# [GRASS-dev] Reg i.pca output

Tue Mar 26 10:37:36 PDT 2013

```That worked.

so what change the rescale option add to the transformation equation?

On Tue, Mar 26, 2013 at 7:40 PM, Markus Metz
<markus.metz.giswork at gmail.com>wrote:

> On Tue, Mar 26, 2013 at 1:21 PM, Rashad M <mohammedrashadkm at gmail.com>
> wrote:
> > 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?
>
> You need to disable rescaling of the PC scores with i.pca rescale=0,0
>
> Markus M
>
> >
> >
> > 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 <
> >> >> 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,
> >> >
> >> >
> >> >
> >> >
> >> > --
> >> > Regards,
> >
> >
> >
> >
> > --
> > Regards,
>

--
Regards,