Update vehicle_local_position.ref_alt comment to reflect how ref_alt … #12658
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julianoes
approved these changes
Aug 12, 2019
dagar
approved these changes
Oct 14, 2019
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…is being used in PX4
(from my original post in slack)
[The comment currently] indicates to me that ref_alt is meant to be the altitude AMSL of the ground immediately below the current position of the vehicle, but when I look at all the uses of ref_alt in PX4, it is never used in this way. ref_alt tends to be set once in an estimator module on the first gps fix, and then is treated as the global reference altitude of the local frame origin by said estimator module. Further, in the mavlink module, the ref_alt value is used to determine current altitude AMSL by adding it to vehicle_local_position.z, but z is relative to the local frame origin, so ref_alt must be altitude AMSL of local frame origin, else such calculations for current altitude AMSL are wrong. All of this to say: I think the comment is wrong...