[GRASS-dev] Reg i.pca output

[Rashad M]

It seems like values are different using the forumla. I can provide a test
case if you need



i tried this:
i.pca in=lsat7_2000_10,lsat7_2000_20 out=mypca

Rescaling to range 0,255...
 100%
Eigen values, (vectors), and [percent importance]:
PC1    436.48 ( 0.6640, 0.7477) [98.84%]
PC2      5.13 (-0.7477, 0.6640) [ 1.16%]


here only first column of eigen vector is important right?

But let me ask does eigen values and percent of importance doesnt have any
role?

here when running the above i.pca i get mypca.1 and mypca.2
P1 and P2 are first pixel row=0, col=0 of mypca.1 and mypca.2 respectively
and mean is the mean of lsat7_2000_10

output is the output obtained from the equation --> (X = P * eigenvector(P,
X) + P * eigenvector(Q, X) + mean(B1) )

and input is the pixel value of lsat7_2000_10 @ row=0, col=0


P1=  21
P2=  112
mean=    79.925
output=  138.4471
input=   72

Any thoughts?


On Tue, Mar 26, 2013 at 4:54 PM, Markus Metz
<markus.metz.giswork at gmail.com>wrote:

> On Tue, Mar 26, 2013 at 12:10 PM, Rashad M <mohammedrashadkm at gmail.com>
> wrote:
> >
> >
> >
> > 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?
>
> yes
>
> >
> >>
> >> 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
>



-- 
Regards,
   Rashad
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