[GRASS-user] i.pca noise reduction

[Markus Neteler]

On Sat, Oct 13, 2012 at 3:46 PM, Markus Metz
<markus.metz.giswork at gmail.com> 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>:
lsat7_2002_reduced.1
lsat7_2002_reduced.2
lsat7_2002_reduced.3
lsat7_2002_reduced.4
lsat7_2002_reduced.5
lsat7_2002_reduced.6

Say, this is not entirely clear to me:
  -f   Output will be filtered input bands
        Applies inverse PCA after PCA

(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).

thanks for any hints,
markusN