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[aprssig] Objects Of Boats Along Waterways

Kai Gunter Brandt kai.brandt at hjemme.no
Mon Jan 22 00:21:13 UTC 2007


Tapio Sokura wrote:
> 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
My program uses ShipPlotter and relays the trafic to UI-View.
Next version is going to have filters and posibilities to connect 
directly to an aprs server.
ShipPlotter is storing MMSI,callsign and names in a "library" so that 
theres no need to do this job every time.
> 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.
This is no really a problem if you configure i.e UI-View to limit the 
amount of traffic. But yes you should check before and after to see if 
you are making to much traffic.

The ships is sendig lots of updates when turning etc. But the 
digi-functions in UI-View you can limiting this.
Setting it to i.e 20-40sec then redusing it a lot. Its working just like 
TinyTrack smart beaconing. lotz of traffic in curves etc.
> 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".
SAR, spesial event or maybe filter out just som nice ships and not 
everything.
Hobby, just4fun, developing things and combine with the HAM hobby and 
another thing is that you can see everything in the same program.
If you disable the digipeat function then only you can see it on your 
computer.

And yes there is some "issue" that goverment do not want this 
information on internet etc because its supposed to be antiterror not to 
show the positions... crap but thats politics. For terorists doesnt need 
either aprs, internet or shippositions to make unwanted things to happen.

Kai Gunter
LA3QMA




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