Grass/Erdas PCA

Agustin Lobo lobo at Jasper.Stanford.EDU
Wed Apr 21 14:54:24 EDT 1993

> From grass-lists-owner at Wed Apr 21 07:29:25 1993
> Date: Wed, 21 Apr 1993 08:51:09 -0500
> From: Anantha Prasad <prasad at>
> Sender: lists-owner at
> Reply-To: grassu-list at
> To: grassu-list at
> Subject: Grass/Erdas PCA
> Content-Length: 492
> Hi Grass/Erdas Users:
> Is anybody in this group aware of the fact that the covariance matrix calculated by r.covar (and hence the eigenvalues/vectors and Principal Components calculated by Grass) is quite different from the results obtained by using PRINCE in Erdas? (When it is run on identical sets of maps). What could be the reason for this? Is there some bug? I have tried with different options but still the problem remains. Thanks. Prasad (prasad at  Ph: 217-244-2166)

I did communicate to the list and to a simmilar problem in March. I'm
looking into this problem. My advice is that you should use m.eigensystem instead of r.pca. I'm not aware of any problem with r.covar, though. I will look into this asap, it's a critic question to me.

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