Send SET_POSITION_TARGET_LOCAL_NED command to request the vehicle fly to a specified 
    location in the North, East, Down frame.

    It is important to remember that in this frame, positive altitudes are entered as negative 
    "Down" values. So if down is "10", this will be 10 metres below the home altitude.

    Starting from AC3.3 the method respects the frame setting. Prior to that the frame was
    ignored. For more information see: 
    http://dev.ardupilot.com/wiki/copter-commands-in-guided-mode/#set_position_target_local_ned

    See the above link for information on the type_mask (0=enable, 1=ignore). 
    At time of writing, acceleration and yaw bits are ignored.

def goto_position_target_local_ned(north, east, down):
    """	
    Send SET_POSITION_TARGET_LOCAL_NED command to request the vehicle fly to a specified 
    location in the North, East, Down frame.

    It is important to remember that in this frame, positive altitudes are entered as negative 
    "Down" values. So if down is "10", this will be 10 metres below the home altitude.

    Starting from AC3.3 the method respects the frame setting. Prior to that the frame was
    ignored. For more information see: 
    http://dev.ardupilot.com/wiki/copter-commands-in-guided-mode/#set_position_target_local_ned

    See the above link for information on the type_mask (0=enable, 1=ignore). 
    At time of writing, acceleration and yaw bits are ignored.

    """
    msg = vehicle.message_factory.set_position_target_local_ned_encode(
        0,       # time_boot_ms (not used)
        0, 0,    # target system, target component
        mavutil.mavlink.MAV_FRAME_LOCAL_NED, # frame
        0b0000111111111000, # type_mask (only positions enabled)
        north, east, down, # x, y, z positions (or North, East, Down in the MAV_FRAME_BODY_NED frame
        0, 0, 0, # x, y, z velocity in m/s  (not used)
        0, 0, 0, # x, y, z acceleration (not supported yet, ignored in GCS_Mavlink)
        0, 0)    # yaw, yaw_rate (not supported yet, ignored in GCS_Mavlink) 
    # send command to vehicle
    vehicle.send_mavlink(msg)