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[aprssig] Re: TIGER maps what-s the problem?

Robert Bruninga bruninga at usna.edu
Fri Jun 16 20:44:05 UTC 2006


>>> jdw at eng.uah.edu 06/16/06 2:23 PM >>>
>> Yes!... and that is why APRSdos automatically assigns ambiguity in
>> EVERY transmitted position based on the scale of the map in use
>> by the initiator of position information.
>
>This is nonsense.  If I know my position and enter coordinates, 
>the scale of the map  I'm viewing when I enter or transmit the 
>data has   absolutely _nothing_ repeat NOTHING to do with 
>the accuracy of those  coordinates.

Please re-read my post.  That sentence applies to a position placed
on the map by the location of the *cursor*... that is, by eyeball.
If you "enter coordinates" then it takes the number of digits
you enter.  No more, and no less.  If you only enter DEGREES,
then APRSdos transmits your position with 60 mile ambiguity.
If you enter only degrees and minutes, then it transmits your position
with 1 mile ambituity, and so forth on down to the 60' precision
APRS standard.

>The scale at which I'm viewing the map is also completely 
>unrelated to  the accuracy of that map data.

It is, if you are using that view for the placement of an object
on the map by eyeball.

>> 13)  Initial capture 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  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.  

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 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.

And my BIGGEST reason 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 trackable cigarette pack (and doesnt even need to see
the SKY!)...

Bob, WB4APR





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