Help for ELVCOR

PURPOSE
     Calculate elevation offsets for a satellite image using a
DTED elevation image and a simple description of the satellite
path relative to the image.
	   
CALL
     The elevation correction is in an IBIS file (the name of the 
file is the third parameter).  It is formatted for GTWARPXD,
meaning that only the name of the file and the four columns
that contain (newl,news,oldl,olds) need to be passed to GTWARPXD.
The four columns are (1,2,15,16).

See avwarp.pdf for a sample of use.  A copy has been saved in the
elvcor.com file for this procedure.
  
OPERATION


PERFORMANCE

Restrictions
------------
The reference output image is presently required to be in
geographic coordinates (Platte Carree).  The dted doesn't 
have to be geographic.  The parameters sensE1, ... have to
be in geographic coordinate (lon-lat)

Original Programmer: A. L. Zobrist, 12 Nov, 2001
Current Cognizant Programmer: A. L. Zobrist
Last change by: A. L. Zobrist, 4 Dec, 2001
Last change by: A. L. Zobrist, 16 Nov, 2002: finally got sign right for c22 calc 
Last change by: A. L. Zobrist, 17 Feb, 2003: shift in rotated direction 
2022-08-10 B. Crocco afids to opensource (untested)