73
votes
Accepted
What is the default plugin folder location in QGIS 3?
Go to menu Settings -> User profiles -> Open active profile folder
From there, you can go to python -> plugins. That's the plugin folder for QGIS v3.
On my GNU/Linux machine:
/home/USER/.local/...
- 36k
63
votes
Accepted
Using QGIS Processing algorithms from PyQGIS standalone scripts (outside of GUI)
You can run a QGIS Processing algorithm in standalone (no GUI) mode in this way:
import sys
from qgis.core import (
QgsApplication,
QgsProcessingFeedback,
QgsVectorLayer
)
# See ...
- 36k
46
votes
Accepted
Was QgsMapLayerRegistry being removed in QGIS 3?
Yes it has been removed, but alternatives exist.
Changes of the 3.0 API are listed here:
https://qgis.org/api/api_break.html
QgsMapLayerRegistry: Its functionality has been moved to QgsProject.
...
- 27.6k
33
votes
Accepted
Writing a python processing script with QGIS 3.0
With the transition from QGIS2.x to QGIS3.x the whole processing framework has been reworked and large parts of it run now as C++ classes that you can interact with using Python. Unfortunately the ...
- 2,375
32
votes
Accepted
Getting the output layer reference returned by Processing tool
Please note that all solutions explained here are related to vector layer used as the input and QGIS native algorithms. The answer doesn't explain the results of other providers' tools. (GRASS, GDAL, ...
- 76.2k
30
votes
Generating equal sized polygons along line with PyQGIS
Interesting question! It's something I've wanted to try myself, so gave it a go.
You can do this in PostGRES/POSTGIS with a function which generates a set of polygons.
In my case, I have a table ...
- 20.3k
30
votes
Accepted
Getting layer extent in PyQGIS?
The answer is almost completely contained in a post I recently wrote.
The extent is returned as a QgsRectangle() object with the following code:
layer = iface.activeLayer() # load the layer as you ...
- 16.1k
28
votes
Creating sectors for telecom towers
Telecom cell site plan and optimization using QGIS
Create Points or Site Locations:
Create database in CSV (make sure antenna sizes are sorted in descending order: highest first to lowest last, such ...
28
votes
Getting list of layer names using PyQGIS
Since version 3, QgsMapLayerRegistry funcionalities have been moved to QgsProject: https://qgis.org/api/api_break.html
Update for QGIS3.x:
from qgis.core import QgsProject
names = [layer.name() for ...
- 6,439
26
votes
Iterating over map layers using PyQGIS
For QGIS 3, QgsMapLayerRegistry's functionality has been moved to QgsProject.
So, for iterating over map layers, you should use that structure:
layers = QgsProject.instance().mapLayers()
....
- 76.2k
25
votes
How do I fix "name 'iface' is not defined"?
The iface module is automatically imported when directly working from the Python Console.
In the other cases (for example, when running a script from the Processing Toolbox), you need to manually ...
- 16.1k
25
votes
Accepted
Protecting QGIS Plugin source code
QGIS is licensed under the GPLv2, this same license applies to QGIS plugins.
QGIS has written a blog post that clarifies on the licensing as well as on the commercial aspects of this.
With respect to ...
- 27.6k
24
votes
Was QgsMapLayerRegistry being removed in QGIS 3?
You can do the same thing easily just do:
QgsProject.instance().addMapLayer(your_Qgs_whaterver_Layer)
for more details, see the following:
https://qgis.org/api/classQgsProject.html#...
- 2,730
24
votes
Accepted
How to fix QGIS being extremely slow?
So after taking into account what ThomasG77 told me to fix my QGIS, I've found that indeed creating a new profile fixes the slowdown, but I didn't want to have to create a new profile everytime it got ...
- 481
23
votes
Accepted
'pyrcc5' is not recognized as an internal or external command
Try running a batch file with the following:
@echo off
call "C:\Program Files\QGIS 3.0\bin\o4w_env.bat"
call "C:\Program Files\QGIS 3.0\bin\qt5_env.bat"
call "C:\Program Files\QGIS 3.0\bin\py3_env....
