Unstructured Scheme - Cube Creation 2D (#39)

* support creation of 2D cubes

* lint fixes

* rewrite test

* remove mesh from _create_cube arguments

* add TODO

* add TODO

esmf_regrid/experimental/unstructured_scheme.py

@@ -1,5 +1,7 @@
 """Provides an iris interface for unstructured regridding."""
 
+import copy
+
 import iris
 from iris.analysis._interpolation import get_xy_coords
 import numpy as np
@@ -75,7 +77,7 @@ def _cube_to_GridInfo(cube):
 #     return result
 
 
-def _create_cube(data, src_cube, mesh_dim, mesh, grid_x, grid_y):
+def _create_cube(data, src_cube, mesh_dim, grid_x, grid_y):
     # Here we expect the args to be as follows:
     # data: a masked array containing the result of the regridding operation
     # src_cube: the source cube which data is regrid from
@@ -86,7 +88,21 @@ def _create_cube(data, src_cube, mesh_dim, mesh, grid_x, grid_y):
 
     new_cube = iris.cube.Cube(data)
 
-    # TODO: add coords and metadata.
+    # TODO: The following code assumes a 1D source cube and mesh_dim = 0.
+    #  This is therefore simple code which should be updated when we start
+    #  supporting the regridding of extra dimensions.
+
+    # TODO: The following code is rigid with respect to which dimensions
+    #  the x coord and y coord are assigned to. We should decide if it is
+    #  appropriate to copy the dimension ordering from the target cube
+    #  instead.
+    new_cube.add_dim_coord(grid_x, mesh_dim + 1)
+    new_cube.add_dim_coord(grid_y, mesh_dim)
+
+    new_cube.metadata = copy.deepcopy(src_cube.metadata)
+
+    for coord in src_cube.coords(dimensions=()):
+        new_cube.add_aux_coord(coord.copy())
 
     return new_cube
 
@@ -111,13 +127,13 @@ def _regrid_unstructured_to_rectilinear__prepare(src_mesh_cube, target_grid_cube
 
     regridder = Regridder(meshinfo, gridinfo)
 
-    regrid_info = (mesh, mesh_dim, grid_x, grid_y, regridder)
+    regrid_info = (mesh_dim, grid_x, grid_y, regridder)
 
     return regrid_info
 
 
 def _regrid_unstructured_to_rectilinear__perform(src_cube, regrid_info, mdtol):
-    mesh, mesh_dim, grid_x, grid_y, regridder = regrid_info
+    mesh_dim, grid_x, grid_y, regridder = regrid_info
 
     # Perform regridding with realised data for the moment. This may be changed
     # in future to handle src_cube.lazy_data.
@@ -129,7 +145,6 @@ def _regrid_unstructured_to_rectilinear__perform(src_cube, regrid_info, mdtol):
         new_data,
         src_cube,
         mesh_dim,
-        mesh,
         grid_x,
         grid_y,
     )

esmf_regrid/tests/unit/experimental/unstructured_scheme/test__create_cube.py

@@ -0,0 +1,37 @@
+"""Unit tests for miscellaneous helper functions in `esmf_regrid.experimental.unstructured_scheme`."""
+
+import iris
+import numpy as np
+
+from esmf_regrid.experimental.unstructured_scheme import _create_cube
+
+
+def test_create_cube_2D():
+    """Test creation of 2D output grid."""
+    data = np.ones([2, 3])
+
+    # Create a source cube with metadata and scalar coords
+    src_cube = iris.cube.Cube(np.zeros(5))
+    src_cube.units = "K"
+    src_cube.attributes = {"a": 1}
+    src_cube.standard_name = "air_temperature"
+    scalar_height = iris.coords.AuxCoord([5], units="m", standard_name="height")
+    scalar_time = iris.coords.DimCoord([10], units="s", standard_name="time")
+    src_cube.add_aux_coord(scalar_height)
+    src_cube.add_aux_coord(scalar_time)
+
+    mesh_dim = 0
+
+    grid_x = iris.coords.DimCoord(np.arange(3), standard_name="longitude")
+    grid_y = iris.coords.DimCoord(np.arange(2), standard_name="latitude")
+
+    cube = _create_cube(data, src_cube, mesh_dim, grid_x, grid_y)
+    src_metadata = src_cube.metadata
+
+    expected_cube = iris.cube.Cube(data)
+    expected_cube.metadata = src_metadata
+    expected_cube.add_dim_coord(grid_x, 1)
+    expected_cube.add_dim_coord(grid_y, 0)
+    expected_cube.add_aux_coord(scalar_height)
+    expected_cube.add_aux_coord(scalar_time)
+    assert expected_cube == cube