GNSS yaw: use dedicated observation noise

src/modules/ekf2/EKF/common.h

@@ -276,6 +276,9 @@ struct parameters {
 	float mag_yaw_rate_gate{0.25f};		///< yaw rate threshold used by mode select logic (rad/sec)
 	const float quat_max_variance{0.0001f};	///< zero innovation yaw measurements will not be fused when the sum of quaternion variance is less than this
 
+	// GNSS heading fusion
+	float gps_heading_noise{0.1f};		///< measurement noise standard deviation used for GNSS heading fusion (rad)
+
 	// airspeed fusion
 	float tas_innov_gate{5.0f};		///< True Airspeed innovation consistency gate size (STD)
 	float eas_noise{1.4f};			///< EAS measurement noise standard deviation used for airspeed fusion (m/s)

src/modules/ekf2/EKF/gps_yaw_fusion.cpp

@@ -70,7 +70,7 @@ void Ekf::fuseGpsYaw()
 
 	// using magnetic heading process noise
 	// TODO extend interface to use yaw uncertainty provided by GPS if available
-	const float R_YAW = sq(fmaxf(_params.mag_heading_noise, 1.0e-2f));
+	const float R_YAW = sq(fmaxf(_params.gps_heading_noise, 1.0e-2f));
 
 	// calculate intermediate variables
 	const float HK0 = sinf(_gps_yaw_offset);
@@ -209,7 +209,7 @@ bool Ekf::resetYawToGps()
 	// GPS yaw measurement is alreday compensated for antenna offset in the driver
 	const float measured_yaw = _gps_sample_delayed.yaw;
 
-	const float yaw_variance = sq(fmaxf(_params.mag_heading_noise, 1.0e-2f));
+	const float yaw_variance = sq(fmaxf(_params.gps_heading_noise, 1.0e-2f));
 	resetQuatStateYaw(measured_yaw, yaw_variance, true);
 
 	_time_last_gps_yaw_fuse = _time_last_imu;