comp.lang.idl-pvwave archive: archive » Re: Algorithm for PCA transform in ENVI

Home » Public Forums » archive » Re: Algorithm for PCA transform in ENVI

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: Algorithm for PCA transform in ENVI [message #80063 is a reply to message #80059]

Wed, 09 May 2012 08:01

Kenneth P. Bowman
Messages: 585
Registered: May 2000

Senior Member

In article <0de35e20-3a9c-4593-8f06-ed3e6461fe60@p21g2000vby.googlegroups.com>,
eva.ivits-wasser@ext.jrc.ec.europa.eu wrote:

> Does anybody know what the algorithm for PCA transform in ENVI is?
> I've compared the eigenvectors and the spatial patterns of ENVI's PCA
> transform with IDL's eigenql, svdc and la_svd procedures. The first PC
> components are the same but from the second component on I have
> negative values where ENVI give positive values and vice versa.
> Accordingly, the first element in the diagonal of the eigenvector
> matrices has the same sign but the rest of the signs are just the
> oppostie comparing results from ENVI and IDL.
> Any clues?
> Thanks in advance,
> Eva

If you have a properly-constructed covariance matrix, the eigenvalues should all
be greater than or equal to zero. If you are getting negative eigenvalues you
are doing something wrong.

http://brunnur.vedur.is/pub/halldor/PICKUP/eof.pdf

Ken Bowman

Report message to a moderator

[Message index]

		Re: Algorithm for PCA transform in ENVI By: lecacheux.alain on Thu, 10 May 2012 05:12
		Re: Algorithm for PCA transform in ENVI By: ivitseva on Thu, 10 May 2012 02:17
		Re: Algorithm for PCA transform in ENVI By: Kenneth P. Bowman on Wed, 09 May 2012 08:01
		Re: Algorithm for PCA transform in ENVI By: ivitseva on Thu, 10 May 2012 07:39

Previous Topic:	Widget to play and pause image stack display
Next Topic:	EOS_SW_CREATE HDF function file path issue

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Fri Nov 28 19:18:12 PST 2025

Total time taken to generate the page: 0.47365 seconds