[GRASS-user] Re: [GRASS-dev] i.pca

Hamish hamish_nospam at yahoo.com
Sun Feb 25 18:19:49 EST 2007

Dylan Beaudette wrote:
> On Monday 19 February 2007 14:59, Brad Douglas wrote:
> > Hello,
> >
> > I just committed a rewritten i.pca module.  It now supports NULL
> > cells without skewing the data and will work properly with
> > float/double maps. It's a bit slower than the original, but that's
> > the price we pay for modules that work. :-)
> >
> > My testing has proved good results, but I'd like to have others
> > test.
> Hi Brad,
> I just tried it out with some ikonos imagery (r,g,b bands only...)
> with good  results. The various vegetation communities standout, along
> with the rock  outcroppings (bright pink) ! I have previously been
> using NDVI for the rock  outcrops, but it looks like this approach
> might work better. Good  performance, total time for 13838448 cells
> was about 1 minute on a 3ghz xeon. 
> commands used:
> i.pca in=ikonos.red,ikonos.green,ikonos.blue output=ikonos.pca
> d.rgb r=ikonos.pca.1 g=ikonos.pca.2 b=ikonos.pca.3
> see the original ikonos image here:
> and the three PCA rasters combined with d.rgb here:

i.oif is interesting to check out too. feed it multi-band data and it
will tell you the three-band combination that will show the most
information. Then experiment with different r= g= b= combinations to
get the best combo.


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