Hello guys, could somebody help me with this question: We are consuming an ADSB-stream. At many airplanes we yield outlier values of the altitude. Example: Imagine you have 50 msg messages. ~40 of them has an altitude of ~10200, 7 of them of ~3100 and maybe 3 of ~5000. We dont believe, that an airplane will change its height in such a short time so often. Can somebody confirm or disagree if there are e.g. different physical units in MSG messages? Are there any rules/patterns to detect these units in the MSG messages? Thanks a lot
There shouldn't be different physical units. https://mode-s.org/decode/adsb/airborne-position.html This page states that the altitude is either encoded in 25 ft or 100 ft increments. This is only mentions airborne position messages and there are other message types with altitude. But i would expect the encoding to be similar. Either the plane has a malfunctioning transmitter or you decoder is wrong. Could also be bit errors, but i wouldn't expect the same differing altitude then. How are you getting the data? Is the problem only with a particular airframe?
We have this behaviour at many airplanes, so we believe that there must be a systematic error. We consume data from adsbhub.org
adsbhub provides Basestation data, this means the raw messages are already decoded. Don't think you can do anything if they have feeders feeding bad data or have an error in their decoding software for incoming raw streams. (for feeding they support raw data as well as Basestation) So the only thing you can do is try and get a better data source.
I've seen this too -- and not just altitude but also latitude and longitude. Probably also groundspeed but I cannot prove it. I've been plagued by it in the stream I receive since Day One and it continues. I've posted about it before but never resolved it satisfactorily. My theory is that some receivers feeding ADSBx sometimes delay their streams. Not every time and not by a specific amount. This causes position reports to be put into the stream from ADSBx out of sequence.
adsbhub.org is bad data. They accept feeds from VRS,etc. What you are likely seeing is delayed and generally shitty data. @jdubner is correct, we try to remove as much delayed and shitty data as we can. But the simple fact is you can't fix stupid and some people are thus.
