On Sat, Oct 13, 2012 at 6:18 PM, Markus Neteler <[email protected]> wrote: > On Sat, Oct 13, 2012 at 3:46 PM, Markus Metz > <[email protected]> wrote: >> i.pca in GRASS 7 can now do noise reduction by reconstructing the >> input bands from a user.defined subset of the principal components. > > This sounds like an interesting extension but the usage is not clear to > me: > > # NC data set: > > g.region rast=lsat7_2002_10 -p > i.pca > input=lsat7_2002_10,lsat7_2002_20,lsat7_2002_30,lsat7_2002_40,lsat7_2002_50,lsat7_2002_70 > -f percent=90 out=lsat7_2002_reduced > > g.mlist rast | grep reduced > raster map(s) available in mapset <neteler>: attempt to explain: lsat7_2002_reduced.1 = filtered lsat7_2002_10 lsat7_2002_reduced.2 = filtered lsat7_2002_20 lsat7_2002_reduced.3 = filtered lsat7_2002_30 lsat7_2002_reduced.4 = filtered lsat7_2002_40 lsat7_2002_reduced.5 = filtered lsat7_2002_50 lsat7_2002_reduced.6 = filtered lsat7_2002_70
with perc=90, 2 PCA scores will be used for reconstruction, that is each cell of the first output band will be input[1] * PCA[1][1] + input[1] * PCA[2][1] and each cell of the last (6th) output band will be input[6] * PCA[1][6] + input[1] * PCA[2][6]. Any scaling and centering is considered. > > Say, this is not entirely clear to me: > -f Output will be filtered input bands > Applies inverse PCA after PCA Added to the manual. > > (Tha manual has a replicated parameters section which needs to > be fixed, too. I can do that as soon as I understand the new > functionality). It seems that replicated parameters are kind of a feature in imagery modules... To be fixed. Markus M _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
