[aprssig] Bug or feature: ambiguity circles that expand with dead-reckoning distance?
Lynn W. Deffenbaugh (Mr)
ldeffenb at homeside.to
Wed Mar 21 14:38:36 CDT 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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