Scheme Comparison

There are a number of objects which can be used to regrid Iris cubes. These each have their own quirks which this page aims to describe.

Overview: Schemes

The top level objects provided by iris-esmf-regrid as the schemes, these are designed to behave the same as the schemes in iris.analysis. The three schemes iris-esmf-regrid provides are ESMFAreaWeighted, ESMFBilinear and ESMFNearest. These wrap the ESMF regrid methods CONSERVE, BILINEAR or NEAREST_STOD respectively. The schemes can be by the pattern:

result_cube = source_cube.regrid(target_cube, ESMFAreaWeighted())

These schemes are flexible and allow the source or target cube to be defined on an unstructured mesh while the other cube is define on a structured grid.

Overview: Regridders

The regridders are objects one level down from schemes. A regridder is a class which is designed to handle the regridding of data from one specific source to one specific target. Regridders are useful because regridding involves a computationally expensive intitialisation step which can be avoided whenever a regridder is reused. iris-esmf-regrid provides the regridders ESMFAreaWeightedRegridder, ESMFBilinearRegridder and ESMFNearestRegridder which correspond to the schemes ESMFAreaWeighted, ESMFBilinear and ESMFNearest respectively. These can be initialised either by:

regridder = ESMFAreaWeightedRegridder(source_cube, target_cube)

or equivalently by:

regridder = ESMFAreaWeighted().regridder(source_cube, target_cube)

This regridder can then be called by:

result_cube = regridder(source_cube, target_cube)

which can be reused on any cube defined on the same horizontal coordinates as source_cube.

There are also the experimental regridders MeshToGridESMFRegridder and GridToMeshESMFRegridder. These were formerly the only way to do regridding with a source or target cube defined on an unstructured mesh. These are less flexible and require that the source/target be defined on a grid/mesh. Unlike the above regridders whose method is fixed, these regridders take a method keyword of conservative, bilinear or nearest. All the functionality in these regridders has now been ported into the above schemes and regridders. Before version 0.10, these were the only regridders capable of being saved and loaded by esmf_regrid.experimental.io, so while the above generic regridders are recomended, these regridders are still available for the sake of consistency with regridders saved from older versions.

Overview: Miscellaneous Functions

The functions regrid_rectilinear_to_rectilinear(), regrid_unstructured_to_rectilinear() and regrid_rectilinear_to_unstructured() exist as alternative ways to call the same regridding functionality:

result = regrid_rectilinear_to_rectilinear(source_cube, target_cube)

This function also has a method keyword which can be conservative, bilinear or nearest, with conservative being the default.

Differences Between Methods

This section is under development, for more details see the API documentation.