[GRASS-user] Inverse PCA in GRASS

[Venkatesh Raghavan]

Michael and Dylan,

Thanks for the response.

The image fusion method that we are trying to implement on GRASS
is briefly described in the paper below and also quite a few
others that I have skimmed through.

Multisensor image fusion in remote sensing: concepts, methods
and applications by POHL and VAN GENDEREN

http://www.cnr.berkeley.edu/~bingxu/UU/spatial/Readings/Pohl1998IJRS.pdf

I had also not heard of Inverse PCA before and was thinking
the the method suggested by Dylan would be adequate.
But, there seems to be more to it than I can comprehend at
this moment, so I am trying by doing some excersise on
PCA based image fusion in GRASS. Will try to look into
the algorithm suggested by Michael too.

Kind regards

Venka

Michael Perdue wrote:
> Venka,
> I think what your asking is if anyone knows how to apply the 
> transformation matrix that was used to derive you pca components in 
> reverse to get back to the original coordinate system. Something like 
> what is done in a decorrelation stretch?
> Hopefully someone more knowledgeable than I can elaborate, but the 
> general idea is as follows;
> 
> if the i.pca is capable of divulging the eigenvectors, you can use 
> r.mapcalc to apply them in reverse. else;
> 
> r.covar -> m.eigensystem -> mapcalc -> "do something with your principal 
> components" -> mapcalc (inverse rotation) -> "original coordinate system"
> 
> You can take a look at the bottom of the r.covar page for more info. The 
> big "if" is on the status of m.eigensystem. I tried the link to the 
> manual page and it is broken so I'm unsure of it's status.
> 
> Cheers,
> 
> Mike
> 
> 
> 
> On 6-Dec-07, at 9:05 AM, Venkatesh Raghavan wrote:
> 
>> Dear All,
>>
>> Commonly described method for image fusion in
>> in several publications involves inverse PCA transform
>> to get the new R,G,B bands of multispectral image from
>> the principle components.
>>
>> Does any of you know a script or an algorithm to implement
>> inverse PCA in GRASS?
>>
>> Thanks in advance.
>>
>> Venka
>> _______________________________________________
>> grass-user mailing list
>> grass-user at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/grass-user
> 
>