AP_L1_Control: use get_distance_NE instead of location_diff

libraries/AP_L1_Control/AP_L1_Control.cpp

@@ -241,13 +241,13 @@ void AP_L1_Control::update_waypoint(const struct Location &prev_WP, const struct
     _L1_dist = MAX(0.3183099f * _L1_damping * _L1_period * groundSpeed, dist_min);
 
     // Calculate the NE position of WP B relative to WP A
-    Vector2f AB = location_diff(prev_WP, next_WP);
+    Vector2f AB = prev_WP.get_distance_NE(next_WP);
     float AB_length = AB.length();
 
     // Check for AB zero length and track directly to the destination
     // if too small
     if (AB.length() < 1.0e-6f) {
-        AB = location_diff(_current_loc, next_WP);
+        AB = _current_loc.get_distance_NE(next_WP);
         if (AB.length() < 1.0e-6f) {
             AB = Vector2f(cosf(get_yaw()), sinf(get_yaw()));
         }
@@ -255,7 +255,7 @@ void AP_L1_Control::update_waypoint(const struct Location &prev_WP, const struct
     AB.normalize();
 
     // Calculate the NE position of the aircraft relative to WP A
-    Vector2f A_air = location_diff(prev_WP, _current_loc);
+    const Vector2f A_air = prev_WP.get_distance_NE(_current_loc);
 
     // calculate distance to target track, for reporting
     _crosstrack_error = A_air % AB;
@@ -276,7 +276,7 @@ void AP_L1_Control::update_waypoint(const struct Location &prev_WP, const struct
     } else if (alongTrackDist > AB_length + groundSpeed*3) {
         // we have passed point B by 3 seconds. Head towards B
         // Calc Nu to fly To WP B
-        Vector2f B_air = location_diff(next_WP, _current_loc);
+        const Vector2f B_air = next_WP.get_distance_NE(_current_loc);
         Vector2f B_air_unit = (B_air).normalized(); // Unit vector from WP B to aircraft
         xtrackVel = _groundspeed_vector % (-B_air_unit); // Velocity across line
         ltrackVel = _groundspeed_vector * (-B_air_unit); // Velocity along line
@@ -369,7 +369,7 @@ void AP_L1_Control::update_loiter(const struct Location &center_WP, float radius
     _L1_dist = 0.3183099f * _L1_damping * _L1_period * groundSpeed;
 
     //Calculate the NE position of the aircraft relative to WP A
-    Vector2f A_air = location_diff(center_WP, _current_loc);
+    const Vector2f A_air = center_WP.get_distance_NE(_current_loc);
 
     // Calculate the unit vector from WP A to aircraft
     // protect against being on the waypoint and having zero velocity