[vtkusers] Extracting subset of unstructured grid given cell Ids

[Matthieu Chabanas]

Is there any way to extract geometry (cells + points used to define
these cells) and associated data given a vtkIdList of cell Ids?
I guess it should work like vtkExtractUnstructuredGrid, but with cell
Ids instead of Bounding box or clipping plane.

Moreover, I would need just shallow copy, so that different
vtkUnstructuredGrid use the same vtkPoints.

I need this to define several components within a single dataset. One
mapper+actor can therefore be defined for each component, then displayed
with different properties.

Thanks for any help,
Matt