""" This is a decoder of ABS-D date from Mode-S receiver. The inputs of most functions are the Hexdecial strings. Created by : Junzi Sun (TU Delft) Date : March 2015 """ import math MODES_CHECKSUM_TABLE = [ 0x3935ea, 0x1c9af5, 0xf1b77e, 0x78dbbf, 0xc397db, 0x9e31e9, 0xb0e2f0, 0x587178, 0x2c38bc, 0x161c5e, 0x0b0e2f, 0xfa7d13, 0x82c48d, 0xbe9842, 0x5f4c21, 0xd05c14, 0x682e0a, 0x341705, 0xe5f186, 0x72f8c3, 0xc68665, 0x9cb936, 0x4e5c9b, 0xd8d449, 0x939020, 0x49c810, 0x24e408, 0x127204, 0x093902, 0x049c81, 0xfdb444, 0x7eda22, 0x3f6d11, 0xe04c8c, 0x702646, 0x381323, 0xe3f395, 0x8e03ce, 0x4701e7, 0xdc7af7, 0x91c77f, 0xb719bb, 0xa476d9, 0xadc168, 0x56e0b4, 0x2b705a, 0x15b82d, 0xf52612, 0x7a9309, 0xc2b380, 0x6159c0, 0x30ace0, 0x185670, 0x0c2b38, 0x06159c, 0x030ace, 0x018567, 0xff38b7, 0x80665f, 0xbfc92b, 0xa01e91, 0xaff54c, 0x57faa6, 0x2bfd53, 0xea04ad, 0x8af852, 0x457c29, 0xdd4410, 0x6ea208, 0x375104, 0x1ba882, 0x0dd441, 0xf91024, 0x7c8812, 0x3e4409, 0xe0d800, 0x706c00, 0x383600, 0x1c1b00, 0x0e0d80, 0x0706c0, 0x038360, 0x01c1b0, 0x00e0d8, 0x00706c, 0x003836, 0x001c1b, 0xfff409, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000, 0x000000 ] def hex2bin(hexstr): """Convert a hexdecimal string to binary string, with zero fillings. """ length = len(hexstr) * 4 msgbin = bin(int(hexstr, 16))[2:] while ((len(msgbin)) < length): msgbin = '0' + msgbin return msgbin def bin2int(binstr): return int(binstr, 2) def hex2int(hexstr): return int(hexstr, 16) def checksum(msg): if len(msg) == 28: offset = 0 elif len(msg) == 14: offset = 112-56 else: # raise exception return False msgbin = hex2bin(msg) checksum = int(msg[22:28], 16) crc = 0 for i in xrange(len(msgbin)): if int(msgbin[i]): crc ^= MODES_CHECKSUM_TABLE[i+offset] if crc == checksum: return True else: return False def get_df(msg): """Decode Downlink Format vaule, bits 1 to 5.""" msgbin = hex2bin(msg) return bin2int(msgbin[0: 5]) def get_ca(msg): """Decode CA vaule, bits: 6 to 8.""" msgbin = hex2bin(msg) return bin2int(msgbin[5:8]) def get_icao_addr(msg): """Get the ICAO 24 bits address, bytes 3 to 8. """ return msg[2:8] def get_tc(msg): """Get Type Code, bits 33 to 37 """ msgbin = hex2bin(msg) return bin2int(msgbin[32:37]) def get_oe_flag(msg): """Check the odd/even flag. Bit 54, 0 for even, 1 for odd.""" msgbin = hex2bin(msg) return msgbin[53] def get_alt(msg): """Calculate the altitude from the message. Bit 41 to 52, Q-bit at 48""" msgbin = hex2bin(msg) q = msgbin[47] if q: n = bin2int(msgbin[40:47]+msgbin[48:52]) alt = n * 25 - 1000 return alt else: return None def get_cprlat(msg): msgbin = hex2bin(msg) return bin2int(msgbin[54:71]) def get_cprlon(msg): msgbin = hex2bin(msg) return bin2int(msgbin[71:88]) def get_position(msg0, msg1, t0, t1): cprlat0 = get_cprlat(msg0) cprlat1 = get_cprlat(msg1) cprlon0 = get_cprlon(msg0) cprlon1 = get_cprlon(msg1) return cpr2position(cprlat0, cprlat1, cprlon0, cprlon1, t0, t1) def cpr2position(cprlat0, cprlat1, cprlon0, cprlon1, t0, t1): ''' This algorithm comes from: http://www.lll.lu/~edward/edward/adsb/DecodingADSBposition.html. 131072 is 2^17 since CPR latitude and longitude are encoded in 17 bits. ''' cprlat_even = cprlat0 / 131072.0 cprlat_odd = cprlat1 / 131072.0 cprlon_even = cprlon0 / 131072.0 cprlon_odd = cprlon1 / 131072.0 air_d_lat_even = 360.0 / 60 air_d_lat_odd = 360.0 / 59 # compute latitude index 'j' j = int(59 * cprlat_even - 60 * cprlat_odd + 0.5) lat_even = float(air_d_lat_even * (j % 60 + cprlat_even)) lat_odd = float(air_d_lat_odd * (j % 59 + cprlat_odd)) if lat_even >= 270: lat_even = lat_even - 360 if lat_odd >= 270: lat_odd = lat_odd - 360 # check if both are in the same latidude zone, exit if not if cprNL(lat_even) != cprNL(lat_odd): return None # compute ni, longitude index m, and longitude if (t0 > t1): ni = cprN(lat_even, 0) m = math.floor(cprlon_even * (cprNL(lat_even)-1) - cprlon_odd * cprNL(lat_even) + 0.5) lon = (360.0 / ni) * (m % ni + cprlon_even) lat = lat_even else: ni = cprN(lat_odd, 1) m = math.floor(cprlon_even * (cprNL(lat_odd)-1) - cprlon_odd * cprNL(lat_odd) + 0.5) lon = (360.0 / ni) * (m % ni + cprlon_odd) lat = lat_odd if lon > 180: lon = lon - 360 return [lat, lon] def get_speed_heading(msg): """Calculate the speed and heading.""" msgbin = hex2bin(msg) v_ew_dir = bin2int(msgbin[45]) v_ew = bin2int(msgbin[46:56]) # east-west velocity v_ns_dir = bin2int(msgbin[56]) v_ns = bin2int(msgbin[57:67]) # north-south velocity v_ew = -1*v_ew if v_ew_dir else v_ew v_ns = -1*v_ns if v_ns_dir else v_ns # vr = bin2int(msgbin[68:77]) # vertical rate # vr_dir = bin2int(msgbin[77]) speed = math.sqrt(v_ns*v_ns + v_ew*v_ew) # unit in kts heading = math.atan2(v_ew, v_ns) heading = heading * 360.0 / (2 * math.pi) # convert to degrees heading = heading if heading >= 0 else heading + 360 # no negative val return [speed, heading] def get_callsign(msg): """Decode aircraft identification, aka. Callsign""" chars = '#ABCDEFGHIJKLMNOPQRSTUVWXYZ#####_###############0123456789######' msgbin = hex2bin(msg) csbin = msgbin[40:96] cs = '' cs += chars[bin2int(csbin[0:6])] cs += chars[bin2int(csbin[6:12])] cs += chars[bin2int(csbin[12:18])] cs += chars[bin2int(csbin[18:24])] cs += chars[bin2int(csbin[24:30])] cs += chars[bin2int(csbin[30:36])] cs += chars[bin2int(csbin[36:42])] cs += chars[bin2int(csbin[42:48])] # clean string, remove spaces and marks, if any. cs = cs.replace('_', '') cs = cs.replace('#', '') return cs def cprN(lat, isodd): nl = cprNL(lat) - isodd return nl if nl > 1 else 1 def cprNL(lat): nz = 60 a = 1 - math.cos(math.pi * 2 / nz) b = math.cos(math.pi / 180.0 * abs(lat)) ** 2 nl = 2 * math.pi / (math.acos(1 - a/b)) return int(nl)