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[aprssig] APRS Leaders and Dead Reckoning on APRS.FI

Heikki Hannikainen hessu at hes.iki.fi
Fri May 25 07:51:47 UTC 2012

On Thu, 24 May 2012, Bob Bruninga wrote:

> Wow, I never noticed it before.  I guess because you have to have a station
> selected to see it.

Yeah, it gets enabled if you highlight a station by clicking it, or if you 
look up a station by entering it's callsign.

>  I am usually looking at the big picture and see all
> these mobile symbols (with no idea their age other than the [show last XXX]
> history selection box.   I guess it would be too data intensive to expect
> all moving mobiles to show it.  But maybe only those less than 10 minutes
> old?

Maybe, I'll have to try at some point when I have time. The DR line is a 
recent addition, and I wanted to introduce it in small steps.

> I wonder how long it DR's until it gives up waiting for a new posit and just
> goes back to the misleading non-DR indication?

1800 seconds currently. I picked a largish number to support balloon 
missions, but it would be nice to have this easily tunable by the user.

It's not misleading, it's just the latest factual information that has 
been received, and users don't have any problem understanding that.

I'd also like to have separate time range selectors for:
- the track line (show track line points newer than 15 minutes)
- the station itself (show the current position of a station if it has 
transmitted within 6 hours)

The track line's existence would then also indicate that the station has 
been recently moving. In tactical use you're mostly interested in the 
positions of the stations, even if they haven't moved (or transmitted) for 
a very long time, but currently selecting a long time range clutters up 
the display a lot with old track lines.

> If I have my [show-last 1 hour] selscted, I wonder if it would be possible
> to use track-history colors to show age?  Then all the histories that are
> more than say 10 miuntes old could be GRAY and only those 1 minute or less
> old could be RED, those 2 minutes or so orange, those 3 minutes old as
> yellow, and 5 minutes old blue, and older than 10 minuets gray.

To make the track lines readable some colors are already used for tracks 
of different stations, so I'll have to try to keep a distinction between 
that and indication of the age. Variable translucency is also available as 
one method.

A single line passing via multiple points in the Google Maps API has a 
single color attribute, so if I need to switch the color of the line in 
the middle, I'll have to draw multiple lines to create the segments in 
different colors. The speed of the maps interface depends greatly on the 
amount of things drawn on the map, so it might have a performance impact, 
especially on slow browsers and devices. We'll see.

For flying things it'd be nice to indicate the altitude with color. That's 
another selector for the user to worry about.

   - Hessu

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