Hi Andrea,

What you propose is essentially what I'm talking about, in
the sense of detecting catalog overlap (that is, one star
referenced in many catalogs). Guide currently detects overlap
between Tycho-2 and GSC-ACT. It can do that because the catalogs
are explicitly matched by number, which makes matters much
simpler. Guide just shows Tycho-2 stars, keeping track of
which ones are on-screen. When it comes across a GSC-ACT star
with the same number, it says, "We already drew this one,
using better Tycho-2 data."

This could be extended to other catalogs, drawn in order
of quality (probably Tycho-2, UCAC-2, A2.0, GSC-ACT). For
the last three catalogs, Guide would say: "We just drew a
star within, say, one arcsecond of the position from this
new catalog. It's probably a repeat."

I can't say that it's a no-brainer, but yes, it's possible.

-- Bill