Creating three-dimensional freeform objects using traditional modelers is tedious and has a steep learning curve. Consequently, there has been active reseurch in designing more intuitive interface and modeling paradigm in recent years. An example is the Teddy system, which allows users to model rotund three-dimensional objects by sketching the object outline. From a closed planar curve, a polygonal mesh is generated, which can then be extruded, bent, or cut, all controlled with simple strokes. Such polygonal representation, however, suffers from several drawbacks in terms of surface smoothness, creating objects with penetrating holes, and merging multiple components. In this thesis, we present an improved sketch- based modeling system based on convolution surfaces, which overcomes these...[ Read more ]

Creating three-dimensional freeform objects using traditional modelers is tedious and has a steep learning curve. Consequently, there has been active reseurch in designing more intuitive interface and modeling paradigm in recent years. An example is the Teddy system, which allows users to model rotund three-dimensional objects by sketching the object outline. From a closed planar curve, a polygonal mesh is generated, which can then be extruded, bent, or cut, all controlled with simple strokes. Such polygonal representation, however, suffers from several drawbacks in terms of surface smoothness, creating objects with penetrating holes, and merging multiple components. In this thesis, we present an improved sketch- based modeling system based on convolution surfaces, which overcomes these drawbacks. We first convert a sketched silhouette curve to a simple polygon, and compute its approximate medial axis consisting of line segments. A linearly weighted kernel is then convolved along the medial axis to obtain a closed-form convolution surface. To add new components, the user draws more silhouette curves on different image planes to generate new convolution surfaces, which are merged together smoothly. The advantages of this system stem from two intrinsic properties of convolution surfaces: ease of merging and smooth blending.