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

[Bob Covill]

On Thu, 2007-04-19 at 01:51 +1200, Hamish wrote:
> Michael:
> > >> 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?
> Glynn:
> > > 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:
> > 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.
> 
> 
> you could try "r.profile -c" with a profile which starts and stops at
> the cell center (length=0). Also it should be very simple to add a flag
> just like "r.profile -c" to r.what, if that helps.

I have a version of r.what that I modified to optionally output RGB
color. If interested I could commit to CVS?

--
Bob


> 
> But probably the most direct solution is a SWIG-Python interface to the
> libgis color-lookup fns themselves.
> 
> 
> Hamish
> 
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