[GRASS-dev] reg i.pca module

[Yann Chemin]

Maybe a complex number structure would be good where only the real part is
analyzed by pca and the imaginary part is keeping a unique id for each
original pixel...
On Feb 10, 2013 11:51 AM, "Markus Neteler" <neteler at osgeo.org> wrote:

> On Thu, Feb 7, 2013 at 10:21 AM, Rashad M <mohammedrashadkm at gmail.com>
> wrote:
> > Hi,
> >
> > I am trying to develop a tool for grass which is one of the things that
> > xgobi[1] does. The idea is from Markus Neteler which is to identify pure
> > pixel/end members from a PCA plot.
>
> Background: it has been shown that pure pixels (endmembers) for spectral
> unmixing are in the corners of the PCA feature space.
>
> Attached an old drawing from my master thesis (1999) about the topic.
>
> > Since i.pca transforms pixel position is lost.
>
> This is why I used the coordinates as raster pixel *attributes* in XGOBI
> to relate original pixels and PCA transformed pixels to each other.
>
> The east, north coordinates I stored as attributes, the PCA in XGOBI
> supported to keep them alongside the transformed pixel. Solved.
>
> What's needed in GRASS: That the i.pca modules allows to keep
> raster pixel text labels in which the original position could be stored.
> Then a little parsing of the category label and the original position
> of a PCA transformed pixel could still be retrieved.
>
> Hope this explains what I did those days in my thesis.
>
> cheers
> Markus
>
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