Freehand Sketch-based Three-dimensional CAD System

This thesis is mainly focus on the study of a new style 3D CAD technology, which is based on feehand sketch. A novel sketch-based interface is introduced into the 3D CAD system. This technology can change the 3D CAD system greatly, make it become a truly user-centric system and support innovative conceptual design effectively.In order to implement such a freehand sketch-based system, a framework of sketch intent expression and capture should be designed carefully, which should be natural, reasonable and efficient enough. This framework must focus on resolving twokinds of questions-what is user doing, and where is he/she doing. The design andimplement of the framework are discussed in details in this thesis. And in further, the resolving methods of correlative problems, such as on-line recognition of 2D freehand sketches, design and recognition of gestures, are studied as well.With the study of this thesis, a prototype system is implemented. The prototype system uses a grip pen and a digital tablet as its input devices. It can construct some complicated 3D solid body and 3D scene in a natural and rapid way. By the integrating practice of this prototype system with a popular 3D CAD system-Solid Works, the possibility of evolvement from traditonal 3D CAD system into new generation freehand sketch-based system is proved.