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[aprssig] APRS return to basics (DR) (new images)

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Thu May 24 17:37:43 UTC 2012


Not sure what software you're running, but APRSISCE/32 does do both 
explicit (CSE/SPD provided) and implicit (course and speed calculated 
either instantaneously or averaged) Dead Reckoning, but in any case will 
drop the DR-forecasted image 5 minutes (eventually to be 
user-configurable) after the last packet was received.  Before I did 
this, I had what you described, "EverReady Bunny" forecasts that kept 
going and going and going...

Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

On 5/24/2012 1:31 PM, Andrew P. wrote:
> Hi, Bob.
>
> Here's an interesting observation on DR.
>
> In my area, I find a large number of "hanging" DR's, because a mobile station didn't send a final "I have stopped moving now" beacon (with speed=0) before powering off. Whether this is because the software I am using infers speed and course from the last few position reports for stations not reporting CSE/SPD, or because Smart Beaconing doesn't work well upon deceleration (as was noted in someone else's post a month or so ago), I do not know, but I have hanging DR's all over my map most of the time.
>
> I'm not sure what to do about this problem, except wait for this misleading station information to expire off the real-time display.
>
> Any ideas?
>
> Andrew Pavlin, KA2DDO
> author of YAAC (Yet Another APRS Client)
> http://www.findtheater.com/ka2ddo/YAAC.html
> ------Original Message------
> From: Bob Bruninga
> To: aprssig at tapr.org
> Sent: May 24, 2012 9:32 AM
> Subject: Re: [aprssig] APRS return to basics (DR) (new images)
>
>
>> I've never used a system that used dead reckoning,
>> but I don't think I would like the feature.
> That's what they said about the telephone, the car, the telegraph and
> facebook.  It also shows why I had asked all authors to have DR enabled by
> default.  SO that people would get a taste of what real-time tactical
> awareness really looks like when they came into APRS.  If it got too messy,
> they could turn it off.  But if it is messy, then it is really telling you
> something important about the latency of your data!  Hiding it is hiding
> that important element.
>
> Again,  DR is fundamental to all military and aviation and other tracking
> systems.  If something is moving then it has FOUR dimensions.  LAT, LONG,
> COURSE and SPEED.  TO ignore CSE and SPD in the display is like looking at a
> Black and white TV and it hides the age of the position.
>
>> but my feeling is that I would rather know what is fact...
> The last known position is always clearly shown with the circle and the
> line.  The length of the line from that last known position to the estimated
> DR'ed position shows the passage of time and the age of the "fact".
>
>> if they kept moving, completely missing the next bend in the road...
> A symbol DR'd at 70 MPH off the interstate because the road turned still
> conveys exactly the same information.  He is that far along his route.
> Looking at the map you can easily see where the road went with him still on
> it and can visualize where he is.  If the DR is very long, such as 5 or 10
> miles, then clearly he can be 5 or 10 miles from that last known position
> and so its "factual" value is vanishing to practically nothing.
>
> In fact at 60 MPH, the error in that "fact" is more than a mile off after
> even just a minute.  Hence, the DR'ed position is always more factual than
> the old stamp on the road just getting older and older.
>
> Bob, WB4APR
>
>
>
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