The `dcr.get_refraction` function is kind of an implementation detail.  This function is the one that users will primarily interact with.  So I think the parameter descriptions should be made explicit here.

Also, I would leave off the LSST references in the `@param` descriptions, since we don't want to be too partisan in GalSim.  :)  Perhaps just a single line in the main part of the docstring: "The default values for temperature and pressure are expected to be appropriate for LSST at Cerro Pachon, Chile, but they are broadly reasonable for most observatories."  Feel free to reword, but something like that one time is probably sufficient.