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) I have being trying to use "i.pca" to transform 4 entire SPOT
   images (52 MBytes each) but when I try to do so 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,

Tony Gale
Research Specialist
City of Austin Electric Utility
Austin, Texas