Drop non-dimensional coordinates in Compositor

satpy/composites/__init__.py

@@ -59,6 +59,9 @@
 
 LOG = logging.getLogger(__name__)
 
+NEGLIBLE_COORDS = ['time']
+"""Keywords identifying non-dimensional coordinates to be ignored during composite generation."""
+
 
 class IncompatibleAreas(Exception):
     """Error raised upon compositing things of different shapes."""
@@ -310,7 +313,7 @@ def apply_modifier_info(self, origin, destination):
                     d[k] = o[k]
 
     def check_areas(self, data_arrays):
-        """Check that the areas of the *data_arrays* are compatible."""
+        """Check that the areas of the *data_arrays* are compatible and drop neglible non-dimensional coordinates."""
         if len(data_arrays) == 1:
             return data_arrays
 
@@ -334,7 +337,17 @@ def check_areas(self, data_arrays):
                       "'{}'".format(self.attrs['name']))
             raise IncompatibleAreas("Areas are different")
 
-        return data_arrays
+        # Drop neglible non-dimensional coordinates (understood to be "close-enough" for most operations)
+        new_arrays = []
+        for ds in data_arrays:
+            drop = [coord for coord in ds.coords
+                    if coord not in ds.dims and any([neglible in coord for neglible in NEGLIBLE_COORDS])]
+            if drop:
+                new_arrays.append(ds.drop(drop))
+            else:
+                new_arrays.append(ds)
+
+        return new_arrays
 
 
 class SunZenithCorrectorBase(CompositeBase):

satpy/tests/compositor_tests/__init__.py

@@ -113,6 +113,14 @@ def test_mult_ds_diff_size(self):
         comp = CompositeBase('test_comp')
         self.assertRaises(IncompatibleAreas, comp.check_areas, (ds1, ds2))
 
+    def test_nondimensional_coords(self):
+        from satpy.composites import CompositeBase
+        ds = self._get_test_ds(shape=(2, 2))
+        ds['acq_time'] = ('y', [0, 1])
+        comp = CompositeBase('test_comp')
+        ret_datasets = comp.check_areas([ds, ds])
+        self.assertNotIn('acq_time', ret_datasets[0].coords)
+
 
 class TestRatioSharpenedCompositors(unittest.TestCase):
     """Test RatioSharpenedRGB and SelfSharpendRGB compositors."""