Review complete; more comments on the PR (but I'll reply to your comments above here).
- I think you can make this work for more types of catalogs by using CatalogT<Record> instead of SortedCatalogT<Record>. That should also be non-ambiguous.
- I very much agree that it'd be good to add Value typedefs to the FunctorKeys. I'd be supportive of either doing that on this ticket or making that a separate ticket.
- I think it is hard to do this generically and make that usable from Python. The more Pythonic thing to do might be to find a way to make ColumnView return Point or Coord columns in a form that's compatible with SkyWcs/Transform, and have a faster, easier way to turn a list of Records or a list of pairs of Records into a Catalog. That's all well beyond the scope of this ticket, of course.