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

Moritz Lennert mlennert at club.worldonline.be
Mon Dec 21 09:08:08 PST 2015

On 21/12/15 16:42, umberto.minora wrote:
> Also, in my specific case, I would have to avoid adding other classes.
> To clarify why it should be like so: my study area is a mountainuous area in
> North-West Italy. I masked features such as water bodies, snow, glaciers,
> vegetation, and so on, to obtain a map of bare soil only. Now, in this
> unmasked area, some rock glaciers (i.e. glaciers that are "buried" in the
> ground) are present. I have their locations in form of polygons, and now I
> want to use these outlines as my region of interests (ROIs) for the
> Supervised Classification with i.maxlik on the RGB composed by 1) the
> elvation map, 2) the band4 of Landsat ETM+, and 3) the cumulative solar
> radiation map.
> The aim is to classify the pixels in the unmasked area out of the rock
> glacier outlines which are similar to the rock glaciers with the maximum
> likelihood algorithm, according to the three mentioned RGB band values. *As
> I don't know what is around the rock glaciers, I am not able to specify
> other classes unfortunately.*
> So, is there a way I can do a Supervised with only one class in GRASS? Would
> you suggest another software (better if open source)?

A maximum likelihood classifier (and most classifiers actually) will 
classify each pixel in the class for which the likelihood that it 
belongs to that particular class is highest. If you only have one class, 
this class will always be the likeliest.

The only option would be to use the reject map, and decide on a 
threshold there. But apparently you've tried that without success.

Can't you visually identify areas for which you know that they are not 
rock glaciers ?


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