\cgidef{-ic -tex -mail -oglu}
\subsection{The installation of the PMM USNO-A2.0 Catalog at CDS}

The original catalog consisted in 24 files, one for a 7.5\deg
 strip in declination. Each file was extended to a directory,
 named {\tt N000}...{\tt N8230} and {\tt S0000}...{\tt S8230}, i.e.
 with the same conventions as those used for the
 \A{/cgi-bin/VizieR?-source=GSC}{GSC Catalog}.

 In each of these directories, there is one file for 30{\em min}
 (i.e. {7.5\deg} at the Equator) in right asension; the total
 number of files is therefore $24\times48 = 1152$ files,
 with an average number of 20,000 (near the poles) to 800,000 objets
 per file. In each of these files, the range of the coordinates is then
 restricted to {7.5\deg}, i.e. a maximal value of 2,700,000 when the 
 coordinates are expressed in their original units of 10mas. 
 The final grouping allowed to reduce one record to 7 or 8 bytes
 (the mean is close to 7).

The resulting catalog
occupies only 3.6Gbytes, including all transformation and query software;
the full $526\times 10^6$ objects are tested in about 45 minutes 
(i.e. $5\mu s$ 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 70% of cpu usage)
for a search by position on the catalog, keeping the 10 closest stars
{\em(actually performed on the USNO-A1.0 which was converted in April 1997
with an almost identical software)}:

\begin{verbatim}
=========================================================================
   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
=========================================================================
\end{verbatim}

A \A{ftp://cdsarc.u-strasbg.fr/pub/cats/cdsclient.tar.Z}{client/server 
 access} to the PMM USNO-A2.0 Catalog -- as well as to other catalogues --
 is also available via the {\em findpmm2} program which is part
 of the {\em cdsclient} package.

\begin{address} Fran\c cois Ochsenbein, \glutag{CDS.home} \\
E-mail: francois@simbad.u-strasbg.fr \\
{\em(October 1998)}
\end{address}