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Thread: Flightradar24 Feeder Chat

  1. #691
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    There are a couple of points:
    1. Most people are not too interested in the altitude and speed of an aircraft - just where it is on the map
    2. It should be possible even with incomplete data to see if the data that has been uploaded by a single station is credible - is the position reported reasonable for the aircraft (by make and model, flying at that altitude) compared to prior positions reported. A B752 at 5000ft is only likely to be within - say - 10km of the position it was in 10s ago type thing.

    The maths would be a pain to work out but if doing Pythagoras and you're only interested the approximate magnitude of the answer - don't do the square root calculation (divide lots of compute) square the other side of the calculation instead (multiply is faster). or even easier just have a lookup table. Its a (B75,b73, a32, a33, a34, etc) 10s since last position - whats the square of the maximum distance it could have travelled ... is the position given within that range?

  2. #692
    Team FR24 Mike's Avatar
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    The first and last data is often the the source for many errors as signal is weak. If altitude is missing what says that position is correct?
    This is a very common when a DVB-T stick feeds with some software https://dl.dropboxusercontent.com/u/5175572/error1.PNG
    You get a first position 100km from the airport and then your suggestion " is the position reported reasonable for the aircraft (by make and model, flying at that altitude) compared to prior positions reported." or "whats the square of the maximum distance it could have travelled ... is the position given within that range?" fails as first position was wrong and you would never get back to correct location again. That is why we are very keep on verifying the first position data.

    I have now explained how this work and we have no intentions to reduce the data quality. We get far too much complains on the data quality that we want to take any steps back in development. We are instead putting our energy on keeping improving the quality. We can never make everybody satisfied, it's just not possible, but we are confident that better quality is the right way to go.

  3. #693
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    Quote Originally Posted by Mike View Post
    MLAT accuracy can be higher than ADS-B and in Europe ATC uses MLAT instead of ADS-B as it is more accurate. Do you suggest that ATC is based on guessing?
    Really?

    I think you'll find that MLAT is used as a lower cost alternative to traditional secondary surveillance radar. I've never seen any evidence that it is more accurate than ADS-B but am happy to be proven wrong.

    However, the current discussion is whether usable data is ignored to the detriment of tracking a flight on FR24.

    I appreciate FR24 has become a major player in flight tracking and cannot investigate every reported issue but maybe it should look at some, if only to identify why there's a mismatch between the local data and that shown on FR24.

    From what I see posted, a data sharer usually reports discrepancies to help FR24 and not pick a fight. But there's an emerging trend to dismiss such reports out of hand together with anyone who questions or debates with the FR24 team. The last time a thread was locked and I hope this doesn't happen here.

    It would be a sad day if the sharers who breathed life into FR24 turn off their data feeds just because they are being ignored or their views dismissed without justification.
    Mike


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  4. #694
    Team FR24 Mike's Avatar
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    Quote Originally Posted by Anmer View Post
    I think you'll find that MLAT is used as a lower cost alternative to traditional secondary surveillance radar. I've never seen any evidence that it is more accurate than ADS-B but am happy to be proven wrong.
    About 4 months ago there was a big ATC outage in Europe. About 10 aircraft were lost from ATC screens over central Europe. We have discussed this issue with Eurocontrol afterwards and compared our data. Eurocontrol told us that they track the traffic with a MLAT system were 12+ MLAT receivers are needed to verify the position. Reason why they used MLAT to track ADS-B aircraft was that they told it gives better accuracy.

    A GPS receiver needs 3-4 GPS satellites to calculate it's position with an accuracy of couple of meters. More satellites give better accuracy down to centimeters. With MLAT you have the same. 3-4 receivers are needed to calculate a position of the tracked aircraft and every extra receiver increases the quality of the calculation. At some point the data will become very accurate. Eurocontrol defines this point at 12+ receivers.

    Quote Originally Posted by Anmer View Post
    I appreciate FR24 has become a major player in flight tracking and cannot investigate every reported issue but maybe it should look at some, if only to identify why there's a mismatch between the local data and that shown on FR24.
    As I have written a couple of times now, we don't use the first data. This is not a bug, this is intentional design. We need to verify that data is correct before we use/show it. If someone reports "my early data was not used" this is exactly what we expect and want it to be. Why should we investigate something that behaves as expected? What should we look for?

  5. #695
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    Quote Originally Posted by Mike View Post
    Reason why they used MLAT to track ADS-B aircraft was that they told it gives better accuracy.
    If MLAT were more accurate than ADS-B, why is ADS-B the preferred choice for most aviation authorities? I watch FR24 MLAT plots for my area showing aircraft approaching my location that have already passed overhead. And trust me, after nearly 10 years using Mode-S receivers, I know where aircraft actually are in relation to your map.

    Quote Originally Posted by Mike View Post
    What we should look for?
    That's for you to decide.

    All I'm suggesting is that, sometimes, some further research may be beneficial.

    I used to be a financial auditor and a small discrepancy could be caused by many bigger ones. But, as I've said before, it's your business and if you're 100% satisfied that FR24 isn't ignoring usable data we can move on. Personally, if I were seeing tracked aircraft from my local receiver which are not shown on FR24, I would be interested to know why.
    Mike


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  6. #696
    Team FR24 Mike's Avatar
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    Quote Originally Posted by Anmer View Post
    If MLAT were more accurate than ADS-B, why is ADS-B the preferred choice for most aviation authorities? I watch FR24 MLAT plots for my area showing aircraft approaching my location that have already passed overhead. And trust me, after nearly 10 years using Mode-S receivers, I know where aircraft actually are in relation to your map.
    A lot of ADS-B installations are being done right now, yes. But AFAIK only Australia is beginning to use ADS-B for ATC on higher altitudes, with very big delays. 2 years after ADS-B becoming mandatory there are still aircraft without ADS-B. FAA is alarming that 37% of US aircraft are sending incorrect position on ADS-B. Eurocontrol has postponed European ADS-B. So I don't see ADS-B taking over in the near future. More and more discussions now mentions MLAT instead, for example FAA.

