ekf2: add mag type init

In this mode, the mag is used to inilialize the heading.
During flight, the heading is predicted using gyros and corrected
by GNSS measurements if available.

src/modules/ekf2/EKF/aid_sources/magnetometer/mag_control.cpp

@@ -130,7 +130,9 @@ void Ekf::controlMagFusion()
 		_innov_check_fail_status.flags.reject_mag_z = (aid_src.test_ratio[2] > 1.f);
 
 		// determine if we should use mag fusion
-		bool continuing_conditions_passing = (_params.mag_fusion_type != MagFuseType::NONE)
+		bool continuing_conditions_passing = ((_params.mag_fusion_type == MagFuseType::INIT)
+						      || (_params.mag_fusion_type == MagFuseType::AUTO)
+						      || (_params.mag_fusion_type == MagFuseType::HEADING))
 						     && _control_status.flags.tilt_align
 						     && (_control_status.flags.yaw_align || (!_control_status.flags.ev_yaw && !_control_status.flags.yaw_align))
 						     && mag_sample.mag.longerThan(0.f)

src/modules/ekf2/EKF/common.h

@@ -101,7 +101,8 @@ enum MagFuseType : uint8_t {
 	// Integer definitions for mag_fusion_type
 	AUTO    = 0,   	///< The selection of either heading or 3D magnetometer fusion will be automatic
 	HEADING = 1,   	///< Simple yaw angle fusion will always be used. This is less accurate, but less affected by earth field distortions. It should not be used for pitch angles outside the range from -60 to +60 deg
-	NONE    = 5    	///< Do not use magnetometer under any circumstance..
+	NONE    = 5,   	///< Do not use magnetometer under any circumstance.
+	INIT    = 6     ///< Use the mag for heading initialization only.
 };
 #endif // CONFIG_EKF2_MAGNETOMETER
 

src/modules/ekf2/EKF2.cpp

@@ -769,6 +769,7 @@ void EKF2::VerifyParams()
 	if ((_param_ekf2_mag_type.get() != MagFuseType::AUTO)
 	    && (_param_ekf2_mag_type.get() != MagFuseType::HEADING)
 	    && (_param_ekf2_mag_type.get() != MagFuseType::NONE)
+	    && (_param_ekf2_mag_type.get() != MagFuseType::INIT)
 	   ) {
 
 		mavlink_log_critical(&_mavlink_log_pub, "EKF2_MAG_TYPE invalid, resetting to default");

src/modules/ekf2/module.yaml

@@ -401,19 +401,18 @@ parameters:
           heading or 3-component vector. The fusion of magnetometer data as a three
           component vector enables vehicle body fixed hard iron errors to be learned,
           but requires a stable earth field. If set to 'Automatic' magnetic heading
-          fusion is used when on-ground and 3-axis magnetic field fusion in-flight
-          with fallback to magnetic heading fusion if there is insufficient motion
-          to make yaw or magnetic field states observable. If set to 'Magnetic heading'
-          magnetic heading fusion is used at all times. If set to 'None' the magnetometer
-          will not be used under any circumstance. If no external source of yaw is
-          available, it is possible to use post-takeoff horizontal movement combined
-          with GPS velocity measurements to align the yaw angle with the timer required
-          (depending on the amount of movement and GPS data quality).
+          fusion is used when on-ground and 3-axis magnetic field fusion in-flight.
+          If set to 'Magnetic heading' magnetic heading fusion is used at all times.
+          If set to 'None' the magnetometer will not be used under any circumstance.
+          If no external source of yaw is available, it is possible to use post-takeoff
+          horizontal movement combined with GNSS velocity measurements to align the yaw angle.
+          If set to 'Init' the magnetometer is only used to initalize the heading.
       type: enum
       values:
         0: Automatic
         1: Magnetic heading
         5: None
+        6: Init
       default: 0
       reboot_required: true
     EKF2_MAG_ACCLIM: