Help for GRIDAVG

PURPOSE
     GRIDAVG is a VICAR applications program which averages two or
     more GEOMV grids into a single grid so that a GEOMV can produce
     the average move of the grids.  This would improve the accuracy
     of the results if the grids were independent estimates of the
     desired GEOM.  The averaging is rowwise.  Only the OLDCOLS are 
     averaged.  The NEWCOLS are checked for agreement, they must be
     the same.
     
     The resulting grid is in a four column IBIS file with the normal
     GEOMV column order (1,2,3,4) in double precision.  The inputs
     can be single or double precision, or integer.  The output will
     be double precision.  See below for a description of the GEOMV
     format.
	   
CALL
     gridavg (GRID_A1,GRID_A2,...) GRID_OUT NEWCOLS=(C1,C2) OLDCOLS=(C3,C4)
  WHERE:
     GRID_A1        is the first grid in an IBIS file.
     GRID_A2        is the second grid in an IBIS file.
     ...            more grids, up to 50 total
     GRID_OUT       is the output grid in GEOMV format.
     NEWCOLS        are the columns of the "new" grid, to be checked.
     OLDCOLS        are the columns of the "old" grid, to be averaged.
     
     The GEOMV format of the warp grid will now be described.

     The IBIS-file form of the grid contains four columns of
single or double precision tiepoint records.  The columns in
order are (newline,newsamp,oldline,oldsamp); or the column order
can be user specified.  NAH and NAV will be calculated from the
grid and the grid must be rectangular.

     The TIEPOINT-GRID is a set of points describing the relation
of the output file to that of the input file using the keyword
TIEPOINT and optionally NAH and NAV which are ignored.
   NAH=nah  NAV=nav
     tiepoint=(nl1,ns1,ol1,os1,nl2,ns2,ol2,os2,...
                   ...nlk,nsk,olk,osk)

where the grid is rectangular in the output image space, nah is
the number of grid cells horizontally (across the top in the sample
direction), nav is the number of grid cells vertically in the output
image space, the point pairs (nli,nsi,oli,osi) are line-sample
coordinates in the output (new) and input (old) spaces respectively.
the number of pairs k must equal (nah+1)*(nav+1).  The grid must be
perfectly rectangular in the output image space (the rows and
columns must be perfectly horizontal and vertical respectively).
Each direction must be evenly spaced as well, but all values can
br fractional.  There are no keywords NAH and NAV, the true
values are calculated from the grid.
  
OPERATION

GRIDAVG copies the second input, keeping the output grid as is
(except perhaps for conversion to double precision), and substituting
for the input grid points, the values that passed through the first
grid would yield the inputs.

For points that fall outside the first grid, an extrapolation process
similar to that of tieconv is used.  This should be avoided, but is
provided as a convenience in case the edge effects are not significant.

PERFORMANCE

Guess about 10 seconds for a two 500 x 500 grids.

Restrictions
------------

THE "NEW" PARTS OF THE GRIDS MUST BE IDENTICAL.

THE COLUMNS OF BOTH "NEW" AND "OLD" MUST BE THE SAME IN ALL OF THE
INPUT FILES, BUT DON'T HAVE TO BE COLUMNS 1,2,3,4.

Original Programmer: A. L. Zobrist, 13 Jul. 2005.
Current Cognizant Programmer: A. L. Zobrist
Revisions:
  2007-12-29 WLB - Switched to USES_ANSI_C AND LIB_CARTO; misc cleanup
  2015-10-23 WLB - Migrated to MIPL
  2019-09-04 WLB - Initialized some variables.
  2021-11-12 WLB - Initialized another variable.

PARAMETERS: