[Proj] proj-datumgrid-1.4 issued
didier.richard at ign.fr
Wed Jul 23 07:48:30 EDT 2008
Le Mardi 22 Juillet 2008 19:28, Paul Kelly a écrit :
> On Tue, 22 Jul 2008, Frank Warmerdam wrote:
> > Richard Greenwood wrote:
> >> On Mon, Jul 21, 2008 at 7:59 PM, Frank Warmerdam <warmerdam at pobox.com>
> >> wrote:
> >>> Folks,
> >>> I have uploaded a new version of the datum grid shift file collection
> >>> that includes the ntf_r93.gsb shift file. Richard, perhaps you could
> >>> more fully
> >>> explain how this grid shift file works?
> >> I wish I could, but I'm still struggling with the .lla files!
> > Rich,
> > Sorry, I actually mean Richard Didier who added this .gsb file in PROJ.
> > :-)
It's me !-)
> I imagine this would be similar to my france.gsb file to convert between
> the French NTF and RGF93 datums, documented in detail here:
> so perhaps that page would be of interest?
Well, there is a difference between your grid and our : while your grid is
correct and our has been built using the same overall process, our grid
ensure the centimeter precision (they are something like 2 more iterations
when computing the grid's nodes).
You can keep our page on by just informing users the difference in precision
between your grid and our.
> (BTW I never pressed to have it included in GRASS or PROJ.4 as I wasn't
> sure about the licence/legal status of the tables I derived it from.)
No problem for the licence/legal status : the original text file found on
IGN's web side is public data. A lot of GIS editors have been using it
directly to implement the projection usign this grid. So, feel free to use by
keeping in mind the above point on precisions.
All the best,
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Didier RICHARD, chef du pôle technique Géoportail pour l'IGN
Institut Geographique National tel: +33/0 18.104.22.168.23
2/4 Avenue Pasteur fax: +33/0 22.214.171.124.88
F-94165 St-Mande Cedex e-mail: Didier.Richard at ign.fr
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