[postgis-users] ST_Unioning invalid multipolygons

[David Jantzen]

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.

Thanks,
David