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

Robert Bruninga bruninga at usna.edu
Tue Jun 6 17:30:54 UTC 2006


I took a fresh look at FINDU to see how APRS position ambiguity
could best be displayed and I noticed that GOOGLE satellite 
maps already do something like this when they dont have enough 
map resolution.  It pops up a sign that says:

"We are sorry, but we don't have imagery 
  at this zoom level  for this region"

I would suggest that FINDU do the same thing when the zoom 
level is too great for meanningful representation of the
ambiguous object.  In fact, I would suggest that FINDU should
display a graphic in place of the map that looks like this:
Hope this comes across...

 | "We are sorry but you are trying to zoom below the     |
 |  point where the map resolution exceeds the precision |
 |  of the ambiguity of the transmitted object.   Zooming  |
 |  further would imply greater precision to the object       |
 |  than is being transmitted by the sender.                       |
 |                                                                                         |
 |  "APRS positions and objects can be transmitted with    |
 |  5 different levels of precision depending on how well    |
 |  the sender defines the actual position.  The levels are  |
 |                                                                                          |
 |     DDMM.HH   - to the nearest 60 feet                            |
 |     DDMM.H_   -  to the nearest .1 mile                             |
 |     DDMM.__   -  to the nearest one mile                          |
 |     DDM_.__    -  to the nearest 10 miles                          |
 |     DD___.__  -   to the nearest 60 miles                          |
 |                                                                                          |
 |  Zoom back out to see the display the sender intended  |

I notice that streets do not show up above the 4 mile range 
scale on Google, so I'd suggest these thresholds:
For .1 mile ambiguity, switch at the 1 mile Range
For  1 mile ambiguity, switch at the 8 mile Range
For  10 mile ambiguity, switch at the 32 mile Range
For   60 mile ambiguity, switch at the 256 mile Range

I would hope that this simple fix would be relatively
easy to implement.  And while you are at it, add the
RANGE SCALE on a line just above the maps.  I assume
that you can easily compute this from the map's zoom 
factor so that FINDU maps present this standard APRS 
display metric to the user like other software  does.

The range scales  dont have to be power's of two like the 
prefered APRS standard, but just whatever they compute
to be is fine.

I think that having range scale information on the display
 would make FINDU maps much more user friendly for
people viewing areas they are not familiar with.


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