ais-decoder-ts

AIS Decoder

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.


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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

,,,,,,

### Important notes:
- Ais payload is represented in a 6bits encoded string

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- 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, session: any): void - decode the raw ais messages
- private validateRawMessage(input: string): boolean - validate if the raw messages

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

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- npm run example

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``javascript
// new Decoder(Array, safeMode)
import { Decoder } from '../lib/index';
const aisMessages:Array = [
'!AIVDM,1,1,,A,400TcdiuiT7VDR>3nIfr6>i00000,0*78',
'!AIVDM,2,1,0,A,58wt8Uig??r217S=:220588OA;0sk,0*7B',
'!AIVDM,2,2,0,A,eQ8823mDm3kP00000000000,2*5D',
'!AIVDM,2,1,0,A,58wt8Uig??r217S=:220588OA;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();

``

### References:
- 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

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