Add iris-esmf-regrid as a dependency

doc/recipe/preprocessor.rst

@@ -926,10 +926,6 @@ example of its usage in an ESMValTool preprocessor is:
             reference: esmf_regrid.schemes:ESMFAreaWeighted
             mdtol: 0.7
 
-.. TODO: Remove the following warning once things have settled a bit.
-.. warning::
-   Just as the mesh support in Iris itself, this new regridding package is
-   still considered experimental.
 
 .. _ensemble statistics:
 

environment.yml

@@ -18,6 +18,7 @@ dependencies:
   - humanfriendly
   - importlib_resources
   - iris>=3.2.1
+  - iris-esmf-regrid
   - isodate
   - jinja2
   - nc-time-axis

esmvalcore/preprocessor/_regrid.py

@@ -1,6 +1,7 @@
 """Horizontal and vertical regridding module."""
 
 import importlib
+import inspect
 import logging
 import os
 import re
@@ -536,8 +537,7 @@ def regrid(cube, target_grid, scheme, lat_offset=True, lon_offset=True):
               extrapolation_mode: nanmask
 
     To use the area weighted regridder available in
-    :class:`esmf_regrid.schemes.ESMFAreaWeighted`, make sure that
-    :doc:`iris-esmf-regrid:index` is installed and use
+    :class:`esmf_regrid.schemes.ESMFAreaWeighted` use
 
     .. code-block:: yaml
 
@@ -547,10 +547,8 @@ def regrid(cube, target_grid, scheme, lat_offset=True, lon_offset=True):
             scheme:
               reference: esmf_regrid.schemes:ESMFAreaWeighted
 
-    .. note::
-
-        Note that :doc:`iris-esmf-regrid:index` is still experimental.
     """
+    scheme_args = None
     if isinstance(scheme, dict):
         try:
             object_ref = scheme.pop("reference")
@@ -568,12 +566,12 @@ def regrid(cube, target_grid, scheme, lat_offset=True, lon_offset=True):
         if separator:
             for attr in scheme_name.split('.'):
                 obj = getattr(obj, attr)
-        loaded_scheme = obj(**scheme)
+        scheme_args = inspect.getfullargspec(obj).args
     else:
         loaded_scheme = HORIZONTAL_SCHEMES.get(scheme.lower())
-    if loaded_scheme is None:
-        emsg = 'Unknown regridding scheme, got {!r}.'
-        raise ValueError(emsg.format(scheme))
+        if loaded_scheme is None:
+            emsg = 'Unknown regridding scheme, got {!r}.'
+            raise ValueError(emsg.format(scheme))
 
     if isinstance(target_grid, str):
         if os.path.isfile(target_grid):
@@ -600,6 +598,13 @@ def regrid(cube, target_grid, scheme, lat_offset=True, lon_offset=True):
     if not isinstance(target_grid, iris.cube.Cube):
         raise ValueError('Expecting a cube, got {}.'.format(target_grid))
 
+    if isinstance(scheme_args, list):
+        if 'src_cube' in scheme_args:
+            scheme['src_cube'] = cube
+        if 'grid_cube' in scheme_args:
+            scheme['grid_cube'] = target_grid
+        loaded_scheme = obj(**scheme)
+
     # Unstructured regridding requires x2 2d spatial coordinates,
     # so ensure to purge any 1d native spatial dimension coordinates
     # for the regridder.
@@ -625,11 +630,13 @@ def regrid(cube, target_grid, scheme, lat_offset=True, lon_offset=True):
             else:
                 fill_value = GLOBAL_FILL_VALUE
             da.ma.set_fill_value(cube.core_data(), fill_value)
-
         # Perform the horizontal regridding
         if _attempt_irregular_regridding(cube, scheme):
             cube = esmpy_regrid(cube, target_grid, scheme)
         else:
+            if isinstance(loaded_scheme, iris.cube.Cube):
+                return loaded_scheme
+
             cube = cube.regrid(target_grid, loaded_scheme)
 
         # Preserve dtype and use masked arrays for 'unstructured_nearest'

setup.py

@@ -32,6 +32,7 @@
         'cf-units',
         'dask[array]',
         'esgf-pyclient>=0.3.1',
+        'esmf-regrid',
         'esmpy!=8.1.0',  # see github.com/ESMValGroup/ESMValCore/issues/1208
         'fiona',
         'fire',

tests/integration/preprocessor/_regrid/test_regrid.py

@@ -92,6 +92,18 @@ def test_regrid__linear(self):
         expected = np.array([[[1.5]], [[5.5]], [[9.5]]])
         self.assert_array_equal(result.data, expected)
 
+    def test_regrid__esmf_rectilinear(self):
+        scheme_name = 'esmf_regrid.schemes:regrid_rectilinear_to_rectilinear'
+        scheme = {
+            'reference': scheme_name
+        }
+        result = regrid(
+            self.cube,
+            self.grid_for_linear,
+            scheme)
+        expected = np.array([[[1.5]], [[5.5]], [[9.5]]])
+        np.testing.assert_array_almost_equal(result.data, expected, decimal=1)
+
     def test_regrid__regular_coordinates(self):
         data = np.ones((1, 1))
         lons = iris.coords.DimCoord([1.50000000000001],
@@ -214,6 +226,27 @@ def test_regrid__area_weighted(self):
         expected = np.array([1.499886, 5.499886, 9.499886])
         np.testing.assert_array_almost_equal(result.data, expected, decimal=6)
 
+    def test_regrid__esmf_area_weighted(self):
+        data = np.empty((1, 1))
+        lons = iris.coords.DimCoord([1.6],
+                                    standard_name='longitude',
+                                    bounds=[[1, 2]],
+                                    units='degrees_east',
+                                    coord_system=self.cs)
+        lats = iris.coords.DimCoord([1.6],
+                                    standard_name='latitude',
+                                    bounds=[[1, 2]],
+                                    units='degrees_north',
+                                    coord_system=self.cs)
+        coords_spec = [(lats, 0), (lons, 1)]
+        grid = iris.cube.Cube(data, dim_coords_and_dims=coords_spec)
+        scheme = {
+            'reference': 'esmf_regrid.schemes:ESMFAreaWeighted'
+        }
+        result = regrid(self.cube, grid, scheme)
+        expected = np.array([[[1.499886]], [[5.499886]], [[9.499886]]])
+        np.testing.assert_array_almost_equal(result.data, expected, decimal=6)
+
     def test_regrid__unstructured_nearest_float(self):
         """Test unstructured_nearest regridding with cube of floats."""
         result = regrid(self.unstructured_grid_cube,