[GRASS-user] create a common colour scale

[Raphael.Viscarra-Rossel at csiro.au]

Hello Hamish,
thank you for the response and the hints. 
They are very useful as i cannot get GRASS7 to work.
Best wishes,
Raphael.




On 29 Jul 2014, at 2:52 pm, Hamish <hamish.webmail at gmail.com> wrote:

> Raphael wrote:
>> I wonder if anyone knows how to create a common colour scale for
>> different raster maps? I want to display all six maps on the same
>> page with the single colour scale but I cannot find how to do this in
>> GRASS.
>> 
>> More specifically, I have six raster maps of rainfall for different
>> time periods (each has a different range of values) and I would like
>> to display them all with the same colour scale. The colour scale
>> needs to be constructed using the min and max values of the set of
>> six maps (and not just individual maps.
> 
> 
> For only 6 maps I wouldn't bother with scripting a mix,max variable,
> just run r.info in a loop and copy out the min,max by hand.
> 
> for MAP in `g.mlist rast pattern=rain*` ; do
>   r.info -r $MAP
> done
> 
> then make a dummy map with r.mapcalc with overall min and max range.
> 
> min=1.2345
> max=9.8765
> r.mapcalc "color_map = if(row < 10, $min, $max)"
> 
> and then apply it with:
> 
> for MAP in `g.mlist rast pattern=rain*` ; do
>   r.colors $MAP rast=color_map
> done
> 
> Or run r.colors with the rules= option to set up some color rules
> by hand, then apply to all in a loop.
> 
> 
> But what I usually do these days in GRASS 6 is to use the r.stack
> addon module to temporarily consider all the maps together, which
> allows for the nice 'r.colors -e' equalized histogram color scaling.
> You can copy the color map to a small dummy raster with the r.colors
> rast= option then delete the stacked raster map if you want to save
> space, then apply it to all maps as in the Bourne shell loop above.
> 
> 
> regards,
> Hamish