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[aprssig] Position Ambituity in APRS!

Curt, WE7U archer at eskimo.com
Tue Jan 8 17:16:30 UTC 2008


On Tue, 8 Jan 2008, Steve Dimse wrote:

> You do not have the ability to place the
> center anywhere you want, just in the center of pre-defined polygons,
> with predetermined radii. (And sorry Curt, my extreme nitpicking
> suggests the linear projection of these polygons is never a rectangle.
> For ambiguities that do not cross the poles or equator (the only case
> allowed by the protocol), the border away from the equator is shorter
> than border towards the equator, making it a trapezoid. Though they
> can't be represented by the APRS implementation, ambiguities that
> cross the equator would be hexagons, and the interesting polar case is
> left as an exercise for the reader!)

Saw your correction right after this calling them a trapezoid.
Trapezoids are correct - For some projections.  They'd be trapezoids
with slightly curved sides (which I'm sure goes against the
_mathematical_ definition of trapezoids, but who cares!).

For unprojected lat/long, they're rectangles, even at the polar
regiions (weird huh?).  Not that any of this matters much to the
current discussion about ambiguity.  hi hi

--
Curt, WE7U: <www.eskimo.com/~archer/>     XASTIR: <www.xastir.org>
  "Lotto:  A tax on people who are bad at math." -- unknown
"Windows:  Microsoft's tax on computer illiterates." -- WE7U
The world DOES revolve around me:  I picked the coordinate system!




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