[R] 3D density plot of point set

[Lutz Gehlen]

Hello everybody,
I would like to solve the problem described below in R (if 
possible). I am very new to R and have therefore no idea what to 
even look for in the docu. Therefore, if someone could tell me if 
this is possible in R and where I might find the respective docu 
then I would already be very thankful.

I have a large set (a few million) of points in 3D. I would like to 
create a contour density plot that would show a surface of constant 
density which includes e.g. 50% of the points. Ideally, the surface 
would be semitransparent, such that I can show two or three at the 
same time.

Alternatively, if I would calculate the contour surfaces myself, 
could I use R to semitransparently visualize a triangulated surface?

Thank you very much for your help
Lutz