code: def toradialvelocity(self, rf, v0):
          
          if is_measure(v0) and v0['type'] == 'doppler':
              return self.doptorv(rf, v0)
          else:
              raise TypeError('Illegal Doppler specified')
docs: Convert a Doppler type value (e.g. in radio mode) to a real
          radialvelocity. The type of velocity (e.g. *LSRK*) should be specified
  
          :param rf: radialvelocity reference code (see :meth:`radialvelocity`)
          :param v0: a doppler measure
  
          Example::
  
              a = dm.doppler('radio',0.4)
              dm.toradialvelocity('topo',a)