#!/usr/bin/python
# Leigh L. Klotz, Jr.
# WA5ZNU
# http://wa5znu.org/2007/08/bearing

import sys, math
 
def latlon(qra):
    c1 = int(qra[0:1], 36)-10
    c2 = int(qra[1:2], 36)-10
    c3 = int(qra[2:3], 10)
    c4 = int(qra[3:4], 10)
    if (len(qra) > 4):
      c5 = int(qra[4:5], 36)-10
      c6 = int(qra[5:6], 36)-10
      lat = (((c2 * 10) + c4 + ((c6 + 0.5)/24)) - 90)
      lon = (((c1 * 20) + (c3 * 2) + ((c5 + 0.5) / 12)) - 180)
    else:
      lat = (((c2 * 10) + c4 ) - 90)
      lon = (((c1 * 20) + (c3 * 2)) - 180)
    return (lat,lon)

# Set your QRA here
(lat1,lon1)=latlon("CM87wk")
# Or use latitude and longitude more precisely here
#lat1=37.428833
#lon1=-122.114667

# Beam rotor offset correction here (or use command-line arg)
offset=0

if len(sys.argv) == 1:
    print "usage: bearing dxqra [+/- offset]"
    exit

if len(sys.argv) == 3:
    offset=int(sys.argv[2])

if len(sys.argv) >= 2:
    dxqra=sys.argv[1]
    (lat2,lon2)=latlon(dxqra)

    k=180.0/math.pi

    lat1r=lat1/k
    lon1r=lon1/k

    lat2r=lat2/k
    lon2r=lon2/k

    dlong = lon2r - lon1r
    dlat = lat2r - lat1r
    arg1=math.sin(dlong) * math.cos(lat2r)
    arg2a = math.cos(lat1r) * math.sin(lat2r)
    arg2b = math.sin(lat1r) * math.cos(lat2r) * math.cos(dlong)
    arg2 =  arg2a -  arg2b
    bearingr = math.atan2(arg1, arg2)

    bearing = round(((360 + (bearingr * k)) % 360))

    bearing = bearing + offset

    if (bearing <= 180):
      antibearing = bearing + 180
    else:
      antibearing = bearing - 180

    print("%d/%d" % (bearing, antibearing))