Michael Perdue wrote:
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.
m.eigensystem has not been ported from GRASS 5 to GRASS 6.
It is available from the GRASS 5 source code:
grass-5.4.0/src.contrib/CERL/misc/m.eigensystem/
online:
http://freegis.org/cgi-bin/viewcvs.cgi/grass/src.contrib/CERL/misc/m.eigensystem/
While it is written in Fortan77 I see no reason why it couldn't be
compiled with g77 or gfortran and run with modern versions of GRASS.
The GRASS raster/imagery engines and file formats have not changed since
GRASS 5 so there shouldn't be many problems.
FWIW ./configure still checks for f2c.h
Hamish