AC_AttitudeControl: add comments for system ID disturbance input code

libraries/AC_AttitudeControl/AC_PosControl.cpp

@@ -643,6 +643,7 @@ void AC_PosControl::update_xy_controller()
     // Position Controller
 
     const Vector3f &curr_pos = _inav.get_position_neu_cm();
+    // determine the combined position of the actual position and the disturbance from system ID mode
     Vector3f comb_pos = curr_pos;
     comb_pos.xy() += _disturb_pos;
     Vector2f vel_target = _p_pos_xy.update_all(_pos_target.x, _pos_target.y, comb_pos);
@@ -655,6 +656,7 @@ void AC_PosControl::update_xy_controller()
     // Velocity Controller
 
     const Vector2f &curr_vel = _inav.get_velocity_xy_cms();
+    // determine the combined velocity of the actual velocity and the disturbance from system ID mode
     Vector2f comb_vel = curr_vel;
     comb_vel += _disturb_vel;
     Vector2f accel_target = _pid_vel_xy.update_all(_vel_target.xy(), comb_vel, _dt, _limit_vector.xy());

libraries/AC_AttitudeControl/AC_PosControl.h

@@ -462,8 +462,8 @@ class AC_PosControl
     float       _jerk_max_xy_cmsss;       // Jerk limit of the xy kinematic path generation in cm/s^3 used to determine how quickly the aircraft varies the acceleration target
     float       _jerk_max_z_cmsss;        // Jerk limit of the z kinematic path generation in cm/s^3 used to determine how quickly the aircraft varies the acceleration target
     float       _vel_z_control_ratio = 2.0f;    // confidence that we have control in the vertical axis
-    Vector2f    _disturb_pos;
-    Vector2f    _disturb_vel;
+    Vector2f    _disturb_pos;           // position disturbance generated by system ID mode
+    Vector2f    _disturb_vel;           // velocity disturbance generated by system ID mode
 
     // output from controller
     float       _roll_target;           // desired roll angle in centi-degrees calculated by position controller