[aprssig] Position Ambituity in APRS!
bruninga at usna.edu
Tue Jan 8 12:53:27 CST 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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