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I have two polygon features: epoca and result.

I would like to select the features that correspond to the number 1 feature (features A and B) and then select the corresponding features with the number 2 feature (features C and D).

enter image description here

I had done the following:

from processing.core.Processing import Processing
import processing.tools

layerResult = processing.getObject('lyr_result')
layerEpoca = processing.getObject('lyr_epoca')

processing.tools.general.runalg('qgis:selectbylocation', layerResult, layerEpoca, u'equals', 0.005,0)

layerResult.invertSelection() #I'm searching for the different polygons
selectFeatures = layerResult.selectedFeatures() #are the features selected in result

processing.tools.general.runalg('qgis:selectbylocation',layerEpoca, layerResult, u'within', 0.005,0) #here select the features in epoca all at once!

What is being done is that you are selecting features A, B and C, D at the same time. I would like to select these features at different times. Is this possible?

I had thought of something like this:

for feat in selectFeatures:
    processing.tools.general.runalg('qgis:selectbylocation',layerEpoca, selectFeatures, u'within', 0.005,0)
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2 Answers 2

Reset to default
8

You can also do this without processing :

layer_select = QgsMapLayerRegistry.instance().mapLayersByName('lyr_result')[0]
layer_to_select = QgsMapLayerRegistry.instance().mapLayersByName('lyr_epoca')[0]

for selected_feat in layer_select.selectedFeatures():
    to_select = []
    for feat_to_select in layer_to_select.getFeatures():
        if feat_to_select.geometry().intersects(selected_feat.geometry()):
            to_select.append(feat_to_select.id())
    layer_to_select.setSelectedFeatures(to_select)
    print to_select #Or do something with the selected Features

That will select the features that intersect the selected Feature for every selected feature separately.

Here I use the print to_select line to print the list of feature's IDs that are selected for each selected result's features.

If you work on a huge dataset, consider using Index to speed up the process.

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4

Please change crs=epsg:4326 to your EPSG code.

Add the QgsVectorLayer creation to fit the requirement of "qgis:selectbylocation" algorithm and create tmp layer for each selected features

# create an empty Temporary QgsVectorelayer 
tempLayer = QgsVectorLayer('Polygon?crs=epsg:4326', tmp_layer_name, 'memory')

for feat in selectFeatures: # Loop throught the selectedfeatures list

    # Create / initialize an empty feature 
    cfeature = QgsFeature()

    # add feature with attributes to tempLayer
    cfeature_Attributes=[]
    cfeature_Attributes.extend(feat.attributes())
    cfeature.setGeometry(feat.geometry())
    cfeature.setAttributes(cfeature_Attributes)         
    
    dataProvider = tempLayer.dataProvider()
    tempLayer.startEditing()
    dataProvider.addFeatures([cfeature])
    tempLayer.commitChanges()
    processing.tools.general.runalg('qgis:selectbylocation',layerEpoca, tempLayer, u'within', 0.005,0)
    ##########################################################################
    # Here do something with selected feature(s) that match selectbylocation #
    ##########################################################################
    # clean the tempLayer
    tempLayer.deleteFeature(cfeature.id())
    tempLayer.commitChanges()

tempLayer.stopEditing()
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8
  • did not work. I think it's because the layerEpoca is a vector layer object and selectFeatures is a feature object. Any idea of conversion?
    – Jayme Muzzi
    Commented Sep 26, 2017 at 12:02
  • I edited the script to add this requirement
    – Hugo Roussaffa
    Commented Sep 26, 2017 at 12:44
  • @HugoRoussaffa With your edit, you will select every features that intersects the selected features exactly the same way as in the question... You just replace the selected features by a temp layer but the features are exactly the same.
    – YoLecomte
    Commented Sep 26, 2017 at 15:02
  • @YoLecomte yes you totally right, big mistake ! With my method we need to create a QgsVectorLayer for each feat in selectFeatures... I will edit to match that. Thanks for your comment
    – Hugo Roussaffa
    Commented Sep 26, 2017 at 15:12
  • @HugoRoussaffa Yep, most welcome ! But it remains a complicated way (copying feature in a temp layer and using processing) to achieve something simple that can be done without so much steps...
    – YoLecomte
    Commented Sep 26, 2017 at 15:19

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