Added vo module

[andamian]

This is a generic VO module for image searches that uses only VO services and standards to implement astroquery basic API. Data providers, such as ALMA or CADC, can further customize this functionality for their own modules.

Note that this PR depends on a number of changes in pyvo that have not been released yet but will be in the near future.

[bsipocz]

Before doing any review here, I suppose we need to discuss the ideas here a bit, both from the user perspective as well as the holistic view of what goes into astroquery vs pyvo.

[andamian]

pyvo contains the IVOA spec implementations (One big exception is VOTable which is already part of the core astropy). It is a library for developers that are familiar with IVOA standards.

astroquery on the other hand offers a common API for accessing data from various data providers. The users of astroquery do not need to know the details of the underlying access mechanisms and protocols. To that end, the vo module proposed in this PR attempts to do just that: implement that generic astroquery API by putting together protocols implemented in pyvo for those data providers that offer VO services. Users need to know little (if anything) about these protocols while the data providers can get instant exposure to the astroquery general community.

[keflavich]

@andamian when you have a chance, could you revisit this? Are the needed pyvo changes done?

[andamian]

This was completely out of my radar. I'll add it to my list of things to do. I don't think there's anything missing in pyvo.

[pllim]

A long time ago, there was also a astropy.vo module, so having astroquery.vo is going to be super confusing.

[bsipocz]

I'm going through the open PRs, and while the motivation here is something more generic I suppose this could certainly address my desire of one/multiple VO based baseclass: #2360

[bsipocz]

Overall, regarding the generic module I think it's an interesting idea and certainly needs more discussion between pyvo and astroquery maintainers.

[andamian]

If there are no objections, I think I'll close this here and try it in PyVO instead to get more exposure from the IVOA folks.

[andamian]

OK. Closing it here.

[bsipocz]

Thanks @andamian!