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[aprssig] Position Ambituity in APRS!

Robert Bruninga bruninga at usna.edu
Tue Jan 8 18:11:53 UTC 2008


>> So, think of ambiguity as representing 
>> a circle, taking the center of the polygon 
>> described by the lowest and highest values of 
>> the missing digits, and with the radius of 
>> the magnitude of the missing digits.
> 
> Yes.  This would have made very good sense 
> in the protocol.  

It is EXACTLY how APRSdos did it originally, but remember in
putting together the APRS SPEC, the follow-on authors refused to
allow ANYHING in the spec to tell them HOW to display anything
in APRS.

This was the fiercest battle.  I wanted the APRS spec to promote
COMMON display techingues for the same data to avoid these kinds
of end user confusion.  All other authors insisted on no RECEIVE
or DISPLAY standards  so they could display things anyway they
wanted.  I was on record as adamantly opposed to this kind of
tower of Babble in APRS.

But the only way to get a spec out was to agree to the lowest
common denominator and that was only what is TRANSMITTED.
Therefore the spec (except where I could sneak it in) has very
little to do with reception.  That is why different users of
different clients now see quite different things...  This is one
of my biggest frustrations with the state of APRS today.

Oh well.  Spilt milk..

> Perhaps with with the addition of random 
> placement of the center for those people 
> that actually have an accurate positional 
> sensor but don't want to convey their exact 
> location.  Kill two birds with one stone.

Yep, That is what APRSdos does and what I wanted all along for
all displays.  I just wish all authors would implement it that
way or something similar.
The Xastir approach is similar and quite acceptible.

But the important thing is to at least display ambiguity
unequivocably to the user.  There are still many applications
that ignore position ambiguity and plot it precisely no matter
how imprecise it is.

That is bad for APRS integrity.

Bob, WB4APR





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