I am trying to automate buffering of objects in QGIS using Python. The function below using QgsGeometryAnalyzer works but the output is blocky. I understand that the smoothness of the buffer edge can be improved by increasing the number segments per quarter but i am unsure of how to do this using Python or even if it is possible.

This note and the linked github pull request suggests not.

Is there an alternate method i am missing that would allow me to increase the number of segments and so the smoothness of the buffer object?

QgsGeometryAnalyzer().buffer(LayerToBeBuffered, "Output.shp", 2000, False, False, -1)

Blocky buffer object output from QgsGeometryAnalyzer

  • 2
    You could also use the Processing algorithm qgis:fixeddistancebuffer which includes a parameter for segments :)
    – Joseph
    Commented Jun 29, 2017 at 13:40
  • 1
    Beautiful. I amended to; import processing processing.runalg("qgis:fixeddistancebuffer", LayerToBeBuffered, 2000, 30, False, "Output.shp")
    – benj
    Commented Jun 29, 2017 at 16:23

1 Answer 1


You can use the buffer() method. It applies to a geometry object. For example, using the following code:

layer = iface.activeLayer() # for example
for feat in layer.getFeatures():
    geom = feat.geometry()
    buffered_geom = geom.buffer(200, 30) # this is the relevant part

you will create a buffer around the current feature with a radius of 200 (expressed in the units of measurement of the project) and composed of 30 segments.

  • I appreciate this would achieve a buffered object but would do so within the existing layer. I need the buffered object to be in a separate layer as with in the original snippet.
    – benj
    Commented Jun 29, 2017 at 16:25
  • @benj you asked for a method and I answered mentioning a method. Instead, if you want to create the object in a new layer, you may follow the suggestion by Joseph (the qgis:fixeddistancebuffer algorithm works using the buffer() method).
    – mgri
    Commented Jun 29, 2017 at 17:10

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