[postgis-users] Z coordinate value changes with st_transform

[Stefano Iacovella]

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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