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[aprssig] APRS DF reporting

Robert Bruninga bruninga at usna.edu
Wed Nov 22 19:07:25 UTC 2006

>>> I disagree, it is a very improtant issue.  
>>> Bearing lines have an estimated length relative 
>>> to the knowledge of the person doing the bearing 
>>> line.  That information must be included in 
> ... I disagree.  The COSPAS/SARSAT hit gave a false
> impression of where the search area should be, and 
> all of our a priori assumptions were wrong.  
> I think I'd prefer to start with a generous
> estimate of the maximum possible range and use that.  

I think we are in violent agreement.  In the example you quote,
seeing that all the bearing linnes were not converging in your
original estimated range is exactly what APRS should have shown.
It would have been obvious that your initial assumptions were
wrong and so simply extend the range parameter.

A case of a wrong assupmption does not negate the value of
having an initial assumption in the first place.

> Ultimately, it should be up to the client software to limit 
> the length of DF lines.  

Yes, the SENDING stations software, so that the recepients all
see the *assumptions* under which the SENDER is searching...

> ....  Still, I don't think it's ever safe to guess at 
> the range.  I've been on t-hunts where the transmitter 
> was a tiny unit buried underground...

I'm not saying anything about "guessing".  I am saying the
searcher with the DF unit that is putting information onto APRS
has some "knowledge" about the area where he is searching,
either the terrain, or the scope of the search, or his
intuition.  But *he* is still the -best_ source of estimated
bearing line length and that "knowledge" should be included in
the bearing line packet.  That is why APRS includes the DF range
in the format.

If he is totally clueless, then he is well within his knowledge
to put 500 miles if he wants.  I'm just saying that if the
information is known, then it should be in there.  If it is NOT
known, then the sender still makes that choice.

We do not want RECEIVEING plots to show anything other than what
the sender intended...  Ever...


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