Setting output layer name of overlay processing with PyQGIS

Question

I am writing a PyQGIS Plugin in which I need to do an overlay.

The code of the function doing the overlay look like:

measure = self.dlg.fcbMeasure.layer()
area = self.dlg.fcbArea.layer()
params = {'INPUT':measure,
 'OVERLAY':area,
 'OUTPUT':"memory:land_water",
 'INTERSECTION':"memory:land_water"}
processing.runAndLoadResults("qgis:intersection", params)
 

I thought either OUTPUT or INTERSECTION should name the output layer, but the layer that is created is just called Intersection - how can I run the intersection and end up with a memory layer named "land_water"?

Answer 1

Looking a bit more around, I found that processing returns a directory with (at least) a key 'OUTPUT'. The value corresponding to this key is a unique layer id.

So I can do:

output = processing.runAndLoadResults("qgis:intersection", params)
newlayer = QgsProject.instance().mapLayer(output['OUTPUT'])
newlayer.setName('land_water') 

Then I know I have the layer I just created, which is something that is not guaranteed if I start using mapLayersByName() as there may be more map layers with the same name in the project.

Answer 2

Perhaps someone will know a better way, but the only way I know is via the following workaround:

measure = self.dlg.fcbMeasure.layer()
area = self.dlg.fcbArea.layer()
params = {'INPUT': measure,
 'OVERLAY': area,
 'OUTPUT': 'memory'}
processing.runAndLoadResults('qgis:intersection', params)
result = QgsProject().instance().mapLayersByName('Intersection')[0]
result.setName('land_water')

E.g. create a reference to the newly created layer and simply change it's name using the setName() method.

---

The following also works providing you have the option in processing settings to 'Use filename as layer name' checked (see image below).

measure = self.dlg.fcbMeasure.layer()
area = self.dlg.fcbArea.layer()
params = {'INPUT': measure,
 'OVERLAY': area,
 'OUTPUT': 'land_water'}
processing.runAndLoadResults('qgis:intersection', params)

enter image description here