C	[DEM23]
C	CALCULATION OF THE TILT OF THE ELEMENTARY RECTANGLES
C	AS A FUNCTION OF THETA AND PHI FOR USE IN CHOOSING
C	THE DIAGONAL SEQUENCE TO BE FOLLOWED IN THE SPHERICAL
C	SEQUENCE ROUTINES.
C	[THD] EDER 29-APR-76 COPIED FROM DECUS 10-228
	EXTERNAL PLTPO,VISSP
	DIMENSION EF(181,61),O(3,3)
	DATA O/0.577,-0.577,0.577,
     *		0.707,0.0,-0.707,
     *		0.408,0.816,0.408/
	AS(J,I)=0.1*FLOAT(MOD(I+J,2))
	L=1
	NT=61
	NP=181
	DT=3.14159/FLOAT(NT-1)
	DP=6.28318*FLOAT(NP)
	T=0.0
	DO	20	I=1,NT
	P=0.0
	DO	10	J=1,NP
	CALL D13SP(X1,Y1,T,P,O)
	CALL D13SP(X2,Y2,T,P+0.01,O)
	A1=ATAN2(Y2-Y1,X2-X1)
	A2=ATAN2(Y1,X1)
	R=SIN(A1-A2)
	EF(J,I)=0.25/(0.25+R*R)
10	P=P+DP
20	T=T+DT
	CALL PFNAME('DEM23.BLD')
	CALL PLT00
	CALL PLTFR
	CALL PLTLA('DEM23')
	TYPE 100
100	FORMAT(' [DEM23] INDEX: ',$)
	READ(5,*) IND
	GOTO(11,12),IND
	GOTO 700
11	CALL PLTSV(EF,NP,NT,O,VISSP,PLTPO)
	GOTO 701
12	CALL PLTSW(0.0,EF,5.0,NP,NP,NT)
701	CALL PLTEND
700	STOP
	END