Help for GRID3PT

PURPOSE

     GRID3PT finds 3 good non-collinear points from a grid or a non-grid
     of points.  The points are assumed to be tiepoints, hence occupy
     four columns of an IBIS file.
     
     The IBIS file indices of the three selected points are also
     returned if desired
     

TAE COMMAND LINE FORMAT

     grid3pt INP=A COLS=(1,2,4,3) v11=rv11 etc
     
     where

     A                   is the input dataset (IBIS file).
     rv11                is a TCL integer variable to get col 1 of 1st point
     rv21                is a TCL integer variable to get col 2 of 1st point
     etc

OPERATION

     The selected columns of the grid are read into an array.
     The center point is calculated, then the furthest point from
     the center becomes point 1.  The second point subtends the largest
     area with the first point and the center.  The third point
     subtends the largest area with the other two.


TIMING

     Dominated by the time to read the array in.
     
RESTRICTIONS

     The input array is mallocked.  Compare the size of the input
     IBIS file with system parameters.  

WRITTEN BY:            A. L. Zobrist, 31 March 2003

COGNIZANT PROGRAMMER:  A. L. Zobrist

REVISIONS:
  2007-12-29 wlb switched to USES_ANSI_C AND LIB_CARTO; misc cleanup
  2022-06-27 B. Crocco afids to opensource