[GRASS-user] r.regression.multi for logistic regression - it is possible?

Nuno Sá nunocesardesa at gmail.com
Fri Sep 5 03:11:42 PDT 2014

Hey Roberto!

Never done it in Grass but its a typical operation.

For me it seems a bit confusing with for me since you are not showing me a
glm fitting but instead just using the occurrence map in the logistic link

What you need to do is to fit a GLM to the binary data you have, something
you can do in R for example check here:


Then you will build your output in grass using the r.mapcalc: F(x) = 1 / (
1+ e^(-GLM)  (That will be your probability map).

But, you can actually do everything using R only, no need to come into
grass but you can if you want.

Good luck!

On 5 September 2014 10:46, Roberto Marzocchi <roberto.marzocchi at gmail.com>

>  Dear all,
> I have dichotomous data (occurrence 1 and non-occurence 0) and I want to
> use the  logistic regression method in order to obtain susceptibility map
> of landslide occurrence.
> I try to use r.regression.multi, but I am not sure to correctly define the
> mapy variable..
> I try to use r.mapcalc
> *r.mapcalc
> expression="logit_occurrence=log(occurrence_map+0.00001)-log(1-occurrence_map+0.00001)"*
> obtaining a map that go from -11.5 (not occurrence) to +11.5 (occurrence)
> when I try to use r.regression.multi I obtain a lot of null values in
> residuals and estimates map.
> i do not understand why..
> Thanks in advanced for the attention
> Roberto
> _______________________________________________
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> grass-user at lists.osgeo.org
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Nuno César de Sá
+351 91 961 90 37
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