[GRASS-user] i.maxlik: strange classification output and reject map

Umberto Filippo Minora umberto.minora at unimi.it
Sun Dec 20 05:43:05 PST 2015

I have three maps which are 1) shortwave infrared reflectances derived 
from Landsat ETM+ (Data Type: FCELL); 2) cumulative solar radiation 
derived using "r.sun" from GRASS (Data Type: FCELL); 3) elevation map 
(DEM, Data Type: CELL).
I am trying to perform a supervised maximum likelihood classification 
over these bands.
So, first I grouped them using "i.group".
Then I imported a shp with rock glacier areas, created a new column in 
its attribute table called "IDmaxlik" and assigned a value of "1" (int)  
to it.
Then I converted the shp to raster with this command:

     v.to.rast in=rg_visible out=rg_visible use=attr 

and I used "i.gensig" to generate the signature file.

     i.gensig trainingmap=rg_visible group=perma_max subgroup=perma_max 

Finally, I run "i.maxlik":

     i.maxlik group=perma_max subgroup=perma_max signaturefile=rg_sig 
output=classification01 reject=classification01_reject

Each pixel of the output map ("classification01") is 1, as if the 
everything was classified as "rock glacier". Moreover, the reject map 
("classification01_reject"), has higher values (closer to 16, or 100%) 
over the same rock glaciers used as the region of interest than elsewhere.

Might be the problem related to the fact that "i.gensig" expected a clip 
of the RGB raster on the ROIs, rather than a mask?

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