Help for SHADY2

PURPOSE

SHADY2 shades a image as though it were being illuminated by a source
at a given azimuth and elevation.
EXECUTION

Example:
To shade the input image as though it were illuminated by a sun in the 
northeast at an elevation of 10 degrees above the horizon, enter

VICAR> SHADY2 inp=input.img out=output.img azimuth=45.0 elev=10.0
OPERATION

SHADY2 uses the four nearest neighbors around each pixel to compute a
local normal.  The cosine between this vector and the illumination
vector is computed and multiplied by SCALE to obtain the output DN.  The
subroutine STACKA is used to allocate buffers so that no size restrictions
exist.
HISTORY

Written by:  M.A. Girard, 25 July 1978
Cognizant programmer:  M. O'Shaughnessy

Revisions: 
J.H. Reimer, 10 April 1983  
	Original documentation
J.H. Reimer, 1 July 1985
	Converted to VICAR2 format
M. O'Shaughnessy, 9 October 1989
	Extended documentation, upgraded SHADY2 to r2lib, 
	wrote unit test procedure
Ron Alley, 7 February 2000
        Made BYTE the default output data format, with HALF optional.