[Paraview] selection label

[oka]

Dear Paraview developer,

I am trying to select surface cells of 3D object.
I am wondering why selected cell-id (label) is greater than
original cell(surface) labels (of cource using "Extract Surface" filter). 
Dose anyone show me how VTK labels such selected cells ?
How can I identify the triangle from such a label refering
a VTK file ?

Best regards,

Oka

-- 
oka <oka at bpe.es.osaka-u.ac.jp>