[GRASS-dev] PCA (i.pca) in G7: filtering and rescaling

[Nikos Alexandris]

On Wednesday 04 of December 2013 16:22:51 Nikos Alexandris wrote:
> Nikos Alexandris wrote:
> > > 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
> 
> okay, to clarify: I mean the resulting images which, initially are Principal
> Components (synthetic images) and, after applying filtering & backward PCA,
> the resulting images approach the original data -- still they are modified.

Example (using i.pca in G7, though r.info below executed from G64):

<http://nikosalexandris.net/owncloud/public.php?service=files&t=e87b1223bf6402786ef7478690099602>

and details for

P=90) r.info -rh PC90N.1

min=171.596979136065
max=1107.42672094831
Data Source:
   
   
Data Description:
   generated by i.pca
Comments:
   Eigen values, (vectors), and [percent importance]:
   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%]
   
   i.pca -n -f input="Blue_DNs,Green_DNs,Red_DNs,NIR_DNs" output_prefix\
   ="PC90N" rescale=0,0 percent=90


P=70) r.info -rh PC70N.1

min=171.596979136065
max=1107.42672094831
Data Source:
   
   
Data Description:
   generated by i.pca
Comments:
   Eigen values, (vectors), and [percent importance]:
   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%]
   
   i.pca -n -f input="Blue_DNs,Green_DNs,Red_DNs,NIR_DNs" output_prefix\
   ="PC70N" rescale=0,0 percent=70

Nikos