Thanks for the heads up Richard. Sounds like important information, could you add it to the ticket ? http://trac.osgeo.org/postgis/ticket/1742
If what you say is correct we really want to always omit transforming Z from ST_Transform(). --strk; On Fri, Mar 30, 2012 at 05:59:16PM -0600, Richard Greenwood wrote: > 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 -- ,------o-. | __/ | Delivering high quality PostGIS 2.0 ! | / 2.0 | http://strk.keybit.net - http://vizzuality.com `-o------' _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
