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I try to compute the centroid of polygons with holes on qgis. I did not manage to do it directly, I had to make a conversion to convex hulls before extraction.

I crashed my pgsql server trying to extract theses using ST_Centroid()

Is there a better way to do it?

Nono
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  • Are you looking for a PostGIS solution or can it be done using QGIS? – Joseph Apr 11 '16 at 11:51
  • For PostGIS solution see here: http://gis.stackexchange.com/questions/724/how-can-i-find-a-point-inside-a-polygon-in-postgis. For general math see: http://math.stackexchange.com/a/623849 – zehpunktbarron Apr 11 '16 at 12:01
  • There may be invalid geometries in your data. PostGIS should handle polygons with holes just fine SELECT ST_AsText( ST_Centroid( ST_GeomFromText( 'POLYGON (( 523 228, 523 238, 535 238, 535 228, 523 228 ), ( 527 231, 531 231, 531 235, 527 235, 527 231 ))') )) – user30184 Apr 11 '16 at 13:06
  • In Qgis (that you tagged as well) the Extension "Real Centroids" does what you want i think. It moves the centroid when it lies outside the polygon itself, what would be the case when it is in a hole. The calculations going on in the background are probably the same as in postgis, as this is mentioned in the extension. – Matte Apr 11 '16 at 14:29
  • What version of PostGIS? Can you post an example of the geometry that crashed the server? – Mike T Apr 11 '16 at 21:50
  • Ty all, "Real centroids" are relevant in my case, I crashed my server on too many polygons centroid calculation or bad geometries, I must run some checks first. Versions info (have to update to 2.2) "POSTGIS="1.5.3" GEOS="3.3.1-CAPI-1.7.1" PROJ="Rel. 4.6.1, 21 August 2008" LIBXML="2.7.8" USE_STATS" – Nono Apr 12 '16 at 05:45

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