environments, meta-astrometry

I got the K+A environments paper closer to being ready for submission.

I discussed with Sam possible projects for his new students working on astrometry projects, including a staged introduction of functionality, from mundane to wondrous, at astrometry.net. In particular, we discussed the value of what I would call a "footprint server" that, for any point on the sky (or every possible image footprint on the sky), returns all the known, public astronomical images whose footprints overlap that point (or image). Although some archive searches come close to this, none of them exactly perform this function, to my knowledge. (I think they fail to do this because the database tables they work off generally know about pointing but generally don't know about imager orientation or geometry.)