leverage cf_xarray to get x_coords (lon) and y_coords (lat)?

Currently - if the coordinates are not named "lat" and "lon" we need to pass them manually, e.g.:

import regionmask
import xarray as xr

rasm = xr.tutorial.load_dataset("rasm")

regionmask.defined_regions.srex.mask(rasm.xc, rasm.yc)

cf_xarray uses attrs to determine cf compliant “coordinates” - irrespective of their name. We could use this to allow

import cf_xarray # require manual import?

regionmask.defined_regions.srex.mask(rasm)

by using

x_coords = data.cf["longitude"]
y_coords = data.cf["latitude"]

internally.

@jbusecke @aaronspring that may be of interest of you.

[aaronspring]

I like the general idea and the mask(ds, use_cf=bool) implementation

[jbusecke]

I like this general idea a lot. I would always raise a warning in the case of potential ambiguity (this might be done by catching errors from cf_xarray or some logic in regionmask itself). This would mean that in simple cases “the magic just works” and if there are options to consider, the user is warned. To me that seems ideal.