intersection between a volume and a plane

hey all, I have a non analitical volume described in cylindrical coordinates as Z=F(rho,theta); I have to find the contour which is created by intersecting this function with an arbitrary plane of my choosing. does anyone know a simple (or if need be complicated) method for doing so?

thanks :)

[Matt J]

I have a non analitical volume described in cylindrical coordinates as Z=F(rho,theta);

If it's a function of 2D coordinates, doesn't that make it a surface, as opposed to a volume? And if it's described by a known F(rho,theta) doesn't that mean that it is analytical?