Hi list and Markus. The i.pca module in G7 offers a "forward/filtering/backward" PCA. I have an issue first with filtering and second with rescaling.
1) I can't see any differences in the derived Principal Components between percent=70 and percent=99 for 4 bands which the PCs (both centered and scaled) are: PC1 2.78 ( 0.4947, 0.5922, 0.5743, 0.2735) [69.53%] PC2 1.08 ( 0.5196, 0.0517,-0.0974,-0.8473) [26.99%] PC3 0.11 ( 0.4210, 0.2486,-0.7926, 0.3644) [ 2.86%] PC4 0.03 (-0.5551, 0.7647,-0.1805,-0.2729) [ 0.63%] What is filtering doing actually? Shouldn't percent=70 just filter out the rest, somehow? 2) a centered but non-scaled attempt, with rescaling (to [0,255] desired] gives me floating point PCs as an output: r.info -rh PC.1 min=167.116641509957 max=1063.871704546 Data Source: Data Description: generated by i.pca Comments: Eigen values, (vectors), and [percent importance]: PC1 142403.37 ( 0.0058,-0.0899,-0.0817,-0.9926) [93.76%] PC2 8979.58 ( 0.4285, 0.7402, 0.5071,-0.1062) [ 5.91%] PC3 416.51 (-0.3800,-0.3668, 0.8483,-0.0388) [ 0.27%] PC4 88.39 (-0.8197, 0.5563,-0.1287,-0.0446) [ 0.06%] i.pca -f input="Blue_DNs,Green_DNs,Red_DNs,NIR_DNs" output_prefix="P\ C" rescale=0,255 percent=99 This isn't expected, right? Thanks for this module as well -- it solved big issues (i.e. with hazed images), Nikos _______________________________________________ grass-dev mailing list grass-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-dev