[aprssig] Position Ambituity in APRS!

Robert Bruninga bruninga at usna.edu
Tue Jan 8 13:53:27 EST 2008

> yeah, those jokers stuck to the spec. Rev G of the spec says:
> "Where the exact position is not known, the mm 
> and hh digits in the latitude and longitude may 
> be progressively replaced by a V (space) character 
> as the amount of imprecision increases."

Exactly.  And since a Degree of latitude is 60 miles and a
minute of latitude is 1 mile, then the degree of ambiguity
conveyed for these four cases is 60, 10, 1 and 0.1 nautical

> a rectangle due to the nature of the coordinate 
> system in use.  It's nowhere close to a circle. 

Sorry, it is a circle in the original APRSdos and any other map
projection that does not have the simplistic mercator projection
distortions.  A mile is a mile no matter where you are on the
earth.  And ambiguity was intended to imply those circles.

I agree that the wording of the spec can be interpreted as a box
of LAT/Long with different sizes all over the earth, but that
interpretation would be a poor choice for a standard.  Hence I
have always tried to make everyone understand that these were
always intended to be circles of ambiguity relative to the
number of digits of precision available in the latitude.


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