Index: trunk/tests/test_predictor_definition.py
===================================================================
diff -u -r175 -r176
--- trunk/tests/test_predictor_definition.py	(.../test_predictor_definition.py)	(revision 175)
+++ trunk/tests/test_predictor_definition.py	(.../test_predictor_definition.py)	(revision 176)
@@ -34,6 +34,8 @@
         result = PredictorDefinition.compute_spatial_gradients(data_array)
 
         assert result is not None
+        assert isinstance(result, xr.DataArray)
+        assert result.dims == data_array.dims
 
 
 class Test_ComputePCA:
Index: trunk/SDToolBox/predictor_definition.py
===================================================================
diff -u -r175 -r176
--- trunk/SDToolBox/predictor_definition.py	(.../predictor_definition.py)	(revision 175)
+++ trunk/SDToolBox/predictor_definition.py	(.../predictor_definition.py)	(revision 176)
@@ -38,7 +38,7 @@
     key_aggregation = "aggregation"
 
     @staticmethod
-    def compute_spatial_gradients(data_array: xr.DataArray):
+    def compute_spatial_gradients(data_array: xr.DataArray) -> xr.DataArray:
         """Computes the spatial gradients.
 
         Arguments:
@@ -111,7 +111,8 @@
                         / 2
                     )
 
-        return derivative_points
+        data_array.values = derivative_points
+        return data_array
 
     @staticmethod
     def compute_PCA(data_set: xr.Dataset):