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[aprssig] Bug or feature: ambiguity circles that expand with dead-reckoning distance?

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Wed Mar 21 19:38:36 UTC 2012


My personal opinion is that position ambiguity is relative to the 
reported position.  I put the station symbol there with an ambiguity 
circle around it.  This is factual display of the received information.

Dead Reckoning is a local observer assistance tool that is not directly 
driven by any particular received information other than a (possibly 
delayed) position packet that includes a speed and heading.  The station 
never said it was anywhere but where the position says, so I leave the 
primary symbol at that position and move a line-connected 50% 
transparent copy of the symbol out from the received position.  This is 
a time-based extrapolation of received information.

So, in APRSISCE/32, ambiguity applies to the received position which is 
continuously displayed and the dead-reckoning extrapolated position 
shows a reduced opacity copy of the station because nothing really said 
the station was really anywhere near that point.

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

PS.  Smartbeaconing's corner pegging has some interesting side effects 
on dead reckoning, especially when large turn angles are involved.  I've 
noticed that the Tracker2-family devices beacon about 1/2 way around a 
90 degree turn resulting in the DR object going off the corner-pegged 
position in the wrong direction.  It's not until the next beacon 
(assuming it is a relatively straight-line and time-triggered beacon) 
that the DR comes back inline with the actual station route.  This 
behavior is really what drove me to keep the received beacon position 
for the station and move a separate DR object away from that anchor.

On 3/21/2012 3:17 PM, Andrew P. wrote:
> Greetings, all.
>
> I was fixing what looked like a bug in my APRS client software when it hit me: is it really a bug to increase ambiguity for a moving station when displaying a dead-reckoned position for that station instead of the last reported position?
>
> The particular "bug" I had showed the ambiguity circle as having a center at the dead reckoned position and the circumference intersecting the last reported position (ie., the station might never have left the last reported point). This was for a last position report with full precision so an unaltered ambiguity circle would have been invisibly small).
>
> So, what is the collected wisdom on this? Is this a bug or a feature?
>
> Just curious.
>
> Andrew Pavlin, KA2DDO
> Sent from my Verizon Wireless BlackBerry
>
>
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