meshing a geometry in NETGEN with specific function
 

Hello NETGEN users !
I work on a geometry with the format .stl (you will find the file in attachment) and I would like to net it so that the grid is refined and fine on the level of the cylinder which perforates surface.
To do that, i would like to be able to write a function which enables me to exploit the various parameters of my grid (size of the mesh, etc…).
Unfortunately I could nt reach that point.
Any help would be brilliant. Thanks.