3DSketch: Modeling by digitizing with a smart 3D pen

We describe a novel system "30Sketch" which demonstrates a two-handed 3D sketching paradigm for 3D modeling by casually digitizing an existing object. The conceptual model of the interface is based on the everyday experience in sketching with a pen on a piece of paper, but in our system, the user holds a 3D digitizing stylus as a 3D pen to sketch in 3D space. We call the pen a "smart pen", since in the Prototyper module, the user just sketches a few strokes on the object, and immediately sees a 3D prototype made of clay lumps; then, in the Refiner module, when the user adds more random strokes over the object, the prototype surface automatically adapts to follow the pen, and the surface features (edges and corners) align with the user specified ones, as if the pen tip applied magnetic attractive force to the prototype; in the autoTracer module, the user sketches over smooth regions, and the system performs intelligent reasoning to infer smooth surfaces, and also extract discontinuity edges and corners from the user's inaccurate and fragmented strokes. The intern surface representation is triangular splines (TriBezier, TriB, TriNURBS), whose advantages in arbitrary triangulation and local subdivision make it flexible to model general surfaces.