[postgis-users] Re: molodensky

[Frank Warmerdam]

pinktomate wrote:
> hi all
> 
> postgis is able to work with datum transformations for instance the
> molodensky badekas model for transformatiosn of datum??

Dear Pinktomate,

PostGIS uses PROJ.4 for coordinate transformation, so the question is what
does PROJ.4 support.  It support 3 and 7 parameter data transforms as well
as the use of grid shift files in a few formats.

I am a little fuzzy on proper mathematical names for the different transforms.
I believe the 3/7 parameter transforms are molodensky transforms (or perhaps
Bursa-Wolf transforms) but they are the normal methods used by other packages.
I just utilized the code from Geotrans from NIMA for PROJ.4.

In particular the 3 parameter transform is a 3D offset in geocentric space.
The 7 parameter includes rotation and scaling factors as well as the offset
in geocentric spaces.

This is discussed at:

   http://proj.maptools.org/gen_parms.html#towgs84

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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