Help for ZCIRCLE

PURPOSE:

	"zcircle" is a VICAR2 applications program which removes
	data in a circular or elliptical pattern from an image.  
	Data may be removed either inside or outside of the
	specified pattern, and is either replaced with lowest
	DN value (i.e., 0 for BYTE data, -32678 for HALF, 
	-214748638 for FULL and -1.7E38 for FULL data) or,
	optionally, with a specified DN value.

OPERATION:
	
	"zcircle" reads the input dataset line by line, modifying
	each if necessary, and writes each line directly to the
	output.  The circle or ellipse defined by the parameters
	may intercept any given line at most 2 times.  If the
	default mode of removing data outside the curve is in
	effect, all data outside of these 2 points is replaced
	with the desired DN value.  If the IN (for inside) option
	is used, all data between the two points is replaced.
	The actual curve is replaced in both modes.  If an ellipse
	is desired, it is possible to generate the axis lengths
	by various combinations of two parameters:

	1) Known average radius and eccentricity, specify R and
	   ECC. If polar radius is larger that equatorial radius,
	   make ECC negative.
	2) Known semimajor and semiminor axis lengths, specify
	   RPOL and REQ as desired.  ECC will be calculated from
	   these two given values.
	3) Known eccentricity and one axis length, specify ECC and
	   RPOL or REQ (as known). If the polar radius is to
	   be larger than the equatorial, make ECC negative.

	The average radius of an ellipse is assumed to be
	(NL+NS)/4.
EXECUTION:

	EXAMPLES	
	   zcircle A B (1 1 500 500)
 	   --This replaces all pixels with zero which are outside
	     of a circle centered at line 250.5, sample 250.5, with
	     radius 250.

	   zcircle A B (1 1 500 500) 'IN
	   --This is similar to the above except that all pixels 
	     inside the circle are replaces with zero.

	   zcircle A B DN=100 XCEN=-10 YCEN=200 R=50 'in
	   --This replaces all pixels with 100 DN which are iside
	     the circle centerd (off the picture) at line 200 and
	     sample -10 with radius 50 pixels.

	   zcircle A B (1 1 500 500) ECC=0.5
	   --This replaces all pixels with zero which are outside of
	     an ellipse centered at (250.5 250.5) and average semi-
	     axis length of 500.  The major axis will be aligned
	     along the sample direction (horizontal).

	   zcircle A B (1 1 500 500) ECC=-0.5
	   --This is similar to the above, except that the major
	     axis is aligned along the line direction (vertical).

	   zcircle A B RPOL=25.3 ECC=0.9 ANG=35.7
	   --This replaces all pixels outside of the ellipse with
	     zero DN defines by an eccentricity of 0.9 and a polar
	     axis length of 50.6 pixels (2*RPOL), with the polar
	     axis pointing to an azimuthal angle of 35.7 degrees
	     clockwise from up.  The major axis length (REQ) is
	     determined by RPOL and ECC to be 116.1 pixels.
PROGRAM HISTORY:
Made portable for UNIX by A. Scop (CRI) 1-JULY-1994