5
Thread safety
QGIS Processing algorithms can be thread-safe or not. According to the docs, the latter are :
[...] algorithms which manipulate the current project, layer selections, or with external dependencies which are not thread-safe.
You can run the following code snippet in a QGIS Python console (Ctrl+Alt+P) to obtain a list of QGIS Processing ...
3
I encountered this problem. Some processing tools worked in QGIS 3.8, but doesn't work in QGIS 3.4.
I don't know the reason, but changing native word into qgis in all processing.run ("native:tool_name", ...) solved the problem. (native:intersection -> qgis:intersection)
3
You have another function for doing this:
from processing import execAlgorithmDialog
params = {} # A dictionary to load some default value in the dialog
execAlgorithmDialog('qgis:extractbyattribute', params)
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In QGIS 3.4, the SAGA provider is already a core plugin. Therefore, you can also change the SagaAlgorithmProvider.py file directly, by:
sudo nano /usr/share/qgis/python/plugins/processing/algs/saga/SagaAlgorithmProvider.py
then change the REQUIRED VERSION from 2.3. to 7.3.
This worked for me.
2
General strategy for the solution:
Compute dissolved buffer area by road width. (Tool: Buffer)
Create bounding box of road layer. (Tool: Extract layer extent)
Remove the portion that overlaps the dissolved buffer. (Tool: Difference)
Convert multipolygon into single polygons since the result of 3 is a multipolygon. (Tool: Multipart to singleparts)
PyQGIS ...
1
I was able to solve this by adding a vector layer input to the script and adding it to the project from the script itself before exporting the layout.
layer = self.parameterAsLayer(parameters, 'LAYER', context)
p = context.project()
p.addMapLayer(layer)
Now this script can be used inside a model where it takes the styled vector layer generated in the ...
1
You may also use the Snap geometries to layer processing tool:
This algorithm snaps the geometries in a layer. Snapping can be done
either to the geometries from another layer, or to geometries within
the same layer.
1
For future reference: in May 2019 the "Make Valid" tool was added to the core QGIS 3 Processing toolbox, as "Fix Geometries" within the Vector Geometry group.
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