PyQGIS Geometry Extraction – Unable to Get Geometry of Temporary Layer Created from Selected Features

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I need a temporary layer with the geometry created from selected features for a processing tool. The temporary layer is created but the geometry is missing. The attribute table is blank.

But when I printed the geometry it's showing on console.

Below is the code I am using:

layer = iface.activeLayer() # layer which has a selection 
feat = layer.selectedFeatures()
fields = layer.fields()

selection = QgsVectorLayer('Point', 'temp', 'memory')
dp = selection.dataProvider()
dp.addAttributes(fields)
feats = selection.selectedFeatures()
for feat in feats:
    geom = feat.geometry()
    wkt = geom.asPoint()
print(wkt)
selection.commitChanges()
selection.updateExtents()

QgsProject.instance().addMapLayer(selection)
temp = QgsVectorLayer("D:\satya\cp.shp", "premises", "ogr")

Best Answer

You try to select the features in the newly created layer and you use commitChanges without startEditing. addAttributes adds the fields' definition to the target layer. It doesn't add the features' attrribute values.

You can use this script:

layer = iface.activeLayer() # layer which has a selection 
feats = layer.selectedFeatures()
fields = layer.fields()

crs = layer.crs().authid()
selection = QgsVectorLayer('Point?crs=' + crs, 'temp', 'memory')
dp = selection.dataProvider()
dp.addAttributes(fields)
selection.updateFields()

for feat in feats:
    feature = QgsFeature(layer.fields())
    feature.setAttributes(feat.attributes())
    feature.setGeometry(feat.geometry())
    dp.addFeatures([feature])
    dp.updateExtents()

QgsProject.instance().addMapLayer(selection)

Related Solutions

[GIS] Geometry from multiple selected features into one geometry

You can use ITopologicalOperator.ConstructUnion.

The steps would be as follows:

Create an instance of the Polygon class and cast that to ITopologicalOperator. This polygon instance will contain the result.
Since ITopologicalOperator.ConstructUnion takes an IEnumGeometry to specify the geometries to union (or in your words, concatenate), create an instance of GeometryBag class, which implements IEnumGeometry.
Cast the geometry bag to IGeometryCollection so that you can add your source polygons to it.
Pass your geometry bag to the ITopologicalOperator.ConstructUnion method on the polygon created in step 1.

As far as enumerating the selection is concerned, your method of retrieving list of IDs and getting the row for every single ID is VERY inefficient. Performance is much better if you just use IFeatureSelection.SelectionSet.Search() method. You would specify a null query filter argument when calling this method since you want all the features in the selection. The result will be a cursor which you can enumerate.

Deleting Selected Features Using PyQGIS – How to Guide

You can loop over the iterator and get the id() for every feature in it:

with edit(layer):
    # build a request to filter the features based on an attribute
    request = QgsFeatureRequest().setFilterExpression('"DN" != 3')

    # we don't need attributes or geometry, skip them to minimize overhead.
    # these lines are not strictly required but improve performance
    request.setSubsetOfAttributes([])
    request.setFlags(QgsFeatureRequest.NoGeometry)

    # loop over the features and delete
    for f in layer.getFeatures(request):
        layer.deleteFeature(f.id())

or with QGIS < 2.12

request = QgsFeatureRequest().setFilterExpression('"DN" != 3')
request.setSubsetOfAttributes([])
request.setFlags(QgsFeatureRequest.NoGeometry)

ids = [f.id() for f in layer.getFeatures(request)]

layer.startEditing()
for fid in ids:
    layer.deleteFeature(fid)
layer.commitChanges()

Best Answer

Related Solutions

[GIS] Geometry from multiple selected features into one geometry

Deleting Selected Features Using PyQGIS – How to Guide

or with QGIS < 2.12

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