Well from my observation it looks like most of those Ops functions (not sure about Union and Intersection) -- first do a 2D operation and then do some sort of apply the Z back on. So the Z is never considered in the basic operation -- thus the cause of a lot of the goofiness.
Take this example. It seems clear to me that these polygon's are not within each other so it should be a multipolygon not a Polygon with a hole. One lies above the other. SELECT ST_AsEWKT(ST_BuildArea('MULTILINESTRING((0 0 1,20 0 1,20 20 1,0 20 1,0 0 1),(10 10 2,10 11 2,11 11 2,11 10 2,10 10 2))')) "POLYGON((0 0 1,0 20 1,20 20 1,20 0 1,0 0 1),(10 10 2,11 10 2,11 11 2,10 11 2,10 10 2))" -----Original Message----- From: geos-devel-boun...@lists.osgeo.org [mailto:geos-devel-boun...@lists.osgeo.org] On Behalf Of strk Sent: Wednesday, January 14, 2009 4:04 AM To: GEOS Development List Subject: Re: 3D operations (Re: [geos-devel] C API coordinate sequencedimensions) On Wed, Jan 14, 2009 at 07:54:21AM +0000, Mark Cave-Ayland wrote: > Can anyone with more experience with BuildArea (like Martin!) comment on > whether this is a GEOS bug or simply a problem with behaviour > 2 > dimensions being undefined? JTS didn't support 3d when I added it to GEOS, so can't really serve as a source of information. The 3d task was added driven by customer needs, so the only working and tested functions was the one the customer needed. If I recall correctly it was mainly Intersection and probably Union. Since other functions are based on the former, there may be side-effects you wouldn't care about if you aren't using 3d features. Paul draw the specs about expected behaviour. Dunno if there's a doc around and I likely lost mine (Oops). --strk; Free GIS & Flash consultant/developer () ASCII Ribbon Campaign http://foo.keybit.net/~strk/services.html /\ Keep it simple! _______________________________________________ geos-devel mailing list geos-devel@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/geos-devel ----------------------------------------- The substance of this message, including any attachments, may be confidential, legally privileged and/or exempt from disclosure pursuant to Massachusetts law. It is intended solely for the addressee. If you received this in error, please contact the sender and delete the material from any computer. _______________________________________________ geos-devel mailing list geos-devel@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/geos-devel