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complete surface position decoding

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This commit is contained in:
junzis
2016-10-19 16:22:28 +02:00
parent b648f4e7a5
commit 4bafa1de19
4 changed files with 120 additions and 27 deletions
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110
pyModeS/adsb.py
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@@ -167,8 +167,8 @@ def cprlon(msg):
return util.bin2int(msgbin[71:88])
def position(msg0, msg1, t0, t1):
"""Decode position from a pair of even and odd position message
def position(msg0, msg1, t0, t1, lat_ref=None, lon_ref=None):
"""Decode position from a pair of even and odd position message
(works with both airborne and surface position messages)
Args:
@@ -181,7 +181,12 @@ def position(msg0, msg1, t0, t1):
(float, float): (latitude, longitude) of the aircraft
"""
if (5 <= typecode(msg0) <= 8 and 5 <= typecode(msg1) <= 8):
return surface_position(msg0, msg1, t0, t1)
if (not lat_ref) or (not lon_ref):
raise RuntimeError("Surface position encountered, a reference \
position lat/lon required. Location of \
receiver can be used.")
else:
return surface_position(msg0, msg1, t0, t1, lat_ref, lon_ref)
elif (9 <= typecode(msg0) <= 18 and 9 <= typecode(msg1) <= 18):
return airborne_position(msg0, msg1, t0, t1)
@@ -233,17 +238,17 @@ def airborne_position(msg0, msg1, t0, t1):
# compute ni, longitude index m, and longitude
if (t0 > t1):
ni = max(_cprNL(lat_even), 1)
m = util.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
nl = _cprNL(lat)
ni = max(_cprNL(lat)- 0, 1)
m = util.floor(cprlon_even * (nl-1) - cprlon_odd * nl + 0.5)
lon = (360.0 / ni) * (m % ni + cprlon_even)
else:
ni = max(_cprNL(lat_odd) - 1, 1)
m = util.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
nl = _cprNL(lat)
ni = max(_cprNL(lat) - 1, 1)
m = util.floor(cprlon_even * (nl-1) - cprlon_odd * nl + 0.5)
lon = (360.0 / ni) * (m % ni + cprlon_odd)
if lon > 180:
lon = lon - 360
@@ -255,7 +260,9 @@ def position_with_ref(msg, lat_ref, lon_ref):
"""Decode position with only one message,
knowing reference nearby location, such as previously
calculated location, ground station, or airport location, etc.
(works with both airborne and surface position messages)
Works with both airborne and surface position messages.
The reference position shall be with in 180NM (airborne) or 45NM (surface)
of the true position.
Args:
msg0 (string): even message (28 bytes hexadecimal string)
@@ -279,7 +286,8 @@ def position_with_ref(msg, lat_ref, lon_ref):
def airborne_position_with_ref(msg, lat_ref, lon_ref):
"""Decode airborne position with only one message,
knowing reference nearby location, such as previously calculated location,
ground station, or airport location, etc.
ground station, or airport location, etc. The reference position shall
be with in 180NM of the true position.
Args:
msg (string): even message (28 bytes hexadecimal string)
@@ -317,15 +325,83 @@ def airborne_position_with_ref(msg, lat_ref, lon_ref):
return round(lat, 5), round(lon, 5)
def surface_position(msg0, msg1, t0, t1):
# TODO: implement surface positon
raise RuntimeError('suface position decoding to be implemented soon...')
def surface_position(msg0, msg1, t0, t1, lat_ref, lon_ref):
"""Decode surface position from a pair of even and odd position message,
the lat/lon of receiver must be provided to yield the correct solution.
Args:
msg0 (string): even message (28 bytes hexadecimal string)
msg1 (string): odd message (28 bytes hexadecimal string)
t0 (int): timestamps for the even message
t1 (int): timestamps for the odd message
lat_ref (float): latitude of the receiver
lon_ref (float): longitude of the receiver
Returns:
(float, float): (latitude, longitude) of the aircraft
"""
msgbin0 = util.hex2bin(msg0)
msgbin1 = util.hex2bin(msg1)
# 131072 is 2^17, since CPR lat and lon are 17 bits each.
cprlat_even = util.bin2int(msgbin0[54:71]) / 131072.0
cprlon_even = util.bin2int(msgbin0[71:88]) / 131072.0
cprlat_odd = util.bin2int(msgbin1[54:71]) / 131072.0
cprlon_odd = util.bin2int(msgbin1[71:88]) / 131072.0
air_d_lat_even = 90.0 / 60
air_d_lat_odd = 90.0 / 59
# compute latitude index 'j'
j = util.floor(59 * cprlat_even - 60 * cprlat_odd + 0.5)
# solution for north hemisphere
lat_even_n = float(air_d_lat_even * (j % 60 + cprlat_even))
lat_odd_n = float(air_d_lat_odd * (j % 59 + cprlat_odd))
# solution for north hemisphere
lat_even_s = lat_even_n - 90.0
lat_odd_s = lat_odd_n - 90.0
# chose which solution corrispondes to receiver location
lat_even = lat_even_n if lat_ref > 0 else lat_even_s
lat_odd = lat_odd_n if lat_ref > 0 else lat_odd_s
# check if both are in the same latidude zone, rare but possible
if _cprNL(lat_even) != _cprNL(lat_odd):
return None
# compute ni, longitude index m, and longitude
if (t0 > t1):
lat = lat_even
nl = _cprNL(lat_even)
ni = max(_cprNL(lat_even) - 0, 1)
m = util.floor(cprlon_even * (nl-1) - cprlon_odd * nl + 0.5)
lon = (90.0 / ni) * (m % ni + cprlon_even)
else:
lat = lat_odd
nl = _cprNL(lat_odd)
ni = max(_cprNL(lat_odd) - 1, 1)
m = util.floor(cprlon_even * (nl-1) - cprlon_odd * nl + 0.5)
lon = (90.0 / ni) * (m % ni + cprlon_odd)
# four possible longitude solutions
lons = [lon, lon + 90.0, lon + 180.0, lon + 270.0]
# the closest solution to receiver is the correct one
dls = [abs(lon_ref - l) for l in lons]
imin = min(range(4), key=dls.__getitem__)
lon = lons[imin]
return round(lat, 5), round(lon, 5)
def surface_position_with_ref(msg, lat_ref, lon_ref):
"""Decode surface position with only one message,
knowing reference nearby location, such as previously calculated location,
ground station, or airport location, etc.
ground station, or airport location, etc. The reference position shall
be with in 45NM of the true position.
Args:
msg (string): even message (28 bytes hexadecimal string)