@Override
 public List<msg_mission_item> packMissionItem() {
   List<msg_mission_item> list = super.packMissionItem();
   msg_mission_item mavMsg = list.get(0);
   mavMsg.x = (float) coordinate.getLatitude();
   mavMsg.y = (float) coordinate.getLongitude();
   mavMsg.z = (float) coordinate.getAltitude();
   return list;
 }
 public void setPosition(LatLong position) {
   coordinate.set(position);
 }
 public void setAltitude(double altitude) {
   coordinate.setAltitude(altitude);
 }