Originally Posted by
Vinnie Boombatz
Implication is that the altitude and groundspeed are from GPS. No air data.
No, ADS-B altitude is normally barometric, although there is provision in the spec for sending GNSS height.
Groundspeed is, of course, GPS-derived, as is true track. FR24 appear to use the terms "track" and "heading" interchangeably, though if they are decoding EHS data they ought to have access to both (and IAS, too).