R: [GRASS-user] r.rescale categories definition

[Aldo Clerici]

John,
tanks for your quick answer.
A correct reclassification can be easily obtained with r.reclass or
r.mapcalc, but I would like to know if the behaviour of r.rescale is correct
and in this case what's the way it uses to define categories (just to
explain it to students working with GRASS).

Thanks again.

A. Clerici

-----Messaggio originale-----
Da: grass-user-bounces at lists.osgeo.org
[mailto:grass-user-bounces at lists.osgeo.org] Per conto di John Tate
Inviato: sabato 12 dicembre 2009 12.20
A: grass-user at lists.osgeo.org
Oggetto: Re: [GRASS-user] r.rescale categories definition

On Saturday 12 December 2009 11:03:35 Aldo Clerici wrote:
> Dear GRASS Users and Developers,
> 
> I'm having some problem in understanding the categories resulting from
> r.rescale
> 
> 
> 
> With:
> 
> r.rescale in=elevation.dem from=1200,1500 to=1,2 out=elev.resc
> 
> 
> 
> I have this result:
> 
> 1   1200 thru 1349
> 
> 2   1350 thru 1500
> 
> 
> 
> Two categories with a range of 150 meters each.
> 
> 
> 
> But with a new three categories subdivision:
> 
>  r.rescale in=elevation.dem from=1200,1500 to=1,3 out=elev.resc
> 
> the result is:
> 
> 1    1200 thru 1274
> 
> 2    1275 thru 1424
> 
> 3    1425 thru 1500
> 
> 
> 
> The first and last categories have a range of 75 meters and the second one
> of 150 meters.
> 
> 
> 
> Similar result with a four categories subdivision:
> 
> r.rescale in=elevation.dem from=1200,1500 to=1,4 out=elev.resc
> 
> 
> 
> 1    1200 thru 1250
> 
> 2    1251 thru 1350
> 
> 3    1351 thru 1450
> 
> 4    1451 thru 1500
> 
> 
> 
> Categories 1 and 4 have a range of 50 meters, 2 and 3 a range of 100
>  meters.
> 
> 
> 
> It seems that the first and last categories have the half range of all the
> others ones. Is this correct? Shouldn't the range be the same for all
> categories?
> 
> (same results with GRASS6.4, GRASS6.3 and GRASS6.2).
> 
> Many thanks in advance
> 
> 
> 
> A. Clerici
> 
> Parma University
> 
> Italy
> 

Hi, I have not used r.rescale (perhaps it uses some form of ratio on the 
amount of points in given categories it assigns, hence the middle categories

being larger ranges). I think r.reclass would be a better option so you can 
classify exactly what the categories would be.

John
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