I tried to improve the wiki page, but never got access. -- Edzer
> > Roger: >> > > Good, thanks. There you say that you are using "some MODIS surface >> > > reflectance products". I guess it will be easier to check things if >> the >> > > data (GRASS location) are available, so that others can try the same >> > > calculations. Would it be possible to make one or more test sets >> > > available, and link them from thw Wiki? > > Nikos: >> Finally, >> I am, sort of, free again :-). > > Sorry for being late. Couldn't make it earlier. I've updated the > wiki-page [1]. > > >> I have prepaired a grass-location >> containing the 3 modis bands I've used for all PCA related examples. I >> will eventually upload them in gregis [check previous post] but if there >> is another place >> (GRASS-wiki?) to upload them would be also ok. > > I have currently some access problem in gregis this why I can't upload > the MODIS bands there. Is there any other place to put them for now? > > > Now, I am more confused than before. Or maybe not... > > There seems to be no problem with the SPOT images, that is, the results > of i.pca are (almost) identical with the results of R's prcomp(x, > center=TRUE) *with* centering. This is completely different than with > the example using MODIS data. > > Perhaps it depends on the range of the input data?! The SPOT bands are > up to max. 255. The MODIS bands are: > > # band 2 > r.info -r mod_b2 > > min=0 > max=5504 > > # band 6 > r.info -r mod_b6 > > min=93 > max=5488 > > # band 7 > r.info -r mod_b7 > > min=0 > max=4133 > > > I ran the same PCA tests (in R) with the _rescaled_ as like with the > "original" MODIS bands (using r.rescale) but no luck, I get the same > contradictory results: _i.pca_ matches with _prcomp(x, center=FALSE)_. > > I suspect that the range of the input data is the reason... but I am not > sure. This is why I tried to repeat the test with _rescaled_ MODIS > bands. Given that the "r.rescale" products are kind of a "rules" file > under the "cats" directory, is "r.rescale" safe? Should I instead > rescale the data with r.mapcalc or is there no difference between > r.rescale and r.mapcalc? > > All explained in the *under construction* wiki. Kind regards, Nikos > --- > > [1] http://grass.osgeo.org/wiki/Principal_Component_Analysis > > _______________________________________________ > grass-stats mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/grass-stats > _______________________________________________ grass-stats mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-stats
