ADS-B shared data


#1

Curious as to how ADS-B data is distributed and shared.

Appreciate the FA site says data may be delayed by 30 seconds or more but am wondering; do FA and Flightradar24 use the same data sources? Reason I ask is that Flightradar24 appears to be real time whereas FA is definitely delayed - unless of course viewing Skyview on my own R-pi.

This discrepancy came to light when I was speaking to a friend in US (I am in UK) and telling her when aircraft would pass overhead, the FA map was too delayed for this to be accurate whereas FR24 appeared to be real time.

Not an issue, just curious.

Geffers


#2

I never checked against FA, but I did notice that FR24 is delayed compared to Planefinder. Whether it’s deliberate, or just the way their web server flows, I don’t know.


#3

If you have the US/Canada Radar (Live) option turned on in FR24, then that may explain the delay. Unless things have changed, the data from the FAA has a deliberate time delay.


#4

I don’t remember if the US/Canada Radar was on or off at the time, but my observations were made while tracking my son’s flights across Europe. Nothing scientific.

Planefinder was consistently ‘more’ real time, and the updates seemed more frequent than FR24. Also, Planefinder seemed to have better coverage at the airport level. I could actually track the planes from/to the gates.

I hope we’re not deviating too much from the acceptable topics on the FA forum.

FA is the only commercial site I currently feed data.:smiley:


#5

FA is the only site I feed data to too.

I live around 12 miles from Heathrow and viewing FA’s Skyview is naturally spot on. When I recently spent a few weeks in California I took my Pi with me and fascinating to identify aircraft details then see them fly overhead.

I was merely thinking about scenarios where two enthusiasts in different parts of the World could both view live data.

I think she needs a permanent Pi in California :sunglasses:

Geffers


#6

My son is on the move again. This time I’m tracking his flight on FA, FR24, and Planefinder.

I was able to track at the airport level on both FR24 and Planefinder. The FA live map was not loaded at the time.

Planefinder is a split second ahead of FR24 on updates. I now think the difference between the two has to do with the web server flow, not deliberate delay, unless both are delaying by the same amount of time.

FA is behind both. The altitude is 2000 feet lower, and the distance traveled is around 10 km behind. After reaching cruising altitude, all 3 were the same, but FA is still 10 km behind on distance traveled.

The flight is about to land. The FA difference in distance traveled is likely related to the web page update frequency. It appears to update every 30 seconds or so. Also, the page was showing landed, while the live map still showed the plane approaching the runway.

Overall, they are all very good as far as basic tracking goes.

I’m simply using the data displayed on their respective web pages and live maps. Nothing scientific.


#7

The time difference is due to FR24 using future projections and FA doesn’t. FR24 will send the last position (also with a 10-15 second delay) and then project the current plane location on the map about 15 seconds into the future to account for the delays. They are mostly estimating speed and direction. If the plane is turning you will see the plane jump around. This is especially noticeable around airports where airplanes are changing direction, altitude and speed.

FA show the actual position of the plane on the map. So the path is correct and will not jump around. The delay isn’t intentional but due to the time cost to process the data. You will also not see planes flying backwards or into buildings or other planes on FA.


#8

Thank you for your explanation, very valuable!

My 30 seconds guess was in the ballpark, then.

This is an irritating ‘feature’ in my opinion. It happens a lot with FR24. I just checked, and for some reason, estimation was enabled and set to 240 minutes. I’m pretty sure I disabled it before.

I do no see this much jumping around on Planefinder, and never saw anything like that with FA.

This is what I referred to as web server flow. Again, another guess in the ball park.

I’m on my way now to guess some lottery numbers for Wednesday’s draw.:rofl:

Thank you very much, David.


#9

I’ve been contributing to FA for many months now, ~2000+ flights/day on an outdoor antenna situated between SFO, OAK, SJC and right next to Google’s private airstrip at KNUQ. I also sent data to FR24, and could see a slight difference in the output from the respective websites and what I was feeding from dump1090 off my RPI system. I recently moved my feed, however, to adsbexchange who don’t take time to censor the feed of all the “special people” who want their privacy - so whatever adsb receiver sites put in comes right back out without any censorship within a second or two. It’s got to be the shortest delay of any site as a result, which is why I now do my MLAT solutions with their system having completed the migration this weekend. While any site is able to give you the air carriers flight locations, adsb exchange gives info on private (BARR LIST) planes that I’m doing the MLAT for when they squawk 1200/mode C flying through my coverage area (250 nm out). I’m curious what others have seen in feed delay there.


#10

SkyView I am assuming is spot on as it is created locally using one’s own data from the tuner.

The delays on map locations I have not found an issue except when I am speaking live to a friend in US and I am in UK. As they do not have their own ADS-B setup I can only refer to map locations for aircraft and as such if I am letting them know of an approaching plane the FR24 map is more suited for this purpose.

I do however only feed data to FlightAware as I like the overall system and the friendly discussion forum.

Geffers


#11

Yes, all my references to live maps referred to the internet web maps of each respective tracking site, not the live map on one’s ads-b receiving station. The day a delay is introduced, by whatever means, on my own site, it’s game over, I’m abandoning the hobby.:grin:

That and MLAT. Hopefully the friendly discussion will continue after 2020.:wink:


#12

The 240 min projection has nothing to do with the short term projection. (the 240 min one is for transatlantic flights out of coverage where a great circle towards the destination is plotted at the last known ground speed)

I get the impression FA focuses on having all data displayed synchronous. So FAA data and MLAT data and ADS-B data are synchronized and for that purpose some data will need to be delayed.

This does not happen on fr24, so their mlat data and radar data regularly lags behind their ADS-B data. Also the vector prediction totally butchers radar data and mlat data to a certain degree.

Sorry to say when i listen to liveatc at some airport and want to “watch” plane tracks i like the “less precise” site much better so i’m feeding both. Only thing i did was install NTP on my pi and redirect all the ntp pools so they don’t get burdened by that strange feeder of theirs.
Sometimes i think about just delaying the liveatc audio and using FA but even then the interface seems to be not quite as nice for that purpose.


#13

The 240 minutes was the setting it defaulted to on its own. I was not tracking a transatlantic flight. The options for the user to select are: OFF, 5, 15, 30, 60, 120, and 240 minutes. I always select OFF.


#14

Yeah and i said the short term projection david.baker talked about is a “feature” you can’t turn off on fr24.
The estimation you can set from 0 to 240 minutes is a different feature that you can turn off.
So the “jumping around” will not stop regardless of what that option is set to.
I hope this is clearer. (At least that is what i was saying and believe to be true i have not seen the code.)
What you can try though is to disable “Animate Aircraft” it’s in the “Map” options.


#15

Yes…that’s another feature I normally disable. I don’t know if these settings are retained by way of cookies on the user’s computer, or not. If they are, the may have expired, or deleted by the browser on closing, or by the security software.

I don’t visit these sites very often, and even less compare them. This was only the second time, maybe. I visit one or the other when there is a reason, such as checking somebody’s flight. They are good enough for this purpose, whether the planes jump around or not.

Business users may have other requirements, but I’m not one of those.


#16

Did you use the adsbexchange image to do do or just change settings on your existing setup?

I haven’t tried feeding any other than FA but might experiment using a different image so I don’t mess up my existing setup.

Geffers