【作者】 孙秀英；

【导师】 李占利；

【作者基本信息】 西安科技大学 ， 计算机应用技术， 2006， 硕士

【摘要】 VRML(virtual Reality Modeling Language)是广泛应用于Web的三维造型语言，同时也是在Internet上传输VR图像的国际规范，能表达模型的颜色纹理信息。使RP系统接受VRML格式可以制造出彩色工件，同时避免STL格式带来的不足，例如精度损失、易出现裂缝等，因此开发能够接受VRML模型的RP软件具有重要工业应用价值。本文对基于VRML的RP分层处理技术进行了系统研究。 首先，在对VRML文件嵌套、编组、引用等技术进行分析的基础上，设计了以三维几何形体为单位、便于模型分层处理的内部模型；分析推导了VRML坐标变换节点Transform的作用矩阵以及与之等价的OpenGL坐标变换语句序列；研究了VRML文件读入及相关信息的提取技术，建立了用于模型显示及分层处理的内部数据模型，实现了VRML模型的可视化。 其次，在分析内部模型表示方式的基础上，提出了适合于VRML模型的分层处理方案及方法。该方案采用不同方法处理VRML基本几何体(球体、圆柱体、圆锥体、长方体)与多面体的分层。若基本几何体转换到世界坐标系中仍是正则几何体，则在世界坐标系中进行分层处理，否则将平面转换到几何体所在局部坐标系中，并在局部坐标系中进行分层处理，然后将分层结果转换到世界坐标系中，对于多面体则在世界坐标系中进行分层处理。在分层方向的选择上，利用OpenGL模型视图矩阵实现了模型的重定位。在全面分析平面与基本几何体各种相交情形的基础上，推导了各情形下的相交条件及交线几何表示，并研究了其离散化方法。该方法具有稳定性强、精度高、速度快的特点，能适应RP加工的层片文件格式要求。 在上述研究成果的基础上，利用VC++6.0和OpenGL开发了基于VRML的RP分层处理软件系统。该系统分层精度比较高，可扩展性好，能适应未来彩色原型、网络与虚拟制造的发展趋势。更多还原

【Abstract】 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.更多还原