H3C is a PostgreSQL library dedicated for astronomy. The Library contains functions to index positions (ra,de) with the HEALPix and others to make a cone search or a crossmatch, it can work with circle, polygon or box.

we use the healpix library provided by the Nasa (see: http://healpix.jpl.nasa.gov/index.shtml)
the library is inpired from Q3C (see http://code.google.com/p/q3c/)
the library use the NESTED numerotation (see NSIDE)

See also: Installation guide; Licence GPL licence; H3C tuning; SQL functions