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[aprssig] Appalachian Trail Tracking

Brett Friermood brett.friermood at gmail.com
Thu Mar 1 15:54:35 UTC 2012

What if you created a second connection to the -IS just for filtering
of the Trail?. Filter the
stream with an Area Filter that narrows it down to within close
proximity of the Trail, then
run your scripts on that much smaller stream to find those that are
actually on the trail.


2012/3/1 John Gorkos <jgorkos at gmail.com>:
> Well… This is a bit harder than I though.  Average message rate through
> APRS-IS is in the 40 msgs/sec range right now.  The way APRS-Alert is set
> up, it first filters on call sign (I.e. It has a list of call signs that
> people are interested in), and then it applies any geospatial rules on the
> far more limited subset of interesting calls that get through, versus
> against the entire message stream.
> Looking for "all stations in a geographic area" means that every position
> report needs to be geospatially tested against every zone that we find
> interesting.  Right now, my setup takes about 3ms per "within" test, meaning
> theoretically, I could do about 8-10 zone tests per message per second.  So,
> for special cases, I can check every position to see if it's coming from
> someone on the Appalachian Trail (I created a polygon that encloses the
> entire length of the trail to do a st_within() test against), but I can't
> make a feature on the web site that allows people to say "notify me any time
> ANY station enters zone X".   Same thing for another great idea I had:  sent
> an APRS message or other notification (I.e. Sms, if the call sign is
> registered) to any station entering an active Severe Thurnderstorm or
> Tornado Warning box.  Again, unfortunately, the math works against me:
>  testing every inbound position against every active severe weather zone is
> more computationally intensive than I'm willing to throw hardware at,
> especially on a night like last night, where we had multiple large swaths of
> the US covered with blizzard warnings, tornado warnings, etc.
> Granted, I'm not as committed to this financially as Hessu is with APRS.FI.
>  I'm sure I could get an amazon cloud instance, or put "real" hardware in a
> "real" datacenter that could keep up.  I might yet do that, since I have
> access to said hardware and colo, but for the immediate future, it's harder
> than it looks.
> John Gorkos

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