5

Sorry folks, I know it sounds like a lame question - and, yes I did read the manual... :-)

I'm trying to make Voronoi diagrams around points I have in a PostgreSQL table.

It should be rather easy - but I can't find a single example on using ST_VoronoiPolygons() on real data (i.e. a table of points).

All I keep seeing is examples similar to that in the docs. like this:

SELECT
    ST_VoronoiPolygons(geom) AS geom
    FROM (SELECT 'MULTIPOINT (50 30, 60 30, 100 100,10 150, 110 120)'::geometry AS geom ) AS g
;

That works fine on my computer. But I want to make Voronoi polygons around my real point, not just example-points hard-coded in the SQL.

Can anybody point me to a working example of SQL that shows the use of ST_VoronoiPolygons() with an existing PostgreSQL Point table as input.

| improve this question | |
  • Can you post an example of a query you are using against one of your table? – Fabien Ancelin May 12 '17 at 16:31
  • 1
    Yes, see gis.stackexchange.com/questions/172198/…. You might need to fiddle with the memory settings in postgresql.conf, but the functionality works well. – John Powell May 12 '17 at 16:45
  • @JohnPowellakaBarça Damn - I didn't look close enough at that page, because it was primarily about the old (<2.3) method... But you are right. Can you post it as a real answer, so I can acknowledge. I would like to post the fully functional solution, for the benefit of others. – Martin May 14 '17 at 14:54
  • @MartinHvidberg. Sure Martin, done. I spent a lot of time on getting voronoi poligonization working in Postgis. Initially I used a Python stored procedure, which worked, but was slow and had memory issues, then I had to build from source because we had old versions of everything at work. Now, thanks to DBaston, Geos developers and several others, it all works like a charm, and is super fast. – John Powell May 14 '17 at 16:56
16

The trick when using a table of points is to feed all the points into ST_VoronoiPolygons by using ST_Collect, which simply combines all the points into a MultiPoint, without performing any spatial operations such as would happen with ST_Union. So, for example, with a random table of points as input, you can do:

WITH points(geom) AS 
 (SELECT 
      ST_MakePoint(random(), random()) 
   FROM generate_series(1, 100))
 SELECT 
     (ST_DUMP(ST_VoronoiPolygons(ST_Collect(geom)))).geom 
 FROM points;

which produces 100 polygons from the 100 input points, as you would expect.

See the questions and answers here for a fuller treatment of some of the issues you might encounter with ST_VoronoiPolygons.

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.