Wait for the vehicle to reach the specified altitude.

        Wait for the vehicle to get within epsilon meters of the
        given altitude.  If rel is True (the default), use the
        global_relative_frame. If rel is False, use the global_frame.
        If timeout is nonzero, raise a TimeoutError if the specified
        altitude has not been reached after timeout seconds.

def wait_for_alt(self, alt, epsilon=0.1, rel=True, timeout=None):
        '''Wait for the vehicle to reach the specified altitude.

        Wait for the vehicle to get within epsilon meters of the
        given altitude.  If rel is True (the default), use the
        global_relative_frame. If rel is False, use the global_frame.
        If timeout is nonzero, raise a TimeoutError if the specified
        altitude has not been reached after timeout seconds.
        '''

        def get_alt():
            if rel:
                alt = self.location.global_relative_frame.alt
            else:
                alt = self.location.global_frame.alt

            return alt

        def check_alt():
            cur = get_alt()
            delta = abs(alt - cur)

            return (
                (delta < epsilon) or
                (cur > alt > start) or
                (cur < alt < start)
            )

        start = get_alt()

        self.wait_for(
            check_alt,
            timeout=timeout,
            errmsg='failed to reach specified altitude')