgis project that contain
auxiliary data for the project. If there are no auxiliary data, the QGD file will be empty.
A QGIS file contains everything that is needed for storing a QGIS project, including:
• project title
• project CRS
• the layer tree
• snapping settings
• relations
28.3. Appendix C: QGIS File Formats 1337
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• the map canvas extent
• project models
• legend
• mapview docks (2D and 3D)
• the layers with links to the underlying datasets (data sources) and other layer properties including extent, SRS,
joins, styles, renderer, blend mode, opacity and more.
• project properties
The figures below show the top level tags in a QGS file and the expanded ProjectLayers tag.
Obr. 28.1: The top level tags in a QGS file
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Obr. 28.2: The expanded top level ProjectLayers tag of a QGS file
28.3.2 QLR - The QGIS Layer Definition file
A Layer Definition file (QLR) is an XML file that contains a pointer to the layer data source in addition to QGIS style
information for the layer.
The use case for this file is simple: To have a single file for opening a data source and bringing in all the related style
information. QLR files also allow you to mask the underlying datasource in an easy to open file.
An example of QLR usage is for opening MS SQL layers. Rather than having to go to the MS SQL connection dialog,
connect, select, load and finally style, you can simply add a .qlr file that points to the correct MS SQL layer with all
the necessary style included.
In the future a .qlr file may hold a reference to more than one layer.
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Obr. 28.3: The top level tags of a QLR file
28.3.3 QML - The QGIS Style File Format
QML is an XML format for storing layer styling.
A QML file contains all the information QGIS can handle for the rendering of feature geometries including symbol
definitions, sizes and rotations, labelling, opacity and blend mode and more.
The figure below shows the top level tags of a QML file (with only renderer_v2 and its symbol tag expanded).
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Obr. 28.4: The top level tags of a QML file (only the renderer_v2 tag with its symbol tag is expanded)
28.4 Appendix D: QGIS R script syntax
Contributed by Matteo Ghetta - funded by Scuola Superiore Sant’Anna
Writing R scripts in Processing is a bit tricky because of the special syntax.
A Processing R script starts with defining its Inputs and Outputs, each preceded with double hash characters (##).
Before the inputs, the group to place the algoritm in can be specified. If the group already exists, the algorithm will
be added to it, if not, the group will be created. In the example below, the name of the group is My group:
##My Group=group
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28.4.1 Inputs
All input data and parameters have to be specified. There are several types of inputs:
• vector: ##Layer = vector
• vector field: ##F = Field Layer (where Layer is the name of an input vector layer the field belongs to)
• raster: ##r = raster
• table: ##t = table
• number: ##Num = number
• string: ##Str = string
• boolean: ##Bol = boolean
• elements in a dropdown menu. The items must be separated with semicolons ;: ##type=selection
point;lines;point+lines
28.4.2 Outputs
As for the inputs, each output has to be defined at the beginning of the script:
• vector: ##output= output vector
• raster: ##output= output raster
• table: ##output= output table
• plots: ##output_plots_to_html (##showplots in earlier versions)
• To show R output in the Result Viewer, put > in front of the command whose output you would like to show.
28.4.3 Syntax Summary for QGIS R scripts
A number of input and output parameter types are offered.
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Input parameter types
Parameter Syntax example Returning objects
vector Layer = vector sf object (or SpatialDataFrame object, if ##load_vector_using_rgdal
is specified)
vector point Layer = vector point sf object (or SpatialDataFrame object, if ##load_vector_using_rgdal
is specified)
vector line Layer = vector line sf object (or SpatialDataFrame object, if ##load_vector_using_rgdal
is specified)
vector
polygon
Layer = vector polygon sf object (or SpatialPolygonsDataFrame object, if
##load_vector_using_rgdal is used)
multiple
vector
Layer = multiple vector sf object (or SpatialDataFrame objects if ##load_vector_using_rgdal
is specified)
table Layer = table dataframe conversion from csv, default object of read.csv function
field Field = Field Layer name of the Field selected, e.g. "Area"
raster Layer = raster RasterBrick object, default object of raster package
multiple
raster
Layer = multiple raster RasterBrick objects, default object of raster package
number N = number integer or floating number chosen
string S = string string added in the box
longstring LS = longstring string added in the box, could be longer then the normal string
selection S = selection
first;second;third
string of the selected item chosen in the dropdown menu
crs C = crs string of the resulting CRS chosen, in the format: "EPSG:4326"
extent E = extent Extent object of the raster package, you can extract values
as E@xmin
point P = point when clicked on the map, you have the coordinates of the point
file F = file path of the file chosen, e.g. „/home/matteo/file.txt“
folder F = folder path of the folder chosen, e.g. „/home/matteo/Downloads“
A parameter can be OPTIONAL, meaning that it can be ignored.
In order to set an input as optional, you add the string optional before the input, e.g:
##Layer = vector
##Field1 = Field Layer
##Field2 = optional Field Layer
Output parameter types
Parameter Syntax example
vector Output = output vector
raster Output = output raster
table Output = output table
file Output = output file
Poznámka: You can save plots as png from the Processing Result Viewer, or you can choose to save the plot directly
from the algorithm interface.
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Script body
The script body follows R syntax and the Log panel can help you if there is something wrong with your script.
