[GRASS-user] r.colors.stddev of a difference map

Anna Petrášová kratochanna at gmail.com
Sat Oct 25 18:43:37 PDT 2014

Hi Veronica,

On Sat, Oct 25, 2014 at 11:49 AM, Veronica Andreo <veroandreo at gmail.com>

> Dear list,
> I'm working at time with anomalies maps, so I set r.colors to differences
> palette, but as my maps also have null values and they appear as white too,
> I edited the differences file to "nv black"... everything fine till
> there... as differences are quite small most of the times (I'm working with
> chlorophyll concentrations in the ocean) it's difficult to see something...
> so i used r.colors.stddev with -z flag
> The problem arise when i use ps.map to generate my figures... somewhere in
> the process "nv black" is over-ruled and my null values appear as white in
> the .eps, which does not make sense... they are no-data and not zero
> difference (if i use ps.map before using r.colors.stddev, nv looks black as
> expected)... boh...
> Could someone explain why? or know of a workaround??? I have hundreds of
> maps to produce...
> Thank you very much in advance!
r.colors.stddev uses default nv, which results in white. So as a
workaround, you can then run r.colors.out and change the line with nv to
use 0:0:0. Then run r.colors with this new rules. This is a also
scriptable. Faster solution is to hack r.colors.stddev (it's a python
script) and add line in the rules which includes the nv 0:0:0. The right
solution for this would be probably to add nv option to r.colors.stddev, it
should be fairly simple, so if you know at least little bit of python, you
can try that yourself:)


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