[geos-devel] WkbReader and Z-geometries

Sandro Santilli strk at keybit.net
Thu Aug 4 17:22:45 EDT 2011

On Thu, Aug 04, 2011 at 07:46:39AM +0200, Oyvind Idland wrote:
> Oh.. sweet chaos!
> The lack of a WKB-spec with Z (and M) ordinates seems to have triggered a
> bunch of WKB-flavours, such as
> - OGR's "Two-and-a-half-D extensions for Simple Features"
> - FDO's FGF-format
> - Postgis EWKB
> I found the EWKB proposal here, but probably not the latest:
> http://postgis.refractions.net/pipermail/postgis-devel/2004-December/000710.html
> As far as I can see, it is fairly similar in structure as the SQL/MM, except
> for the optional SRID. The object-type ID's are of course not the same.
> In addition, SQL/MM specifies CircularString/CurvePolygon/CompundCurve etc
> aswell, would be nice to have these implemented in GEOS aswell (PostGIS has
> done some work here, not sure what)
> I got two versions of the SQL/MM spec in PDF, the earliest (2nd edtion)
> dates from 2002. I'll send you the newest right away.
> For now, I'll try to make a simple hack on the existing WkbReader.
> Would be nice with a more united WKB-world...

Please use an enum for different WKB types, it's the best we can have.
I confirm any extension support comes from PostGIS EWKB, which is
documented in doc/ZMSgeoms.txt, which is the document submitted as
proposal to the OGC (not sure about the outcome of that).


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