[GRASSLIST:5405] Re: Other Datum.

[Paul Kelly]

Hello

On Thu, 30 Jan 2003, javier garcia - CEBAS wrote:

> Hi all;
> I would like how to manage data that use different representation systems.
> The first topic is that maps in my country use a datum not included in the
> options in GRASS, this is:
>
> Geodetic Datum Transformation Parameters (Local to WGS-84) From NIMA 8350.2 4
> July 1977 and MADTRAN 1 October 1996:
>
>
> Datum                Ellipsoid                  dX    dY     dZ
> -------------------------------------------------------------------------------------
> European 1950  International 1924  -84   -107 -120 Ours (not included in
> GRASS)
> European 1950  International 1924  -87   -98   -121 Mean (the one included in
> GRASS)
>
> Is it possible to specify this datum in GRASS?

If you edit the PROJ_INFO file in the PERMANENT directory in your location
as follows:
delete the line 'datum: eur50' (or if it's not there don't add it)
Add or change the following lines to:
dx: -84
dy: -107
dz: -120
If there is a 'datum:' line in the PROJ_INFO file, the datum
transformation parameters (dx dy dz) will be looked up in the central
list. But if you delete the datum: line then the dx dy dz values in the
PROJ_INFO file will be used directly. I think this should work. Let me
know if it doesn't and I will try to fix it (of course you need to be
using the latest CVS version of GRASS for all this).

> The next question is about how to translate landsat imagery (wgs84) into my
> datum to incorporate them into my database.

Once you have your location set up with the correct datum (by editing the
PROJ_INFO file) you should just be able to use r.proj to reproject the
image from a separate wgs84 location into your local eur50 location.

In future it will be possible to add your own datum line to
/usr/local/grass5/etc/datum.table (or wherever) and enter this directly in
g.setproj or edit your PROJ_INFO file. This won't work at present but I
intend to fix it.

But manually editing the dx dy dz values should work for now. If you have
a 7-parameter transform you may also add the line, for example,
towgs84: dx,dy,dz,rx,ry,rz,m
to PROJ_INFO, this time making sure there are no 'datum' or 'dx', 'dy', or
'dz' lines.

Hope it works for you,

Paul