[aprssig] Position Ambituity in APRS!

Jason KG4WSV kg4wsv at gmail.com
Tue Jan 8 11:44:22 EST 2008

On Jan 8, 2008 9:58 AM, Robert Bruninga <bruninga at usna.edu> wrote:

> Partly right.  Because the uncertainty is not a precise polygon;
> it is a lack of additional precision.  It is an uncertanty of
> the number of digits of precision by the sender, and an EXACT
> transfer of that same uncertany to the recepient.

So it's not precise, but it is exact. I'll have to think about that one.
Maybe it depends on what my definition of is is?

The position ambiguity as implemented in APRS has an upper bound, and that
bound is _known_ and _precise_.  Out here in the real world, that bound is
(very nearly, sorry Steve) a rectangle due to the nature of the coordinate
system in use.  It's nowhere close to a circle.

It may not fit with the reality of some APRS implementations
> that took the simplistic approach of truncating digits,

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."

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