    The delay on FR24 is because FR24 is waiting up to 20 seconds for MLAT feeds with slow internet. That has nothing to do with the accuracy of MLAT. A fast network with low latency can have MLAT plots with just 1-2 seconds delay.

    Quote Originally Posted by Anmer View Post
    That's for you to decide.

    All I'm suggesting is that, sometimes, some further research may be beneficial.

    I used to be a financial auditor and a small discrepancy could be caused by many bigger ones. But, as I've said before, it's your business and if you're 100% satisfied that FR24 isn't ignoring usable data we can move on. Personally, if I were seeing tracked aircraft from my local receiver which are not shown on FR24, I would be interested to know why.
    And we are satisfied with the behavior right now. We are not saying we will not tweak the values in the future, but we don't see any bugs from expected behavior, from the reports we get.

  7. #697
    Super Moderator Amper's Avatar
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    I understand you guys want this problem solved. I would like too.
    But I think Mike is trying to say that between two evils, they choose less one.
    And I agree with him....this time.
    It was pain in the *ss to see plane, that i know is on the rwy (GND), shown in the middle of Adriatic sea turning arround himself....
    I believe that, in time, this problem that you are reporting, and I see it as well, will be solved in the near future when coverage is even more improved.
    Last edited by Amper; 2014-10-27 at 09:47.
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  8. #698
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    Quote Originally Posted by Mike View Post
    The first and last data is often the the source for many errors as signal is weak. If altitude is missing what says that position is correct?
    This is a very common when a DVB-T stick feeds with some software https://dl.dropboxusercontent.com/u/5175572/error1.PNG
    You get a first position 100km from the airport and then your suggestion " is the position reported reasonable for the aircraft (by make and model, flying at that altitude) compared to prior positions reported." or "whats the square of the maximum distance it could have travelled ... is the position given within that range?" fails as first position was wrong and you would never get back to correct location again.
    Yes I see what you mean, but if that data was retained - even if not plotted - maybe it could be used to statistically increase the confidence in other data received.

    something like
    feed (a) says this aircraft is at position long(1), lat(1) - we have only 50% confidence that this is correct (so will not plot it) - but we will remember it in short term memory for verification purposes.
    feed (b) says this aircraft is at position long(2), lat(2) - we have only 50% confidence that this is correct (so will not plot it)

    just let it be a sliding time window - non-plotted data over - say - 2 mins old, is discarded ... certainly for the initial position ... that would take care of never being able to plot the plane again


    but the feed (b) data does corroborate with the feed (a) data (bearing in mind they may be seconds apart) - increasing the confidence that both are correct to 75% - this could be over the threshold to allow it to be plotted.

    Taking possible positions into account based on last known position and time difference would also filter the jagged lines where a bad radar sends duff data (though I've not seen that for a while)

    Please see this as a constructive suggestion.

  9. #699
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    Quote Originally Posted by Mike View Post
    If aircraft disappear then there is no coverage. No coverage is not a bug.
    Mike,

    Your responses clearly indicate that you haven't bothered (for whatever reason) to have a look at the issue I've raised. It's NOT about 'NO COVERAGE'. There is acres of coverage in the Sydney area (both ground and airside), so it's actually just the opposite. It's simply a matter of using playback for each of the examples I've quoted and you'll see it's about aircraft that SHOULD be displaying on FR24 but AREN'T. As has been picked up by some of the guys already on this thread, I'M TRYING TO HELP.

    I'll give you a hint. I think one of the 'F' feeders is interfering with the data being placed on the map and preventing it from being displayed correctly.

    You obviously aren't getting it but- I can only lead you to the water- you'll have to do the drinking yourself.

    I went to the trouble of cropping each image I posted so you had the date and UTC time to verify what's going on. I dont know what more I can do but this is just a bloody ridiculous way to handle an issue reported with the map. You're doing a great job of making me feel like it isn't worth the trouble to let you know about issues with FR24. As you are aware I've got a disability and it takes a great deal of effort on my part to do so. To be so dismissive is nothing short of insulting.

    Try listening to a bloke with a little local knowledge and quite a few years of tracking flights around the Sydney area. One day this issue, if not nipped in the bud, may be something far more of a serious problem for you to deal with if it is occurring, or begins to occur, across the board. For God's sake Mike, look at this with an open mind, if that's at all possible. I'm going back to bed.

    Regards,
    Gregg
    Last edited by fungus; 2014-10-27 at 21:01.
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  10. #700
    Team FR24 Mike's Avatar
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    Fungus, I read what you write but as I said we can't do anything without the raw data that was picked up by the receiver. Playback does not say what was picked up, if it was processed or how it was processed. I can only note that the aircraft was not visible. Without the raw data I can only speculate.
    * It was flying below coverage
    * Transponder was off
    * Transponder was sending crap that was not possible to decode
    I checked some other trackers and could not find that flight as well. If you want to blame FR24 for that I leave it up to you.

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