[Paraview] Extracting boundary regions

[Renato N. Elias]

I'm looking for a way to extract boundary regions from solid 
unstructured meshes (tetrahedra). The purpose of this is simple: use 
ParaView to set boundary conditions for a CFD code. In PV 2.6.2 I'm able 
to extract plane aligned regions using the following pipeline: (as an 
example, let's consider I'm extracting those boundary nodes lying on the 
maximum X coordinate:)

Unstructured mesh (tetrahedra) --> Extract surface --> Calculator (get 
coords_0 scalar per point values) --> Threshould (Scalars = Result of 
the calculator filter, Lower and Upper set to the maximum value).

Ok, it works just fine. My problem is regarding non aligned boundaries. 
Here is an example of what I'm trying to do 
http://www.nacad.ufrj.br/~rnelias/paraview/regions.jpg . In this 
example, I can extract the plane boundary regions but I can't extract 
the cylinder at the middle of the domain. Any idea?

Regards

Renato.