Adding temporary output of processing algorithm to the map canvas using PyQGIS

Question

Let's say I run a simple algorithm like this

import processing
https://docs.qgis.org/3.16/en/docs/user_manual/processing_algs/qgis/vectoranalysis.html?highlight=count%20points%20polygon#id3
processing.run("qgis:countpointsinpolygon", { 
    'POLYGONS' : 'polygons', 
    'POINTS': 'points',
    'OUTPUT': 'TEMPORARY_OUTPUT'
    })

How do I materialize/visualize/add the temporary layer in the Layers Panel?

Check this tutorial for details: PyQGIS 101: Running Processing tools — Taras, Oct 01 '21 at 05:51
Also related: https://gis.stackexchange.com/questions/76594/how-to-load-memory-output-from-qgis-processing — Taras, Oct 01 '21 at 05:58

score 11 · Accepted Answer · edited Oct 01 '21 at 05:46

11

Another option is runAndLoadResults().

As was mentioned in the QGIS Documentation:

Unlike when an algorithm is executed from the toolbox, outputs are not added to the map canvas if you execute that same algorithm from the Python console using run(), but runAndLoadResults() will do that.

processing.runAndLoadResults("qgis:countpointsinpolygon", { 
    'POLYGONS' : 'polygons', 
    'POINTS': 'points',
    'OUTPUT': 'TEMPORARY_OUTPUT'
    })

(But I like @MrXsquared option better, since you get the layer as a variable you can then use in the next processing steps).

edited Oct 01 '21 at 05:46

Taras

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answered Sep 28 '21 at 13:25

BERA

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your version gives you the layer as a variable, too: proc = processing.runAndLoadResults("qgis:refactorfields",<<>>) outputlayer = proc['OUTPUT'] – Sickboy Jul 31 '22 at 09:05

score 6 · Answer 2 · edited Oct 01 '21 at 05:50

Can't tell if that is the "best" way, but its one straight forward:

import processing
# https://docs.qgis.org/3.16/en/docs/user_manual/processing_algs/qgis/vectoranalysis.html?highlight=count%20points%20polygon#id3
proc = processing.run("qgis:countpointsinpolygon", { 
    'POLYGONS' : 'polygons', 
    'POINTS': 'points',
    'OUTPUT': 'TEMPORARY_OUTPUT'
    })
outputlayer = proc['OUTPUT']
QgsProject.instance().addMapLayer(outputlayer)

Adding temporary output of processing algorithm to the map canvas using PyQGIS

https://docs.qgis.org/3.16/en/docs/user_manual/processing_algs/qgis/vectoranalysis.html?highlight=count%20points%20polygon#id3

2 Answers2

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