[aprssig] Position Ambituity in APRS!

J. Lance Cotton joe at lightningflash.net
Tue Jan 8 14:27:59 EST 2008

on 1/8/2008 12:24 PM Robert Bruninga said the following:
> 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.

It's not that it's a "box" that implies a precise boundary -- it's the LINE 
drawn that implies a boundary. Lines have been implying boundaries for a 
very long time, whether they are straight or curved.

It's nice that APRSdos wants to show ambiguity with a circle, but I disagree 
that a line curved into a circle implies anything different that a line 
formed into a box *ON THE FACE OF IT*. Now, since you say the amb. circle is 
a representation of something not known, that is fine as it is documented. 
However, you could have just as easily had APRSdos draw a box and defined 
the box as the representation of ambiguity. If it's just a representation, 
it doesn't matter what the exact shape is, right?

Ideally, I guess, an ambiguity should be represented by a shading gradient 
shape rather than some shape with sharp boundaries. A shape of any kind with 
sharp boundaries will always imply (on the face) a reality with sharp 

(Yes, I know a gradient shape would be difficult if not impossible to 
implement in 16-bit GWBASIC that is the basis for APRSdos. I am not faulting 
Bob on the limitations of the programmign environment. But Bob, wouldn't it 
be more constructive to encourage authors of other APRS clients to overcome 
the limitations in APRSdos graphics rather than insisting that if it's not 
done like APRSdos it's wrong?)

-Lance KJ5O

> 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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J. Lance Cotton, KJ5O
joe at lightningflash.net
Three Step Plan: 1. Take over the world. 2. Get a lot of cookies. 3. Eat the 

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