ekf2: add param to enable synthetic mag Z fusion mode

src/modules/ekf2/EKF2.cpp

@@ -159,6 +159,7 @@ EKF2::EKF2(bool multi_mode, const px4::wq_config_t &config, bool replay_mode):
 	_param_ekf2_pcoef_z(_params->static_pressure_coef_z),
 	_param_ekf2_move_test(_params->is_moving_scaler),
 	_param_ekf2_mag_check(_params->check_mag_strength),
+	_param_ekf2_synthetic_mag_z(_params->synthesize_mag_z),
 	_param_ekf2_gsf_tas_default(_params->EKFGSF_tas_default)
 {
 }

src/modules/ekf2/EKF2.hpp

@@ -495,6 +495,8 @@ private:
 
 		(ParamFloat<px4::params::EKF2_REQ_GPS_H>) _param_ekf2_req_gps_h, ///< Required GPS health time
 		(ParamExtInt<px4::params::EKF2_MAG_CHECK>) _param_ekf2_mag_check, ///< Mag field strength check
+		(ParamExtInt<px4::params::EKF2_SYNT_MAG_Z>)
+		_param_ekf2_synthetic_mag_z, ///< Enables the use of a synthetic value for the Z axis of the magnetometer calculated from the 3D magnetic field vector at the location of the drone.
 
 		// Used by EKF-GSF experimental yaw estimator
 		(ParamExtFloat<px4::params::EKF2_GSF_TAS>)

src/modules/ekf2/ekf2_params.c

@@ -1326,6 +1326,20 @@ PARAM_DEFINE_FLOAT(EKF2_REQ_GPS_H, 10.0f);
  */
 PARAM_DEFINE_INT32(EKF2_MAG_CHECK, 0);
 
+/**
+ * Enable synthetic magnetometer Z component measurement.
+ *
+ * Use for vehicles where the measured body Z magnetic field is subject to strong magnetic interference.
+ * For magnetic heading fusion the magnetometer Z measurement will be replaced by a synthetic value calculated
+ * using the knowledge of the 3D magnetic field vector at the location of the drone. Therefore, this parameter
+ * will only have an effect if the global position of the drone is known.
+ * For 3D mag fusion the magnetometer Z measurement will simply be ingored instead of fusing the synthetic value.
+ *
+ * @group EKF2
+ * @boolean
+*/
+PARAM_DEFINE_INT32(EKF2_SYNT_MAG_Z, 0);
+
 /**
  * Default value of true airspeed used in EKF-GSF AHRS calculation.
  * If no airspeed measurements are avalable, the EKF-GSF AHRS calculation will assume this value of true airspeed when compensating for centripetal acceleration during turns. Set to zero to disable centripetal acceleration compensation during fixed wing flight modes.