180 lines
5.5 KiB
Python
180 lines
5.5 KiB
Python
# ------------------------------------------
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# BDS 0,6
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# ADS-B TC=5-8
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# Surface movement
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# ------------------------------------------
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from pyModeS import common
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def surface_position(msg0, msg1, t0, t1, lat_ref, lon_ref):
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"""Decode surface position from a pair of even and odd position message,
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the lat/lon of receiver must be provided to yield the correct solution.
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Args:
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msg0 (string): even message (28 hexdigits)
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msg1 (string): odd message (28 hexdigits)
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t0 (int): timestamps for the even message
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t1 (int): timestamps for the odd message
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lat_ref (float): latitude of the receiver
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lon_ref (float): longitude of the receiver
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Returns:
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(float, float): (latitude, longitude) of the aircraft
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"""
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msgbin0 = common.hex2bin(msg0)
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msgbin1 = common.hex2bin(msg1)
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# 131072 is 2^17, since CPR lat and lon are 17 bits each.
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cprlat_even = common.bin2int(msgbin0[54:71]) / 131072
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cprlon_even = common.bin2int(msgbin0[71:88]) / 131072
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cprlat_odd = common.bin2int(msgbin1[54:71]) / 131072
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cprlon_odd = common.bin2int(msgbin1[71:88]) / 131072
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air_d_lat_even = 90 / 60
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air_d_lat_odd = 90 / 59
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# compute latitude index 'j'
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j = common.floor(59 * cprlat_even - 60 * cprlat_odd + 0.5)
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# solution for north hemisphere
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lat_even_n = float(air_d_lat_even * (j % 60 + cprlat_even))
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lat_odd_n = float(air_d_lat_odd * (j % 59 + cprlat_odd))
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# solution for north hemisphere
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lat_even_s = lat_even_n - 90
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lat_odd_s = lat_odd_n - 90
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# chose which solution corrispondes to receiver location
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lat_even = lat_even_n if lat_ref > 0 else lat_even_s
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lat_odd = lat_odd_n if lat_ref > 0 else lat_odd_s
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# check if both are in the same latidude zone, rare but possible
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if common.cprNL(lat_even) != common.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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lat = lat_even
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nl = common.cprNL(lat_even)
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ni = max(common.cprNL(lat_even) - 0, 1)
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m = common.floor(cprlon_even * (nl - 1) - cprlon_odd * nl + 0.5)
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lon = (90 / ni) * (m % ni + cprlon_even)
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else:
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lat = lat_odd
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nl = common.cprNL(lat_odd)
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ni = max(common.cprNL(lat_odd) - 1, 1)
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m = common.floor(cprlon_even * (nl - 1) - cprlon_odd * nl + 0.5)
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lon = (90 / ni) * (m % ni + cprlon_odd)
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# four possible longitude solutions
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lons = [lon, lon + 90, lon + 180, lon + 270]
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# make sure lons are between -180 and 180
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lons = [(l + 180) % 360 - 180 for l in lons]
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# the closest solution to receiver is the correct one
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dls = [abs(lon_ref - l) for l in lons]
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imin = min(range(4), key=dls.__getitem__)
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lon = lons[imin]
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return round(lat, 5), round(lon, 5)
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def surface_position_with_ref(msg, lat_ref, lon_ref):
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"""Decode surface position with only one message,
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knowing reference nearby location, such as previously calculated location,
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ground station, or airport location, etc. The reference position shall
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be within 45NM of the true position.
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Args:
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msg (str): even message (28 hexdigits)
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lat_ref: previous known latitude
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lon_ref: previous known longitude
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Returns:
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(float, float): (latitude, longitude) of the aircraft
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"""
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mb = common.hex2bin(msg)[32:]
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cprlat = common.bin2int(mb[22:39]) / 131072
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cprlon = common.bin2int(mb[39:56]) / 131072
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i = int(mb[21])
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d_lat = 90 / 59 if i else 90 / 60
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j = common.floor(lat_ref / d_lat) + common.floor(
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0.5 + ((lat_ref % d_lat) / d_lat) - cprlat
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)
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lat = d_lat * (j + cprlat)
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ni = common.cprNL(lat) - i
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if ni > 0:
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d_lon = 90 / ni
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else:
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d_lon = 90
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m = common.floor(lon_ref / d_lon) + common.floor(
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0.5 + ((lon_ref % d_lon) / d_lon) - cprlon
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)
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lon = d_lon * (m + cprlon)
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return round(lat, 5), round(lon, 5)
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def surface_velocity(msg, source=False):
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"""Decode surface velocity from a surface position message
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Args:
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msg (str): 28 hexdigits string
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source (boolean): Include direction and vertical rate sources in return. Default to False.
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If set to True, the function will return six values instead of four.
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Returns:
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int, float, int, string, [string], [string]: Four or six parameters, including:
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- Speed (kt)
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- Angle (degree), ground track
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- Vertical rate, always 0
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- Speed type ('GS' for ground speed, 'AS' for airspeed)
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- [Optional] Direction source ('TRUE_NORTH')
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- [Optional] Vertical rate source (None)
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"""
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if common.typecode(msg) < 5 or common.typecode(msg) > 8:
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raise RuntimeError("%s: Not a surface message, expecting 5<TC<8" % msg)
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mb = common.hex2bin(msg)[32:]
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# ground track
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trk_status = int(mb[12])
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if trk_status == 1:
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trk = common.bin2int(mb[13:20]) * 360 / 128
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trk = round(trk, 1)
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else:
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trk = None
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# ground movement / speed
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mov = common.bin2int(mb[5:12])
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if mov == 0 or mov > 124:
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spd = None
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elif mov == 1:
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spd = 0
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elif mov == 124:
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spd = 175
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else:
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mov_lb = [2, 9, 13, 39, 94, 109, 124]
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kts_lb = [0.125, 1, 2, 15, 70, 100, 175]
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step = [0.125, 0.25, 0.5, 1, 2, 5]
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i = next(m[0] for m in enumerate(mov_lb) if m[1] > mov)
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spd = kts_lb[i - 1] + (mov - mov_lb[i - 1]) * step[i - 1]
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if source:
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return spd, trk, 0, "GS", "TRUE_NORTH", None
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else:
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return spd, trk, 0, "GS"
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