[Proj] Official source for some NTv2 files?

Mikael Rittri Mikael.Rittri at carmenta.com
Fri Sep 11 05:49:23 EST 2009

Hamish wrote:
> will a summary of all these be posted to the proj4 wiki site?

Well, I am not so experienced in creating new wiki pages, but here 
is the summary in wiki-format.  Maybe someone can put it on
the Proj4 wiki, and perhaps straighten out some of the question marks. 

=== Grid Shift Files in NTv2 format. === 
Links to some NTv2 files can be found below. For most of them, I think
the target datum 
is something that is equivalent to '''WGS84''' on the 1 meter level.
(For example, the Spanish
files convert the old datum '''ED50''' to '''ETRS89''', whose main
difference from '''WGS84''' 
is due to continental drift.) However, note that the Swiss file has a
national target datum.

The word "Official" after the link, means that the NTv2 files are the
officially recommended way
to convert coordinates.  "Semi-official" means that there is a more
official way, but the
NTv2 files have been prepared by a National Mapping Agency as an
alternative way (perhaps
slightly less precise.)  "Official?", with a question mark, means I
don't know whether
the files are Official or just Semi-official. 
  * [http://www.icsm.gov.au/icsm/gda/gdatm 
     Australia] Official.
  * [http://www.geod.nrcan.gc.ca/tools-outils/ntv2_e.php 
     Canada] Official, free for end users, but may not be redistributed
  * [http://lambert93.ign.fr/index.php?id=30#c71 
     France] Semi-official. 
  	Germany] Official?
  * [http://lists.maptools.org/pipermail/proj/2006-November/002658.html 
  	Great Britain] Files constructed by Paul Kelly.  Very good (on
land), but not official.
     New Zealand] Official.
     Spain] Official?
	Switzerland] Semi-official. (Goes only from '''CH1903''' to
'''CH1903+''', so a final 3-parameter shift is needed to reach

Mikael Rittri
Carmenta AB

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