Others more knowledgeable than myself should probably weight in on this, but I don't believe the Z value from a horizontal datum transform should be applied to an orthometric or ellipsoidal Z value. Proj.4 returns a Z value which is a delta when transforming lat/long (with no heights) between different datums when doing a 3 or 7 parameters datum transform (but not a grid shift tranform). 3 and 7 parameters transforms are done in XYZ geocentric space and the Z value is just the "artifact" but does not represent a geographic change in height.
The vertical datum support in Proj.4 is new and I don't think it is what you are seeing here. If I'm correct in my assumptions then there should be a ST_Transform() and a ST_Transform3D(). The Z value should be disregarded in ST_Transform() and in ST_Transform3D() vertical transformation should be explicitly requested from the Proj.4 lid. Rich On Fri, Mar 30, 2012 at 1:30 PM, Paul Ramsey <pram...@opengeo.org> wrote: > Turns out this is just because the definition of 23030 has been > updated to include a to_wgs84 parameter. You get the same behavior in > any version of proj. This is a feature, not a bug (our projection > information is now better). If you want the old behaviour, change the > proj4text of 23030 back to the 1.5 version. > > For a future release you might file a ticket to allow users to apply > transforms x/y but to skip the z-coordinate. > > P. > > On Fri, Mar 30, 2012 at 10:27 AM, Paul Ramsey <pram...@opengeo.org> wrote: >> Yeah, bad news, 2.0 is showing this behavour but not 1.5. >> >> http://trac.osgeo.org/postgis/ticket/1742 >> >> P. >> >> On Fri, Mar 30, 2012 at 9:59 AM, Stefano Iacovella >> <stefano.iacove...@gmail.com> wrote: >>> Hi Jose >>> >>> Im sure which version of PostGis are you using. >>> On my box, Postgis 1.5.3 with Proj 4.8 it seems to work without any >>> change to elevation: >>> >>> template_postgis=# select >>> st_asewkt(st_transform(st_geomfromtext('POINT (700000 4500000 100)', >>> 23030), 4326)); >>> WARNING: OGC WKT expected, EWKT provided - use GeomFromEWKT() for this >>> st_asewkt >>> ---------------------------------------------------------- >>> SRID=4326;POINT(-0.635451186670006 40.6259397158234 100) >>> (1 row) >>> >>> >>> template_postgis=# select postgis_full_version(); >>> postgis_full_version >>> >>> -------------------------------------------------------------------------------- >>> ------------------ >>> POSTGIS="1.5.3" GEOS="3.3.2-CAPI-1.7.2" PROJ="Rel. 4.8.0, 6 March 2012" >>> LIBXML= >>> "2.7.6" USE_STATS >>> (1 row) >>> >>> >>> Regards >>> >>> Stefano >>> >>> 2012/3/30 Jose Carlos Martinez <jomar...@cgf.upv.es>: >>>> I didnt get nay answers from now. >>>> Someone can tell me why postgis is changing the z coordinate and how i can >>>> change this default behavior? >>>> Should I keep using proj4.7 instead of proj4.8? >>>> >>>> >>>> Before: >>>> pg20=# select st_astext(st_transform(st_geomfromtext('POINT (700000 4500000 >>>> 100)', 23030), 4326)); >>>> st_astext >>>> -------------------------------------------------------------- >>>> POINT Z (-0.63662073736203 40.6248036513963 100) >>>> >>>> >>>> Now: >>>> pg20=# select st_astext(st_transform(st_geomfromtext('POINT (700000 4500000 >>>> 100)', 23030), 4326)); >>>> st_astext >>>> -------------------------------------------------------------- >>>> POINT Z (-0.63662073736203 40.6248036513963 168.35361468256) >>>> >>>> >>>> >>>> On 27/03/2012 21:56, Jose Carlos Martinez Llario wrote: >>>>> >>>>> From proj4.8 changelog: >>>>> >>>>> "Preliminary support has been added for vertical datums using the >>>>> +geoidgrids= directive. The geoidgrids are assumed to provide a >>>>> transformation from geoid elevations to ellipsoidal elevations and they >>>>> are >>>>> discussed a bit in the VerticalDatums topic on the web site" >>>>> >>>>> I dont like the st_transform method can change my z coordinates by default >>>>> though, dont know if it is because PostGIS is not ready still for proj4.8 >>>>> or >>>>> because it is the proj4.8 default behaviour. >>>>> >>>>> cheers, >>>>> Jose >>>>> >>>>> >>>>> On 27/03/2012 19:02, Jose Carlos Martinez wrote: >>>>>> >>>>>> Hi, dont know if this is the expected behavior, maybe its because I built >>>>>> postgis with proj 4.8 or because something has changed in >>>>>> spatial_ref_sys. >>>>>> Dont know at what time it happened (I missed it). >>>>>> >>>>>> Before: >>>>>> pg20=# select st_astext(st_transform(st_geomfromtext('POINT (700000 >>>>>> 4500000 100)', 23030), 4326)); >>>>>> st_astext >>>>>> -------------------------------------------------------------- >>>>>> POINT Z (-0.63662073736203 40.6248036513963 100) >>>>>> >>>>>> >>>>>> Now: >>>>>> pg20=# select st_astext(st_transform(st_geomfromtext('POINT (700000 >>>>>> 4500000 100)', 23030), 4326)); >>>>>> st_astext >>>>>> -------------------------------------------------------------- >>>>>> POINT Z (-0.63662073736203 40.6248036513963 168.35361468256) >>>>>> >>>>>> Using ST_AsKml Its changing the Z coordinate too. >>>>>> >>>>>> Someone can confirm when this change happened in PostGIS? >>>>>> >>>>>> Regards, >>>>>> Jose >>>>>> >>>>>> >>>>>> _______________________________________________ >>>>>> postgis-users mailing list >>>>>> postgis-users@postgis.refractions.net >>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-users >>>>> >>>>> >>>> >>>> _______________________________________________ >>>> postgis-users mailing list >>>> postgis-users@postgis.refractions.net >>>> http://postgis.refractions.net/mailman/listinfo/postgis-users >>> _______________________________________________ >>> postgis-users mailing list >>> postgis-users@postgis.refractions.net >>> http://postgis.refractions.net/mailman/listinfo/postgis-users > _______________________________________________ > postgis-users mailing list > postgis-users@postgis.refractions.net > http://postgis.refractions.net/mailman/listinfo/postgis-users -- Richard Greenwood richard.greenw...@gmail.com www.greenwoodmap.com _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
