51 lines
1.2 KiB
Plaintext
51 lines
1.2 KiB
Plaintext
https://mode-s.org/1090mhz/content/mode-s/1-basics.html
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p(x)：crc计算结果
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符号解释
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A：是ICAO地址
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P：是后24位置零，crc的计算结果，任何消息都能算这个值
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AP=A^P
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异或可逆性性
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AP = A^P
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A = AP^P
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P = AP^A
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DP = BDS^AAA^P //DP是数据奇偶校验，目前没看到那种24位，存这种东西
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df = 11 17 18 ： 消息后24位存放P, A明文存放在消息中,直接获取
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df = 0 4 5 16 20 21 消息后24位存放AP， 先计算P，然后根据 A=AP^P 计算出A
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// 上面这个df pyModeS-master 项目 源码py_common.py ：119
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// pyModeS-master项目 作者也是 那个文档的作者
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def icao(msg: str) -> Optional[str]:
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"""Calculate the ICAO address from an Mode-S message.
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Applicable only with DF4, DF5, DF20, DF21 messages.
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Args:
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msg (String): 28 bytes hexadecimal message string
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Returns:
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String: ICAO address in 6 bytes hexadecimal string
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"""
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addr: Optional[str]
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DF = df(msg)
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if DF in (11, 17, 18):
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addr = msg[2:8]
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elif DF in (0, 4, 5, 16, 20, 21):
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c0 = crc(msg, encode=True)
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c1 = int(msg[-6:], 16)
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addr = "%06X" % (c0 ^ c1)
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else:
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addr = None
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return addr
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