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[aprssig] Objects Of Boats Along Waterways

Tapio Sokura oh2kku at iki.fi
Sun Jan 21 23:00:00 UTC 2007


Joe Della Barba wrote:
> I am very interested in AIS>APRS. If anyone has any info on this, could 
> they send it my way.

Basically you just decode the AIS traffic (9600 bps GMSK) from marine 
vhf band per the AIS specification and re-encode suitable parts of the 
information to form an APRS packet. You probably want to cache some 
information at the conversion point as well, as static data (ship name, 
dimensions, etc) is sent less often in AIS than location updates. And 
you'll probably want to do considerable rate-limiting, if 1200 bps APRS 
on the band is involved. A 2-channel AIS network has 4500 time slots (~ 
location updates) per minute. That's a 100-fold difference in capacity 
compared to APRS.

I just haven't really gotten the point in it, why would you want to see 
AIS targets in the APRS network? Maybe that can be useful in a special 
event situation that includes both APRS stations and AIS equipped ships, 
but in the general case? Ok, this is a hobby, so "just for fun" is a 
valid answer as well.. just watch out for those that might not like it. 
I've heard stories of some players in the marine world that consider AIS 
information to be "secret".

   Tapio




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