i.pca, r.mapcalc, i.rectify

[imager at ccwf.cc.utexas.edu]

Hi (Y')all, 

I have a few questions concerning some problems that I'm having using
GRASS. Hopefully some one out there might know of solutions to the 
following:

1) When I try to use "i.pca" to transform 4 entire SPOT images (52 MBytes
   each) the job gets killed by the system. Is this a normal response when
   trying to carry out PCA on a large dataset or is it related to the 
   problems with the porting of GRASS to the RISC 6000 platform?

2) I have been trying to ratio two SPOT images using "r.mapcalc"
   as follows r.mapcalc ratio=band3/band1 but the output image only
   has minimum value=0, maximum value=1. I have checked the band
   statistics for both bands and although I wouldn't expect the maxmimum 
   theoretical range of 256*256 values I certaintly expected a greater
   range of values than 1 or 0. Is there something I need to do (like set
   number of decimal places or reference a ratio lookup table) to carry out
   image ratioing?

3) I was recently using "i.target,i.points and i.rectify" to reference a 
   previously (State Plane) rectified SPOT image in ROW, COL format to 
   State Plane coordinates. I would like to know if the i.rectify algorithm
   uses a third order polynomial to rectify the input images or whether
   it matches the most appropriate transformation equation to the inputted
   control point coordinates?


Thanks in advance,

Tony Gale
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Research Specialist
City of Austin Electric, Tx.
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