[AstroPy] Some Feedbacks about Astropy

[Erik Tollerud]

> 2. Though there's astropy.coordinates.matching.match_coordinates_sky to cross-correlate two catalogs, it doesn't allow user to specify matching radius and matching mode (e.g., one-one match). I've made a function to do so, and hope similar function can be included in astropy (https://github.com/Guang91/Astronomers_Tool_Box/blob/master/my_srcor.py).

The idea is to use it like this (this is astropy 0.4 syntax - for
astropy 0.3 it's similar, but replace SkyCoord with `ICRS` or whatever
class makes sense for your coordinates):

catalog = SkyCoord(ra_cat*u.deg, dec_cat*u.deg, frame='icrs')
coordstomatch = SkyCoord(ra*u.deg, dec*u.deg, frame='icrs')

idx, d2d, d3d = coordstomatch.match_to_catalog_sky(catalog)

coordinateswithmatches = coordstomatch[d2d < 3*u.arcmin]
catalogwithmatches = catalog[idx[d2d < 3*u.arcmin]]


As for the "matching mode", the idea is that there are a lot of
different "modes" people use, and match_to_catalog_sky (or
match_to_catalog_3d) along with the `nthneighbor` argument should be
flexible enough to take care of most of them.  Can you be more
specific about exactly what sort of mode you think is missing?


This was not too thoroughly documented before v0.4 (the version about
to be release), but there's a lot more there in v0.4. See
http://devdocs.astropy.org/coordinates/matchsep.html#matching-catalogs
(that's the developer documentation, but this will become
http://docs.astropy.org/en/stable/coordinates/matchsep.html#matching-catalogs
when 0.4 is released).



-- 
Erik T