[postgis-devel] Re: Patch for PostGis Envelope Bug
cfis at savagexi.com
Tue Sep 18 20:57:47 PDT 2007
Anyone have feedback on this patch? It seems like the current behavior
is incorrect, and I don't see any easy way to work around it without
Charlie Savage wrote:
>>> However, is this another bug then?
>>> select astext(extent(GeomFromText('POINT(-104 40)')))
>>> "POLYGON((-104 40,-104 40,-104 40,-104 40,-104 40))"
> Martin Davis wrote:
>> Looks like the same bug/design issue. JTS would return the envelope
>> as a POINT in this case.
> This issue has been causing me problems, so I dug into. Geos in fact
> does return a POINT when you ask for the envelope of a POINT.
> It's PostGIS that is wrong. The method LWGEOM_envelope (line 2493 in
> lwgeom_functions_basic.c) *always* returns a polygon. So I changed it
> to return a point if the input geometry is a point.
> I've attached a patch that fixes this issue. The patch checks to see if
> the input geometry is a point or a multipoint with just one geometry.
> There may be 2 issues with the patch:
> 1. The check ins't foolproof, one could subvert it by:
> select asText(Envelope(GeomFromText('MULTIPOINT(10 10, 10 10)')));
> Maybe checking the bounds (or area) of the envelope would be better?
> 2. I'm not sure I handled the SRID correctly for a mutlipoint. I just
> took it from the multipoint itself. Can the first point in a multipoint
> have a different SRID?
> Anyway, it would be great if someone could review this patch and apply
> it if it seems ok. I think its important because its easy to create
> invalid geometries that don't work with GeomUnion/Contains/Within/etc.
> We run into this problem a lot now that we've upgraded to GEOS 3 (GEOS
> 2.1 seemed to work ok, although maybe that was pure luck.).
-------------- next part --------------
A non-text attachment was scrubbed...
Size: 3237 bytes
Desc: S/MIME Cryptographic Signature
More information about the postgis-devel