[postgis-users] Z coordinate value changes with st_transform

[Jose Carlos Martinez Llario]

 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
>
>
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