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[aprssig] CHART Traffic Data Testing

Bob Bruninga bruninga at usna.edu
Sun Feb 14 00:39:25 UTC 2010


This sounds like a great project.  In reviewing your email some thoughts and some concerns come to mind...

> I've am testing a traffic data server for
> Maryland ... When I get it working correctly it
> will refresh this data hourly

For traffic data, an hour is an eternity and any thing an hour old or having to wait an hour for, is of no practical value...

> but send new listings and kill objects 
> (for deleted events) every 5 minutes.

The APRS concept never intended to used fixed beaconing for new data.  Fixed rates are either not often enough to assure immediate retries or is too often and adds QRM.  Please use the original APRS Decay algorith for new data.  Send it immediately, then 30 seconds later, then 1 min, then 2 mins then 4 mins, then 8 mins....

Please do not send KILL objects for this much data.  It will add unnecessary QRM on the channel.  Sinec APRS is a real time system, and your objects will be time stamped on transmission, just let them decay after they are no longer valid...

I assume you have thresholds and will only send slow-traffic objects when the speed drops below some threshold?  And that should be low enough so that it only triggers when there is something Unusual, not routine slow downs that all commuters already know about.

Further, evry such object should preferably be sent DIRECT and only in the immediate area of each object.  Of course that is impossible unless you get lots of volunteers scattered throughtout the metro area to run and maintain additonal copies of your program.  Failing that, your softwware should allow for definitions of  different PATHS for different areas.  And this should include HOME stations near traffic routes.

The idea is that you want to use the LOWEST and SHORTEST range digi for each objedct to contain the QRM in other areas.  Each object generated, should check your PATH table and chose the proper callsign to use as a digi.  In no case should 2 hops be used via wide area digis.  Though 2 hops via low short range home stations might be OK...

>   I have found several other states and cities that
>   provide capabilities similar to Maryland CHART, and
>   even Great Britian has such a query capability for
>   the entire country at one site, so I am open to
>   sharing this software once it is beta-test ready. 

That would be fantastic!  But please put all kinds of nannycode to make sure that users cannot abuse it and generate inordinate QRM.  SYSOPING a traffic system is a big responsibility and will take a lot of detail, local, and very fine-tuned effort.  We dont want people just slapping it up without thought because it is so kool.

Go for it!
thanks
Bob, Wb4apr



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