[GRASS5] New Datums

[Paul Kelly]

Hello Michel (and anybody else who would like to test this)

On Tue, 3 Jun 2003, Michel Wurtz wrote:

> [...]
> > Another point is that it was very hard to find transformation parameters
> > for France (I tried to add support for a few European countries but of
> > course it is not complete). The above website only had one 3-parameter
> > transformation for the whole of France which couldn't be very accurate.
>
> Look at the official french survey site : all parameters and even the algorithms
> used are described.  You can also load a grid af correction parameters to do
> accurate transformation between NTF and GRS80 systems (same style as NAD to NAD ?)

I have had a chance to have a good look at this now and while the grid was
nothing like the nad2nad format, I think I have managed to convert it into
a format (gsb) that can be used by PROJ and GRASS. There was too much for
an e-mail so I put details on a webpage at
http://www.stjohnspoint.co.uk/gis/france.htm and you can download my
version of the gridshift file from there as well.

If we get some feedback and it works, maybe we can include it in the GRASS
distribution the way the USA and Canada files are there now (and perhaps
add Australia and New Zealand as well, which are freely available).
Somebody would need to check any copyright issues though probably.

Paul