[postgis-users] 3D Datum shifts from postgis

[Nathaniel]

Sandro,

I can't provide reliable test data, but I've just
installed a recent postgis SVN snapshot and wanted to
thank you for your very rapid inclusion of this
feature.

Working against 42 British OS and 12 Dutch RD test
points (from www.ordnancesurvey.co.uk and www.rdnap.nl
respectively), where the heights are given in the
respective nationally defined vertical datums (i.e.
not ellipsoidal heights--hence I don't have test
points!) height transformations through PostGIS/Proj4,
using 7-parameter approximations, are within the kind
of error limits I'd expect. Namely,

	SRID             Mean Error(m)  SD of Error(m)
	28992 (Dutch)    0.31           0.18
	27700 (British)  1.1            0.83

Many, many thanks for the quick inclusion of this.



		
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