Hello all,
I'm trying to understand AIS messages that are passed around between boats.
My sotware job is requiring I write or reuse a parser.
I've read some documentation by Eric S Raymond but he's not all that clear for a beginner like me.
Now to begin with the messages are typically in a NMEA0183 format, which I wont explain here. In the case of AIS they begin with
AIVDM or AIVDO, then there are three fields:
1) a number that indicates the number of NMEA messages that are used to send one AIS message
2) a number that indicates the message number (must be less or equal to the previous)
3) a sequence number for multi-sentence messages.
This 3rd number is the mysterious one: from the description it looks like it's exactly the same as the second. But they would not have made it up if it was that. So just what is the difference? Am I misinterpreting something in my description?
And and by the way the next fields are "channel number" and the AIS payload, and some more we won't go into
Thankyou for your attention
Larry