BUG: Empty image support in image_from_xarray

Required for map_blocks.

Author: thewtex

Wrapping/Generators/Python/Tests/extras.py

@@ -387,6 +387,12 @@ def custom_callback(name, progress):
         assert False
     except ValueError:
         pass
+
+    empty_array = np.array([], dtype=np.uint8)
+    empty_array.shape = (0,0,0)
+    empty_image = itk.image_from_array(empty_array)
+    empty_da = itk.xarray_from_image(empty_image)
+    empty_image_round = itk.image_from_xarray(empty_da)
 except ImportError:
     print('xarray not imported. Skipping xarray conversion tests')
     pass

Wrapping/Generators/Python/itkExtras.py

@@ -444,8 +444,10 @@ def image_from_xarray(data_array):
     origin = [0.0]*spatial_dimension
     spacing = [1.0]*spatial_dimension
     for index, dim in enumerate(spatial_dims):
-        origin[index] = float(data_array.coords[dim][0])
-        spacing[index] = float(data_array.coords[dim][1]) - float(data_array.coords[dim][0])
+        coords = data_array.coords[dim]
+        if coords.shape[0] > 1:
+            origin[index] = float(coords[0])
+            spacing[index] = float(coords[1]) - float(coords[0])
     spacing.reverse()
     itk_image.SetSpacing(spacing)
     origin.reverse()