... Previous: Why Indexing the Sky is Desirable . ... An alternative algorithm, proposed here, is based on covering the sky with pixels of approximately equal area, and assigning a unique integer to each pixel. ... For each table, the pixel code value corresponding to the central position (RA, Dec) of each source is computed and inserted into a new column called PCODE. ... This cannot be the primary index of a table since PCODE values are not necessarily unique: one pixel may contain more than one...