Add a module and class for handling sky grids for pycbc_multi_inspiral

[titodalcanton]

Calculating the coherent network SNR (pycbc_multi_inspiral) requires a grid of points in the sky. This adds a module and class to manage such grids in a more centralized way.

Standard information about the request

This is mostly refactoring existing code into a new module. This change affects PyGRB but does not change any output.

Motivation

pycbc_multi_inspiral is a very long script at this point, and pycbc_make_sky_grid might also become very long as we implement various algorithms for placing sky grids available in the literature. Centralizing the management of sky grids, including reading/writing them from/to files, seems beneficial.

Contents

I added a pycbc.tmpltbank.sky_grid module which currently contains a SkyGrid class, with methods to read and write sky grids from HDF5 files, calculate the antenna patterns and time delays over the grid for a network of detectors, and handle CLI arguments related to sky grids.

Links to any issues or associated PRs

None.

Testing performed

I wrote a short script to plot the antenna patterns and time delays over a sky grids of random points for various detectors, and visually checked that those made sense:

Additional notes

None.

• The author of this pull request confirms they will adhere to the code of conduct

[titodalcanton]

Note that I posed a couple design questions in the constructor of SkyGrid, and that I want to add explicit units and angular convention to the docstring, which I have not done yet.

[spxiwh]

Francesco should probably give final approval for this, but it all looks good to me. I left comments in response to the questions raised.

[titodalcanton]

@pannarale this is now ready for your review.