3D operations (Re: [geos-devel] C API coordinate sequencedimensions)

[Obe, Regina]

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-bounces at lists.osgeo.org
[mailto:geos-devel-bounces at 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; 

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