[GRASS-user] Inverse PCA in GRASS

[Michael Perdue]

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
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