Hi, I am trying to develop a tool for grass which is one of the things that xgobi[1] does. The idea is from Markus Neteler which is to identify pure pixel/end members from a PCA plot. Since i.pca transforms pixel position is lost. So I need to find out how the pixel values are changed during a PC Analysis. spectral unmixing (i.spec.unmix) needs pure pixels for classification which is not easy to obtain or needs a device field spectrometer which is expensive. So a module in GRASS GIS to do will make the life a lot easier
[1] http://www2.research.att.com/areas/stat/xgobi/ On Thu, Feb 7, 2013 at 1:16 PM, Nikos Alexandris <[email protected]>wrote: > [all deleted] > > Hey Rashad, > > i.pca will output for you Principal Components. As many variables you will > feed to the algorithm (PCA), as many Principal Components you will get. > > You don't need, normally, to do anything else than use the Principal > Components. I.e., you can selectively reject some Principal Components > which > are not of interest and play with the rest. The simplest example that > falls > into my mind is, e.g. to discard the last Pincipal Component which is > "famous" > as to hold noise. > > Could you please elaborate a bit more on what exactly you are after? It > depends on how much detail you want to squeeze out of PCA -- I mean, > understand each and every step and, possibly, modify the algorithm (?). > > Best, Nikos -- Regards, Rashad
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