Allow MeshCoord to have a coord-system

lib/iris/experimental/ugrid/mesh.py

@@ -2781,6 +2781,11 @@ def fix_repr(val):
  )
  raise ValueError(msg)
 
+ # Don't use 'coord_system' as a constructor arg, since for
+ # MeshCoords it is deduced from the mesh.
+ # (Otherwise a non-None coord_system breaks the 'copy' operation)
+ use_metadict.pop("coord_system")
+
  # Call parent constructor to handle the common constructor args.
  super().__init__(points, bounds=bounds, **use_metadict)
 
@@ -2806,8 +2811,19 @@ def axis(self):
 
  @property
  def coord_system(self):
- """The coordinate-system of a MeshCoord is always 'None'."""
- return None
+ """The coordinate-system of a MeshCoord comes from its origin coords."""
+ select_kwargs = {
+ f"include_{self.location}s": True,
+ "axis": self.axis,
+ }
+ try:
+ location_coord = self.mesh.coord(**select_kwargs)
+ coord_system = location_coord.coord_system
+ except CoordinateNotFoundError:
+ # No location coord : possible in UGRID but probably not Iris (at present).
+ coord_system = None
+
+ return coord_system
 
  @coord_system.setter
  def coord_system(self, value):