add test grid cell area

Author: NicolasColombi

climada/util/coordinates.py

@@ -460,7 +460,7 @@ def get_gridcellarea(lat, resolution=0.5, unit="ha"):
     return area
 
 
-def compute_grid_cell_area(res: float) -> tuple[np.ndarray]:
+def compute_grid_cell_area_validation(res: float) -> tuple[np.ndarray]:
     """
     This function computes the area of each grid cell on a sphere (Earth), using latitude and
     longitude bins based on the given resolution. The area is computed using the spherical cap
@@ -524,10 +524,10 @@ def compute_grid_cell_area(res: float) -> tuple[np.ndarray]:
         areas[:, np.newaxis], (1, len(lon_bins) - 1)
     )  # each row as same area
 
-    return grid_area, [lat_bins, lon_bins]
+    return grid_area, lat_bins, lon_bins
 
 
-def compute_grid_cell_area_(
+def compute_grid_cell_area(
     res: float = 1.0, projection: str = "WGS84", units: str = "km^2"
 ) -> np.ndarray:
     """
@@ -556,7 +556,6 @@ def compute_grid_cell_area_(
     >>> area = compute_grid_areas(res = 1, projection ="sphere", units = "m^2")
     """
     geod = Geod(ellps=projection)  # Use specified ellipsoid model
-
     lat_edges = np.linspace(-90, 90, int(180 / res))  # Latitude edges
     lon_edges = np.linspace(-180, 180, int(360 / res))  # Longitude edges
 

climada/util/test/test_coordinates.py

@@ -565,8 +565,30 @@ def test_get_gridcellarea(self):
         self.assertAlmostEqual(area2[0], 1781.5973363005)
         self.assertTrue(area2[0] <= 2500)
 
-    def test_compute_grid_area_():
-        pass
+    def test_compute_grid_area(self):
+        """Test that the two twin functions calculate the area of a gridcell correctly. Using
+        an absolute reference and mutual validation by comparison."""
+        res = 1
+        area = u_coord.compute_grid_cell_area(
+            res=res, projection="sphere", units="km^2"
+        )
+        area_test, *_ = u_coord.compute_grid_cell_area_validation(res=res)
+
+        self.assertEqual(area.shape, (179, 359))
+        self.assertEqual(area_test.shape, (179, 359))
+        # check that all rows have equal area with 1e-5 tolerance for relative and absolute precision
+        for i in range(area.shape[0]):
+            self.assertTrue(
+                np.all(np.isclose(area[i, :], area[i, 0], rtol=1e-5, atol=1e-5))
+            )
+            self.assertTrue(
+                np.all(
+                    np.isclose(area_test[i, :], area_test[i, 0], rtol=1e-5, atol=1e-5)
+                )
+            )
+
+        # check that both methods give similar results with 0.01% tolerance in relative difference
+        self.assertTrue(np.allclose(area, area_test, rtol=1e-2, atol=1e-5))
 
     def test_read_vector_pass(self):
         """Test one columns data"""