Go straight down and turn off the motors.

        Do not call this function if you use the with keyword. Landing is
        done automatically when the context goes out of scope.

        :param velocity: The velocity (meters/second) when going down
        :return:

def land(self, velocity=VELOCITY):
        """
        Go straight down and turn off the motors.

        Do not call this function if you use the with keyword. Landing is
        done automatically when the context goes out of scope.

        :param velocity: The velocity (meters/second) when going down
        :return:
        """
        if self._is_flying:
            self.down(self._thread.get_height(), velocity)

            self._thread.stop()
            self._thread = None

            self._cf.commander.send_stop_setpoint()
            self._is_flying = False