C	PROGRAM BNDHEM.FT
C	----------------
C
C
	SUBROUTINE BNDHEM(A1,A2,ADIFF)
C
C	PETER LEMKIN
C	IMAGE PROCESSING UNIT, DCBD
C	NATIONAL CANCER INSTITUTE
C	NATIONAL INSTITUTES OF HEALTH
C	9000 ROCKVILLE PIKE
C	BETHESDA, MD. 20014
C
C	JULY 14, 1977
C
C	INTRODUCTION
C	------------
C	BNCHEMISPHERE CONVERTS A1,A2 ANGLES (A1 BEFORE A2)
C	TO THE PROPER DIFFERENCE ANGLE DEPENDING
C	ON THE HEMISPHERE A1-A2 FALLS IN. RETURN THE RESULT IN ADIFF.
C
C	[1] TEST IF IN SAME HEMISPHERE
	IA1=A1
	IA2=A2
C	IF IA1< 4 AND IA2 < 4
C		THEN IHEMI_1
S	TAD \IA1
S	TAD (-4
S	SMA CLA
S	JMP \601
S	TAD \IA2
S	TAD (-4
S	SMA CLA
S	JMP \601 /NO
	IHEMI=1
	GOTO 610
C
C	[2] TEST IF A1 IN [0:180] AND A2 IN [180+:360].
C	IF IA1 GEQ 4 AND IA2 GEQ 4
C		THEN IHEMI_2
S\601,	TAD \IA1
S	TAD (-4
S	SPA CLA
S	JMP \602
S	TAD \IA2
S	TAD (-4
S	SPA CLA
S	JMP \602 /NO
	IHEMI=2
	GOTO 610
C
C	[3] TEST IF A1 IN [180+:360] AND A2 IN[0:180].
C	IF IA1 < 4 AND IA2 GEQ 4
C		THEN IHEMI_3
S\602,	TAD \IA1
S	TAD (-4
S	SMA CLA
S	JMP \604
S	TAD \IA2
S	TAD (-4
S	SPA CLA
S	JMP \604 /ELSE
	IHEMI=3
	GOTO 610
C		ELSE IHEMI_4;
604	IHEMI=4
C
C	[4] COMPUTE ADIFF AS A FUNCTION OF THE HEMISPHERES OF A1, A2
610	ADIFF=A1-A2
	GOTO(611,612,613,614),IHEMI
C
C	[4.1] A1,A2 < 180 DEGREES.
611	CONTINUE
	GOTO 620
C
C	[4.2] A1,A2 GEQ 180 DEGREES.
612	CONTINUE
	GOTO 620
C
C	[4.3] A1 < 180 DEGREES, A2 GEQ 180 DEGREES
C	IF ADIFF LEQ -4
C		THEN ADIFF_-8.0-ADIFF
613	IF(ADIFF+4.0)615,615,620
615	ADIFF=8.0+ADIFF
	GOTO 620
C
C	[4.4] A1 GEQ 180 DEGREES, A2 < 180 DEGREES
C	IF ADIFF GEQ 4
C		THEN ADIFF_8.0-ADIFF
614	IF(ADIFF-4.0)620,616,616
616	ADIFF=8.0-ADIFF
C
620	CONTINUE
	RETURN
	END