[GRASS-windows] (no subject)
Moritz Lennert
mlennert at club.worldonline.be
Thu Oct 2 11:46:51 EDT 2008
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
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