[vtkusers] How to retrieve STL modal's information?

[hp.shen]

Hi, all
 
With vtkSTLReader we can read a STL file and render the modal.While ,I
want to retrieve some information of the modal, 
such as the center of the modal and the boundary of the modal.
Please show me the way to  make it.
 
Thanks.
 
peace
 
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