[GRASS-dev] Reg i.pca output

[Rashad M]

On Tue, Mar 26, 2013 at 3:58 PM, Markus Metz
<markus.metz.giswork at gmail.com>wrote:

> On Tue, Mar 26, 2013 at 10:25 AM, Rashad M <mohammedrashadkm at gmail.com>
> wrote:
> >
> >
> >
> > On Tue, Mar 26, 2013 at 2:44 PM, Markus Metz <
> markus.metz.giswork at gmail.com>
> > wrote:
> >>
> >> On Tue, Mar 26, 2013 at 8:39 AM, Rashad M <mohammedrashadkm at gmail.com>
> >> wrote:
> >> > Hi,
> >> >
> >> > i.pca creates 6 raster maps for 6 input raster
> >> >
> >> > eg:
> >> >
> >> > i.pca
> >> >
> >> >
> in=lsat7_2002_10,lsat7_2002_20,lsat7_2002_30,lsat7_2002_40,lsat7_2002_50,lsat7_2002_70
> >> > \
> >> >     out=lsat7_2002_pca
> >> >
> >> >
> >> > I have a doubt here
> >> >
> >> > Does the output lsat7_2002_pca.1 is the corresponding map for
> >> > lsat7_2002_10?
> >>
> >> No. lsat7_2002_pca.1 contains the principal component with the highest
> >> eigenvalue and is calculated using all input bands. More generally,
> >> each lsat7_2002_pca.* map is calculated using all input bands. Look at
> >> the eigenvectors to find out the weights with which each input map
> >> contributes to a specific PCA.
> >>
> >
> > So by knowing a pixel value of lsat7_2002_pca.1 can I get the value
> before
> > transformation in PCA.
> > consider this:
> > I have two bands B1,B2 and after i.pca I get PC1,PC2. Then is there a
> way to
> > derive value of X,Y where X belongs to B1 and Y belongs to B2 by only
> > knowing P,Q
> > where P belongs to PC1 and Q belongs to PC2
> >
> > and also X,Y and P,Q are of same index (row,col)
>
> X = P * eigenvector(P, X) + P * eigenvector(Q, X) + mean(B1)
>
> Using the example from the manual:
>
> X = 0.2824 * PC1 + 0.2541 * PC2 + 0.3801 * PC3 +  0.1752 * PC4 -
> 0.6170 * PC5 - 0.5475 * PC6 + mean(band 1)
>

Thanks.

just a small clarification:
PC1 is the pixel value at (i,j) of output band  pca.1 and X is the pixel
value at (i,j) of input band b1

This is correct?


> Markus M
>
> >
> > I hope this is clear
> >
> >>
> >> Markus M
> >>
> >> >
> >> > If so the lsat7_2002_10_pca.1 contains PCA transformed pixel for
> >> > lsat7_2002_10
> >> >
> >> > Is this correct?
> >> >
> >> > --
> >> > Regards,
> >> >    Rashad
> >> >
> >> > _______________________________________________
> >> > grass-dev mailing list
> >> > grass-dev at lists.osgeo.org
> >> > http://lists.osgeo.org/mailman/listinfo/grass-dev
> >
> >
> >
> >
> > --
> > Regards,
> >    Rashad
>



-- 
Regards,
   Rashad
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