def _createFilenames(self):
        """
        Create a masked records array of all filenames for the given set of
        pixels and store the existence of those files in the mask values.

        Parameters:
        -----------
        None

        Returns:
        --------
        recarray : pixels and mask value
        """
        nside_catalog = self['coords']['nside_catalog']
        npix = hp.nside2npix(nside_catalog)
        pixels = np.arange(npix)

        catalog_dir = self['catalog']['dirname']
        catalog_base = self['catalog']['basename']
        catalog_path = os.path.join(catalog_dir,catalog_base)

        mask_dir    = self['mask']['dirname']
        mask_base_1 = self['mask']['basename_1']
        mask_base_2 = self['mask']['basename_2']
        mask_path_1 = os.path.join(mask_dir,mask_base_1)
        mask_path_2 = os.path.join(mask_dir,mask_base_2)

        data = np.ma.empty(npix,dtype=[('pix',int), ('catalog',object), 
                                       ('mask_1',object), ('mask_2',object)])
        mask = np.ma.empty(npix,dtype=[('pix',bool), ('catalog',bool), 
                                       ('mask_1',bool), ('mask_2',bool)])

        # Build the filenames
        data['pix']     = pixels
        data['catalog'] = np.char.mod(catalog_path,pixels)
        data['mask_1']  = np.char.mod(mask_path_1,pixels)
        data['mask_2']  = np.char.mod(mask_path_2,pixels)

        # Build the mask of existing files using glob
        mask['catalog'] = ~np.in1d(data['catalog'],glob.glob(catalog_dir+'/*'))
        mask['mask_1']  = ~np.in1d(data['mask_1'],glob.glob(mask_dir+'/*'))
        mask['mask_2']  = ~np.in1d(data['mask_2'],glob.glob(mask_dir+'/*'))

        for name in ['catalog','mask_1','mask_2']:
            if np.all(mask[name]): logger.warn("All '%s' files masked"%name)

        # mask 'pix' if all files not present
        mask['pix'] = mask['catalog'] | mask['mask_1'] | mask['mask_2']

        if np.all(mask['pix']): logger.warn("All pixels masked")

        return np.ma.MaskedArray(data, mask, fill_value=[-1,'','',''])
Create a masked records array of all filenames for the given set of
        pixels and store the existence of those files in the mask values.

        Parameters:
        -----------
        None

        Returns:
        --------
        recarray : pixels and mask value