Mrb 807 avoid regridding forecasts

src/verification/spatial.py

@@ -121,7 +121,17 @@ def map_forecast_to_truth(fcst: xr.Dataset, truth: xr.Dataset) -> xr.Dataset:
     xr.Dataset
         Mapped forecast dataset.
     """
-    # TODO: return fcst unchanged when forecast and truth are already aligned
+    fcst_lat = fcst["lat"].values
+    fcst_lon = fcst["lon"].values
+    truth_lat = truth["lat"].values
+    truth_lon = truth["lon"].values
+    if (
+        fcst_lat.shape == truth_lat.shape
+        and fcst_lon.shape == truth_lon.shape
+        and np.max(np.abs(fcst_lat - truth_lat)) < 1e-6
+        and np.max(np.abs(fcst_lon - truth_lon)) < 1e-6
+    ):
+        return fcst
 
     truth_is_grid = "y" in truth.dims and "x" in truth.dims
 

tests/unit/test_spatial_mapping.py

@@ -91,6 +91,37 @@ def test_map_forecast_to_truth_maps_forecast_to_truth_locations():
     )
 
 
+def test_map_forecast_to_truth_returns_fcst_unchanged_when_grids_are_aligned():
+    fcst_time = np.array(["2024-01-01T00:00"], dtype="datetime64[ns]")
+    lat = np.array([[46.0, 46.0], [47.0, 47.0]])
+    lon = np.array([[7.0, 8.0], [7.0, 8.0]])
+
+    fcst = xr.Dataset(
+        data_vars={"T_2M": (("time", "y", "x"), np.array([[[1.0, 2.0], [3.0, 4.0]]]))},
+        coords={
+            "time": fcst_time,
+            "y": [0, 1],
+            "x": [0, 1],
+            "lat": (("y", "x"), lat),
+            "lon": (("y", "x"), lon),
+        },
+    )
+    truth = xr.Dataset(
+        data_vars={"T_2M": (("time", "y", "x"), np.zeros((1, 2, 2)))},
+        coords={
+            "time": fcst_time,
+            "y": [0, 1],
+            "x": [0, 1],
+            "lat": (("y", "x"), lat),
+            "lon": (("y", "x"), lon),
+        },
+    )
+
+    result = map_forecast_to_truth(fcst, truth)
+
+    assert result is fcst
+
+
 def test_map_forecast_to_truth_restores_grid_when_truth_is_gridded():
     fcst_time = np.array(["2024-01-01T00:00"], dtype="datetime64[ns]")