[Paraview] Paraview: using contour filter directly on a velocity componant

[Buffat]

Hello,
I am using Paraview to visualize large 3D velocity field (uniform
rectilinear grid) I want to draw 3D Isovalue (contour filter) of a
component of the field.
In paraview 3.10, I cannot  select the contour filter directly and I
have to create with the calculator a new scalar field equal to the
velocity component and then use the contour filter to visualize the 3D
iso-value.
As the data is large, the creation of this new field with the calculator
is very slow, and it seems that the data is duplicate.
Is it possible with paraview or using a python script to use the contour
filter directly on a component of a velocity field.

Regards,
Marc

-- 
Marc BUFFAT, Pr. Universite Claude Bernard LYON I
tel:  (33) 04/72/43/11/02 (UCBL)
fax:  (33) 04/72/44/80/54
marc.buffat at univ-lyon1.fr | http://www.ufrmeca.univ-lyon1.fr/~buffat