regridding regular grids with similar coordinates (#1567)

* replace regular lat/lon coords of source cube with target ones when points are close enough

* add test for regular grid comparison (#1551)

* test regular grid coordinates are the same using iris Resolve

* fix bug in previous commit for regrid test

esmvalcore/preprocessor/_regrid.py

@@ -647,6 +647,11 @@ def regrid(cube, target_grid, scheme, lat_offset=True, lon_offset=True):
                     "'%s': %s", original_dtype, cube.core_data().dtype,
                     str(exc))
             cube.data = da.ma.masked_equal(cube.core_data(), fill_value)
+    else:
+        # force target coordinates
+        for coord in ['latitude', 'longitude']:
+            cube.coord(coord).points = target_grid.coord(coord).points
+            cube.coord(coord).bounds = target_grid.coord(coord).bounds
 
     return cube
 

tests/integration/preprocessor/_regrid/test_regrid.py

@@ -92,6 +92,23 @@ def test_regrid__linear(self):
         expected = np.array([[[1.5]], [[5.5]], [[9.5]]])
         self.assert_array_equal(result.data, expected)
 
+    def test_regrid__regular_coordinates(self):
+        data = np.ones((1, 1))
+        lons = iris.coords.DimCoord([1.50000000000001],
+                                    standard_name='longitude',
+                                    bounds=[[1, 2]],
+                                    units='degrees_east',
+                                    coord_system=self.cs)
+        lats = iris.coords.DimCoord([1.50000000000001],
+                                    standard_name='latitude',
+                                    bounds=[[1, 2]],
+                                    units='degrees_north',
+                                    coord_system=self.cs)
+        coords_spec = [(lats, 0), (lons, 1)]
+        regular_grid = iris.cube.Cube(data, dim_coords_and_dims=coords_spec)
+        result = regrid(regular_grid, self.grid_for_linear, 'linear')
+        iris.common.resolve.Resolve(result, self.grid_for_linear)
+
     def test_regrid__linear_do_not_preserve_dtype(self):
         self.cube.data = self.cube.data.astype(int)
         result = regrid(self.cube, self.grid_for_linear, 'linear')