AC_PosControl: add shift_pos_xy_target

libraries/AC_AttitudeControl/AC_PosControl.cpp

@@ -532,6 +532,19 @@ void AC_PosControl::set_xy_target(float x, float y)
     _pos_target.y = y;
 }
 
+/// shift position target target in x, y axis
+void AC_PosControl::shift_pos_xy_target(float x_cm, float y_cm)
+{
+    // move pos controller target
+    _pos_target.x += x_cm;
+    _pos_target.y += y_cm;
+
+    // disable feed forward
+    if (!is_zero(x_cm) || !is_zero(y_cm)) {
+        freeze_ff_xy();
+    }
+}
+
 /// set_target_to_stopping_point_xy - sets horizontal target to reasonable stopping position in cm from home
 void AC_PosControl::set_target_to_stopping_point_xy()
 {

libraries/AC_AttitudeControl/AC_PosControl.h

@@ -209,6 +209,9 @@ public:
     /// set_xy_target in cm from home
     void set_xy_target(float x, float y);
 
+    /// shift position target target in x, y axis
+    void shift_pos_xy_target(float x_cm, float y_cm);
+
     /// get_desired_velocity - returns xy desired velocity (i.e. feed forward) in cm/s in lat and lon direction
     const Vector3f& get_desired_velocity() { return _vel_desired; }