Fix start index bug (#301)

* fix start index bug * extend tests, update changelog
SciTools · Aug 30, 2023 · 70f3c25 · 70f3c25
1 parent 92ea6f6
commit 70f3c25
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -5,6 +5,15 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## [Unreleased]
+
+### Fixed
+
+- [PR#301](https://github.com/SciTools-incubator/iris-esmf-regrid/pull/301)
+  Fixed a bug which caused errors when regridding with the node locations
+  of a mesh whose face_node_connectivity had non-zero start_index.
+  [@stephenworsley](https://github.com/stephenworsley)
+
 ## [0.8] - 2023-08-22
 
 ### Added

diff --git a/esmf_regrid/experimental/unstructured_regrid.py b/esmf_regrid/experimental/unstructured_regrid.py
@@ -75,17 +75,19 @@ def __init__(
         if location == "face":
             field_kwargs = {"meshloc": esmpy.MeshLoc.ELEMENT}
             shape = (len(face_node_connectivity),)
+            index_offset = self.esi
         elif location == "node":
             field_kwargs = {"meshloc": esmpy.MeshLoc.NODE}
             shape = (len(node_coords),)
+            index_offset = self.nsi
         else:
             raise ValueError(
                 f"The mesh location '{location}' is not supported, only "
                 f"'face' and 'node' are supported."
             )
         super().__init__(
             shape=shape,
-            index_offset=self.esi,
+            index_offset=index_offset,
             field_kwargs=field_kwargs,
             mask=mask,
         )

diff --git a/esmf_regrid/tests/unit/experimental/unstructured_scheme/test_GridToMeshESMFRegridder.py b/esmf_regrid/tests/unit/experimental/unstructured_scheme/test_GridToMeshESMFRegridder.py
@@ -74,8 +74,9 @@ def test_flat_cubes():
     assert expected_cube == result_transposed
 
 
+@pytest.mark.parametrize("nsi", [0, 1])
 @pytest.mark.parametrize("method", ["bilinear", "nearest"])
-def test_node_friendly_methods(method):
+def test_node_friendly_methods(method, nsi):
     """
     Basic test for :class:`esmf_regrid.experimental.unstructured_scheme.GridToMeshESMFRegridder`.
 
@@ -86,8 +87,8 @@ def test_node_friendly_methods(method):
     lon_bounds = (-180, 180)
     lat_bounds = (-90, 90)
     src = _grid_cube(n_lons, n_lats, lon_bounds, lat_bounds, circular=True)
-    face_tgt = _gridlike_mesh_cube(n_lons, n_lats, location="face")
-    node_tgt = _gridlike_mesh_cube(n_lons, n_lats, location="node")
+    face_tgt = _gridlike_mesh_cube(n_lons, n_lats, location="face", nsi=nsi)
+    node_tgt = _gridlike_mesh_cube(n_lons, n_lats, location="node", nsi=nsi)
 
     src = _add_metadata(src)
     src.data[:] = 1  # Ensure all data in the source is one.

diff --git a/esmf_regrid/tests/unit/experimental/unstructured_scheme/test_MeshToGridESMFRegridder.py b/esmf_regrid/tests/unit/experimental/unstructured_scheme/test_MeshToGridESMFRegridder.py
@@ -68,8 +68,9 @@ def test_flat_cubes():
     assert expected_cube == result
 
 
+@pytest.mark.parametrize("nsi", [0, 1])
 @pytest.mark.parametrize("method", ["bilinear", "nearest"])
-def test_node_friendly_methods(method):
+def test_node_friendly_methods(method, nsi):
     """
     Basic test for :class:`esmf_regrid.experimental.unstructured_scheme.MeshToGridESMFRegridder`.
 
@@ -80,8 +81,8 @@ def test_node_friendly_methods(method):
     lon_bounds = (-180, 180)
     lat_bounds = (-90, 90)
     tgt = _grid_cube(n_lons, n_lats, lon_bounds, lat_bounds, circular=True)
-    face_src = _gridlike_mesh_cube(n_lons, n_lats, location="face")
-    node_src = _gridlike_mesh_cube(n_lons, n_lats, location="node")
+    face_src = _gridlike_mesh_cube(n_lons, n_lats, location="face", nsi=nsi)
+    node_src = _gridlike_mesh_cube(n_lons, n_lats, location="node", nsi=nsi)
 
     face_src = _add_metadata(face_src)
     node_src = _add_metadata(node_src)

diff --git a/esmf_regrid/tests/unit/schemes/test__mesh_to_MeshInfo.py b/esmf_regrid/tests/unit/schemes/test__mesh_to_MeshInfo.py
@@ -73,7 +73,7 @@ def _example_mesh():
     return mesh
 
 
-def _gridlike_mesh(n_lons, n_lats):
+def _gridlike_mesh(n_lons, n_lats, nsi=0):
     """
     Generate a global mesh with geometry similar to a rectilinear grid.
 
@@ -159,9 +159,9 @@ def _gridlike_mesh(n_lons, n_lats):
 
     # Translate the mesh information into iris objects.
     fnc = Connectivity(
-        fnc_ma,
+        fnc_ma + nsi,
         cf_role="face_node_connectivity",
-        start_index=0,
+        start_index=nsi,
     )
     enc = Connectivity(
         enc_array,
@@ -191,8 +191,8 @@ def _gridlike_mesh(n_lons, n_lats):
     return mesh
 
 
-def _gridlike_mesh_cube(n_lons, n_lats, location="face"):
-    mesh = _gridlike_mesh(n_lons, n_lats)
+def _gridlike_mesh_cube(n_lons, n_lats, location="face", nsi=0):
+    mesh = _gridlike_mesh(n_lons, n_lats, nsi=nsi)
     mesh_coord_x, mesh_coord_y = mesh.to_MeshCoords(location)
     data = np.zeros_like(mesh_coord_x.points)
     cube = Cube(data)