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-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user