ST_Transform will not touch Z-value unless you defined the towgs84 parameter in project definition. The towgs84 parameter reflect the difference between ellipsoids.
-- Gr Ralf -----Ursprüngliche Nachricht----- Von: [email protected] [mailto:[email protected]] Im Auftrag von Olivier Courtin Gesendet: Donnerstag, 12. November 2009 13:14 An: PostGIS Users Discussion Betreff: Re: [postgis-users] Third dimension units On Nov 12, 2009, at 12:06 PM, Gilles Bassière wrote: Hi Gilles, > I've always thought that WGS84 is expressed in decimal degrees for > *all* > dimension (even if 100° deep does not make sense to me). EPSG:4326 is only defined for 2D, for 3D with WGS84 you should have a look on EPSG:4979 <http://spatialreference.org/ref/epsg/4979/> > Does this means that Z coordinates are always expressed in meters? Yes, at least the case for EPSG:4979 Not really clear indeed (for me) if it's above the mean sea level, or above WGS84 ellipsoid. > How does ST_Transform normally behaves with 3rd coordinate? My guess is that ST_Transform just don't care about the Z dimension, as altitude should be the same before and after point reprojection. SELECT ST_AsEWKT(ST_Transform( ST_GeomFromEWKT('SRID=4326;POINT(5 5 100)'), 4979)); Give: SRID=4979;POINT(5 5 100) HTH, -- Olivier _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
