Altitude display
It is always height above launch / arming point.
There are two altitude display options available in the GUI configurator – "altitude" and "GPS altitude".
There are 3 alt indicators - "AGL","ALT:" and "ALT::"
"ALT:" - This is the altitude from prime source
"ALT::" - This is GPS altitude
"AGL:" - This is displayed when any altitude displayed is below the threshold set by “High resolution altitude display cutoff”. The default value for this is zero. Typically this is used when the aircraft has LIDAR or an FC that can send altitude data with accuracy of less than 1 meter. Recommend using only for iNAV copter users and Ardupilot PX4 users with barometric data. AGL is displayed with extra digit of precision
Ardupilot/PX4 – always GPS unless using custom install with LIDAR, depth sensor.
Fixed Wing – always GPS.
Copter – usually barometric altitude.