- 856
22
votes
Duplicating layer in memory using PyQGIS
In QGIS 3 you can make a copy of a layer without saving any reference to the parent layer in this way:
layer.selectAll()
clone_layer = processing.run("native:saveselectedfeatures", {'INPUT': ...
- 1,343
22
votes
Creating Virtual Layer with PyQGIS
For QGIS 3, instead use QgsProject:
from qgis.core import QgsVectorLayer, QgsProject
sql_query = "SELECT * FROM road WHERE type = 'Expressway'"
vlayer = QgsVectorLayer(f"?query={...
- 221
22
votes
Accepted
Making layer or group private/hidden/invisible in Layers Panel of QGIS
Just to clarify, private/hidden layers/groups will not appear in the Layers Panel, but they can still be seen in the canvas or used in joins/relations with other layers.
Native approach (QGIS API)
You ...
- 36k
22
votes
Accepted
Reading and setting label settings in PyQGIS
I found the answer for QGIS 3.0:
layer_settings = QgsPalLayerSettings()
text_format = QgsTextFormat()
text_format.setFont(QFont("Arial", 12))
text_format.setSize(12)
buffer_settings = ...
- 856
21
votes
How to get the map canvas CRS in EPSG code?
In QGIS3 API changed:
iface.mapCanvas().mapSettings().destinationCrs().authid()
'EPSG:3045'
- 1,375
21
votes
Accepted
"AttributeError: 'QgisInterface' object has no attribute 'legendInterface'" in PyQGIS 3
You could just replace
layers = iface.legendInterface().layers()
with
layers = [layer for layer in QgsProject.instance().mapLayers().values()]
- 75.3k
20
votes
Accepted
Loading style (*.qml file) to layer via PyQGIS?
I have my qml styles in a fix path (c:/pyqgis_data/Styles/). So, to load arrows_red_orange.qml (exclusively for point layers), next lines at the Python Console of QGIS work:
>>>layer = ...
- 29.7k
20
votes
Accepted
Duplicating layer in memory using PyQGIS
The following code works for me from both the Python Console and plugin. It takes the features from the source input layer and copies the attributes to a memory layer (in this case, a polygon layer ...
- 75.3k
20
votes
Accepted
Maximum value of field of vector layer using PyQGIS
It is not necessary to get a complete list of field values. In QgsVectorLayer exists 'maximumValue' method. So, this works well and it's shorter:
layer = iface.activeLayer()
idx = layer....
- 29.7k
20
votes
How to read user defined project variables using Python
Since QGIS 3.0 you need also to specify the project when setting and reading a variable:
project = QgsProject.instance()
QgsExpressionContextUtils.setProjectVariable(project,'myvar','Hello World!')
...
- 371
20
votes
Accepted
Optimizing intersections and rubber band representations with PyQGIS
Nice question!
You can apply several optimizations, like these 5:
1. Remove any print() statement.
Print statements are nice for debugging (although there are better options, see this answer). However,...
- 36k
19
votes
Accepted
Activating layer by its name in PyQGIS
TL;DR
To get all features of a layer by the layer name you do not need to activate it. Just use
name = 'counties'
layer = QgsProject.instance().mapLayersByName( name )[0]
poles = layer.getFeatures()
...
- 27.6k
19
votes
Accepted
Iterating over layers and exporting them as PNG images with PyQGIS in standalone script
In order to solve this question, we need to use timers or something that delays the execution of the script, so the canvas can reflect the layer arrangement at the time the map is exported. In other ...
- 36k
19
votes
Accepted
Creating predefined values in field using PyQGIS
You need to assign and configure a ValueMap widget to your layer's field in this way:
QGIS 3.x
fieldIndex = layer.fields().indexFromName( 'myField' )
editor_widget_setup = QgsEditorWidgetSetup( '...
- 36k
19
votes
Accepted
Make QGIS python plugin for both versions 2.x and 3.x?
Documentation
Here you can find what is new and what is break under the PyQGIS API.
To get details about how to port Python2 to Python3 go there
You can find some detail about testing from QGIS2 to ...
- 2,191
Only top scored, non community-wiki answers of a minimum length are eligible