i.pca <main>	      GRASS Reference Manual	     <main> i.pca



NAME
     i.pca - Principal components analysis (pca) program for
     image processing.
     (GRASS Image Processing Program)

SYNOPSIS
     i.pca
     i.pca help
     i.pca input=name,name[,name,name,...] output=name
     rescale=min,max

DESCRIPTION
     i.pca is an image processing program based on the algorithm
     provided by Vali (1990), that processes n (2 >= n) input
     raster map layers and produces n output raster map layers
     containing the principal components of the input data in
     decreasing order of variance ("contrast").	 The output
     raster map layers are assigned names with .1, .2, ... .n
     suffixes.	The current geographic region definition and mask
     settings are respected when reading the input raster map
     layers. When the rescale option is used, the output files
     are rescaled to fit the min,max range.


     Parameters:

     input=name,name[,name,name,...]
		       Name of two or more input raster map
		       layers.

     output=name       The output raster map layer name to which
		       suffixes are added.  Each output raster
		       map layer is assigned this user-specified
		       name with a numerical (.1, .2, ... .n)
		       suffix.

     rescale=min,max   The optional output category range.
		       (Default: 1,255) If rescale=0,0,	 no
		       rescaling is performed on output files.


     Richards (l986) gives a good example of the application of
     principal components analysis (pca) to a time series of
     LANDSAT images of a burned region in Australia.

SEE ALSO
     Richards, John A., Remote Sensing Digital Image Analysis,
     Springer-Verlag, 1986.

     Vali, Ali R., Personal communication, Space Research Center,
     University of Texas, Austin, 1990.




GRASS 5.0beta6	      GRASS Development Team			1






i.pca <main>	      GRASS Reference Manual	     <main> i.pca



     i.cca, i.class, i.fft, i.ifft, m.eigensystem, r.covar,
     r.mapcalc

AUTHOR
     David Satnik, GIS Laboratory, Central Washington University
     Major modifications for GRASS 4.1 were made by Olga
     Waupotitsch and Michael Shapiro, U.S. Army Construction
     Engineering Research Laboratory















































2		      GRASS Development Team	   GRASS 5.0beta6