Helper funtion to define pertinent variables from catalog data.

        ADW (20170627): This has largely been replaced by properties.

def _defineVariables(self):
        """
        Helper funtion to define pertinent variables from catalog data.

        ADW (20170627): This has largely been replaced by properties.
        """
        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)))