On Tue, Mar 26, 2013 at 1:21 PM, Rashad M <[email protected]> wrote: > It seems like values are different using the forumla. I can provide a test > case if you need > > > > i tried this: > i.pca in=lsat7_2000_10,lsat7_2000_20 out=mypca > > Rescaling to range 0,255... > 100% > Eigen values, (vectors), and [percent importance]: > PC1 436.48 ( 0.6640, 0.7477) [98.84%] > PC2 5.13 (-0.7477, 0.6640) [ 1.16%] > > > here only first column of eigen vector is important right? > > But let me ask does eigen values and percent of importance doesnt have any > role? > > here when running the above i.pca i get mypca.1 and mypca.2 > P1 and P2 are first pixel row=0, col=0 of mypca.1 and mypca.2 respectively > and mean is the mean of lsat7_2000_10 > > output is the output obtained from the equation --> (X = P * eigenvector(P, > X) + P * eigenvector(Q, X) + mean(B1) ) > > and input is the pixel value of lsat7_2000_10 @ row=0, col=0 > > > P1= 21 > P2= 112 > mean= 79.925 > output= 138.4471 > input= 72 > > Any thoughts?
You need to disable rescaling of the PC scores with i.pca rescale=0,0 Markus M > > > On Tue, Mar 26, 2013 at 4:54 PM, Markus Metz <[email protected]> > wrote: >> >> On Tue, Mar 26, 2013 at 12:10 PM, Rashad M <[email protected]> >> wrote: >> > >> > >> > >> > On Tue, Mar 26, 2013 at 3:58 PM, Markus Metz >> > <[email protected]> >> > wrote: >> >> >> >> On Tue, Mar 26, 2013 at 10:25 AM, Rashad M <[email protected]> >> >> wrote: >> >> > >> >> > >> >> > >> >> > On Tue, Mar 26, 2013 at 2:44 PM, Markus Metz >> >> > <[email protected]> >> >> > wrote: >> >> >> >> >> >> On Tue, Mar 26, 2013 at 8:39 AM, Rashad M >> >> >> <[email protected]> >> >> >> wrote: >> >> >> > Hi, >> >> >> > >> >> >> > i.pca creates 6 raster maps for 6 input raster >> >> >> > >> >> >> > eg: >> >> >> > >> >> >> > i.pca >> >> >> > >> >> >> > >> >> >> > >> >> >> > in=lsat7_2002_10,lsat7_2002_20,lsat7_2002_30,lsat7_2002_40,lsat7_2002_50,lsat7_2002_70 >> >> >> > \ >> >> >> > out=lsat7_2002_pca >> >> >> > >> >> >> > >> >> >> > I have a doubt here >> >> >> > >> >> >> > Does the output lsat7_2002_pca.1 is the corresponding map for >> >> >> > lsat7_2002_10? >> >> >> >> >> >> No. lsat7_2002_pca.1 contains the principal component with the >> >> >> highest >> >> >> eigenvalue and is calculated using all input bands. More generally, >> >> >> each lsat7_2002_pca.* map is calculated using all input bands. Look >> >> >> at >> >> >> the eigenvectors to find out the weights with which each input map >> >> >> contributes to a specific PCA. >> >> >> >> >> > >> >> > So by knowing a pixel value of lsat7_2002_pca.1 can I get the value >> >> > before >> >> > transformation in PCA. >> >> > consider this: >> >> > I have two bands B1,B2 and after i.pca I get PC1,PC2. Then is there a >> >> > way to >> >> > derive value of X,Y where X belongs to B1 and Y belongs to B2 by only >> >> > knowing P,Q >> >> > where P belongs to PC1 and Q belongs to PC2 >> >> > >> >> > and also X,Y and P,Q are of same index (row,col) >> >> >> >> X = P * eigenvector(P, X) + P * eigenvector(Q, X) + mean(B1) >> >> >> >> Using the example from the manual: >> >> >> >> X = 0.2824 * PC1 + 0.2541 * PC2 + 0.3801 * PC3 + 0.1752 * PC4 - >> >> 0.6170 * PC5 - 0.5475 * PC6 + mean(band 1) >> > >> > >> > Thanks. >> > >> > just a small clarification: >> > PC1 is the pixel value at (i,j) of output band pca.1 and X is the pixel >> > value at (i,j) of input band b1 >> > >> > This is correct? >> >> yes >> >> > >> >> >> >> Markus M >> >> >> >> > >> >> > I hope this is clear >> >> > >> >> >> >> >> >> Markus M >> >> >> >> >> >> > >> >> >> > If so the lsat7_2002_10_pca.1 contains PCA transformed pixel for >> >> >> > lsat7_2002_10 >> >> >> > >> >> >> > Is this correct? >> >> >> > >> >> >> > -- >> >> >> > Regards, >> >> >> > Rashad >> >> >> > >> >> >> > _______________________________________________ >> >> >> > grass-dev mailing list >> >> >> > [email protected] >> >> >> > http://lists.osgeo.org/mailman/listinfo/grass-dev >> >> > >> >> > >> >> > >> >> > >> >> > -- >> >> > Regards, >> >> > Rashad >> > >> > >> > >> > >> > -- >> > Regards, >> > Rashad > > > > > -- > Regards, > Rashad _______________________________________________ grass-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-dev