Remember that you have to load all additional libraries in the script:
library(sp)
28.4.4 Examples
Example with vector output
Let’s take an algorithm from the online collection that creates random points from the extent of an input layer:
##Point pattern analysis=group
##Layer=vector polygon
##Size=number 10
##Output=output vector
library(sp)
spatpoly = as(Layer, "Spatial")
pts=spsample(spatpoly,Size,type="random")
spdf=SpatialPointsDataFrame(pts, as.data.frame(pts))
Output=st_as_sf(spdf)
Explanation (per line in the script):
1. Point pattern analysis is the group of the algorithm
2. Layer is the input vector layer
3. Size is a numerical parameter with a default value of 10
4. Output is the vector layer that will be created by the algorithm
5. library(sp) loads the sp library
6. spatpoly = as(Layer, "Spatial") translate to an sp object
7. Call the spsample function of the sp library and run it using the input defined above (Layer and Size)
8. Create a SpatialPointsDataFrame object using the SpatialPointsDataFrame function
9. Create the output vector layer using the st_as_sf function
That’s it! Just run the algorithm with a vector layer you have in the QGIS Legend, choose the number of random
point. The resulting layer will be added to your map.
Example with raster output
The following script will perform basic ordinary kriging to create a raster map of interpolated values from a specified
field of the input point vector layer by using the autoKrige function of the automap R package. It will first
calculate the kriging model and then create a raster. The raster is created with the raster function of the raster R
package:
##Basic statistics=group
##Layer=vector point
##Field=Field Layer
##Output=output raster
##load_vector_using_rgdal
require("automap")
require("sp")
require("raster")
(continues on next page)
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(pokračujte na předchozí stránce)
table=as.data.frame(Layer)
coordinates(table)= ~coords.x1+coords.x2
c = Layer[[Field]]
kriging_result = autoKrige(c~1, table)
prediction = raster(kriging_result$krige_output)
Output<-prediction
By using ##load_vector_using_rgdal, the input vector layer will be made available
as a SpatialDataFrame objects, so we avoid having to translate it from an sf object.
Example with table output
Let’s edit the Summary Statistics algorithm so that the output is a table file (csv).
The script body is the following:
##Basic statistics=group
##Layer=vector
##Field=Field Layer
##Stat=Output table
Summary_statistics<-data.frame(rbind(
sum(Layer[[Field]]),
length(Layer[[Field]]),
length(unique(Layer[[Field]])),
min(Layer[[Field]]),
max(Layer[[Field]]),
max(Layer[[Field]])-min(Layer[[Field]]),
mean(Layer[[Field]]),
median(Layer[[Field]]),
sd(Layer[[Field]])),
row.names=c("Sum:","Count:","Unique values:","Minimum value:","Maximum value:",
→"Range:","Mean value:","Median value:","Standard deviation:"))
colnames(Summary_statistics)<-c(Field)
Stat<-Summary_statistics
The third line specifies the Vector Field in input and the fourth line tells the algorithm that the output should be
a table.
The last line will take the Stat object created in the script and convert it into a csv table.
Example with console output
We can use the previous example and instead of creating a table, print the result in the Result Viewer:
##Basic statistics=group
##Layer=vector
##Field=Field Layer
Summary_statistics<-data.frame(rbind(
sum(Layer[[Field]]),
length(Layer[[Field]]),
length(unique(Layer[[Field]])),
min(Layer[[Field]]),
max(Layer[[Field]]),
max(Layer[[Field]])-min(Layer[[Field]]),
mean(Layer[[Field]]),
median(Layer[[Field]]),
sd(Layer[[Field]])),row.names=c("Sum:","Count:","Unique values:","Minimum value:",
→"Maximum value:","Range:","Mean value:","Median value:","Standard deviation:"))
colnames(Summary_statistics)<-c(Field)
>Summary_statistics
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The script is exactly the same as the one above except for two edits:
1. no output specified (the fourth line has been removed)
2. the last line begins with >, telling Processing to make the object available through the result viewer
Example with plot
To create plots, you have to use the ##output_plots_to_html parameter as in the following script:
##Basic statistics=group
##Layer=vector
##Field=Field Layer
##output_plots_to_html
####output_plots_to_html
qqnorm(Layer[[Field]])
qqline(Layer[[Field]])
The script uses a field (Field) of a vector layer (Layer) as input, and creates a QQ Plot (to test the normality of
the distribution).
The plot is automatically added to the Processing Result Viewer.
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KAPITOLA 29
Literature and Web References
GDAL-SOFTWARE-SUITE. Geospatial data abstraction library. https://gdal.org, 2013.
GRASS-PROJECT. Geographic resource analysis support system. https://grass.osgeo.org, 2013.
NETELER, M., AND MITASOVA, H. Open source gis: A grass gis approach, 2008.
OGR-SOFTWARE-SUITE. Geospatial data abstraction library. https://gdal.org, 2013.
OPEN-GEOSPATIAL-CONSORTIUM. Web map service (1.1.1) implementation specification. https://portal.
opengeospatial.org, 2002.
OPEN-GEOSPATIAL-CONSORTIUM. Web map service (1.3.0) implementation specification. https://portal.
opengeospatial.org, 2004.
POSTGIS-PROJECT. Spatial support for postgresql. http://postgis.refractions.net/, 2013.
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