基于边界匹配的多张裁剪曲面的三角化算法研究

本文提出一种多张裁剪曲面的三角剖分算法。该算法在进行多张裁剪曲面的三角化时,首先采用匹配的方法离散各曲面的边界,确保离散后的各曲面边界在相交处重合。然后再对各曲面进行三角化,从而有效地防止了曲面相交处出现裂缝、孔洞和覆盖等现象。该算法已经成功应用于“超人ＣＡＤ／ＣＡＭ”曲面造型及加工系统,主要用于快速原型技术（ＲＰＴ） 的ＳＴＬ文件生成,算法表现稳定     

空间三角网格曲面的补洞方法*

由三维扫描仪对文物表面进行扫描得到网格数据后,先提取出破洞的边界,利用破洞边界三角形的法矢信息将破洞边界上的点投影到一个平面上,形成一个二维多边形;然后基于该二维多边形各内角及各边长度在多边形内插入新的离散点, 再将多边形内离散点三角网格化;最后用移动最小二乘近似法将破洞附近的点拟和成曲面,以此求出插入点的高度值,这样就得到了在三维空间中的网格数据。     

一种多张裁减曲面的快速三角化算法

针对多张裁减曲面的三角化问题,提出一种多张裁减曲面三角化边界的算法。该算法在进行多张裁减曲面的三角化时,采用点对应的方法离散曲面的公共边界,因而能有效地防止曲面相交处出现裂缝、孔洞和覆盖等现象,提高了多张裁减曲面三角化算法的正确性。同时采用了目前比较先进的基于局部优先的平面任意区域三角剖分算法,因而提高了三角化的效率。     

空间三角网格曲面的补洞方法

由三维扫描仪对文物表面进行扫描得到网格数据后，先提取出破洞的边界，利用破洞边界三角形的法矢信息将破洞边界上的点投影到一个平面上，形成一个二维多边形；然后基于该二维多边形各内角及各边长度在多边形内插入新的离散点，再将多边形内离散点三角网格化；最后用移动最小二乘近似法将破洞附近的点拟和成曲面，以此求出插入点的高度值，这样就得到了在三维空间中的网格数据。     

STL模型分割截面的三角剖分算法

针对分割STL模型时需要对分割截而进行三角剖分的问题,提出STL模型分割截面的Delauay三角剖分算法,将截面轮廓围成区域分成一个或多个区域单元,分别进行Delaunay三角剖分,并按STL模型标准拾取三角形,文中算法不用对分割截面轮廓进行复杂的凸划分和多轮廓的单轮廓化处理,提高了STL模型分割截面的三角剖分效率,尤其适合对具有复杂型腔的STL模型的截面进行三角剖分,应用实例表明：文中算法是正确有效的,具有实用价值。     

一个利用法矢的散乱点三角剖分算法

曲面上散乱点的三角剖分在曲面重建中发挥着重要作用,借助于曲面上的法矢信息和三维Delaunay三角剖分算法,该文给出了一种新的散乱点三角剖分算法,输入一组散乱点以及所在曲面S在这些散乱点处的一致定向的法矢信息,该算法将产生一张插值散乱点的三角网格曲面M,并且曲面M可以近似地看成是曲面S的三角剖分,算法的主要步骤分为两步：首先通过曲面S的一致定向的法矢信息,在曲面S的同一侧添加辅助点,利用这些辅助点来剔除Delaunay三角剖分中产生的不需要的三角片;然后将剩余的三角片连接成一张完整的网格曲面,与基于中轴的三角剖分算法相比,该文算法需要更少和更简单的计算,与局部三角剖分算法相比,该文算法可以更有效地避免重建后的曲面产生自交,该文的算法可用于任意拓扑的光滑曲面重建。     

曲面的自适应三角网格剖分

在传统的映射法基础上 ,采用自适应三角网格加密法能有效地处理带有特征约束条件的任意曲面的三角剖分问题 .在平面三角化算法中对环边统一处理 ,并且采取了一种简单有效的曲率估算方法 ,提高了运行效率 ;并在保持外观的基础上进行了网格质量的优化     

基于地层轮廓的三维重构的设计和实现

在进行海底地质地层调查勘探时,通常根据测量仪器采集的数据生成地层断面轮廓线,按照这些连续的轮廓线的分布特征及其灰底不同来粗略地分辨地层的性质.然而这些单一的剖面轮廓还不足以直观地反映该地域整体地层的三维形状分布信息.根据地质地层分布的特性,通过对相邻断层轮廓线点集的匹配和三角剖分算法来进行地层分布的三维重构,并利用基于三角域的Bernstein-Bezier曲面构造三次光滑曲面,从而模拟三维的地层分布效果图.     

