[Gmsh] Retrieve and use of Element Barycenter coordinates

[Laurent Mattei]

Hello,

I have created a mesh with Gmsh. I would like to reattribute some elements 
at specific physical surface on the condition that these elements are in 
the area.
I think that i can use the barycenter of the element to say if the specific 
element belong to the specific physical surface. But i don't know the 
command code to manipulate parameter of the element like coordinates of his 
barycenter or his number and i don't know the command code to say that this 
list of elements is reattibuted to this physical surface. Can you help me?

Thanks you
Best regards
Laurent MATTEI
mattei at emse.fr
Ecole nationale supérieure des Mines de Saint Etienne