def ais_to_nmea_0183(payload: str, ais_talker_id: str, radio_channel: str,
fill_bits: int) -> AIS_SENTENCES:
"""
Splits the AIS payload into sentences, ASCII encodes the payload, creates
and sends the relevant NMEA 0183 sentences.
HINT:
This method takes care of splitting large payloads (larger than 60 characters)
into multiple sentences. With a total of 80 maximum chars excluding end of line
per sentence, and 20 chars head + tail in the nmea 0183 carrier protocol, 60
chars remain for the actual payload.
@param payload: Armored AIs payload.
@param ais_talker_id: AIS talker ID (AIVDO or AIVDM)
@param radio_channel: Radio channel (either A or B)
@param fill_bits: The number of fill bits requires to pad the data payload to a 6 bit boundary.
@return: A list of relevant AIS sentences.
"""
messages = []
max_len = 61
seq_id = ''
frag_cnt = math.ceil(len(payload) / max_len)
if len(ais_talker_id) != 5:
raise ValueError(
"AIS talker is must have exactly 6 characters. E.g. AIVDO")
if len(radio_channel) != 1:
raise ValueError("Radio channel must be a single character")
for frag_num, chunk in enumerate(chunks(payload, max_len), start=1):
tpl = "!{},{},{},{},{},{},{}*{:02X}"
dummy_message = tpl.format(ais_talker_id, frag_cnt, frag_num, seq_id,
radio_channel, chunk, fill_bits, 0)
checksum = compute_checksum(dummy_message)
msg = tpl.format(ais_talker_id, frag_cnt, frag_num, seq_id,
radio_channel, chunk, fill_bits, checksum)
messages.append(msg)
return messages
def is_valid(self) -> bool:
return self.checksum == compute_checksum(self.raw)