Optionally download only astrometry index files for a specific part of the sky.

[juanep97]

It would be nice to be able to optionally download only the index files required to perform the astrometry of a given part of the sky. That way, we could reduce the download time and the storage needed to perform some tests (e.g. in CI actions).

As far as I know, right now the module tries to download all files for the selected series and scales (and it tries

Do you think this is feasible? I will try to look on how to do it to contribute, but if anyone can give me some guidelines on how this might be implemented, I would be thankful.

[alexw-im]

AFAIK only some catalogs at smaller FOVs are split up into separate healpixes in separate .fits files. I imagine you mean "I know my solution is in 4200-12.fits so just get that one"?

I wonder how astrometry itself does this when given a location hint? I've only worked with wider FOVs than get split up into healpixes, and thus I only ever get speedup improvements from scale hints rather than location hints.

[aMarcireau]

Astrometry.net indexes are indeed divided into smaller files. You can download them individually from http://data.astrometry.net (which is what this package does under the hood).

The function index_files is a short-hand for "download these files and return a list of paths". If you downloaded one (or several) files individually, you can bypass it and initialize a solver directly.

import pathlib

import astrometry

index_files = [pathlib.Path("path/of/manually/downloaded/file/1"), pathlib.Path("path/of/manually/downloaded/file/2")]

solver = astrometry.Solver(index_files=index_files)

You can also inherit astrometry.Series if you wish to re-use the existing download logic.