Resolving ambiguities to create a natural computer-based sketching environment

Current computer-based design tools for mechanical engineers are not tailored to the early stages of design. Most designs start as pencil and paper sketches, and are entered into CAD systems only when nearly complete. Our goal is to create a kind of "magic paper" capable of bridging the gap between these two stages. We want to create a computer-based sketching environment that feels as natural as sketching on paper, but unlike paper, understands a mechanical engineer's sketch as it is drawn. One important step toward realizing this goal is resolving ambiguities in the sketch--- determining, for example, whether a circle is intended to indicate a wheel or a pin joint---and doing this as the user draws, so that it doesn't interfere with the design process. We present a method and an implemented program that does this for freehand sketches of simple 2-D mechanical devices.