[pstricks] drawing level curves with pst-3dplot

[Herbert Voss]

In-Sung Cho schrieb:
> I am looking for a trick to draw level curves on the graph of a
> function and its projection onto the plane, for example, with the
> funciton $z=\sqrt{xy}$ or any other function.
>
> Specifically, I want to draw the level curve $1=\sqrt{xy}$ on the xy
> plane and the same thing up on the graph itself.
>   
only possible as a colored contour plot:
http://tug.org/PSTricks/main.cgi?file=pst-plot/3D/contour

Herbert