def torestfrequency(self, f0, d0):
        """Convert a frequency measure and a doppler measure (e.g.
        obtained from another spectral line with a known rest frequency) to
        a rest frequency.

        :param f0: frequency reference code (see :meth:`frequency`)
        :param v0: a doppler measure

        Example::

            dp = dm.doppler('radio', '2196.24984km/s')  # a measured doppler speed
            f = dm.frequency('lsrk','1410MHz')    # a measured frequency
            dm.torestfrequency(f, dp)        # the corresponding rest frequency

        """
        if is_measure(f0) and f0['type'] == 'frequency' \
                and is_measure(d0) and d0['type'] == 'doppler':
            return self.torest(f0, d0)
        else:
            raise TypeError('Illegal Doppler or rest frequency specified')
Convert a frequency measure and a doppler measure (e.g.
        obtained from another spectral line with a known rest frequency) to
        a rest frequency.

        :param f0: frequency reference code (see :meth:`frequency`)
        :param v0: a doppler measure

        Example::

            dp = dm.doppler('radio', '2196.24984km/s')  # a measured doppler speed
            f = dm.frequency('lsrk','1410MHz')    # a measured frequency
            dm.torestfrequency(f, dp)        # the corresponding rest frequency