[GRASS-user] i.pca fixes in trunk

[Benjamin Ducke]

Sounds like a very sensible couple of fixes to me.
Could these be backported to 6.4.x?

Cheers,

Ben

On 11/04/2011 11:53 AM, Markus Metz wrote:
> Hi all,
>
> based on the wiki for Principal Components Analysis [0], numerous
> discussions in the mailing lists [1,2,3,4], particularly a comment by
> Edzer Pebesma [5], and personal demand, I have fixed a few issues in
> i.pca in trunk r49090.
>
> - the faulty or missing centering of the input bands described in [0]
> for should be fixed
> - i.pca has a new flag -n to normalize input bands with (x - mean) / stddev
> - values of the output maps are now calculated depending on the input
> band transformation (centering or normalization). Is this OK?
> - Eigen values, (vectors), and [percent importance] are now written to
> stdout instead of stderr
>
> The results of i.pca for the examples using SPOT imagery in the wiki
> [0] are now identical to R's princomp() results. If the new -n flag is
> used, the results of i.pca are identical to princomp(center = TRUE,
> scale = TRUE).
>
> Tested also with 9 input maps in a region with 400 million cells.
>
> Markus M
>
>
> [0] http://grass.osgeo.org/wiki/Principal_Components_Analysis
> [1] http://lists.osgeo.org/pipermail/grass-user/2009-February/048722.html
> [2] http://lists.osgeo.org/pipermail/grass-stats/2009-March/000933.html
> [3] http://lists.osgeo.org/pipermail/grass-stats/2009-March/000942.html
> [4] http://lists.osgeo.org/pipermail/grass-stats/2009-April/001028.html
> [5] http://lists.osgeo.org/pipermail/grass-stats/2009-April/000977.html
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-- 
Benjamin Ducke
{*} Geospatial Consultant
{*} GIS Developer

   benducke at fastmail.fm