(Regridder unification) improve curvilinear regridding, generalise _c…

…reate_cube (#4807)

* make _create_cube more generic

* reinstate original _create_cube

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* fix tests

* fix tests

* fix curvilinear regridding

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* fix curvilinear regridding

* fix curvilinear regridding

* fix 1D regridding

* improve support for scalar lat-lon

* fix regridding for circular case

* fix scalar handling

* fix mask handling

* fix handling of higher dimensional cases

* include new derived coord/scalar coord support in tests

* remove old _create_cube method

* update docstrings

* fix regrid_conservative

* make _create_cube more robust for extra dims

* fix and test for derived coords

* add benchmark

* address review comments

* address review comments

* add whatsnew

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: lbdreyer <[email protected]>

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,
  )