Colours from categories

[Conn Copas]

Some more novice colour questions, I'm afraid (has anyone thought about writing
a tutorial for this whole colour management thing?)

I have an elevation map with categories ranging from 40 thru 278. When
displaying this in floating mode, the system objects to those categories
greater than 255, and presumably performs some sort of truncation. This occurs
to me as being odd, as I thought I had 256 available colours, and I am only
trying to display 238. OK, the next strategy is to use r.mapcalc to subtract
40 from all categories, which gives the same problems as before. Finally, in
desperation, I used r.mapcalc to transform all categories greater than 254 into
the one value, which eliminates my error warnings, at the cost of skewing the
data. So it seems that I 'really' only have 214 colours available, no? (release
4.0, nb).

Second problem: the elevation map has no value labels for the categories. I
know I can add these one-by-one using r.support or r.reclass, but is there a 
faster way of doing it? ie, I want to compute the label as a function of the
category number.

The man pages also talk about a green thru brown thru yellow colourtable for
elevation maps. Is this some sort of cartographers' standard? I was under the 
impression that the literature in fact recommends grey scale as being easiest
to interpret.

-- 
Conn V Copas
Loughborough University of Technology          tel : +44 (0)509 222689
Computer-Human Interaction Research Centre     fax : +44 (0)509 610815      
Leicestershire  LE11 3TU              e-mail - (Janet):C.V.Copas at uk.ac.lut   
G Britain                                      (Internet):C.V.Copas at lut.ac.uk