Sketching as a solid modeling tool

This paper describes'Quick-sketch', a 2d and 3d modeling tool for pen based computers.Users of this system define a model by simple pen strokes drawn directly on the screen of a pen-based PC.Lines, circles, arcs, or B-spline curves are automatically distinguished, and interpreted from these strokes.The system also automatically determines relations, such as right angles, tangencies, symmetry, and parallelism, from the sketch input, These relationships are then used to clean up the drawing by making the approximate relationships exact.Constraints are established to maintain the relationships in further editing.A constraint maintenance system, which is based on gestural manipulation and soft constraints, is employed in this system.Several techniques for sketch based definitions of solid objects are provided as well, including extrusion, surface of revolution, ruled surfaces and sweep.Feat ures can be sketched on the surfaces of 3d objects, using the same 2d-and 3d techniques.This way, objects of medium complexity can be sketched in seconds.The system can be used as a front-end to more sophisticated modeling, rendering or animation environments, serving as a hand sketching tool in the preliminary design phase.