Clarification on TAT/OAT and winds data source

[guidocioni]

I'm trying to save the values of TAT/OAT and wind speed/direction shown into the web interface inside a database for further analysis. As these are not saved into the history of tar1090 (as far as I know) I'm writing a Pyhton script which queries aircraft.json, which I believe is the same source of data for tar1090, and save only these parameters into a DB.

Unfortunately I noticed that the temperature/winds data shown in aircraft.json are usually not in line with what I see in web interface of tar1090: usually I see only one aircraft reporting weather data in aircraft.json, while in the web interface most of the aircrafts at cruise level have that value. I tried to also look into the history files but it seems to be the same...

Am I missing something? Are the weather data sourced from aircraft.json or enriched from somewhere else?

[wiedehopf]

for compatibility with dump1090-fa the javascript can calculate the data itself but the accuracy will be lower as readsb enforces the base data to be close in time. might be that you're not getting the data at the same time due to bad reception or for some reason.

It works fine for me ... i'd have to look at the raw data, are you able to share your MLAT name on adsbexchange? I could look into the raw data that you're sending that way.

[wiedehopf]

Look at the code for the calculations please. It uses true airspeed / ground speed / magnetic heading / ground track true heading is calculated using a magnetic declination lookup. that's all mashed together and you get the wind vector.

TAT / OAT are calculated from TAS / mach number.

Are you even running readsb? tar1090 javascript calculates the same stuff in the browser but doesn't know when the data points where received so it's inaccurate for turns especially.

History files don't have wind. Really that's as much as i'm going to write, you'll have to dig into the source.

[wiedehopf]

Im not sure what you're running ... your data shows me wind for 19 aircraft out of 34 for with position. The 15 without wind just means you don't have sufficient reception on them.

[guidocioni]

Look at the code for the calculations please. It uses true airspeed / ground speed / magnetic heading / ground track true heading is calculated using a magnetic declination lookup. that's all mashed together and you get the wind vector.

TAT / OAT are calculated from TAS / mach number.

Ok sorry, I thought that wind and temperature informations were directly sent into the ADS-B message.

Are you even running readsb? tar1090 javascript calculates the same stuff in the browser but doesn't know when the data points where received so it's inaccurate for turns especially.

I'm not running readsb, tar1090 gets the data automatically from an already running instance of dump1090-fa. Ok so that may explain the winds in the interface.

History files don't have wind. Really that's as much as i'm going to write, you'll have to dig into the source.

I've actually seen some temperature and wind information in the aircraft.json so I'm not sure where is coming from.

Anyway this was just a question to get to know more, feel free to ignore it if it's not relevant :)

[guidocioni]

Im not sure what you're running ... your data shows me wind for 19 aircraft out of 34 for with position. The 15 without wind just means you don't have sufficient reception on them.

Not sure why, I should get correct data. You can see the running instance here ****

[wiedehopf]

That doesn't seem to be readsb as a backend, use it!

https://github.com/wiedehopf/adsb-scripts/wiki/Automatic-installation-for-readsb