[GRASS-dev] GRASS-dev] On i.histo.match (Re: On (Landsat) imagery naming patterns)

[Nikos Alexandris]

Michael:

> >>>> What about just using r.rescale to rescale this?

Nikos:

> >>> Already tried (in the past) and I don't think it works from DCELL>  
> >>> 8-bit. It seems to chew-up (silently, as Moritz mentioned I think among
> >>> the lines in ticket #2^11) values.

> >>> It seems that "integerising" manually, in this case, is the best
> >>> approach. With the essential question remaining on "how many fine digits
> >>> should be preserved?".

Moritz:

> >> r.rescale is just a frontend to r.reclass. and as such is meant for CELL
> >> maps. It should'nt make a difference whether it is 8-bit or more, though.
> >> For DCELL you can try to use r.recode.

Nikos:
 
> > Didn't work also (tried the previous days) -- I can try again.

Moritz:
 
> Please be more precise than "didn't work"...

Right, "be more precise" is the key to "freedom" :D.  Indeed, I used to say 
(either in a "rules" file, or directly using "...<< EOF"

0.0:1.0:0:255

This did not work.  Both stats and histogram of the recoded raster map, e.g. a 
Red-Reflectance image ranging in

r.info Red_ToAR -r

min=0
max=0.774115699104528

were kinda flattened out

r.stats Red_ToAR_recoded_255
 100%

0
255

Looking at the image I want to recode

r.stats Red_ToAR | head
 100%

0-0.003036
0.02125-0.024286
0.024286-0.027322
0.027322-0.030357
0.030357-0.033393
0.033393-0.036429
0.036429-0.039465
0.039465-0.0425
0.0425-0.045536
0.045536-0.048572

I altered the rules file like

0.001:1.0:0:255


This works-out!  Now, the recoded image is

r.recode in=Red_ToAR out=Red_ToAR_recoded_255 rules=recode_rules  --o
r.stats Red_ToAR_recoded_255
 100%
5
6
7
.
..  
...  \
....  > Many values in-between
...  /
..
.
195
196
197
*

And the histogram looks "nice" as well. I didn't grasp that -- from where 
should I?  In the manual there is only an example from int to float (however, 
indeed, instructing 0.1 as the "target" min value).

Thanks, Nikos