Agustin: > >> Nikos, I'm probably missing a message (I do not see which is > >> exactly the difference between the spot and the modis example), > >>
Nikos: > > Hi Agus. The difference is: > > Using SPOT (range up to max. 255): > > i.pca == prcomp(x, center=TRUE, scale=FALSE) > > Using MODIS (range varries between bands, up to max. ~5500): [...] Markus M: > Sure? Valid range: -100 - 16000 for MODIS e.g. Surface Reflectance 8-Day > L3 Global 500m. I am referring to the range of the specific MODIS bands that I've used, that is: # 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 > As I would use the max possible for SPOT (255) I would also use the max > possible for other sensors, not the observed max, otherwise statistics > that don't do proper normalization on the fly are not comparable between > different sensors. > But any PCA should do normalization beforehand, not sure what R or i.pca > are doing. That's the question _now_ (if I am right with my tests): why isn't normalisation (=data centering in this case) performed with the MODIS bands I use? > Please excuse my random comments :-) Markus, your comments are required :-) Cheers, Nikos _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
