EKF: Protect against ground effect induced static pressure rise during landing and takeoff.

Apply a dead-zone to the vertical position innovation if using baro for height and if in the ground effect region during and just after takeoff.
Method needs to be activated externally.
Turns off automatically after 10 seconds or if specified height gained.

EKF/estimator_interface.h

@@ -208,6 +208,15 @@ public:
 	// set flag if synthetic sideslip measurement should be fused
 	void set_fuse_beta_flag(bool fuse_beta) {_control_status.flags.fuse_beta = (fuse_beta && _control_status.flags.in_air);}
 
+	// set flag if static pressure rise due to ground effect is expected
+	// use _params.gnd_effect_deadzone to adjust for expected rise in static pressure
+	// flag will clear after GNDEFFECT_TIMEOUT uSec
+	void set_gnd_effect_flag(bool gnd_effect)
+	{
+		_control_status.flags.gnd_effect = gnd_effect;
+		_time_last_gnd_effect_on = _time_last_imu;
+	}
+
 	// set flag if only only mag states should be updated by the magnetometer
 	void set_update_mag_states_only_flag(bool update_mag_states_only) {_control_status.flags.update_mag_states_only = update_mag_states_only;}
 
@@ -473,6 +482,7 @@ protected:
 	uint64_t _time_last_airspeed{0};	// timestamp of last airspeed measurement in microseconds
 	uint64_t _time_last_ext_vision{0}; // timestamp of last external vision measurement in microseconds
 	uint64_t _time_last_optflow{0};
+	uint64_t _time_last_gnd_effect_on{0};	//last time the baro ground effect compensation was turned on externally (uSec)
 
 	fault_status_u _fault_status{};