MLAT questions re: approaching planes

FlightAware ADS-B Flight Tracking
21

much appreciated! sorry for my missing the forest through the trees - so the aircraft-data-sets where i find the (always empty) sub-key ‘altitude’ are the ones that are entirely computed without transponder altitude? or in other words example1 has the less altitude precision than example2 ?

example1:
{“hex”:“~2bbd80”,“type”:“tisb_other”,“lat”:51.357499,“lon”:10.036774,“nucp”:0,“seen_pos”:22.8,“altitude”:43025,“vert_rate”:0,“track”:14,“speed”:519,“mlat”:[“lat”,“lon”,“altitude”,“track”,“speed”,“vert_rate”],“tisb”:,“messages”:1170,“seen”:22.8,“rssi”:-49.5},

example2:
{“hex”:“3c4a28”,“squawk”:“2554”,“flight”:"BER8680 ",“lat”:48.327414,“lon”:10.582075,“nucp”:0,“seen_pos”:8.8,“altitude”:25000,“vert_rate”:0,“track”:167,“speed”:326,“mlat”:[“lat”,“lon”,“track”,“speed”,“vert_rate”],“tisb”:,“messages”:24716,“seen”:0.0,“rssi”:-2.3},

22

It’s not a key, it’s just a data value (the value containing it is an array, not an object)

You can’t distinguish the no-transponder-altitude case currently. The “mlat” key just tells you the datasource of various fields. A “mlat”-sourced altitude means that the altitude came from a mlat result, it doesn’t tell you about the inputs to the solver.

23

finally i got it :grinning: so my guessing that i could differentiate the altitude-quality in mlat results by the different behavior: “mlat”:[“lat”,“lon”,“altitude”,“track”,“speed”,“vert_rate”] vs “mlat”:[“lat”,“lon”,“track”,“speed”,“vert_rate”] was false. i was just wondering if there is any meaning that i can use from this different behavior …

24

the second thing i was wondering if this-altitude thing reflects in key ‘nucp’ and what the exact meaning of the different values (mostly 0 or between 7-8 at my site) is? but i see i have to dive into dump1090 sources again and start learning about. that’s not easy but a good lesson in coding too :smiley:

25

nucp is the Navigation Uncertainty Category - see the ADS-B specs (v0; later versions replaced it with a different set of measurements, but dump1090 hasn’t caught up with that yet). mlat results will always report 0 here.

1 Like
26

perfect - thanx :smiley:

27

that’s why i said i’m quite happy with flightaware mlat. this is an airport 4 miles away from me without direct sight - anyhow i get nearly always such perfect mlat positions and altitudes down to 50-100 feet above their runway. and over here in my neighborhood we have very very few sites. so in my eyes this is a great result!

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