[GRASS-user] shaded relief of srtm tiles

[Maciej Sieczka]

thorsten wrote:
> thank you Hamish,
> 
> patching works fine  ( http://www.flickr.com/photos/h2guide/329431459 ),
> but i try to create a shaded relief of a hughe area,
> so i will have to process it tile by tile.
> 
> what i am actually doing is:
> 
> r.in.srtm input=N42W005 output=tile  #r.in.srtm input=N42W004 output=tile
> g.region rast=tile
> r.colors map=tile rules=srtm
> r.shaded.relief map=tile shadedmap=relief altitude=44 azimuth=270
> units=meters
> r.his h_map=tile i_map=relief r_map=final.red g_map=final.green
> b_map=final.blue
> r.composite red=final.red green=final.green blue=final.blue levels=32
> output=final;
> 
> "final" is the shaded and colored relief.
> 
> what do you mean by "absolute" color table?
> i am  using the  predefined color table "srtm"

That's OK. The problem is that r.shaded.relief script internally uses
"r.colors "$ELEVSHADE" color=grey" internally. Since the "grey"
colortable is defined as follows:

$ cat /usr/local/grass-6.3.cvs/etc/colors/grey
0% black
100% white

the colortable depends on min/max value in the input raster.

A workaround: you can check the max and min height in *all* your
rasters, choose the maximal max an minimal min out of them, and modify
the r.shaded.relief script to assign your absolute-grey colortable instead.

Maciek