[postgis-users] Z coordinate value changes with st_transform

[Paul Ramsey]

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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