[GRASS-user] create a common colour scale

[Hamish]

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