Postgis TopologyException: side location conflict at 226.001 39.5158, what's the problem?

Question

after st_union() PgSQL returns a note:

NOTE:  TopologyException: side location conflict at 226.001 39.5158

And in the results there are two rows with empty geometry and other rows are ok.
What causes that problem? How to solve it?

Answer 1

I've found the problem. It was a self intersecting polygon. I used ST_IsValidReason to find it.

Answer 2

The solution arrived in PostGIS 2.0, ST_IsValid() and ST_MakeValid(). You can ask PostGIS to fix broken geometries. You must be careful with it tough it the source geometry's integrity is important for some reason.

Answer 3

Googling found this related post: http://lists.refractions.net/pipermail/jts-devel/2009-March/002939.html

So it seems your features may be suffering from rounding errors, and it may be solvable by cleaning up the geometry a bit.

It might be worth creating a minimum reproducible case, and post a message on the postgis mailing list.