(Regridder unification) improve curvilinear regridding, generalise _create_cube

benchmarks/benchmarks/regridding.py

@@ -12,8 +12,11 @@
 # importing anything else
 from iris import tests  # isort:skip
 
+import numpy as np
+
 import iris
-from iris.analysis import AreaWeighted
+from iris.analysis import AreaWeighted, PointInCell
+from iris.coords import AuxCoord
 
 
 class HorizontalChunkedRegridding:
@@ -53,3 +56,48 @@ def time_regrid_area_w_new_grid(self) -> None:
         out = self.chunked_cube.regrid(self.template_cube, self.scheme_area_w)
         # Realise data
         out.data
+
+
+class CurvilinearRegridding:
+    def setup(self) -> None:
+        # Prepare a cube and a template
+
+        cube_file_path = tests.get_data_path(
+            ["NetCDF", "regrid", "regrid_xyt.nc"]
+        )
+        self.cube = iris.load_cube(cube_file_path)
+
+        # Make the source cube curvilinear
+        x_coord = self.cube.coord("longitude")
+        y_coord = self.cube.coord("latitude")
+        xx, yy = np.meshgrid(x_coord.points, y_coord.points)
+        self.cube.remove_coord(x_coord)
+        self.cube.remove_coord(y_coord)
+        x_coord_2d = AuxCoord(
+            xx,
+            standard_name=x_coord.standard_name,
+            units=x_coord.units,
+            coord_system=x_coord.coord_system,
+        )
+        y_coord_2d = AuxCoord(
+            yy,
+            standard_name=y_coord.standard_name,
+            units=y_coord.units,
+            coord_system=y_coord.coord_system,
+        )
+        self.cube.add_aux_coord(x_coord_2d, (1, 2))
+        self.cube.add_aux_coord(y_coord_2d, (1, 2))
+
+        template_file_path = tests.get_data_path(
+            ["NetCDF", "regrid", "regrid_template_global_latlon.nc"]
+        )
+        self.template_cube = iris.load_cube(template_file_path)
+
+        # Prepare a regridding scheme
+        self.scheme_pic = PointInCell()
+
+    def time_regrid_pic(self) -> None:
+        # Regrid the cube onto the template.
+        out = self.cube.regrid(self.template_cube, self.scheme_pic)
+        # Realise the data
+        out.data

docs/src/whatsnew/latest.rst

@@ -62,6 +62,9 @@ This document explains the changes made to Iris for this release
    both dim and aux coords of the same type e.g. ``longitude`` and ``grid_longitude``.
    (:issue:`3916`, :pull:`5029`).
 
+#. `@stephenworsley`_ added the ability to regrid derived coordinates with the
+   :obj:`~iris.analysis.PointInCell` regridding scheme. (:pull:`4807`)
+
 
 🐛 Bugs Fixed
 =============
@@ -135,6 +138,10 @@ This document explains the changes made to Iris for this release
    :meth:`iris.coords.Coord.intersect`.
    (:pull:`4955`)
 
+#. `@stephenworsley`_ improved the speed of the :obj:`~iris.analysis.PointInCell`
+   regridding scheme. (:pull:`4807`)
+
+
 🔥 Deprecations
 ===============
 

lib/iris/analysis/_area_weighted.py

@@ -11,7 +11,7 @@
 
 from iris._lazy_data import map_complete_blocks
 from iris.analysis._interpolation import get_xy_dim_coords, snapshot_grid
-from iris.analysis._regrid import RectilinearRegridder
+from iris.analysis._regrid import RectilinearRegridder, _create_cube
 import iris.analysis.cartography
 import iris.coord_systems
 from iris.util import _meshgrid
@@ -1111,18 +1111,32 @@ def _regrid_area_weighted_rectilinear_src_and_grid__perform(
     )
 
     # Wrap up the data as a Cube.
-    regrid_callback = RectilinearRegridder._regrid
-    new_cube = RectilinearRegridder._create_cube(
+
+    _regrid_callback = functools.partial(
+        RectilinearRegridder._regrid,
+        src_x_coord=src_x,
+        src_y_coord=src_y,
+        sample_grid_x=meshgrid_x,
+        sample_grid_y=meshgrid_y,
+    )
+    # TODO: investigate if an area weighted callback would be more appropriate.
+    # _regrid_callback = functools.partial(
+    #     _regrid_area_weighted_array,
+    #     weights_info=weights_info,
+    #     index_info=index_info,
+    #     mdtol=mdtol,
+    # )
+
+    def regrid_callback(*args, **kwargs):
+        _data, dims = args
+        return _regrid_callback(_data, *dims, **kwargs)
+
+    new_cube = _create_cube(
         new_data,
         src_cube,
-        src_x_dim,
-        src_y_dim,
-        src_x,
-        src_y,
-        grid_x,
-        grid_y,
-        meshgrid_x,
-        meshgrid_y,
+        [src_x_dim, src_y_dim],
+        [grid_x, grid_y],
+        2,
         regrid_callback,
     )