Order Tray | Contact Us | Home | SIG Lists

[aprssig] APRS return to basics (DR) (fade-to-gray)

Bob Bruninga bruninga at usna.edu
Thu May 24 18:33:16 UTC 2012

> In my area, I find a large number of "hanging" DR's, 
> because a mobile didn't send a final (with speed=0)
> ... I have hanging DR's all over my map most of the time.
> I'm not sure what to do about this problem, 

Yes!  Great observation!  To coin a phrase, The truth hurts, <GRIN>.  

All of those stations were still moving at the time of that last
transmission so they are not there anyway. 

All of those "problems" are not really problems, but are in-your-face
indicators not only of every ICON that is no longer where the guy actually
is but also a representation of how long ago that was.  When the map is
covered with them, isn't it nice to know all those posits are useless
anyway.  At least with DR on, you can instantly see which stations are old
and no-longer-valid.

> Any ideas?

One is to do what many APRS newbee's do and ignore the truth, turn off DR,
and have a nice pretty map with mostly wrong display of various
points-in-time of minutes, hours, or days ago and not know it without
clicking on every one of them.

The other is to do like the original APRS, that is, adjust the fade-to-gray
time from the standard default of 80 minutes down to as short as a few
minutes and then anything that had a DR position more than a few minutes old
would "fade-to-gray".  Then all you would see are the currently active
stations with current info, still DR'd, but only a few minutes old..  All
the others would be faded-to-gray.

BUT!  to make sure that no one was ever mislead by seeing old icons (and
forgetting that he had changed the fade-to-gray from the default), then the
fade-to-gray itself would age itself back to the default if the operator
never did anything for the same time period.  Thus if he came back to his
map 30 minutes later, then all the DR's would all be back again showing
movement up to 30 minutes old, and anything older would fade-to-gray.  So
again, he would never be mislead by old icons (by forgetting his
fade-to-gray setting (which controls how much of the DR you see).  And,
again, he could adjust fade-to-gray back to what he wanted to see.

A fade-to-gray of zero is the same as no DR.  But no mobile over a minute
old would appear.  If I was still actively programming, I would implement it
this way:
1) The fade-to-black (inactive) would still default to the 80 minute
standard for ALL symbols, fixed and moving.  These stations are assumed to
be not on line (the 30 minute fixed stations had two chances to be seen, and
the mobiles much more.  Also all the stations via satellites or ISS would
definitely be faded and ready for the next pass.

2) The fade-to-gray would default to 10 minutes.  This would gray out most
of the older longer "zoomers" and clean up the map, but still reveal those
active up till 10 minutes ago. (actually 11 minutes to give 2 chances to
hear a 5m mobile).

3) The operator can dial the fade-to-gray all the way back down to 1 minute
or even zero to eliminate all but the most recent mobiles.  But as time
moves on from that adjustment, then so does the fade-to-gray grow back to
its default.  Thus making sure the operator away from his screen is never
left blind to the best estimates on moving stations.

Navy consoles had a similar function on an analog knob that you could adjust
the length of the DR display even into future time to see where everyone
might be at some time in the future.

DR Really adds the 4th, 5th and 6th dimensions of time, course and speed to
otherwise relative flat, not moving and mostly stagnant displays.


> ------Original Message------
> From: Bob Bruninga
> To: aprssig at tapr.org
> Sent: May 24, 2012 9:32 AM
> Subject: Re: [aprssig] APRS return to basics (DR) (new images)
>> I've never used a system that used dead reckoning,
>> but I don't think I would like the feature.
> That's what they said about the telephone, the car, the telegraph and
> facebook.  It also shows why I had asked all authors to have DR enabled by
> default.  SO that people would get a taste of what real-time tactical
> awareness really looks like when they came into APRS.  If it got too
> they could turn it off.  But if it is messy, then it is really telling you
> something important about the latency of your data!  Hiding it is hiding
> that important element.
> Again,  DR is fundamental to all military and aviation and other tracking
> systems.  If something is moving then it has FOUR dimensions.  LAT, LONG,
> COURSE and SPEED.  TO ignore CSE and SPD in the display is like looking at
> Black and white TV and it hides the age of the position.
>> but my feeling is that I would rather know what is fact...
> The last known position is always clearly shown with the circle and the
> line.  The length of the line from that last known position to the
> DR'ed position shows the passage of time and the age of the "fact".
>> if they kept moving, completely missing the next bend in the road...
> A symbol DR'd at 70 MPH off the interstate because the road turned still
> conveys exactly the same information.  He is that far along his route.
> Looking at the map you can easily see where the road went with him still
> it and can visualize where he is.  If the DR is very long, such as 5 or 10
> miles, then clearly he can be 5 or 10 miles from that last known position
> and so its "factual" value is vanishing to practically nothing.
> In fact at 60 MPH, the error in that "fact" is more than a mile off after
> even just a minute.  Hence, the DR'ed position is always more factual than
> the old stamp on the road just getting older and older.
> Bob, WB4APR

More information about the aprssig mailing list