[GRASSLIST:2262] Re: r.patch -- problem solved

Rich Shepard rshepard at appl-ecosys.com
Fri Aug 3 15:39:07 EDT 2001

On Fri, 3 Aug 2001, Malcolm Williamson wrote:

> Check out the man page for r.colors; it describes how color ramps are defined.
> If you actually look at your color table (under $LOCATION/colr), you'll see how
> it works. Most of the colortables (excluding "rules" and "random", I think)
> defined in r.colors are written as ramps, meaning that there are not specific
> colors written in the colr file. Try zooming in to part of your DEM, so that you
> can see individual cells, and compare nlev=32 to nlev=256. I believe you'll see
> a difference, using d.what.rast to identify cell values associated with
> different colors. I just tested this, so I know it to be true.


  I'll have to read r.colors again until I fully understand this. Looking at
one of the files in colr/, I see this:

[rshepard at salmo colr]$ less temp_dem
% 1200 2721.300048828125
1200:255:85:85 1453.550008138:170:170:0
1453.550008138:170:170:0 1707.100016276:85:255:85
1707.100016276:85:255:85 1960.6500244141:0:170:170
1960.6500244141:0:170:170 2214.2000325521:85:85:255
2214.2000325521:85:85:255 2467.7500406901:170:0:170
2467.7500406901:170:0:170 2721.300048828125:255:85:85

  It looks to me that there are 12 colors and each is assigned to a range of
values, the lower bound of which is specified? The range of elevation values
here (I believe in meters) is on the first line. FWIW, I had nlev=256 set
for this display.

  I'll have to keep digging and working to understand colors in GRASS.



Dr. Richard B. Shepard, President

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