[postgis-users] ST_Unioning invalid multipolygons

Michael Michaud michael.michaud at free.fr
Thu Aug 28 23:24:05 PDT 2008

David Jantzen a écrit :
> Hi again,
> I'm trying to ST_Union multipolygons from the Zillow neighborhood data.
> When I do this I occasionally see:
> NOTICE:  TopologyException: found non-noded intersection between
> -73.812....
> This appears to be due to invalid geometries, as the following query
> returns over a hundred rows:
> select * from neighborhoods where not ST_IsValid(the_geom)
> Can anyone suggest a workaround here?  The resulting geometry needs to
> be a multipolygon.  Also, what is ST_Is_valid actually testing for?  The
> documentation isn't very explicity about the definition of validity.
Most of time, invalid polygons are polygons with a self intersecting 
boundaries (as in the number '8') or self-touching boundary (two non 
contiguous points of the boundary are touching each other)
The best solution is to correct those geometries if you can.
Another solution which *may* work is to replace the geometry by a buffer 
of size 0 around the geometry in your select statement (using a 0-buffer 
is a work-around which generally works with JTS library from which 
postgis functions are derived).

> Thanks,
> David
> _______________________________________________
> postgis-users mailing list
> postgis-users at postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users

More information about the postgis-users mailing list