( Pedro, I kindly ask you to keep the discussion on the list - it's very interesting (to me at least) and of wider interest (I guess) as a small challenge for grass. I am sure others can help here.
Also, accept my apologies for re-structuring the mail to make it easy to follow for other readers. ) Pedro wrote: > > > I need to implement a Quadratic Mahaloanobis Distance by using GRASS. > > > This is based on medium vector and covariance matrix. > > > 1- As anyone implemented anything similar? > > > 2- If not, Is there any GRASS script that accesses medium vector and > > > Covariance matrix in its processing? Nikos: > > Not sure at all but my guess is that it's a (simple) job for grass if you > > know the formula. I am not familiar with the term "medium" vector. But > > there is "r.covar" to get the covariance (or correlation) matrix based on > > raster maps. Pedro: > Medium vector is a vector/array in which each element is the average of > that class in each image > [average in image1; average in image2, ...] > The problem of implemeting this in a script is that it required matrix > calculation. I mean, for each pixel in a class, I will have to multiplicate > byt the covariance matriz and this vector. I don't have a quick answer on how to do it within grass using r.mapcalc. But I am convinced that using grass + R is a solution. Also, is the following matlab (open source?) code of any use? <http://www.hackchina.com/en/r/129852/mahalanobis.m__html> I've read on the net efforts trying to link R and matlab. If the latter is practically doable, then you can even avoid writing the code (again). So, I imagine something like: 1. import data in grass and prepare/process etc. 2. load data of interest in R 3. calculate the (qudratic) mahalanobis distances of interest (within R with R code/ with matlab code ?) 4. export results (or even maps) in grass back again Cheers, Nikos _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
