def get_update_tile(self, params, values):
pass<EOL>
This method returns a :class:`~peri.util.Tile` object defining the
region of a field that has to be modified by the update of (params,
values). For example, if this Component is the point-spread-function,
it might return a tile of entire image since every parameter affects
the entire image::

    return self.shape



Parameters
-----------
params : single param, list of params
    A single parameter or list of parameters to be updated

values : single value, list of values
    The values corresponding to the params

Returns
-------
tile : :class:`~peri.util.Tile`
    A tile corresponding to the image region