Compression Of Free-Form Curve And Surface In CAD Models

3D CAD complex models lead to low efficiency for data exchange and data transmission in a network-based collaborative development environment. Compression of the 3D CAD models is a hot research topic nowadays. Supported by NSFC (No:50375058) named" the CAD model compression method oriented to collaborative development and progressive transmission technology", this dissertation analyses the character of free-form curve and surface, and proposes geometry compression algorithm about 3D CAD models .The contributions are followed:Curve and surface is main part of model. To get better compression, a Differential Pulse Code Modulation (DPCM) coder about free-form curve and surface is proposed. The coder with prediction and quantizer,followed with entropy coding,reduces the redundant of the control points of the free-form curve and surface.Optimizing the prediction about the control points is key technology in DPCM coder. Considering efficiency of prediction and character of the control points of the free-form curve and surface, optimal linear prediction achieved by optimizing the coefficient of the prediction, is realized by theory of Minimum Mean Square Error.To get the accurate data of CAD models and achieve better compression ratio, a new algorithm of lossless compression about free-form curve and surface is proposed . Mantissa coding with optimal linear prediction is introduced according to the character of floating-point values in IEEE standard, followed by entropy coding, as a result, the control points'coordinates in free-form curve and surface are compressed in completely lossless manner.To get high compression ratio , a loss compression algorithm is proposed .The scheme uses DPCM coder with optimal linear prediction for control points , coupled with a scalar quantizer which precision appointed by user, followed by bit-plane arithmetic entropy coder.Based on theories mentioned above, those approaches are applied in some 3D models .Furthermore , compression module of free-form curve and surface in the 3D models is developed to apply to the lightweight system named InteVue developed by Huazhong University of Science & Technology and achieves good compression ratio.