[postgis-users] union operation

[Paragon Corporation]

Nathan,

Which version of PostGIS and GEOS are you using.

Do a 

Select postgis_full_version();

(you should be ideally running GEOS 3.1.1 and above)


Shared vertices should not be an issue but there are some annoying rounding
problems we are working on isolating when they occur.  

What does cause this problem more frequently are invalid geometries.  So as
a first step,

Verify all your polygons are valid with a 

SELECT count(*) where ST_IsValid(the_geom) = false  

Will return number of invalid geometries and you can exclude these from your
union just to verify your problems are with valid geometires. 

If your problem is with all valid geometries, it would be helpful if you can
isolate the issue to unioning subset of polygons and attach that so we can
investigate.

Hope that helps,
Regina

 

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Nathan
Widmyer
Sent: Thursday, August 06, 2009 6:41 PM
To: PostGIS Users Discussion
Subject: [postgis-users] union operation

I have many polygons I'm trying to make a union of.  The polygons have a
high possibility of shared vertices which causes the "NOTICE:
TopologyException: found non-noded intersection between ..." error.

How can I avoid this error?

I did find a reasonable query that used linework which solved that problem,
but was problematic in other ways I think (I forgot those other
circumstances).
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