Just a question: why not just make one method like
```
def inverse(self):
    """Return the inverse transformation, i.e. the transformation that swaps the roles of 
    the "image" and "world" coordinates.
    """
    return self._local_wcs._inverse()._newOrigin(self.world_origin, self.origin)
```
rather than having both `_inverse()` (which gets overwritten for the LocalWCS classes), and `inverse()`.  Or am I being dense?