[GRASS-dev] [GRASS GIS] #576: i.pca fails to center data prior to analysis

[GRASS GIS]

#576: i.pca fails to center data prior to analysis
--------------------------+-------------------------------------------------
  Reporter:  nikos        |       Owner:  grass-dev@…                                     
      Type:  defect       |      Status:  closed                                          
  Priority:  normal       |   Milestone:  6.4.4                                           
 Component:  Raster       |     Version:  svn-develbranch6                                
Resolution:  fixed        |    Keywords:  i.pca, data centering, prcomp(), R, eigenvectors
  Platform:  Unspecified  |         Cpu:  Unspecified                                     
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Changes (by nikos):

  * status:  new => closed
  * resolution:  => fixed


Comment:

 I confirm that this works fine now (GRASS 6.4.4svn (2014) / Revision:
 50937), ie:

 `i.pca input=mod07_b2,mod07_b6,mod07_b7 rescale=0,0 out=pca_mod_b267_2014`

 gives

 {{{
 PC1 778244.03 (-0.4372,-0.7210,-0.5376) [79.20%]
 PC2 192494.58 (-0.8310, 0.0953, 0.5481) [19.59%]
 PC3  11876.45 ( 0.3439,-0.6863, 0.6408) [ 1.21%]
 }}}

 which is essentially identical to R's equivalent action via

 `prcomp(mod07_b267, center=TRUE, scale=FALSE)`

 which in turn gives


 {{{
 Standard deviations:
 [1] 882.1814 438.7420 108.9791

 Rotation:
                PC1         PC2        PC3
 mod07_b2 0.4372107  0.83099407 -0.3439413
 mod07_b6 0.7210155 -0.09527873  0.6863371
 mod07_b7 0.5375718 -0.54806096 -0.6408165
 }}}

 Just for clarity/completeness, R reports: 1) column-wise and b) the
 "square roots of the eigenvalues", which in this case match GRASS' i.pca
 reported eigenvalues. Some R code:


 {{{
 > ev <- c ( 778244.03, 192494.58, 11876.45) # GRASS-reported eigenvalues
 > sapply(ev, sqrt)
 [1] 882.1814 438.7420 108.9791
 }}}

-- 
Ticket URL: <http://trac.osgeo.org/grass/ticket/576#comment:4>
GRASS GIS <http://grass.osgeo.org>