[aprssig] Position Ambituity in APRS!

Robert Bruninga bruninga at usna.edu
Wed Jan 9 12:36:24 EST 2008

>> No, it is preferred to be a circle of the 
>> right ambiguity size centered on approximately 
>> 35N and 83W.  The word "approximately"
>> is because it should be randomized there.  
>> Probably within say half or less of the 
>> radius of ambiguity...
> If you eliminate the "randomized" portion, 
> where would you plot a station that
> gave you 35N and 83W as it's position? 
> 3400.00N and 08300.00W ?

If the guy is saying his best estimate of his position to the
nearest whole degree is at 35N I don't see any reason why you
would suggest plotting him at 34N.  If he says he is at 35N 83W,
then plot him at 35N and 83W with a 60 mile ambiguity circle.

Your software then has to use whatever internal math it needs to
be able to activate the right pixels on the screen.  This
includes offsets, scale, mercator projection distrotion
elimination, etc.  But in my code, the entry for for "35"
degrees is just 35.

Good luck.

> >> So if my APRS packet says 35  .  N\083  .  W,
> >> I could actually be at 3467.85N\08272.45W ?
> >
> > Unfortunately, neither of those is a valid posit.  Minutes
> > only be 00 to 59.  But assuming you meant
> > then yes, the coordinates of  35N and 83W are closest to
> > position.
> Yes, I was thinking in base 100, not 60 when I made up those
> [big snip]
> -- 
> William McKeehan
> http://mckeehan.homeip.net

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