[postgis-devel] Re: [postgis-users] 3D Datum shifts from postgis

strk at refractions.net strk at refractions.net
Tue Oct 24 06:42:52 PDT 2006

I've committed a patch sending Z values to pj_transform().
When input is 2d only Z are sent as 0.0.
We need some test cases to check if it's really working.


On Mon, Oct 23, 2006 at 03:40:58PM -0400, Frank Warmerdam wrote:
> 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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