[vtkusers] Subset of vtkPoints in vtkUnstructuredGrid

[Dirk Fressmann]

I am using multiple instances of vtkUnstructuredGrid to setup a finite 
element mesh, consisting of multiple materials, e.g.

grid1 = vtkUnstructuredGrid()
grid1.Allocate(1,1)
grid1.SetPoints(vtkNodes)              <- ?
# defining cell points pts = vtk.vtkIdList() ...
grid1.InsertNextCell(12,pts)
map1 = vtk.vtkDataSetMapper()
map1.SetInput(grid1)
act1 = vtk.vtkActor()
act1.SetMapper(map1)

grid2 = vtkUnstructuredGrid()
grid2.Allocate(1,1)
grid2.SetPoints(vtkNodes)              <- ?
# defining cell points pts = vtk.vtkIdList() ...
grid2.InsertNextCell(12,pts)
map2 = vtk.vtkDataSetMapper()
map2.SetInput(grid2)
act2 = vtk.vtkActor()
act2.SetMapper(map2)

Ideally I only want to deal with one instance of vtkPoints to store all 
nodal points of the mesh.
Is it possible to create a subset of this vtkPoints instance, which is 
set in [vtkUnstructuredGrid].SetPoints(...)?
I could certainly use the whole vtkPoints object (as in the example 
above), but then vtkUnstructuredGrid methods like
GetBounds(), GetCenter(), etc. don't work anymore.

Has anyone an idea?

Regards Dirk