Making small raster areas

[Malcolm Williamson]

Steve Culshaw writes:
> 
> Can someone help on this problem. I've got our DTM in (finally - thanks 
> to all who helped), and drawn it. The range of values if such that large 
> areas look the same colour - I assume this is a limitation of GRASS with 
> a pallette of 255 colours ??
> 
> If I was to select a smaller area, e.g. a single river catchment, how 
> could I change the colour range such that only the values in the smaller 
> area were used - thus increasing the spread of colours.
> 
> Can I copy a chunk of the large DTM to produce a small raster ??
> 
> Thanks for any help,
> 

GRASS reflects the limits of your 8-bit color display with its pallette. There
are actually substantially less than 256 colors available, due to colors 
reserved for your desktop, etc. - see the GRASShopper archive for discussion
on this. As for your particular question, if you use r.resample to isolate
a small portion of your DTM you should be able to display more category colors.
Make sure that you have your colormode set to "float" (d.colormode float;d.erase
). You may have to reset your color table using r.colors, after you resample.

Regards,
-- 
Malcolm D. Williamson - Research Assistant       E-mail: malcolm at cast.uark.edu
Center for Advanced Spatial Technologies      Telephone: (501) 575-6159
Ozark Rm. 12                                        Fax: (501) 575-3846 
University of Arkansas              
Fayetteville, AR 72701