hello
my wish is , that vray chceck fist , based on camera , visiable object displacement and where is not visiable than dont vastly calculate it ( saving some quality time 
)
sorry for my quite strange english …
Turn off the “Tight bounds” option for the displacement, and you should get what you want.
Best regards,
Vlado
2 vlado : thanks very much
edit : i takeing my thanks back, because i did it and still calculating displacement for all that i can t see any displacement objects by camera 
Note, that everything visible in reflections / refraction counts as “visible” too. For example, if you’ve got a glossy surface there somewhere in the open, it will pretty much reflect everything, so directly non visible displacement will need to be calculated too.
Best regards,
A.
Ah, if you mean to turn off displacement completely for invisible objects, then you can’t do this - the reason being that you might, for example, see the displaced object in a mirror or through glass, for example. The tight bounds option only skips the precalculation phase for the displacement.
Best regards,
Vlado
But if you render the displacement with view dependent meshing, than the non visible (nor indirectly) parts will be calculated pretty efficiently, won’t they?
Another thing, I was wondering, if something like this could be used to speed up renders, for example dynamically decreasing the mesh resolution of an object based on a given threshold, pixel width for instance. A dense mesh visible as only a few pixels in the actual image would be degraded to only a few faces, etc… I believe to this some kind of reduction algorythm would be needed too. Combined with rendertime subdivision, this could produce even surface tessalation trough any object distances. Anyway, I’m not sure that this would mean any increase in speed… well, maybe in some cases. 
Best regards,
A.