[GRASS-user] i.pca noise reduction

GRASS GRASS user
1

i.pca in GRASS 7 can now do noise reduction by reconstructing the
input bands from a user.defined subset of the principal components.

Markus M

2

On Sat, Oct 13, 2012 at 3:46 PM, Markus Metz
<markus.metz.giswork@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

3

On Sat, Oct 13, 2012 at 6:18 PM, Markus Neteler <neteler@osgeo.org> wrote:

On Sat, Oct 13, 2012 at 3:46 PM, Markus Metz
<markus.metz.giswork@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>:

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