ekf_att_pos_estimator: fixed saving params when landed

fixed logic such that parameters are saved when vehicle just landed.
only save parameters once when state changed from in_air to landed.

Signed-off-by: tumbili <roman@px4.io> and bkueng <beat-kueng@gmx.net>

src/modules/ekf_att_pos_estimator/AttitudePositionEstimatorEKF.h

@@ -224,6 +224,7 @@ private:
     bool            _vibration_warning; ///< high vibration levels detected
     bool            _ekf_logging;       ///< log EKF state
     unsigned        _debug;             ///< debug level - default 0
+    bool            _was_landed;        ///< indicates if was landed in previous iteration
 
     bool            _newHgtData;
     bool            _newAdsData;

src/modules/ekf_att_pos_estimator/ekf_att_pos_estimator_main.cpp

@@ -216,6 +216,7 @@ AttitudePositionEstimatorEKF::AttitudePositionEstimatorEKF() :
 	_vibration_warning(false),
 	_ekf_logging(true),
 	_debug(0),
+	_was_landed(true),
 
 	_newHgtData(false),
 	_newAdsData(false),
@@ -381,8 +382,8 @@ void AttitudePositionEstimatorEKF::vehicle_land_detected_poll()
 
 		orb_copy(ORB_ID(vehicle_land_detected), _vehicle_land_detected_sub, &_vehicle_land_detected);
 
-		// Save params on landed
-		if (!_vehicle_land_detected.landed) {
+		// Save params on landed and previously not landed
+		if (_vehicle_land_detected.landed && !_was_landed) {
 			_mag_offset_x.set(_ekf->magBias.x);
 			_mag_offset_x.commit();
 			_mag_offset_y.set(_ekf->magBias.y);
@@ -390,6 +391,8 @@ void AttitudePositionEstimatorEKF::vehicle_land_detected_poll()
 			_mag_offset_z.set(_ekf->magBias.z);
 			_mag_offset_z.commit();
 		}
+
+		_was_landed = _vehicle_land_detected.landed;
 	}
 }