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 _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
