[aprssig] info for TM-D710E in car
jmaslak-aprs at antelope.net
Mon Jan 14 15:17:18 CST 2008
On Jan 14, 2008, at 9:27 AM, Robert Bruninga wrote:
> Smartbeaconing has the objective of a more accurate track in the
> spacial domain (on the map). But all of its packets go the full
> path length to all surrounding areas.
Actually it has nothing to do with accuracy of the track.
It has to do with accuracy of location, while minimizing packets.
I'll try to explain with Navy terms. ;)
Let's say you have an aircraft carrier traveling due East from
Charleston at a speed of 15 knots. If you know the time it left
port, and you know what time it is now, you know pretty much exactly
where the carrier is. You don't need any information other than the
first position report with speed. This is where APRSDOS's plotting
BUT...let's say that ship turned south about 200 miles east of
Charleston. You need another packet to be sent at some point so
that people know the turn was made. Once that packet is received,
until the ship changes course, you know exactly (well, nearly-
exactly) where the ship is. It doesn't matter if the exact corner
was pegged or not (which helps the track, but not the location
finding stuff), but it does matter that sometime after it was sent
that it is logged.
That's not quite corner pegging. That's what does the "accurate
track" and that's what you should be portraying as having the
objective of an accurate track. Smartbeaconing has the objective of
helping someone determine where an object is if they have a smart
There's another part of it too - let's say the ship is going .5
knots. Even if it is doing *tons* of turns, the last position
transmitted is "close" to where it is now, even if it is 15 minutes
later. But, let's say the same ship is going in a straight line at
25 knots...all of a sudden, that last position isn't anywhere close
to where the ship is (in relative terms). So it probably needs to
send out a few more beacons, more often. This is particularly
helpful to the dumb clients, like the D700.
Basically the idea of SmartBeaconing is to send less packets yet
convey more information at the same time. It isn't about having nice
looking tracks, and if someone is worrying about the nice looking
tracks, they are probably using it wrong, whether they are generating
those tracks with proportional pathing, too-frequent beaconing, or
SmartBeaconing - and they need an education about QRM.
SmartBeaconing most shines not on the highway, but for things like
balloons, ships, aircraft, etc.
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