The automatic identification system (AIS) is an automatic Tracking system used on ships and by vessel traffic services (VTS). When satellites are used to detect AIS signatures, the term Satellite-AIS (S-AIS) is used. AIS information supplements marine radar, which continues to be the primary method of collision avoidance for water transport.

1. Position[0] format: !AIVDM, identifies this as an AIVDM packet (AIS format).
2. Position[1] message_count: Messages counter (number of messages), sometimes the ais messages will be split over several messages.
3. Position[2] message_id:
4. Position[3] sequence_id: Sequential message, the current message number
5. Position[4] channel: vhf channel A/B
6. Position[5] payload: the ais data itself
7. Position[6] size: number of bits required to fill the data

<format>,<message count>,<message id>,<sequence id>,<channel A/B>,<data>,<fill bits>

• Ais payload is represented in a 6bits encoded string

• constructor(AIS_Messages, safeMode)
  • AIS_Messages: Array of ais messages.
  • safeMode: set to false by default. when true the module will never throw an error (silent mode).
• getResults() - return a collection of the parse messages
• private decode(input: Array<any>, session: any): void - decode the raw ais messages
• private validateRawMessage(input: string): boolean - validate if the raw messages

• node dist/bin/parse <ais message> for example: node ./dist/bin/parse "!AIVDM,1,1,,A,13u?etPv2;0n:dDPwUM1U1Cb069D,0*24"

• npm run example

// new Decoder(Array<AIS_Messages>, safeMode<Boolean>)
import { Decoder } from '../lib/index';
const aisMessages:Array<string> = [
  '!AIVDM,1,1,,A,400TcdiuiT7VDR>3nIfr6>i00000,0*78',
  '!AIVDM,2,1,0,A,58wt8Ui`g??r21`7S=:22058<v05Htp000000015>8OA;0sk,0*7B',
  '!AIVDM,2,2,0,A,eQ8823mDm3kP00000000000,2*5D',
  '!AIVDM,2,1,0,A,58wt8Ui`g??r21`7S=:22058<v05Htp000000015>8OA;0sk,0*7B ',
  '!AIVDM,2,2,0,A,eQ8823mDm3kP00000000000,2*5D',
];
const safeMode = false;
const aisDecoder_ex2 = new Decoder(aisMessages, safeMode);

// results will hold a collection of the parsed ais messages
const results = aisDecoder_ex2.getResults();

• Gov:
  • https://www.navcen.uscg.gov/?pageName=AISMessagesA
• Gpsd:
  • https://gpsd.gitlab.io/gpsd/AIVDM.html [recommended]
• OpenCPN:
  • https://github.com/OpenCPN/OpenCPN [file: AIS_Bitstring.cpp]
    • http://fossies.org/linux/misc/gpsd-3.11.tar.gz/gpsd-3.11/test/sample.aivdm
• online AIS decoder:
  • http://www.maritec.co.za/tools/aisvdmvdodecoding/
  • http://www.maritec.co.za/aisvdmvdodecoding1.php
• Wikipedia:
  • https://en.wikipedia.org/wiki/Automatic_identification_system
• OpenCPN
  • Github: https://github.com/OpenCPN/OpenCPN/blob/45504f35c005ed1ffcd117c67797279da42d53ae/src/AIS_Decoder.cpp

• If you find any bug please feel free to open an issue. PR are always welcome.