RP-Oriented Visualization And Slicing Of VRML Model

VRML(Virtual Reality Modeling Language) format as an international standard for VR, has already been widely adapted for graphical representation of 3D objects over the Web. VRML models can be created with geometry, texture and color. If VRML format is used in RP, colorized models can be fabricated using RP technique, and the weak points of STL format can be overcome, such as accuracy loss, holes, etc. Hence developing RP software system based on VRML is of industrial interest. RP slicing technique based on VRML has been investigated.Firstly, based on the analysis of nested hierarchy, grouping and USE techniques in VRML, a data structure was designed which could completely express model information and facilitate slicing processing; Matrix of Transform node in VRML and equivalent realization using OpenGL were deprived; By studying the techniques of reading VRML file and extracting related information, internal data model for slicing was built, and scene rendering was realized using OpenGL.Secondly, slicing strategy and method for VRML format were proposed based on the analysis of representation method of internal data model. Slicing of geometrical elements and polyhedron models were processed respectively. If the geometrical element is regular in word coordinate system (WCS), it will be sliced in WCS, or else, slicing plane will be transferred into local coordinate of each geometry, and slicing will be processed in local geometry system, then slicing data will be transferred into WCS. And polyhedron models will be sliced in WCS. Method of model reorientation using modelview matrix of OpenGL was introduced in selection of fabrication orientation. Based on the analysis of intersection of plane-geometrical element, condition and geometrical description of intersection were deduced in each crossing case, and method of linear discretization for intersection was proposed. The method has the characteristics of good stability, high precision and efficiency adapting to file format of layer data in RP manufacturing.