code: def _defineVariables(self):
          
          logger.info('Catalog contains %i objects'%(len(self.data)))
  
          mc_source_id_field = self.config['catalog']['mc_source_id_field']
          if mc_source_id_field is not None:
              if mc_source_id_field not in self.data.dtype.names:
                  array = np.zeros(len(self.data),dtype='>i8') # FITS byte-order convention
                  self.data = mlab.rec_append_fields(self.data,
                                                     names=mc_source_id_field,
                                                     arrs=array)
              logger.info('Found %i simulated objects'%(np.sum(self.mc_source_id>0)))
docs: Helper funtion to define pertinent variables from catalog data.
  
          ADW (20170627): This has largely been replaced by properties.