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[aprssig] Can objects/items dead-reckon?

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Mon Feb 27 22:03:12 UTC 2012


If they do, then they better toggle their symbol between a Weather 
Station and something else.  That's the only resolution of the 
ambiguity.  A weather station symbol's "speed and course" are actually 
the wind speed and direction.  So by extrapolation, a weather station 
itself can move (change the posit), but it can't say where it's headed 
nor how fast (that'd be the wind).  At least, that's my understanding.

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

On 2/27/2012 4:54 PM, Andrew P. wrote:
> Ok, so one more question. Can weather stations move? The protocol spec isn't clear about separating the wind speed and bearing from the station's speed and course in position reports. There is no ambiguity when sending positionless weather reports.
>
> In other words, do storm chasers use APRS to transmit weather data from their moving vehicles? ;-)
>
> Andrew Pavlin, KA2DDO
> Sent from my Verizon Wireless BlackBerry
>
> -----Original Message-----
> From: Bob Bruninga<bruninga at usna.edu>
> Date: Mon, 27 Feb 2012 16:57:14
> To:<aprssig at tapr.org>
> Subject: Re: [aprssig] Can objects/items dead-reckon?
>
>> If Objects can have a course and speed, is the
>> sending station and/or the receiving stations supposed
>> to dead-reckon the future position of the Object based
>> on that course/speed?
> All APRS clients are supposed to DR all objects and stations on receipt on a
> 1 minute basis.  The display of such a DR should be clearly obvious to even
> the most casual observer.   The way this was done in the original APRSdos is
> to mark the reported position with a DOT or small circle, then draw a DR
> line to the new position and put the Symbol at that location including the
> CSE/SPD header.  The circle (dot) and DR line and symbol and header were all
> shown.  But the SYMBOL was light-blue colored to clearly show that it was a
> DR symbol and not the exact reported position.
>
> If the DR was beyond the edge of the current viewed map, then the DR was not
> shown, but the symbol was shown in a darker gray to show that it was OLD.
>
> HOWEVER, for EVENTS, I also wrote a special version of APRSdos called
> APRSdr.  It's job was to do DR on TRANSMIT for EVENTS which follow a given
> track.  You could place just about any observed runner on the APRSdr map and
> it would DR each such object along the event track.  Anytime a fresh visual
> sighting came in by voice radio, then the OBJECT was selected, moved to its
> new reported position, and the DR was recaulclated to give him a new
> velocity based on the time.
>
> This way, everyone else was seeing all of these 1 minute moving objects as
> if they had their own GPS on them.  Give the LEAD a 9 knot velocity and the
> pack and 8 Kt velocity and tail-end-charlie a 3 kt and it would do a pretty
> good job of letting everyone with an APRS display see the progress of the
> event.
>
>> If so, how long should such dead-reckoning be carried on
>> before the original position/velocity report is considered
>> too stale to continue extrapolating?
> For APRSdos, anything beyond a DAY was assumed irrelevant.  But for a 3 hour
> event, then at the end of the 3 hours.
>
> Some people do not like seeing the long lines of old objects.  But to me, it
> is better to see the long DR line on the map and KNOW that the object is
> stale and by how much, than to see a nice clean object on the map that is an
> hour old but looks the same as if it was 10 secondds old....
>
> We found the APRSdr to be so reliable at showing the movement of the lead
> runner, we never outfitted the lead again with a GPS.  For a marathon, even
> if he falls over dead, then someone else becomes the lead  and he still also
> is running at about 9 knots.  So the moving object LEAD on the map still is
> the best information available at how the event is progressing.
>
> Bob, Wb4APR
>
>
>
>
> Andrew Pavlin, KA2DDO
> Sent from my Verizon Wireless BlackBerry
>
>
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