Agustin: > Nikos, I'm probably missing a message (I do not see which is > exactly the difference between the spot and the modis example),
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): i.pca == prcomp(x, center=FALSE, scale=FALSE) > but Perhaps you must use r.mapcalc to rescale and not r.rescale, or > if using r.rescale you must use r.mapcalc afterwards to rewrite the > output raster, as r.rescale is modifying the categories only and not > the actual raster values which is what i.pca is probably using. Maybe, > as i.pca is quite old, it considers the categories only up to 255. In > any case, using r.mapcalc you know better what you are doing. That's the confirmation I needed. I think rescaling the MODIS data to 0~255 will confirm that: IF "r.info -r" =< max. 255 THEN i.pca == prcomp(x, center=TRUE, scale=FALSE) > Also, note that you must rescale > using the mean, not max min values. In other words > r.mapcalc "band1c = band1 - mean(band1)" Thanks for the tip. Maybe this can be added in the grass-wiki FAQ !? Cheers, Nikos _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
