Modelling complex objects with generalized sweeps

Recently, constructive solid geometry (CSG) techniques have been generalized to include set operations on certain sculptured surface solid models. This advancement has reemphasized the need for modelling techniques that create vasod objects. The definition of a valid object is somewhat cumbersome in a mathematical sense, but can be conceptually described (within the context of a sculptured surface modelling solid system) as an object which is completely enclosed or bounded by a set of non-intersecting surfaces. The construction of multiple-surface objects (surfaces which, when grouped together. enclose a volume) has largely been accomplished with surface tools whose intent and design has been to model single surfaces. The design of objects using these surface tools has often required that the user explicitly determine the constraints and designs of each and every surface in the object with very little guidance from the design system. Oftentimes, the design of a supplemental surface that serves to complete a model seems simple in concept, yet is technically complex, for example 'capping' the open-end of a linear extrusion with a planar surface. The construction of these types of surfaces often requires a great deal of user guidance and intelligence. This thesis presents several modelling tools for designing a large class of sculptured objects easily and naturally. Generalized sweeps, surfaces formed by "sweeping" one arbitrarily shaped curve along another, are the underlying modelling scheme of this thesis. Also described are several surface tools which can, for certain subclasses of objects, automatica/sy create the supplemental surfaces needed to construct a valid model.