How to do grounding in FDTD ?

Hi!

I recently started with electromagnetic simulations (FDTD), so my questions might appear stupid to some of you...
Is there anybody who can explain to me how to do "grounding"?
In the most examples I've seen a PEC boundary condition was chosen for the plane which should be the groundplane. But what to do if the grounded object is not a plane?
In my case I would like to have a grounded cylinder shell. Is it comparable to grounding if I simply set the material to PEC? What is the difference between PEC and grounding?

Thanks for your your answers