unstructured grids

Has anyone used xesmf to regrid from unstructured grids like ICON, MPAS or FESOM?

Unstructured grids like ICON just have one spatial dimension like ncells and 2 spatial coordinates clon and clat.

I tried and failed.

https://gist.github.com/aaronspring/fd54970f71a39e26ab54a8b47170533d

[sol1105]

Using locstream to at least offer nearest neighbour remapping is a nice idea, since apparently the data on unstructured grids of the CMIP models is stored in this locstream-like format. I tested it for CMIP6 published ICON-OES and FESOM data: https://nbviewer.jupyter.org/github/roocs/regrid-prototype/blob/main/docs/notebooks/xESMF_unstructured_locstream_ref.ipynb

The only problem I encountered originates from the following lines in xesmf/backend.py:

def esmf_regrid_build( [...]):
[...]
    # ESMF bug? when using locstream objects, options src_mask_values
    # and dst_mask_values produce runtime errors
    allow_masked_values = True
    if isinstance(sourcefield.grid, ESMF.api.locstream.LocStream):
        allow_masked_values = False
    if isinstance(destfield.grid, ESMF.api.locstream.LocStream):
        allow_masked_values = False
[...]

Due to an ESMF bug masks are ignored when generating the weights. I tried then to apply a mask for target grid, by manipulating the weights after their creation and by applying the mask on the regridded data. Both options worked. So one could

• add the option to manipulate the weights when a mask for the target grid is defined and the locstream option is used to make up for at least half of the ESMF bug
• add the possibility to apply a mask on the regridded data to frontend.BaseRegridder.__call__ to be able to call it like: ds_out=regridder(ds, keep_attrs, skipna, na_thres, mask_out)
• Should a warning be issued when a mask is ignored? It would have helped me at least 😃 What do you think?

[kthyng]

ok thanks.