Convex body implementation

Sorry for not being clear. I'm looking for a C++ library that has a class, or a set of classes, representing a generic convex polyhedron, with the following minimal capabilities:
- "manual" construction adding points / faces / edges;
- Clip() function taking a plane;
Thank you for you help.

Clipping a 3D convex polyhedra against a plane is simple. All you have to do is clip each line against the place. This will give you the new point in the clipping place. From them you can construct the polygon in the clipping plane. See <a href="http://www.cubic.org/docs/3dclip.htm">http://www.cubic.org/docs/3dclip.htm</a>[<a href="http://www.cubic.org/docs/3dclip.htm" target="_blank" title="New Window">^</a>].

For adding new points, lines, or polygon. I think you need to define problem more clearly. How does a new point connect to the polyhedra? Does the new polygon has to be convex as well? Intuitively I think this is not always possible.

-Saurabh