[vtkusers] Pick & delete cell

[David Doria]

> for(unsigned int i = 10; i < 20; i++)
>     {
>     ids->InsertNextValue(i);
>     }

This simply specifies that we want to extract cells 10 through 19
(arbitrary, just to serve as the example).

> I don't know how to extract informations(cells position) from the selected
> data of vtkExtractSelection. And somehow I have to stock them in
> vtkIdTypeArray.... I guess

The selected cells are accessible through the vtkUnstructuredGrid
called "selected" that is created (simply the output of
extractSelection->GetOutput() ).

David