[GRASS-dev] any way to know color assigned to a cell?

Michael Barton michael.barton at asu.edu
Thu Apr 12 19:35:04 EDT 2007

I was contemplating a wxPython histograming module, like the TclTk profiling
module, and liked the option in d.histogram of being able to use the color
table for the histogram colors. But this seems like a pretty intensive batch
of calculations to do it.


On 4/12/07 4:08 PM, "Glynn Clements" <glynn at gclements.plus.com> wrote:

> Michael Barton wrote:
>> If have a map with values from 0-255 I create a set of color rules such that
>> 0% = green
>> 100% = red
>> GRASS will create a color table that will assign a nice gradient of colors
>> from 0:255:0 to 255:0:0 to the values from 0-255.
>> Is there any way when querying a single cell of that map to know what color
>> has been assigned to it?
> Set a 1x1 region around the cell, then r.out.ppm | pnmnoraw | sed.
> Or r.mapcalc 'out = (r#map * 256 + g#map) * 256 + b#map', query the
> composite map and decode the category number.
>> Similarly, is there any way to know what color has
>> been assigned to any value in the 0-255 range?
> Set a 1x1 region, r.mapcalc "tmp = $value", r.out.ppm ...
> Seriously; this is how d.rast.edit.tcl does it.
> Yeah; we could probably do with a "r.what.colors" module.

Michael Barton, Professor of Anthropology
School of Human Evolution & Social Change
Center for Social Dynamics and Complexity
Arizona State University

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton 

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