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[aprssig] Local Repeater Freq Object Ambiguity.

Jason Winningham jdw at eng.uah.edu
Thu Feb 1 17:27:03 UTC 2007


On Feb 1, 2007, at 9:59 AM, Robert Bruninga wrote:

> That is precisely what bothers me about some displays.  To say
> that AMBIGUITY must be displayed precisely!

Instead of the arbitrary term ambiguity, use a more correct term like  
uncertainty.  "Over there" or "up yonder" is ambiguous; 34 45.67N 87  
54.32W is assumed to be precise to plus or minus .005 minutes of  
uncertainty (else it would have rounded to something else).

Coordinates are discrete values, be those discrete units be degrees  
or hundredths of a minute, that indicate opposite corners of  
_rectangular_ area.  The uncertainty associated with these discrete  
values also delineates a rectangular area.  Not an ellipse, or  
circle, or anything else - a _rectangle_.  (Yes, I'm ignoring the  
fact that the planet in question is more or less but not quite  
spherical; I'm talking about our typical flat 2D representation of  
its surface.)

> In my opinion it shouldn't.  I prefer a consistent "circle" (or
> elipse) to imply ambiguity.

Then you're displaying incorrect information.  If a position were  
inside that ellipse but outside the rectangle that the coordinate  
uncertainty indicates, the actual coordinates would be _different_.   
Any indication of position outside that rectangle is _wrong_ because  
it contradicts the information provided.

-Jason
kg4wsv






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