Counting points in polygon using PyQGIS

Question

Is there any simple integration for calculating count of points in polygon using QGIS-Python integration?

In other words, are there any pre-defined functions for points in polygon of QGIS using python, so that we can use them in our python script?

• Aaron: Great questions, although It would be best to wrap these questions into a single question.
• Jakob: You can find some parallel code in this question counting points in current atlas feature: gis.stackexchange.com/questions/152296/…

Answer 1

I rewrote my answer from a parallel question counting points in current atlas feature: How to count points within the current Print composer atlas feature in QGIS 2.8?

Build a new function in the expression editor:

from qgis.core import *
from qgis.gui import *
from qgis.utils import iface
@qgsfunction(args="auto", group='Custom')
 def countPointsInPolygon(pointLayerName, geom, feature, parent):
 # If point geom is empty, return 0
 if (geom is None):
 return 0
 # Get point layer reference from layername
 pointLayer = QgsMapLayerRegistry.instance().mapLayersByName(pointLayerName)[0]
 # Raise if layer not found
 if pointLayer is None:
 raise Exception("Layer not found: " + pointLayerName)
 # Count point within current polygon feature
 countPoint = 0
 for pointFeature in pointLayer.getFeatures():
 pointGeom = pointFeature.geometry()
 if (pointGeom is None):
 continue
 if pointGeom.within(geom):
 countPoint += 1
 return countPoint 

Use it as a expression on the polygon layer where 'mypoints' is the name of the point layer: countPointsInPolygon( 'mypoints', $geometry )

If you don't want it implemented as an expression, you can call the function from your own script looping the features of the polygon layer calling countPointsInPolygon for each feature.

Answer 2

There are also tools from the Processing Toolbox which you could call from your script (this is assuming you are running scripts inside QGIS):

• Count points in polygon
• Counts points in polygon (weighted)
• Count unique points in polygon

Taking the first tool, you could call it using:

import processing
Result = "path\to\saved_output.shp"
processing.runalg("qgis:countpointsinpolygon", "path\to\polygon_layer.shp", "path\to\point_layer.shp", 'NUMPOINTS', Result)

where NUMPOINTS is the name of the field which stores the number of points.

I'm using QGIS 2.8.2-Wien, Processing plugin v2.9.3.

Answer 3

The simplest way is to use "Join attribute by location". You can do it from the menu (data managment > Join by location), or with Python ("qgis:joinbylocation") with the option "take summary of intersecting features", computing the sum of a field with "1" at each point.

Answer 4

I have never worked with QGIS's python API, so my answer is a wild guess. But it looks like QGIS is using GEOS geometry objects similar to django. So this could work in QGIS too:

len(geom.coords)

• Rajagopal Vajja: Good guess but that is not what I am asking. I have every thing points, polygon. what I just want is to calculate the points in the polygon using pyqgis

Answer 5

I assume your polygon is a qgsfeature :

http://qgis.org/api/classQgsFeature.html

I didn't test it but I guess it would work :

len(polygon.geometry().asPolygon())

polygon.geometry() gives a qgsgeometry class.

qgsgeometry.asPolygon() gives a list of the point of your polygon.

Edit : You want the points inside the polygon? You have points in an other layer and wonder which ones intersect your polygon?

Answer 6

QGIS 3 has a processing tool for this task - Count points in polygon.

You can call it with pyqgis using this code:

processing.run(
"native:countpointsinpolygon", 
{'POLYGONS':'D:/POLYGONS.gpkg|layername=POLYGONS',
'POINTS': 'D:/POINTS.gpkg|layername=POINTS',
'WEIGHT':'',
'CLASSFIELD':'',
'FIELD':'NUMPOINTS',
'OUTPUT':'TEMPORARY_OUTPUT'}
)