[postgis-users] GeomUnion Bug?
Charlie Savage
cfis at savagexi.com
Fri Sep 7 10:28:16 PDT 2007
Hi Martin,
> Two observations:
> - This does look like a bug, or at least a porting problem in GEOS. In
> JTS, the envelope of a Point is itself a Point. This means that the
> return value is always a valid geometry, and thus can be safely used in
> further operations.
Ok, I'll submit a bug report.
>
> - Are you sure you want to compute the union of the bounding boxes,
> rather than the bounding box that contains them both? If the latter is
> the case, perhaps the ST_extent function is what you want. (In raw
> GEOS, there should be an Envelope.expandToInclude function which does this)
Good point, you are right.
However, is this another bug then?
select astext(extent(GeomFromText('POINT(-104 40)')))
"POLYGON((-104 40,-104 40,-104 40,-104 40,-104 40))"
But luckily, this actually works:
select astext(extent(collect(envelope(GeomFromText('POINT(-104 40)')),
envelope(GeomFromText('POINT(-105 39)')))))
"POLYGON((-105 39,-105 40,-104 40,-104 39,-105 39))"
So that solves my issue.
I will file these both as bug reports - thanks for your help Martin!
Charlie
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