Direct manipulation of surfaces using NURBS-based free-form deformations

The paper demonstrates how NURBS-based Free-Form Deformations (NFFDs) can be used to generate and sculpt NURBS based objects in a way that avoids many of the limitations of ordinary FFDs. A system is described in which the user interacts with the NFFD through a set of direct acting tools, removing the need to manipulate the mesh directly. As the user applies the tools to the object, the NFFD is updated automatically. Objects are represented as isosurfaces of the NFFD volume, giving a good insight into the way an NFFD would deform a general object