10 REM================================
15 REM HAVERSINE FORMULA
20 REM
25 REM 2021-09-24
30 REM EN.WIKIPEDIA.ORG/WIKI/HAVERSINE_FORMULA
35 REM
40 REM C64 HAS PI CONSTANT
45 REM X1 LONGITUDE 1
50 REM Y1 LATITUDE 1
55 REM X2 LONGITUDE 2
60 REM Y2 LATITUDE 2
65 REM
70 REM V1, 2021-10-02, ALVALONGO
75 REM ===============================
100 REM MAIN
105 DR=π/180:REM DEGREES TO RADIANS
110 PRINT CHR$(147);CHR$(5);"HAVERSINE FORMULA"
120 PRINT "GREAT-CIRCLE DISTANCE"
130 R=6372.8:REM AVERAGE EARTH RADIUS IN KILOMETERS
200 REM GET DATA
210 PRINT
220 INPUT "LONGITUDE 1=";X1
230 INPUT "LATITUDE  1=";Y1
240 PRINT
250 INPUT "LONGITUDE 2=";X2
260 INPUT "LATITUDE  2=";Y2
270 GOSUB 500
280 PRINT
290 PRINT "DISTANCE=";D;"KM"
300 GET K$:IF K$="" THEN 300
310 GOTO 210
490 END
500 REM HAVERSINE FORMULA ------------
520 A=SIN((X2-X1)*DR/2)
530 A=A*A
540 B=COS(Y1*DR)*COS(Y2*DR)
550 C=SIN((Y2-Y1)*DR/2)
560 C=C*C
570 D=SQR(C+B*A)
580 E=D/SQR(1-D*D)
590 F=ATN(E)
600 D=2*R*F
610 RETURN