[postgis-users] TopologyException : another example.

[strk at refractions.net]

On Fri, Mar 03, 2006 at 06:21:15PM +0100, Guillaume Sueur wrote:
> Hi list,
> 
> I think I've got a good example of TopologyException too.
> I try to aggregate my cities boundaries on a district field to get 
> districts boundaries. The geom of cities is valid (set as a constraint). 
> When I run the simple query "CREATE TABLE districts as SELECT 
> iddistrict, geomUnion(the_geom) from cities, if gives back :
> NOTICE:  TopologyException: no outgoing dirEdge found (436814,2.01401e+06)
> ERROR:  GEOS union() threw an error!
> 
> Taken individually, my district build fine until some specific case :
> when a city and another one to merge with are only sharing one point. I 
> think the module tries to do a unique shape then, which gives a non vaid 
> geometry, instead of building two distinct parts.
> 
> What do you think ?

Can you try building a small testcases illustrating your assumption, or
showing the exact bug you're running into ?
If geomunion returns an invalid geometry, that'd be a bug.

--strk;