Fix resampling to same area not working

pyresample/gradient/__init__.py

@@ -501,6 +501,8 @@ def __init__(self, source_geo_def, target_geo_def):
 
     def precompute(self, **kwargs):
         """Precompute resampling parameters."""
+        if self.source_geo_def == self.target_geo_def:
+            return
         if self.indices_xy is None:
             self.indices_xy = resample_blocks(gradient_resampler_indices_block,
                                               self.source_geo_def, [], self.target_geo_def,
@@ -509,6 +511,8 @@ def precompute(self, **kwargs):
     @ensure_data_array
     def compute(self, data, method="bilinear", cache_id=None, **kwargs):
         """Perform the resampling."""
+        if self.source_geo_def == self.target_geo_def:
+            return data
         if method == "bilinear":
             fun = block_bilinear_interpolator
         elif method in ["nearest_neighbour", "nn"]:

pyresample/test/test_gradient.py

@@ -31,6 +31,7 @@
 
 from pyresample.area_config import create_area_def
 from pyresample.geometry import AreaDefinition, SwathDefinition
+from pyresample.gradient import ResampleBlocksGradientSearchResampler
 
 
 class TestOGradientResampler(unittest.TestCase):
@@ -266,9 +267,8 @@ def test_resample_swath_to_area_3d(self):
 class TestRBGradientSearchResamplerArea2Area:
     """Test RBGradientSearchResampler for the Area to Area case."""
 
-    def setup(self):
+    def setup_method(self):
         """Set up the test case."""
-        from pyresample.gradient import ResampleBlocksGradientSearchResampler
         self.src_area = AreaDefinition('src', 'src area', None,
                                        {'ellps': 'WGS84', 'h': '35785831', 'proj': 'geos'},
                                        100, 100,
@@ -288,6 +288,12 @@ def test_precompute_generates_indices(self):
         self.resampler.precompute()
         assert self.resampler.indices_xy.shape == (2, ) + self.dst_area.shape
 
+    def test_precompute_does_nothing_when_src_equals_dst(self):
+        """Test that precomputing does nothing when src and dst areas are equal."""
+        resampler = ResampleBlocksGradientSearchResampler(self.src_area, self.src_area)
+        resampler.precompute()
+        assert self.resampler.indices_xy is None
+
     def test_resampler_accepts_only_dataarrays_if_not_2d(self):
         data = da.ones(self.src_area.shape + (1,), dtype=np.float64, chunks=40)
         self.resampler.precompute()
@@ -485,6 +491,15 @@ def test_resample_area_to_area_nn(self):
         np.testing.assert_allclose(res, expected_resampled_data)
         assert res.shape == dst_area.shape
 
+    def test_resample_does_nothing_when_src_equals_dst(self):
+        """Test that resampling does nothing when src and dst areas are equal."""
+        data = xr.DataArray(da.arange(np.prod(self.src_area.shape), dtype=np.float64).reshape(self.src_area.shape),
+                            dims=['y', 'x'])
+
+        resampler = ResampleBlocksGradientSearchResampler(self.src_area, self.src_area)
+        result = resampler.resample(data)
+        assert result.data is data.data
+
 
 class TestRBGradientSearchResamplerArea2Swath:
     """Test RBGradientSearchResampler for the Swath to Area case."""