mc_att_control: adapt setpoint on estimation reset

There was a gap where the attitude controller already used the estimate
with a new reference but the last known attitude setpoint was still based
on the old reference. This leads to a big glitch on reset because until
the attitude setpoint gets updated the error is wrong and as large as the
attitude delta of the reset.

src/modules/mc_att_control/AttitudeControl/AttitudeControl.hpp

@@ -77,6 +77,13 @@ public:
 	 */
 	void setAttitudeSetpoint(const matrix::Quatf &qd, const float yawspeed_setpoint) { _attitude_setpoint_q = qd; _yawspeed_setpoint = yawspeed_setpoint; }
 
+	/**
+	 * Adjust last known attitude setpoint by a delta rotation
+	 * Optional use to avoid glitches when attitude estimate reference e.g. heading changes.
+	 * @param q_delta delta rotation to apply
+	 */
+	void adaptAttitudeSetpoint(const matrix::Quatf &q_delta) { _attitude_setpoint_q = q_delta * _attitude_setpoint_q; }
+
 	/**
 	 * Run one control loop cycle calculation
 	 * @param q estimation of the current vehicle attitude unit quaternion

src/modules/mc_att_control/mc_att_control_main.cpp

@@ -286,7 +286,9 @@ MulticopterAttitudeControl::Run()
 		// Check for a heading reset
 		if (prev_quat_reset_counter != _v_att.quat_reset_counter) {
 			// we only extract the heading change from the delta quaternion
-			_man_yaw_sp += Eulerf(Quatf(_v_att.delta_q_reset)).psi();
+			const Quatf delta_q_reset(_v_att.delta_q_reset);
+			_man_yaw_sp += Eulerf(delta_q_reset).psi();
+			_attitude_control.adaptAttitudeSetpoint(delta_q_reset);
 		}
 
 		const hrt_abstime now = hrt_absolute_time();