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I am using QGIS to create Voronoi / Thiessen polygons for 4 rain gauges.

I am having issues with both the QGIS 'Voronoi polygons' tool and the Grass equivalent 'v.voronoi' where one of my 4 points is skipped and only 3 polygons are generated in the output.

As a test I have added an additional point and have found that both tools output a polygon with the correct number of parts (5). Is there a reason it will not work correctly on 4 or less points?

Edit - image showing the configuration of points and the output Voronoi polygons skipping the central point

image showing the configuration of points and the output Voronoi polygons skipping the central point

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  • I can't reproduce by digitizing 4 points to a new layer and creating Voronoi polygons through the Geometry tools menu. Testing with QGIS 2.16.3. Except when the points are located over a straight line.
    – user30184
    Commented Dec 7, 2016 at 14:58
  • Have you tried repairing Geometry on your file? Sometimes geometry errors can cause QGIS processing to skip features, that may be what is causing it. If it is Geometry errors try look at some of the methods to rectify geometry errors in my answer here: gis.stackexchange.com/questions/218757/…
    – user32496
    Commented Dec 7, 2016 at 17:39
  • I've tried cleaning the geometry with no luck, the same results are produced. I have noticed the following warnings when using v.voronoi: 'WARNING: Number of centroids exceeds number of areas: 4 > 3 WARNING: Number of duplicate centroids: 1'
    – AJ Walsh
    Commented Dec 8, 2016 at 10:03
  • There were several bugs in the QGIS Voronoi code. Many fixes has been applied in the QGIS 3.2.2 code. Could be worth trying again with that version.
    – Håvard Tveite
    Commented Aug 25, 2018 at 19:32

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