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[aprssig] APRS return to basics (DR)

Bob Bruninga bruninga at usna.edu
Sun May 20 21:06:54 UTC 2012


Dead dogs on the road.

I always look forward to the APRS travel day to Dayton, but get so frustrated that it is nothing like it was 15 years ago before we got swamped with fixed ICONS instead of moving symbols.  Now we just have these ICONS on maps that have no CSE/SPD headers and that do not move, no matter how old they are, like dead dogs on the highway.

I was using a client with full color APRS symbols and perfect maps and found it was practically useless to find someone while moving.  You see a callsign come into view and don't know if is there now, or something left from 3 hours ago!  You pass the spot on the road and it is like every other spot on the road, nothing there... 

The original APRS dead-reckoned (DR'ed) all symbols.  That is, if they were moving when they transmitted then APRS moved it on receipt until updated.  It gave REAL-TIME knowledge as to what was happening, not some pretty map with 90% of all info not only out-of-date, but not even indicating what is fresh and what is old dogs...  

Back with the original APRS, If someone was 1/4 mile ahead of you, then his SYMBOL kept moving on your display the same 1/4 mile ahead of you (though still dragging an anchor line back to a tiny circle showing when that was updated).  This was a fundamental concept of APRS that went out the window when we started just slapping fixed ICONS on windows or google maps.

I know some software has dead reckoning, so I am not complaining about them, but if you are not seeing everything MOVING on your display, then you are not seeing LIVE APRS.  I guess I am going to look deeper at what clients bypassed this fundamental part of APRS.

Im thinking of a new way to suggest implementation.  That is, maybe only DR for 10 minutes, and paint a DR'd symbol a light blue.  If the position (which had CSE and SPD) has not updated in 10 minutes (2 attempts for a 5 minute commuter) then his symbol changes to GREY, and no longer a full color symbol and is not DR'd..  As usual, if it is older than 80 minutes, then it should disappear unless called for.

This will make it instantly visible what is really happening on APRS with respect to moving stations. But the color, and the anchor circle and line back to last reported position gives no one a false impression of where someone was last reported and how much time has elapsed since that knowledge was true.

We MUST make sure that all software at least has CSE/SPD leaders (showing the direction and speed).  The length of the leader is proportional to the log of speed so that 600 MPH aircraft have about a 2" leader and someone walking at 3 MPH has a leader at least as wide as his symbol.

I need to go check the COMPATIBILITY tables and make sure that all APRS clients do have leaders and DR.  If not, expect to hear from me.

Bob, WB4APR



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