regridding regular grids with similar coordinates

[tomaslovato]

Description

Regridding regular grid needs to produce an exact matching of the source lat/lon coordinates with those of the target cube.

Closes #1551

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[codecov]

Codecov Report

Merging #1567 (a233fdd) into main (be6f654) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1567   +/-   ##
=======================================
  Coverage   90.99%   91.00%           
=======================================
  Files         201      201           
  Lines       10676    10679    +3     
=======================================
+ Hits         9715     9718    +3     
  Misses        961      961           

Impacted Files	Coverage Δ
esmvalcore/preprocessor/_regrid.py	97.18% <100.00%> (+0.02%)	⬆️

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[zklaus]

Thanks, @tomaslovato. Perhaps we should add a test for this functionality?

[tomaslovato]

@zklaus maybe something like this could do the job ...

diff --git a/tests/integration/preprocessor/_regrid/test_regrid.py b/tests/integration/preprocessor/_regrid/test_regrid.py
index 7a6b87e1a..a156bfb6f 100644
--- a/tests/integration/preprocessor/_regrid/test_regrid.py
+++ b/tests/integration/preprocessor/_regrid/test_regrid.py
@@ -92,6 +92,24 @@ class Test(tests.Test):
         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')
+        expected = np.array([[[1.5]], [[1.5]], [[1.]]])
+        self.assert_array_equal(result.data, expected)
+
     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')

[tomaslovato]

@zklaus I added the test for the regular grid coordinate ... let me know if it works for you!

[sloosvel]

I would say the changes are fine, but it would be good people from @ESMValGroup/esmvaltool-coreteam who have followed the issue closer double checked.