[postgis-users] Finding a TopologyException

[Martin Davis]

JTS/GEOS can sometimes does some internal transformation of  geometries 
to try and overcome robustness errors.  So the coordinates in 
TopologyException error messages may not always correspond to the 
coordinate system of the input geometries.

Ben Madin wrote:
> G'day all,
>
> I have a topology exception with a file I clean up with GRASS and exported back into PostGIS, which I discovered when I tried to merge provinces into countries:
>
> CREATE TABLE new_country AS 
> 	SELECT country::varchar(3), st_union(the_geom) as the_geom
> 	FROM new_prov
> 	GROUP BY country;
>
> NOTICE:  TopologyException: found non-noded intersection between LINESTRING (-0.204257 0.999226, -0.204257 0.99858) and LINESTRING (-0.204257 0.995743, -0.204257 0.999226) at -0.204257 0.999226
>
> There is obviously information here on where the problem lies, but my entire project is in Lat / Long (EPSG:4326) in South East Asia, so I'm guessing this is not (nor is it on a unit square)
>
> So :
>
> How does the coordinates returned by the error relate to my geometry? or What do they mean? Can I use this information to find the problem part of the geometry.
>
> (as an aside, changing the query to st_union(st_buffer(the_geom,0)) let it through (and it works as I wanted)
>
> cheers
>
> Ben
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>
>   

-- 
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022