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
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