[aprssig] Dead Reckoning in APRS

[Robert Bruninga]

>>> ve7gdh at rac.ca 06/17/06 10:02 PM >>>
>Bob WB4APR wrote...
>> Those of us that are used to seeing this [dead reckoned]
>>multi-dimensional represetation of the passage of time, 
>>space and distance on each mobile symbol or weather 
>>object feel very blind when we dont have it.
>
>You must be looking at someone else's APRS client

Yes, APRSdos

>I've never had "dead reckoning" so I have never missed 
>it. I do know that if I want to know the time last heard, 
>the bearing and distance, status, course and speed, and 
>height if included, I only have to hover the cursor over it 
>for a fraction of a second. 

Well,  you must be a very busy person.  In our area with
say over 70 mobiles on the map in the local area at any
given time, you must have to do an awful lot of "hovering"
to get the real tactical picture of what is going on.  I prefer
to see in an instant, at a glance, the entire picture.

- Active mobiles w msg capability less than 1 m old are WHITE 
- Active Trackers less than 1m old are GRAY
- Any mobile more than a  minute old is light blue
- Any mobile that has not been heard for a while will
   start to show a line between his last reported position
   (a circle) and his current estimated position
- Any mobile more than 80 minutes old is an almost
  inperceptible dark gray

>If I want a graphical representation of the direction, I can 
>double-click on it and see the station details. 

APRS was designed for emergency use to facilitate
communications and maintaining the local tactical
situation to all viewers.  I cannot imagine trying to
use a system that required the operator to click on 
each of say 250 objects (the Wash DC area) on the 
map to see the most important attributes necessary for
maintaning tactical situational awareness.

>From your earlier description of dead reckoning in 
>APRSdos, it sounds like it is well implemented. 
>Dead reckoning must work well IF the road is 
>straight and there aren't any intersections. 

I fear you are still missinterpreting what "dead reckoning"
means in APRS.  It is not and never was an intention
to display a "position".  I say again, the display is to show
to the casual observer (without clicking) the passage
of time and distance since that station was last heard.

>Again, I only have to hover over a station to see when 
>last heard.

Abd I say, APRS viewers should be able to see at-a-glance
the tactical situation without having to click around
on the map.  

I designed APRS with all of the tactical display fundamentals 
that exist in some of the most modern military combat 
systems.  I served 20 years as a communication/combat 
system engineer in the Navy and my last 3 years were as 
the US Navy's "Senior Combat System Insepctor" for all new 
construction ships.  In that capacity, I was responsible
for thoroughly testing the combat system and accepting
or faulting the combat system on all new construction
Aircraft Carriers, AEGIS class Cruisers and DD-51
class destroyers.

Believe me, the Navy knows how to present real-time
information (including ambiguity), latency and all manner
of attributes, and it does not require the operator to
go around clicking on the hundreds of targets that may
be attacking him.

APRS provides for all these capabilities to display in
real-time, all the information the viewers need to see
to be able to fully comprehend the tacctical situation
at a glance.  It is too bad that many APRS clients 
other than the original left out many of these features.

Be careful about comparing arm-chair casual APRS observing
with what it was designed for, and that is tactical real-time
display for busy operators with other communications
responsibilities while operating under stress.

de Wb4APR, Bob


 I know I have the expire time set for 
60 minutes (at least on the machine I'm on right now) so I know that no 
station is older than that. I have on occasion set it to for a longer 
period, but a week??? When was the last time you saw someone set their 
expire time for a week?

> Though at least most programs fade them to gray after the
> recommended 80 minutes I hope.

The program that I use fades them to grey when the expire time has been 
reached. A minute later, the expired station disappears. If I was tracking 
the station (UI-Route or UIHeightTrack) the track will remain on the screen 
even after the station has expired.

73 es cul - Keith VE7GDH
--
"I may be lost, but I know exactly where I am!" 


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