[GRASSLIST:5088] Rescaling

Michael Ash mash at econs.umass.edu
Wed Nov 27 08:45:23 EST 2002

> > Now I have a new problem with my recently-created roughness map: When I 
> > compare it with other similar map made with Arcview, I see that there's
> > a little difference in the scale of the roughness. In the arcview's map,
> > the scale goes from 1 (planar area) to 1.23, but in the GRASS's map, it 
> > goes from 0 (planar area) to 67. I guess I have o normalise the values, 
> > but I don't know how. Any ideas?

> If you want 67 to be 1.23, and 0 to be 1, try something like:
> r.mapcalc newmap='1+(oldmap*(0.23/67))'

Another approach is

r.rescale input=my_oldmap from=0,67 output=my_newmap to=1,1.23

(In fact, I would guess that r.rescale does not work with
decimal values.  r.rescale appears intended to generate
integer color scales, e.g., 0 to 255; so the r.mapcalc
approach would be appropriate for this example, but you
might want to know about r.rescale for future use.)



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