[GRASSLIST:1754] Re: Gauss-Krueger Location

[Markus Neteler]

On Sat, Apr 21, 2001 at 11:19:27AM +0700, Artemis wrote:
> Hi all,
> 
> I wonder how to create a Gauss-Krueger location within GRASS
Hi Artemis:

to define Gauss-Krueger:
1. start GRASS as usual, enter new location/mapset name.
2. coordinate system: other (D)
3. one line description for location: something
4. projection name: tmerc
5. ellipsoid name: bessel
6. map datum: potsdam      #if you are in Germany, currently not yet
                           #utilized, so no need to specify
7. Central Parallel: 0N    # equator
8. Central Meridian: 9E    # change to your Central Meridian
9. Scale Factor at the Central Meridian: 1
10.False Easting: 3500000  # first number is Central_Meridian/3
                           # example: for central_meridian=24, enter 8500000
11.plural form of units:  meters
12. enter boundary coordinates and standard grid resolution...

Then you import your data. If you don't know the boundary coordinates in
UTM, use 
 g.region -p
to get these numbers in Gauss-Krueger, then use
 m.proj 
to convert to UTM. These new coordinates store somewhere.

Leave GRASS, start it again, define UTM now (new location). Choose
UTM from the menu, enter additional parameters and the boundary coordinates
which you have calculated with m.proj (make it little bigger, round the
UTM coordinates to something nice so that the map will fit into.

Now, while still in UTM, we can transform easily the data from Gauss-Krueger
location into your fresh UTM location:

r.proj in=gk_map location=gklocation mapset=gkmapset 

This will transform the map "gk_map" from the other Gauss-Krueger
location into our new UTM location. Ready.

Do the same with vector and sites data (v.proj, s.proj).

Summary: You transform *into* a location. So you need two locations,
then this can be done pretty straighforward. 

Hope this helps,

 Markus

PS: Datum transform shall be added in GRASS 5.1 near future.

-- 
Markus Neteler *  University of Hannover
Institute of Physical Geography and Landscape Ecology
Schneiderberg 50 * D-30167 Hannover * Germany
Tel: ++49-(0)511-762-4494  Fax: -3984