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[aprssig] Position Ambituity in APRS!

Robert Bruninga bruninga at usna.edu
Tue Jan 8 18:53:27 UTC 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
mile.

> 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.

Bob, WB4APR





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