[postgis-users] 3D Datum shifts from postgis

[Frank Warmerdam]

Paul Ramsey wrote:
> Well, I am pretty sure PostGIS only does transform() in 2d, no matter what. But 
> I also suspect that Proj4 only has a 2d internal model, which means at the 
> library level nothing may be available either.
> 
> Frank, can you confirm what proj4 provides in terms of 3d shifts?

Paul,

The PROJ.4 pj_transform() function attempts to transform "z" as well
as x and y.  Note that datum shifts performed with grid shift files
normally have no z shift.  But 3/7 parameter transformations also affect
Z, and if the shift is done strictly ellipsoid to ellipsoid then Z shifts
are also possible.

I think it would be desirable to connect up this Z shifting in pj_transform()
to the Z coordinate of postgis geometries.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | President OSGeo, http://osgeo.org