[GRASS-windows] (no subject)

[Moritz Lennert]

On 02/10/08 16:48, Louis Becker wrote:
> Hi
> 
> I have downloaded a number of file sets, but the first two I used are
> called 33J and 33K, where number 33 indicates the UTM Zone 33 and J is a
> tile of that with bottom left corner 32S 12E and top right corner 24S
> 18E (8 x 6). 33K is the tile just north of 33J.
> 
> A file set from this site comes with the following folders and (files):
> 
> Clutter - (dt, dt.hdr, index and menu)
> Dtm - (dtm, dtm.hdr, index and projection)
> Map - Geotif files (.TAB, .tfw, .tif and index)
> Ortho - (.TAB, .tfw, .tif and index)
> 
> I am only able to define a location from a Georeferenced file if I use
> the DTM file under DTM (let's call it DtmLocation). If I then display
> the region settings, I get the following for DTM 33J:
> 
> projection: 0 (x,y)
> zone:       0
> north:      7345125
> south:      6453125
> west:       192375
> east:       807375
> nsres:      250
> ewres:      250
> rows:       3568
> cols:       2460
> cells:      8777280

This is not UTM (projection: 0 (x,y)), so it means that the projection 
info in the file is not recognized. However, the extents seem reasonable.

BTW, for precise projection info about a location, use g.proj -p.

> 
> If I use the tif file from the Map folder to create a location (let's
> call it UTMLocation), I get the following if I display the region
> settings for 33J:
> 
> projection: 1 (UTM)
> zone:       -33
> datum:      wgs84
> ellipsoid:  wgs84
> north:      7345000
> south:      6453000
> west:       192500
> east:       807500
> nsres:      125
> ewres:      125
> rows:       7136
> cols:       4920
> cells:      35109120

This seems right for a 33S.

> 
> If is not an issue to import the dtm file into the 33J_DtmLocation, but
> is not properly referenced for further use. 

What makes you say that ?

> If I want to import the dtm
> into the 33J_UTMLocation, I have to override the projection check.

Logical, since, as stated above, GRASS does not recognize the projection 
info in your file.

> 
> Defining a location for 33K DTM yields:
> 
[...]
> 
> Defining a location (called 33 of 33K_UtmLocation) Tif yields:

[...]


Same as above, so rather encourageing (as expected, you are in the same 
UTM zone).

> 
> I am able to import the 33K_Dtm into the 33K_UtmLocation by overriding
> the projection check. If in now try to re-project using r.proj for the
> raster file in 33J_UtmLocation into the 33K_UtmLocation, then it just
> does not seem to work.

You do not need to reproject. Both location seem have exactly the same 
projection (which they should).

So:

1) Create a location with your tif (or using the relevant EPSG code - 
see http://www.epsg-registry.org/).
2) Import all your DTMs into this location, overriding the projection 
check and using the -e flag to extend default location extents.
3) If you need to combine all files into one, use r.patch.

Moritz