pub fn database_density(db_name: &str) -> Option<f64>Expand description
The star density, in stars per square degree, that the database db_name is
built to, or None if it is not known.
ASTAP’s databases are density-limited: every tile holds the brightest Gaia stars
up to a fixed number per square degree, and ASTAP reads that number from the
name, two digits times 100 (d80 8000, d50 5000, d20 2000, d05, v05 and
g05 500, v50 5000). The exceptions are the old 17/18 databases, which were
magnitude-limited (no figure), and w08, whose digits are its magnitude limit,
8: its single all-sky file holds 41 265 stars, one per square degree.
A field can hold no more catalogue stars than this density times its area, so detecting more image stars than that only adds patterns that cannot match.