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[aprssig] findu.com Location off by 100 miles.

Robert Bruninga bruninga at usna.edu
Tue Jun 6 02:29:22 UTC 2006


>> That is a failure of the display software to properly display
>> position ambiguity.   Software should never display an ICON
>> at a point other than where the sender intended.
>
>This worked fine for the original AORSdos, but does not translate  
>well into the world of modern internet mapping. For that reason findU  
>translates the spaces [degrees of ambiguity] into zeros 
>[a precise position].

I really wish you could try to fix that.  It violates the integrity of 
APRS for FINDU to be making precise positions to the nearest few feet
for stations, positions, and objects that simply do not have that
kind of precision.  It undermines the whole basis of APRS if the
sender's intent is not displayed to the viewer of *all* APRS systems.

If you cannot draw an ambiguity circle or rectangle, then I suggest
that you simply not allow the ICON of the postion, object, station to 
appear on the map at all below the zoom scale where the transmitted
ambituity is much larger than the present size of the ICON.  If the map
system you are using has to draw something, then draw a big
Question mark in place of the ICON.  Or better, draw a special 
symbol such as  "AMBIGUITY"

This way, there is no violation of APRS integrity and the sender's
intent is maintained to the receiver.   Using the example in the
previous email, it is rediculuous to show a thunderstorm
to the precision of a few feet when zoomed into a neighborhood.

Those objects are intended to be meaningful typically at the county
level or an APRS Range Scale of about 16 miles or so or larger.


> Not an optimum solution, but I've  never heard a single argument 
>I found convincing in favor of position  ambiguity. Either you want 
>people to know where you are or not. 

Not me and not APRS.  APRS wants wants the VIEWER of APRS data 
to see what the *sender* intended.  And often the sender never 
intended to give a  thunderstorm a 60 foot position.   Nor, when he 
manually enters his estimated or approximate position into the keypad 
of the D7, his FD PC or his Mobile does he want FINDU to place him in 
the middle of somone's yard, when in fact, he is only intending to 
transmitting the fact that he is in that neighborhood or in that city
and does not happen to be bothering with a GPS right now.

Hooking up a GPS just to walk around the park is just not worth it
in APRS when all you may need to say is "Im in the park"...
I rarely carry a GPS with my D7, yet I have a pocket card with the
1 mile ambiguity positions of sevaral places I am frequently found
and manually enter them in my D7 when I am visiting there.  SUre
is a lot less hassle than fussing with a GPS all the time.  Yet
people can see where i am.

It is simply a violation of the integrity of APRS to force stations,
positions and objects to exact positions, when the sender never
intended them that way.

>The  most common argument is that people do not want to show 
>their home or  digi position for security reasons. In this case, 
>the best answer is  to pick a location other than the real QTH 
>for the near-but-not-too- near security position and transmit that.

That  really, really compounds the integrity issue.  Sure someone
can do that if they want to, but that is *their* choice.    Such
deciet should not be forced on unsuspecting users simply because
software has not properly implemented the display of the senders
intended precision information.

Please consider just omitting the ambiguous ICONS from FINDU map 
displays whenever the zoom is below a meaningful scale.  Here is where
APRSdos transitions from SYMBOL to the ambiguous circle without any
symbol:

.1 milie  - symbol not shown below the 2 mile range scale
1    mile  -  symbol not shown below the 4 mile range scale
10 mile  -  symbol not shown below the 64 mile range scalse
60 mile  -  symbol not shown below the 256 mile range scale

You may still show the CALL or object NAME to indicate it is in the
area if you want, but not the precise position of an ICON which falsely 
implies precision where precision does not exist.

I am hopeful that with some clever programming that you can figure
out a way to convey position ambiguity on FINDU so that FINDU
remains an honest and acurate display of the sender's intent.

Thanks
Bob, WB4APR


Steve K4HG

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