Andy Piper 6c9a6d2a46 AP_GroundEffect: drop the touchdown gate far from takeoff ...

The baro fallback gates touchdown on height-since-takeoff assuming flat
ground. Beyond 20m from the launch point that assumption may not hold,
but disabling touchdown compensation there left mission landings and
rally-point RTLs on baro-only vehicles with none at all, a regression
from the pre-gate behaviour, while the no-position branch assumed flat
ground everywhere.

Beyond 20m fall back to any gentle descent counting as a landing, as
before the gate existed and as the comment on the constant already
described. Rangefinder, near-launch and no-position paths are
unchanged.

SITL, GNDEFF_ALT=1.0, GUIDED to 3m, land 30m from takeoff:
touchdown_expected 0.0s -> 9.6s (6.9s landing at the takeoff point,
9.8s with GNDEFF_ALT=5).

2026-09-01 20:09:07 +09:00

..

AP_GroundEffect_config.h

…

AP_GroundEffect.cpp

AP_GroundEffect: drop the touchdown gate far from takeoff

2026-09-01 20:09:07 +09:00

AP_GroundEffect.h

AP_GroundEffect: measure HAGL from the on-ground reading

2026-09-01 20:09:07 +09:00