Use crates (from CIAO) for I/O + coordinate transforms rather than use astropy.io

[DougBurke]

Given that we (edit added for clarification by 'we' I mean the CXC) don't have a good story for all users on installing astropy within CIAO (for various reasons), I'd like to help update the scripts to use the CIAO python I/O library (i.e. crates) rather than astropy.io. Would there be an interest in this?

[darafferty]

I think it would be very nice to change the scripts to use crates if that would avoid the issues with CIAO and astropy, and I'd be happy to do so. I guess http://cxc.harvard.edu/ciao/ahelp/crates.html gives the relevant info?

[DougBurke]

I'm willing to do the conversion, since I don't think we have good-enough documentation for some of the things used here (e.g. the coordinate transformation parts)- but the changes will need some validation to check I've got the logic right.

[DougBurke]

You can see my initial attempts at https://github.com/DougBurke/Xmaps/tree/replace-astropy-by-crates - I had hoped to get to it earlier as I am on vacation starting the 2nd. It's not complete, but is a start (and I fully expect it to fail ...).

[DougBurke]

I've now done a "full" conversion on the https://github.com/DougBurke/Xmaps/tree/replace-astropy-by-crates branch. I fully expect it to contain bugs, in particular in how the various coordinate transformations are read in from files and applied (since I haven't been able to test any of this on real data).

Let me know where the problems are, although I'm going to be on holiday Aug 2 - 17th.

[DougBurke]

The code is available via PR #4 .