code: def asbaseline(self, pos):
          
          if not is_measure(pos) or pos['type'] not in ['position', 'baseline']:
              raise TypeError('Argument is not a position/baseline measure')
          if pos['type'] == 'position':
              loc = self.measure(pos, 'itrf')
              loc['type'] = 'baseline'
              return self.measure(loc, 'j2000')
          return pos
docs: Convert a position measure into a baseline measure. No actual
          baseline is calculated, since operations can be done on positions,
          with subtractions to obtain baselines at a later stage.
  
          :param pos: a position measure
          :returns: a baseline measure