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[aprssig] USNS and APRS

Robert Bruninga bruninga at usna.edu
Mon Jun 1 13:00:27 UTC 2009

> Let's say that I use the B0 format to specify 10 discrete 
> positions.  Let's say 100 people show up to my event.  Does 
> the software dither the positions slightly, or does everyone 
> at a particular location "stack up" on top of one another?

In a proper APRS system, each of those positions will have a
position ambiguity appropriate to the application.  If the
ambiguity is .1 mile, then a proper APRS implementation will
plot them all within about .1 mile of the indicated position
randomly with the indication of ".1" mile ambiguity so they will
all be splattered around the position so that they are all more
or less distinguishible.

However, most follow-on APRS systems did not implement any of
the original "position ambiguity" display features and so in
those simplistic systems, they will all stack andyou will only
see the top one.

Good luck.

Bob, WB4aPR

> Wes
> On Mon, Jun 1, 2009 at 06:02, Bob Bruninga <bruninga at usna.edu>
> 	>Bob, any thoughts on using USNG with APRSTT?
> 	The beauty of APRStt is that it is a LOCAL system, 
> SIMPLEX rnage only from the sender.  Thus, each APRStt is set 
> up to match the needs of its users (usually one club) and 
> this is independent of how APRStt might be used somewhere
> 	And APRStt can use any grid system, lat/long, SAR 
> GRIDS, Mile marks, and even flea-market spaces at Dayton.  
> And any one APRStt can support many of these at the same time 
> if needed.
> 	At our first system in Dayton, we defined the position 
> format to be Bxy*  Just one digit in X and one digit in Y.  
> But the spec has always said there would be xxyy, xxxyyy, 
> xxxxyyyy versions for greater precision, or greater coverage
> 	So after dayton, we formalized this as follows.  There 
> are 10 possible Position formats that can be implemented in 
> any instance.  In most cases, only the one that is applicable 
> at any parcicular APRStt will be used.  But that does not 
> prevent the engine from accepting more than one if needed.  
> Here are their definitions:
> 	B0x*        One of 10 special positions
> 	B1xy*       1 digit XY  ( 10 mi in 60 mi area) (default)
> 	                      (or 1 mi in 10 mi area)
> 	                      (or.1 mi in  1 mi area)
> 	B2xxyy*     2 digit XY   ( 1 mi in 60 mi area) (default)
> 	                     (or .1 mi in 10 mi area)
> 	                     (or 60 ft in  1 mi area)
> 	B3xxxyyy*   3 digit XY  ( .1 mi in 60 mi area) (default)
> 	                     (or 60 ft in 10 mi area)
> 	B4xxxxyyyy* 4 digit XY  ( 60 ft in 60 mi area) (default)
> 	B5zzzmm*    at bearing zzz range mm miles
> 	B6EEENNN*   SAR UTM Grid - Easting and Northing
> 	B7RRRMMM*   Road RRR, Milemark MMM
> 	B8......*   Table interpolation
> 	B9...   *   TBD
> 	What we used at Dayton is now B1xy*.  This added digit 
> also is kind of a redundant check to make sure the proper 
> number of digits has been received for a given posit.
> 	Back to the original question,  So what each XY grid 
> represents and how much precision is independent of whether 
> it is UTM or LAT/LONG or USNS.  That is established at se-up 
> time at that location.
> 	Again, dont panic at all the options.  Usually, only 
> one format will be used in a given applcation depending on 
> the area covered and the degree of precision desired.  At 
> Dayton, we only used B1xy*.  At the 2010 Scout Jamboree, we 
> will use B2xxyy* because the published map that will be in 
> the hands of every scouter will have an XX YY grid already on
> 	Hope that helps
> 	Bob, Wb4APR
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> -- 
> Wes
> ---
> Where there's silence, there is no Hope.

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