tripolar grid

I’m trying to regrid the cmip5 data from the ocean model NEMO, which used a tripolar grid (still curvilinear). It seems none of the bilinear, patch and conservative method works. I thought bilinear and patch do not require grid corners but do they require some other specific grid configurations? The conservative method doesn’t work because I can’t figure out the corners. The corners in the data are specified as 4 vertices but the orientations seem not constant. I mean in the tripolar grid the four faces of the grid are not necessarily oriented east-west or north-south, what is the orientation that is acceptable? The notebook is uploaded here. https://github.com/JianghuiDu/cmip5

[JianghuiDu]

Thanks! Finally figured out the orientation convention.

[bekozi]

CF convention, as far as I know, follows from SCRIP which ESMF adheres to closely: http://cfconventions.org/Data/cf-conventions/cf-conventions-1.7/cf-conventions.html#cell-boundaries. And, yes, cell boundaries should defined in a CCW manner in ESMF.

I put a short notebook together to demonstrate how the corner conversion functions I linked to are used. This was for my own benefit as well. ocgis corners may be out of compliance with CF…never confirmed it was compliant necessarily (hence the lack of convention in the function names). You may find you need to adjust indexing. In case it’s useful, this is where the (m, n, 4) conversion to ESMF corners is used in ocgis-esmpy.

I guess that get_esmf_corners_from_ocgis_corners() assumes Fortran-ordering (lon, lat)?

It does produce Fortran ordering, but it only works off a single coordinate array. Need to call the function twice for lat and lon corners.