8

In the QGIS GUI, the select-by-location algorithm has a choice to only use the selected features from the INTERSECT layer. How can I do this (or use any other algorithm) in a python script for QGIS 3?

I do not want to save temporal layer as mentioned in Run QGIS Model on selected features only?

I have been running this script but it does not use the selected features.

import processing

input_vlayer = 'Some path'
intersect_vlayer = 'Some path'


input_vlayer = iface.addVectorLayer(input_vlayer, 'input_vlayer', 'ogr')
intersect_vlayer = iface.addVectorLayer(intersect_vlayer, 'intersect_vlayer', 'ogr')


Pass the first 5 features


for i in range(5):


# Select the features
intersect_vlayer.select(i)
# Set input params
params = {'INPUT':input_vlayer,
          'PREDICATE':0,
          'INTERSECT':intersect_vlayer, # USE HERE THE SELECTED FEATURES
          'METHOD':0}
result = processing.run("qgis:selectbylocation", params)

# Remove the current selection and then pass to the next one
intersect_vlayer.removeSelection()

Also, from QGIS select by location doesn't use selected features only they mentioned to enable [Processing] > [Options] > [General] > [Use only selected features]. However I can't see this option in my qgis version. I'm using QGIS Madeira 3.4.3

enter image description here

Taras
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Jose
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1 Answers1

11

For only selected feature use the QgsProcessingFeatureSourceDefinition class.

Code below with the input of selected features only:

import processing

input_vlayer = 'Some path'
intersect_vlayer = 'Some path'


input_vlayer = iface.addVectorLayer(input_vlayer, 'input_vlayer', 'ogr')
intersect_vlayer = iface.addVectorLayer(intersect_vlayer, 'intersect_vlayer', 'ogr')


for i in range(5):


# Select the features
intersect_vlayer.select(i)
# Set input params
params = {'INPUT':input_vlayer,
          'PREDICATE':0,
          'INTERSECT':QgsProcessingFeatureSourceDefinition(intersect_vlayer.id(), True), # USE HERE THE SELECTED FEATURES
          'METHOD':0}
result = processing.run("qgis:selectbylocation", params)

# Remove the current selection and then pass to the next one
intersect_vlayer.removeSelection()
Taras
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Fran Raga
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  • Thanks @Francisco Raga. Just one thing, I had to add QgsProcessingFeatureSourceDefinition(intersect_vlayer.id(), True) to get it work. Thanks. – Jose Feb 05 '19 at 21:36
  • Ooops!yes,your are correct!add this to my answer – Fran Raga Feb 05 '19 at 21:40
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    When I add QgsProcessingFeatureSourceDefinition to the INPUT parameter it says me : Could not load source layer for INPUT: layerXXX not found – dmjf08 Feb 07 '19 at 08:04
  • you can use this parameter in the INPUT flag!Put your code in other question,because probably the INPUT layer is not correct – Fran Raga Feb 07 '19 at 09:46
  • I posted my question with my code : https://gis.stackexchange.com/questions/311336/run-pyqgis-algorithm-on-selected-features-in-layer – dmjf08 Feb 07 '19 at 10:14