We have developed a prototype modeling environment based on the D-NURBS model. The system is written in C and it currently runs under Iris Explorer on Silicon Graphics workstations. Our parallelized iterative numerical algorithm takes advantage of a 4D/340VGX multiprocessor. To date, our D-NURBS modules implement 3D curve and surface objects with basis function orders of 2, 3, or 4 (i.e., from linear to cubic D-NURBS) with linear geometric constraints. They may be combined with existing Explorer modules for data input and object rendering.
Using our system, designers can sculpt shapes in conventional
geometric ways, such as by sketching control polygons, repositioning
control points, and adjusting associated weights. They can also
satisfy design requirements by adjusting the D-NURBS internal physical
parameters, various applied-force terms, and constraints. Physical
parameters such as the mass, damping, and stiffness densities, and
force gain factors are interactively adjustable through Explorer
control panels.
Our D-NURBS system also implements, as special cases, rational B-splines (fixed weights values) and ordinary B-splines (unit weights), hence it encompasses three related free-form modeling schemes into one unified physics-based implementation. The following sections describe several applications.