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implement gillham altitude decoding

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This commit is contained in:
Jakob Ketterl 2023-08-31 20:15:18 +02:00
parent a2a3991784
commit 5f931821e5
2 changed files with 26 additions and 1 deletions
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0
modes_test.py Normal file
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27
owrx/adsb/modes.py
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@ -188,7 +188,9 @@ class ModeSParser(PickleModule):
if q:
message["altitude"] = altitude * 25 - 1000
elif altitude > 0:
message["altitude"] = self._grayDecode(altitude) * 100
altitude = self._gillhamDecode(altitude)
if altitude is not None:
message["altitude"] =
elif type == 19:
# airborne velocity
@ -373,3 +375,26 @@ class ModeSParser(PickleModule):
output |= bit << i
previous_bit = bit
return output
gianniTable = [None, -200, 0, -100, 200, None, 100, None]
def _gillhamDecode(self, input: int):
c = ((input & 0b10000000000) >> 8) | ((input & 0b00100000000) >> 7) | ((input & 0b00001000000) >> 6)
b = ((input & 0b00000010000) >> 2) | ((input & 0b00000001000) >> 2) | ((input & 0b00000000010) >> 1)
a = ((input & 0b01000000000) >> 7) | ((input & 0b00010000000) >> 6) | ((input & 0b00000100000) >> 5)
d = ((input & 0b00000000100) >> 1) | (input & 0b00000000001)
dab = (d << 6) | (a << 3) | b
parity = dab.bit_count() % 2
offset = self.gianniTable[c]
if offset is None:
# invalid decode...
return None
if parity:
offset *= -1
altitude = self._grayDecode(dab) * 500 + offset - 1000
return altitude