[Gmsh] About tags.

[Cécile Giorla]

Hi,
I have a question about how we can tag elements in GMSH.
In my case, I create surface elements with extrusion (in z direction) 
from various ground surfaces (creating buildings).
So I can not control the number of the elementary geometrical entity for 
this surfaces.
I control the number of the physical entity by assigning the same number 
for all the elements of the ground and the surfaces created. (the ground 
AND the buildings' surfaces then are a unique surface).
But I need to keep an information about from which ground surface a 
building is created. I know GMSH has information about mesh partition, 
but how can I assign this number?
Or maybe there is a way in GMSH to assign user defined tag when we 
create elements (other than the physical number)?
Thank you.
Cecile Giorla.