ekf2: add fake height fusion logic

When there is no vertical aiding, fake height is started to constrain
the vertical channel of the EKF

src/modules/ekf2/EKF/ekf.h

@@ -402,6 +402,7 @@ public:
 	const auto &aid_src_baro_hgt() const { return _aid_src_baro_hgt; }
 	const auto &aid_src_rng_hgt() const { return _aid_src_rng_hgt; }
 
+	const auto &aid_src_fake_hgt() const { return _aid_src_fake_hgt; }
 	const auto &aid_src_fake_pos() const { return _aid_src_fake_pos; }
 
 	const auto &aid_src_ev_yaw() const { return _aid_src_ev_yaw; }
@@ -479,7 +480,7 @@ private:
 	uint64_t _time_last_healthy_rng_data{0};
 	uint8_t _nb_gps_yaw_reset_available{0}; ///< remaining number of resets allowed before switching to another aiding source
 
-	Vector2f _last_known_posNE{};		///< last known local NE position vector (m)
+	Vector3f _last_known_pos{};		///< last known local position vector (m)
 
 	uint64_t _time_acc_bias_check{0};	///< last time the  accel bias check passed (uSec)
 	uint64_t _delta_time_baro_us{0};	///< delta time between two consecutive delayed baro samples from the buffer (uSec)
@@ -549,6 +550,7 @@ private:
 	estimator_aid_source_1d_s _aid_src_airspeed{};
 
 	estimator_aid_source_2d_s _aid_src_fake_pos{};
+	estimator_aid_source_1d_s _aid_src_fake_hgt{};
 
 	estimator_aid_source_1d_s _aid_src_ev_yaw{};
 
@@ -932,6 +934,13 @@ private:
 	// control fusion of fake position observations to constrain drift
 	void controlFakePosFusion();
 
+	void controlFakeHgtFusion();
+	void startFakeHgtFusion();
+	void resetFakeHgtFusion();
+	void resetHeightToLastKnown();
+	void stopFakeHgtFusion();
+	void fuseFakeHgt();
+
 	void controlZeroVelocityUpdate();
 
 	void controlZeroInnovationHeadingUpdate();