Hi David, Hi Sadie,

In the regridding functionality, there currently is a restriction on the size of the dimensions of the grid: any dimension needs to be greater than one.

But after some testing, I found out that it is only problematic to have a size 1 dimension on the source grid, but not on the destination grid. Indeed, ESMF only raises an error when the source grid has a size 1 dimension (see https://github.com/esmf-org/esmf/blob/b4c535d3b3925f43ccad78191f40d6c51f6f2e7e/src/Infrastructure/Field/src/ESMF_FieldRegrid.F90#L2840-L2847). I am not sure what is the underlying reason for this restriction in ESMF, and it is surprising that it complains only for the source grid.

Nevertheless, as a user, I see some situations where I could benefit from the ability to regrid to a destination resolution composed of a single grid cell (e.g. pre-process some gridded data to get a lumped value for a given region). Since it seems to be working for all regridding methods, I thought it may be good to lift the restriction on the destination grid in cf-python.

What do you think?
Also, do you have any idea why ESMF would restrict the size 1 dimension on the source grid only?