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

[Dylan Beaudette]

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

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