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