[GRASS-dev] Reg i.pca output

Mohammed_Rashad · March 26, 2013, 7:39am

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?

If so the lsat7_2002_10_pca.1 contains PCA transformed pixel for lsat7_2002_10

Is this correct?

–

Regards,
Rashad

Markus_Metz · March 26, 2013, 9:14am

On Tue, Mar 26, 2013 at 8:39 AM, Rashad M <mohammedrashadkm@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.

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@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-dev

Mohammed_Rashad · March 26, 2013, 9:25am

On Tue, Mar 26, 2013 at 2:44 PM, Markus Metz
<markus.metz.giswork@gmail.com>wrote:

On Tue, Mar 26, 2013 at 8:39 AM, Rashad M <mohammedrashadkm@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)

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@lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/grass-dev

--
Regards,
Rashad

Markus_Metz · March 26, 2013, 10:28am

On Tue, Mar 26, 2013 at 10:25 AM, Rashad M <mohammedrashadkm@gmail.com> wrote:

On Tue, Mar 26, 2013 at 2:44 PM, Markus Metz <markus.metz.giswork@gmail.com>
wrote:

On Tue, Mar 26, 2013 at 8:39 AM, Rashad M <mohammedrashadkm@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)

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@lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/grass-dev

--
Regards,
Rashad

Mohammed_Rashad · March 26, 2013, 11:10am

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

On Tue, Mar 26, 2013 at 10:25 AM, Rashad M <mohammedrashadkm@gmail.com>
wrote:
>
>
>
> On Tue, Mar 26, 2013 at 2:44 PM, Markus Metz <
markus.metz.giswork@gmail.com>
> wrote:
>>
>> On Tue, Mar 26, 2013 at 8:39 AM, Rashad M <mohammedrashadkm@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@lists.osgeo.org
>> > http://lists.osgeo.org/mailman/listinfo/grass-dev
>
>
>
>
> --
> Regards,
> Rashad

--
Regards,
Rashad

Markus_Metz · March 26, 2013, 11:24am

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

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

On Tue, Mar 26, 2013 at 10:25 AM, Rashad M <mohammedrashadkm@gmail.com>
wrote:
>
>
>
> On Tue, Mar 26, 2013 at 2:44 PM, Markus Metz
> <markus.metz.giswork@gmail.com>
> wrote:
>>
>> On Tue, Mar 26, 2013 at 8:39 AM, Rashad M <mohammedrashadkm@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@lists.osgeo.org
>> > http://lists.osgeo.org/mailman/listinfo/grass-dev
>
>
>
>
> --
> Regards,
> Rashad

--
Regards,
Rashad

Mohammed_Rashad · March 26, 2013, 12:21pm

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@gmail.com> wrote:

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

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

On Tue, Mar 26, 2013 at 10:25 AM, Rashad M <mohammedrashadkm@gmail.com>
wrote:

On Tue, Mar 26, 2013 at 2:44 PM, Markus Metz
<markus.metz.giswork@gmail.com>
wrote:

On Tue, Mar 26, 2013 at 8:39 AM, Rashad M <mohammedrashadkm@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@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-dev

–
Regards,
Rashad

–
Regards,
Rashad

–

Regards,
Rashad

Markus_Metz · March 26, 2013, 2:10pm

On Tue, Mar 26, 2013 at 1:21 PM, Rashad M <mohammedrashadkm@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@gmail.com>
wrote:

On Tue, Mar 26, 2013 at 12:10 PM, Rashad M <mohammedrashadkm@gmail.com>
wrote:
>
>
>
> On Tue, Mar 26, 2013 at 3:58 PM, Markus Metz
> <markus.metz.giswork@gmail.com>
> wrote:
>>
>> On Tue, Mar 26, 2013 at 10:25 AM, Rashad M <mohammedrashadkm@gmail.com>
>> wrote:
>> >
>> >
>> >
>> > On Tue, Mar 26, 2013 at 2:44 PM, Markus Metz
>> > <markus.metz.giswork@gmail.com>
>> > wrote:
>> >>
>> >> On Tue, Mar 26, 2013 at 8:39 AM, Rashad M
>> >> <mohammedrashadkm@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@lists.osgeo.org
>> >> > http://lists.osgeo.org/mailman/listinfo/grass-dev
>> >
>> >
>> >
>> >
>> > --
>> > Regards,
>> > Rashad
>
>
>
>
> --
> Regards,
> Rashad

--
Regards,
Rashad

Mohammed_Rashad · March 26, 2013, 5:37pm

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@gmail.com> wrote:

On Tue, Mar 26, 2013 at 1:21 PM, Rashad M <mohammedrashadkm@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@gmail.com>
wrote:

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

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

On Tue, Mar 26, 2013 at 10:25 AM, Rashad M <mohammedrashadkm@gmail.com>
wrote:

On Tue, Mar 26, 2013 at 2:44 PM, Markus Metz
<markus.metz.giswork@gmail.com>
wrote:

On Tue, Mar 26, 2013 at 8:39 AM, Rashad M
<mohammedrashadkm@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@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-dev

–
Regards,
Rashad

–
Regards,
Rashad

–
Regards,
Rashad

–

Regards,
Rashad

Markus_Metz · March 26, 2013, 5:57pm

On Tue, Mar 26, 2013 at 6:37 PM, Rashad M <mohammedrashadkm@gmail.com> wrote:

That worked.

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

The rescale option rescales the output maps with the PC scores to the
given min,max range (default 0,255).

Markus M

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

On Tue, Mar 26, 2013 at 1:21 PM, Rashad M <mohammedrashadkm@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@gmail.com>
> wrote:
>>
>> On Tue, Mar 26, 2013 at 12:10 PM, Rashad M <mohammedrashadkm@gmail.com>
>> wrote:
>> >
>> >
>> >
>> > On Tue, Mar 26, 2013 at 3:58 PM, Markus Metz
>> > <markus.metz.giswork@gmail.com>
>> > wrote:
>> >>
>> >> On Tue, Mar 26, 2013 at 10:25 AM, Rashad M
>> >> <mohammedrashadkm@gmail.com>
>> >> wrote:
>> >> >
>> >> >
>> >> >
>> >> > On Tue, Mar 26, 2013 at 2:44 PM, Markus Metz
>> >> > <markus.metz.giswork@gmail.com>
>> >> > wrote:
>> >> >>
>> >> >> On Tue, Mar 26, 2013 at 8:39 AM, Rashad M
>> >> >> <mohammedrashadkm@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@lists.osgeo.org
>> >> >> > http://lists.osgeo.org/mailman/listinfo/grass-dev
>> >> >
>> >> >
>> >> >
>> >> >
>> >> > --
>> >> > Regards,
>> >> > Rashad
>> >
>> >
>> >
>> >
>> > --
>> > Regards,
>> > Rashad
>
>
>
>
> --
> Regards,
> Rashad

--
Regards,
Rashad