The TrackStruct structure include an ‘altitude_feet’ field. What is the referential for that data (MSL, Ellipsoide, Baro corrected/non corrected…)?
Thank you.
It is typically dependent upon source of the data. From the website FAQs
Are displayed flight altitudes AGL (above ground level) or MSL (mean sea level)?
Displayed altitudes are dependent on the data source for the position data. FlightAware receives many different types of altitude data, including uncorrected pressure altitude, corrected pressure altitude, flight levels, GPS-based height above mean sea level (MSL) and GPS-based height above ellipsoid. Data received from the FAA or other air navigation service providers is typically MSL. ADS-B data is frequently height above ellipsoid but there are exceptions. In general, it is best to assume altitudes are uncorrected pressure altitudes (a variation of MSL). FlightAware does not display AGL altitudes.
I understand that the answer in the FAQ applies to the displayed altitude on the website. It is unclear to me what source/reference is used for the altitude in the API.
It is the same data. In some calls, there will be a source field and you could match that up to what altitudes different sources provide according to the FAQ answer above.