A Go library to read AIS sentences and decode AIS messages.

The most simple example of decoding and printing an AIS message:

$ cd examples/example
$ echo '!AIVDM,1,1,,A,14eGrSPP00ncMJTO5C6aBwvP2D0?,0*7A' | go run example.go
=== Class A Position Report (1) ===
 Repeat       : 0
 MMSI         : 316013198 [Ship, Canada]
 Nav.Status   : Under way using engine
 Turn (ROT)   : no turn information
 Speed (SOG)  : 0.0 knots
 Accuracy     : High accuracy (<10m)
 Coordinates  : 130°18.9742'W  54°19.2666N
 Course (COG) : 237.9°
 Heading (HDG): not available
 Manuever ind.: not available
 RAIM         : in use

While I was working for marine.travel —a social site for sea lovers— I wanted to polish my Go skills. I thought a nice project would be an AIS parser, which later we could use to implement new functionality for our product.

I wrote aislib outside my work duties and time, but intended to use it there. Unfortunately marine.travel didn't make it. Thankfully we are on new, equally exciting adventures now. Since aislib didn't have any prospects anymore, I asked for permission to release my code under a permissive license. It was granted and here is the repository. :)

Please bare in mind that this was my first big-ish project in golang, some poor choices are to be expected. I am pretty certain that the main functionality is robust though, so if it doesn't fit your needs, you could use the decoding parts and implement your ideal management parts.

Inside the examples/ directory you will find two examples to get you going. Start with the simple one, example.go. To run:

 $ cat nmea-sample.txt | go run example.go

aislib can decode type 1, 2, 3 (Class A Position Report), 4 (Base Station Report), 5 (Static Voyage Data), 18 (Class B Position Report) messages. It may also understand type 8 (binary Broadcast) messages, report their respective type and extract the binary payload.

These are the most common types you will find. If you are interested in extending aislib, it is worth implementing type 21 and 24 decoding.

A limitation is multi-sentence messages. Messages that span across AIS sentences will only be decoded if (a) they come in order and (b) do not interleave with other multi-sentence messages.

In my experience from capturing AIS data from ais1.shipraiser.net for many hours, the messages you receive almost always meet these criteria. I think I never saw a sentence parsing failing due to this restriction.

As stated, some poor choices may have been made.

Each AIS message type has different fields. Thus I implement a router, that receives sentences, checks their type, their checksum and if the message they carry spans across many sentences (and it reconstructs the message's payload) and pass back the type and the payload. This work is done through channels, an incoming channel to the router, to pass AIS sentences and an outgoing channel to receive message payloads (and types). There is also a second outgoing channel where you receive the sentences that the router failed to recognize for any reason (e.g bad checksum or out of order multi-span message). It is useful for debugging.

So in sort you send AIS sentences into the router and get tuples with AIS message type and payload.

You should switch on the message type to the proper decoding function.

In retrospect, now I know that I could return just the message and let you use type assertion. This wouldn't change much though, as again you would need a select statement to deal with the result.

Check example.go to understand how the router and decoding function works.

Check LICENSE file. In sort it is GPL version 3 or greater.