Algorithm

The installation of the PMM USNO-A1.0 Catalog at CDS and CADC

The original catalog consisted in 24 files, one for a 7.5° strip in declination. Each file was extended to a directory, named N000...N8230 and S0000...S8230, i.e. with the same conventions as those used for the GSC Catalog.

In each of these directories, there is one file for 30min (i.e. 7.5° at the Equator) in right asension; the total number of files is therefore 24×48 = 1152 files, with an average number of 20,000 (near the poles) to 800,000 objets per file. The resulting catalog occupies only 3.4Gbytes, including all transformation and query software; the full 488×106 objects are tested in about 40 minutes (i.e. 5µs per object) on a Sparc-20 (72MHz).

A few benchmarks made on a Sparc-20 (72MHz) give the following average elapsed times (between 15 and 70for a search by position on the catalog, keeping the 10 closest stars:

========================================================================= Search Tested stars Time required Reading time Radius (') per target (s) for 1 star (microsec) ------------------------------------------------------------------------- 2.5 14153 0.09 6.4 10.0 66394 0.24 3.6 30.0 201351 0.67 3.3 =========================================================================

A client/server access to the PMM USNO-A1.0 Catalog - as well as to other catalogues - is also available via the findpmm program which is part of the cdsclient package.

François Ochsenbein, CDS
E-mail: francois@simbad.u-strasbg.fr
(March 1997)

Please report any problems to CADC