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[aprssig] Vicinity Plotting in the original APRS

Robert Bruninga bruninga at usna.edu
Fri Jun 16 20:54:09 UTC 2006


>> 13)  Vicinity Plotting of first packet from a station and tentative
>> plotting in vicinity of his first digi so that he is known to 
>> the system until an eventual posit packet comes in.
>
>Plotting a position on the map when you have no idea where 
>the station is (as defined by an actual position report) is 
>located doesn't make  sense. 

Making a vicinity plot was designed into the original APRS and makes 
perfect sense to me for several reasons:

1) Its better than many programs that completely IGNORE the 
    existence of a station until it gets a position.  This violates the
    principle of least astonishment in a system that is supposed to
    be tactical and keep everyone aware of what is going on...

2) The sotware has a very good idea where the station is by
    simply looking at the first digi in the path.

3) You probably have not see an APRSdos vicinity plot or you would
   know that it does not plot an ICON.  It only plots a VICINITY symbol
   randomly within 1 mile of the digi that it heard it from.  And NO callsign
   is shown, unless the viewer clicks on the sumbol, or does a FIND
   on the callsign.  The intent here is not the map view, but to accept
   the station into the system with the best position avaiable as soon
   as he is heard the first time.

In either case, there is no missrepresentation of the persons position
when it is assigned a "vicinity plot".  BUT, the station is entered 
completely in the APRS system and all tables.   I consider it a worse
travisty of many popular programs that ignore the presence of 
a station and in fact will not even allow two-way communication 
through an IGate unless a person transmits a valid position first!

> This makes  no sense to me.  Especially given the state of the 
>APRS network and the dumb devices that are digis, you 
>cannot_ be sure which digi heard a packet  first.

That is one of the reasons for the New-N paradigm... so that
all packets are traced, and this includes their first digi.  Most
digis in the USA are now New-N and quite traceable.  If there
is no first digi shown, then no vicinity plot is made...

>This _may_ make a _limited_ amount of sense _if_ you hear 
>the station  direct.

Yep, which is what the first digi *always* does.

>Any data that does not contain positional information doesn't 
>belong on a map, IMO. 

Ah, but the path does indicate the position of the station
transmitting the packet!  It is in the vicinity of the first
digi!

> Imprecision I can deal with, but don't make wild guesses.

1) It is not a wild guess.  It is based on data  included in the packet.
2) It -is- inprecise and  it is CLEARLY displayed that way.
3) The way it is displayed leaves no manner of missinterpretation
    - The position of the vicinty plot is listed as VICINITY PLOT in the Position table
    - The vicinity plot is only so the station can be accepted into the system
    - The symbol on the map is only a special VICINITY PLOT symbol
      (a big question mark) with the callsign suppressed unless clicked
      or searched for.
4) This allows the station to be a full participant in all of the 
wonders of APRS until he is able to update his position with 
his own report.
5) If one searches by callsign, he WILL be in the system,
his position comment will say VICINITY PLOT" and his
location on a map will be a big quesition mark.

It is nice to see a bunch of people at a venue messaging each
other all show up on their first packet in the vicinity of the
local digi and not have to wait 30 minuets to an hour before
some software will even recognize they exist.

And my BIGGEST reason back in 1995 for putting VIcinity Plotting 
in the original APRS was so that I could track a tiny battery powered
tracker (with no GPS to run the batteries down) for over a year
all over the country running on just 4 AA alkaline cells.  WIthout
having to power up the GPS, it only would draw 500 mA for
one scond every 10 minutes and would last a year and fit in
a cigarette pack (and doesnt even need to see the SKY!)...

Yet, with the original APRS, I could track it anywhere in the country
to the nearest 10 miles or so.  At least to know what city or town
it was in.  Again, this capability was left out of so many follow-on
clones.   I was very pleased a few years ago when Steve Dimse
finally added it to FINDU.

Now FINDU can vicinty plot someone too.  It simply displays
the location of the first digi and says "VICINITY PLOT" so
there can be no missinterpretation.

Bob, WB4APR





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