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

[Dylan Beaudette]

On Sunday 25 February 2007 15:19, Hamish wrote:
> 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:
> > http://169.237.35.250/~dylan/temp/ikonos.rgb.jpg
> >
> > and the three PCA rasters combined with d.rgb here:
> > http://169.237.35.250/~dylan/temp/i.pca-ikonos.jpg
>
> 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.
>
>
> Hamish

Thanks Hamish!

I will be sure to try this out with our local landsat data.

cheers,

dylan

-- 
Dylan Beaudette
Soils and Biogeochemistry Graduate Group
University of California at Davis
530.754.7341