FlightAware Discussions

Coverage Graph Question


#1

Hi,

I was wondering why for example if I see my history of positions in Flightfeeder Skyview I might have like 1,000 positions in less than a minute (depending on time of the day of course) but for example if I watch the positions table by day or the coverage graph of the last 24 hours in the stats page, there will be much less positions reported.

What causes this??


#2

Not all messages carry position information, the stats page only shows messages with positions, iirc


#3

Yes the stats page only shows messages with positions.

In SkyView it also makes the distinction. There is a messages/per second (including all kind of messages) but there is also a position messages history.


#4

That counter is deeply flawed. It is more for counting all points in the polygon lines which make up the tracks.
If you change the altitude by 25ft for example the javascript logic starts drawing a new line segment adding two positions.

Apart from that the FlightAware stats page only counts 1 position per 10 seconds per plane.
If you get more positions i don’t think you get credit.

Because yes you are correct the actual number of positions received (dump1090-fa has stats for that if you access pi/dump1090-fa/stats.json for example) then those are much higher.

For example i’m getting around 70 positions per second right now as i can see in my graphs.
That’s 70*3600 = 252 000 positions per hour.

But i only get around 15 000 positions per hour on the FA stats.
So maybe it’s every 15 seconds or something that you get credit for a plane position.
Not sure.


#5

TBH it was added more as a debug thing to make sure it’d eventually reach a steady state and not leak points, and then it stuck…

The logic for this starts around here: https://github.com/flightaware/dump1090/blob/9c124b3f2b3cd421148766457e56bb7d4a8a114e/net_io.c#L2149


#6

we are probably on the ground, increase the update rate
Below 10000 feet, emit up to every 5s when changing, 10s otherwise.
Above 10000 feet, emit up to every 10s when changing, 30s otherwise.


#7

I get the impression whoever wrote that logic didn’t like Javascript and web development very much :slight_smile:

Anyway i know that the counter isn’t meant to be a position counter, people just perceive it that way sometimes.

So i should rephrase:
That counter is mostly unrelated to the number of positions being received.


#8

Thanks for the info, so nothing to do with positions.