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I have a problem that ST_VoronoiPolygons started to give me GEOSVoronoiDiagram: TopologyException: Input geom 1 is invalid: Self-intersection

The function that I use it for have worked for a long time for me.

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  • That's odd to see; ST_VoronoiPolygons essentially interprets its inputs as a MultiPoint, no matter what the actual geometry type is, so the concept of validity doesn't really apply.
    – dbaston
    Jun 21, 2018 at 12:40
  • I filed a related ticket at trac.osgeo.org/postgis/ticket/4335#ticket
    – tilt
    Feb 27, 2019 at 15:54
  • This is caused by a robustness problem in the underlying GEOS library. This has been fixed and will show up in PostGIS in the next release.
    – dr_jts
    Sep 7, 2019 at 22:16

2 Answers 2

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The problem was connected to that the data I had was in a perfect grid. I don't know why but ST_VoronoiPolygons couldn't handle it.

So what I did was that I altered the points slightly (I use Python to populate the data so I added import random and + random.gauss(0.00000001, 0.00000001) to the x and y coordinate)

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  • You could probably fix this more elegantly by using ST_SnapToGrid in Postgis. These sorts of errors are usually caused by spurious precision in geometries, so reducing the number of decimal places generally works.
    – John Powell
    Jun 21, 2018 at 10:48
  • Well, I tried with ST_SnapToGrid, hence when I used a size "small enough" I got the same problem.
    – axel_ande
    Jun 21, 2018 at 10:59
  • Exactly. But it is much more deterministic than using random, which could still result in topology exceptions occasionally.
    – John Powell
    Jun 21, 2018 at 16:04
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Maybe there was a self-intersection... Have you tried ST_isValid and ST_isValidDetail functions? The second one could tell you where exactly this intersection is. The simplest way to deal with them is to use ST_Buffer function with radius = 0 - that's because ST_Buffer is creating brand new geometry based on origin and this geometry is always valid. With radius 0 you'll get exactly the same geometry but without self-intersections.

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  • Is ST_MakeValid(geom) a better option to ST_Buffer(geom, 0)? Seems more intentional.
    – alphabetasoup
    Oct 18, 2021 at 22:33

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