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

Glynn Clements glynn at gclements.plus.com
Thu Apr 12 19:08:29 EDT 2007

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.

Glynn Clements <glynn at gclements.plus.com>

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