[Insight-users] ImageMomentsCalculator question

[Benjamin King]

Hi Luis,

> If you want to do Principal Components Analysis,
> you can use directly the Moments Calculator.
> [...]
> Reading the Doxygen documentation of 
> this class will certainly help you  :-)
> [...]

Unfortunately, after reading the documentation again, I still don't understand 
the relationship between principal moments and the variance of a point set 
projected onto the principal axes.
I also grep'd the ITK source for GetPrincipalMoments, but apart from a test 
program, no other code is using it.

I hope the attached program better illustrates my problem:

$ tar xvzf CalculateMoments.tar.gz
$ cd moments/binary
$ cmake ../source
$ make
$ cd ..
$ ./CalculateMoments data/ellipse.hdr

This will print the image moments according to itk::ImageMomentsCalculator 
before and after PCA. The third output block is a manual calculation of the 
mean index and index variance after PCA. The index variance is what I'm 
looking for.

Is it possible to derive this value directly from the moments before PCA?


Thanks for your help,
	Benjamin


-- 
Benjamin King
Experimentelle Radiologie
Medizinische Hochschule Hannover
Tel.: +49  511  532-2663
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