We present algorithms for computing the kernel of a closed freeform rational surface. The kernel computation is reformulated as a problem of finding the zero-sets of polynomial equations; using these zero-sets we characterize developable surface patches and planar patches that belong to the boundary of the kernel. Using a plane-point duality, this paper also explores a duality relationship between the kernel of a closed surface and the convex hull of its tangential surface. © World Scientific Publishing Company.
