When I view Skyview map the accuracy seems very good. I live on a Heathrow flightpath and they pass overhead around 8000 feet or 2400m, when I expect them to pass overhead they do. My data is not being transferred live as my tuner is receiving it so how are the mapping systems from FR24 and adsbX so accurate? What data are they using?
Geoff
Yours. But it takes time to save that to a data packet confirmed not dud data. Then upload and store in a database. collate and translate the data (from a number of sources). Then make a plotable position. Then send that to a web server, then distribution to cdns
All up you end up with about 3-4sec lag on fr24
But my ‘stats’ page is not showing feeder check in every few seconds, sometimes it’ll go a couple of minutes. That is what is puzzling me.
Appreciate flight plans are submitted so within reason planned route is known and positions anticipated. I understand dump1090 is continuously passing data but I don’t think data is being fed continuously.
Geoff
I can’t speak for fa. And likely neither will they citing commercial sensitivity
But fr24 validate beforehand.
If you monitor the raw stream logs from fr, you can see it send x aircraft every few seconds.
Aircraft also send ~2 messages a second. So there is not continual/small delays from the get go. But a connection to the servers is established full time. And data sent down it as it so chooses. And if udp. It doesn’t rely on acknowledgement it was received. It’s just pushed.
Also, fr24s stat servers are totally separate from inbound feed severs. I expect everyone’s are.
Interesting, not really thought too deeply about it but out of curiosity I shall monitor the data more closely.
Pi Zero dedicated to adsb so may install ntopng - may need to use my Pi3 for that perhaps.
Geoff
Short answer is that we don’t update the stats database which backs the stats page on every message. Stats is a separate processing path to the main data path.
Aircraft transmission to API delivery (e.g. Firehose) latency is typically << 10 seconds and usually more like 3-5 seconds. Some of this is a small deliberate delay that we introduce to wait for additional data from other receivers to arrive.
An individual receiver might only be reporting a position every, say, 10 seconds; but when we have many receivers seeing the same aircraft, that means that on average we get frequent updates. The reported data is also the most up to date at the time of report, so even with a single receiver we still get low-latency data – just not as often.
I can say that FR24 positioning is a little behind my own map. An Aircraft at high elevation and speed it can be up to 2 km.
However FR24 seem to use a kind of smoothing to make sure the aircraft on the map are not jerking
Thank you for clarification. So much happens transparently with computers it is nice to understand, albeit vaguely, what actually occurs.
Geoff
Part of the reason I turn estimations off.
Yep. At x rate and x direction every * second. Position likely to be calculated as x. Corrected on next confirmation packet.
So you get little dances and so on if zoomed right in.
Uh, there is a setting? Using it for years now and never seen it 
Anyways i use it primarily only for additional data request.
Settings, visibility, estimations.
It has a 240 min time max so can go crazy
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