PyQGIS – What Is the Algorithm Name for Count Points in Polygon Using PyQGIS

algorithmpyqgisqgis-processing

I want to count points in polygon, using PyQGIS. When I check the documentation, I find the description of the {parameter_dictionary}, but not the algorithm name which must also be provided.

What is the name of the algorithm which I have to write in here processing.run("algorithm_id", {parameter_dictionary})?

Best Answer

In case you do not know a name or id, you can use:

searchstring = 'count' # to get all algorithms just leave this empty
for alg in QgsApplication.processingRegistry().algorithms():
    if searchstring in alg.id(): 
        print(alg.id())

to search for it. In your case its native:countpointsinpolygon

Related Solutions

[GIS] Using PyQGIS processing runalg clipvectorsbypolygon

You may continue using the memory layer by loading it as an object. Before doing this, you need to know how the output from the algorithm is called, so typing these lines in the Python Console:

import processing
processing.alghelp('gdalogr:clipvectorsbypolygon')

you will see that the output's name is OUTPUT_LAYER:

ALGORITHM: Clip vectors by polygon
INPUT_LAYER <ParameterVector>
CLIP_LAYER <ParameterVector>
OPTIONS <ParameterString>
OUTPUT_LAYER <OutputVector>

This means that you will be able to use it if you add a new variable and call it in this way:

# change 'my_algorithm' name as you want
my_algorithm = general.runalg('gdalogr:clipvectorsbypolygon', 'lokale_orte.shp', 'kleine_kreise.shp', None, None)

# change 'my_output' name as you want
my_output = processing.getObject(my_algorithm['OUTPUT_LAYER'])

By now, my_output will be the object to use for calling the layer returned by the clip operation and you are ready to do something with it.

EDIT For getting your script working, you may try using the following code (slightly different from yours):

import sys
from qgis.core import *
import qgis.utils

qgs = QApplication([], True)
QgsApplication.setPrefixPath("/usr", True)
QgsApplication.initQgis()

# Prepare processing framework 
sys.path.append('/usr/share/qgis/python/plugins') # Dir where Processing is located
from processing.core.Processing import Processing
from processing.tools import *
Processing.initialize()

# load base layer
blayer = QgsVectorLayer("path/to/the/shapefile/lokale_orte.shp", "lokale_orte", "ogr")
if not blayer.isValid():
    print "Layer failed to load!"
else:
    print "success:  load layer"

# load clip layer
clayer = QgsVectorLayer("path/to/the/shapefile/kleine_kreise.shp", "kleine_kreise", "ogr")
if not clayer.isValid():
    print "Layer failed to load!"
else:
    print "success:  load layer"

# run clip
# change 'my_algorithm' name as you want
my_algorithm = general.runalg('gdalogr:clipvectorsbypolygon', 'lokale_orte.shp', 'kleine_kreise.shp', None, None)

# change 'my_output' name as you want
my_output = processing.getObject(my_algorithm['OUTPUT_LAYER'])

QgsApplication.exitQgis()
qgs.exit()

PyQGIS – Creating Different Numbers of Random Points Inside Polygons

You pass the index number of the field when using num. Just use QgsProperty.fromExpression('"vlp1_num"') for parameter 'VALUE'.

Best Answer

Related Solutions

[GIS] Using PyQGIS processing runalg clipvectorsbypolygon

PyQGIS – Creating Different Numbers of Random Points Inside Polygons

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