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[aprssig] Position Ambituity in APRS!

Robert Bruninga bruninga at usna.edu
Tue Jan 8 18:24:06 UTC 2008


I still don't like polygons.  These Boxes drawn exactly on a
LAT/LONG grid imply a precise boundary of ambiguity which is
totally missleading and of drastically differrent sizes from the
eauator to the poles.  They just convey the wrong information
completely.

I like the original APRSdos circles whos radius approximates the
degree of ambiguity.  This completely eliminates any distortion
no matter where on the planet they occur.

Bob WB4APR
 

> -----Original Message-----
> From: aprssig-bounces at lists.tapr.org 
> [mailto:aprssig-bounces at lists.tapr.org] On Behalf Of Curt,
WE7U
> Sent: Tuesday, January 08, 2008 12:17 PM
> To: TAPR APRS Mailing List
> Subject: Re: [aprssig] Position Ambituity in APRS!
> 
> 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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