[postgis-users] Z coordinate value changes with st_transform

[Paul Ramsey]

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 <pramsey at 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.iacovella at 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 <jomarlla at 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 at postgis.refractions.net
>>>>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>>>>
>>>>
>>>
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