[geos-devel] GeomUnion Bug?

[Martin Davis]

Both polygons are invalid.  The first is degenerate (a point, which 
obviously self-intersects.  The second has a non-closed ring.

That's why the result is incorrect - JTS/GEOS methods usually are only 
guaranteed to work for valid inputs.

Charlie Savage wrote:
> This makes sense to me:
>
> SELECT astext(GeomUnion(GeomFromText('POINT(-104 40)'),
>                      GeomFromText('POINT(-105 40)')))
>
> "MULTIPOINT(-105 40,-104 40)"
>
>
>
> But this not so much:
>
> SELECT astext(GeomUnion(GeomFromText('POLYGON((-104 40,-104 40,-104
>                                                  40,-104 40,-104 40))'),
>                         GeomFromText('POLYGON((-105 40,-105 40,-105
>                                                  40,-105 40,-105 0))')))
>
> "GEOMETRYCOLLECTION EMPTY"
>
> Is this a bug?  Or is it supposed work this way?  It used to be 
> different with Geos 2.2.1 (I assume this is a geos issue so I included 
> that mailing list).
>
> Charlie
>
>
>
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>
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-- 
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022