docs: 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,'','',''])