[postgis-users] GEOS union() error

[Martin Davis]

You could try doing the union and then the buffer - that should be more 
robust.  Something like:

select buffer(geomunion(the_geom), 400) as the_geom from main

(although I may not have quite the right syntax)

Lee Keel wrote:
>
> Hello list.
>
> I am trying to get a multipolygon from a union of buffered 
> linestrings.  See attached (bad_drawing.jpg) to see what I am trying 
> to achieve.  I have some linestrings, I want to buffer each line by 
> 400 feet, then combine all of those buffers to create one 
> multipolygon.  My thought was to do something like:
>
> select geomunion(buffer(the_geom, 400)) as the_geom from main
>
> However, when I do this, then I get the following error:
>
> NOTICE:  TopologyException: side location conflict 
> (901411,1.03413e+006,1.03413e+006)
>
> ERROR: GEOS union() threw an error!
>
> SQL state: XX000
>
>
> Now my guess is that the geomunion is throwing the error because the 
> buffers overlap and of course that would be an invalid polygon.  So, 
> could someone purpose a different approach to doing this?  Or tell me 
> what I am doing wrong.
>
>
> <<bad_drawing.jpg>>
>
> Thanks in advance,
>
> Lee
>
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-- 
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022