Pro/ENGINEER中的IGES破面修补技术探索

IGES是许多CAD软件通用的数据转换中间格式。在Pro/ENGINEER中导入IGES格式文档时,由于几何算法和精度设置的不同,一般都会出现未修剪的面、重叠的面或者曲面间有间隙,统称破面。一旦出现破面,系统就无法生成实体。该文介绍了在Pro/ENGINEER中对破面进行修补的步骤和方法。     

散乱数据点的增量快速曲面重建算法

给出了一个新的散乱数据的曲面重建算法.算法充分利用邻近点集反映出的局部拓扑和几何信息,基于二维Delaunay 三角剖分技术快速地实现每个数据点的局部拓扑重建,然后通过自动矫正局部数据点的非法连接关系,以增量扩张的方式把局部三角网拼接成一张标准的整体二维流形网格.该算法在重建过程中能自动进行洞的检测,判断出散乱数据所蕴涵的开或闭的拓扑结构.实验结果表明,该算法高效、稳定,可以快速地直接重构出任意拓扑结构的二维流形三角形网格.     

基于MC算法的CT序列图像快速成型文件生成方法

快速成型技术在医学领域有着广泛而重要的应用,为了从医学图像中得到快速成型文件,详细论述了MC(marchingcubes)算法生成STL文件的步骤及需要注意的问题,并将其与轮廓连接生成STL文件的方法进行比较,说明了所提方法优势及可行性。方法先对CT序列图像进行阈值分割、区域增长等图像预处理,然后用MC算法得到用三角片组成的几何模型,最后根据文件格式标准,生成STL文件,其中着重讨论了STL文件中三角面片顶点顺序如何确定这一问题。     

基于压缩体素模型的快速成型直接切片算法*

基于STL文件模型的间接分层切片算法存在缺乏拓扑信息, 面误差诊断修复困难等问题,结合压缩表示形式的体素模型特点,提出了一种新的基于压缩体素模型直接切片分层优化算法.该算法利用Dexel模型记录的Dexel射线和物体交点所表达的物体表面点位置,通过设定分层平面厚度等参数获得截面轮廓数据,生成可直接适用于快速成型系统的共用层接口CLI文件.该算法在虚拟油泥造型系统中得到了应用,实验结果表明算法稳定、分层效果良好.     

Viewer,converter and preprocessor for smart machining process using an industrial robot

In this paper, viewer and converter softwares are presented for smart machining process using an industrial robot. The viewers for NC, CLS, DXF and STL files illustrate their surface representation with normal direction vectors. For example, the DXF is a data format developed by Autodesk to realize data interoperability among different makers’ CAD systems. The STL means Stereolithography which is a file format proposed by 3D Systems and recently is supported by many design tools and CAD/CAM softwares. In addition, the converters for DXF and STL files generate the corresponding CLS files with normal direction vectors for machining. Further, the proposed preprocessor allows the developed machining robot to work based on information included in STL files. The convenience and user-friendliness of the proposed integrated system are confirmed through experiments of viewing, converting and machining.     

基于2维流形的STL曲面网格重建算法

STL（stereo lithography）作为3D扫描数据和快速原型制造事实上的标准,其广泛应用于娱乐、制造业和Internet等领域.但随着3D模型越来越复杂,数据量越来越庞大,从STL文件难以快速获得完整拓扑关系以及其存在大量冗余信息的缺点,制约着STL网格模型的进一步优化处理与应用.为此,需要针对STL网格模型进行网格重建.本文针对2维流形的STL三角形曲面网格模型,提出了一种快速的网格重建方法.主要利用删除在重建过程中达到饱和的顶点,以便减少需要比对的顶点数,并结合STL文件数据的相关性来提高顶点搜索与比较的效率.对于非封闭的曲面网格,本文算法在提高曲面网格重建效率的同时,还能有效地提取曲面网格模型的边界信息.另外,重建的曲面网格数据文件大大地减少了存储空间,有效地去除了冗余数据.实验结果表明本文算法的高效性及鲁棒性.     

A new Steiner patch based file format for Additive Manufacturing processes

Additive Manufacturing (AM) processes adopt a layering approach for building parts in continuous slices and use the Standard Tessellation Language (STL) file format as an input to generate the slices during part manufacturing. However, the current STL format uses planar triangular facets to approximate the surfaces of the parts. This approximation introduces errors in the part representation which leads to additional errors downstream in the parts produced by AM processes. Recently, another file format called Additive Manufacturing File (AMF) was introduced by ASTM which seeks to use curved triangles based on second degree Hermite curves. However, while generating the slices for manufacturing the part, the curved triangles are recursively sub-divided back to planar triangles which may lead to the same approximation error present in the STL file. This paper introduces a new file format which uses curved Steiner patches instead of planar triangles for not only approximating the part surfaces but also for generating the slices. Steiner patches are bounded Roman surfaces and can be parametrically represented by rational Bezier equations. Since Steiner surfaces are of higher order, this new Steiner file format will have a better accuracy than the traditional STL and AMF formats and will lead to lower Geometric Dimensioning and Tolerancing (GD&T) errors in parts manufactured by AM processes. Since the intersection of a plane and the Steiner patch is a closed form mathematical solution, the slicing of the Steiner format can be accomplished with very little computational complexity. The Steiner representation has been used to approximate the surfaces of two test parts and the chordal errors in the surfaces are calculated. The chordal errors in the Steiner format are compared with the STL and AMF formats of the test surfaces and the results have been presented. Further, an error based adaptive tessellation algorithm is developed for generating the Steiner representation which reduces the number of curved facets while still improving the accuracy of the Steiner format. The test parts are virtually manufactured using the adaptive Steiner, STL and AMF format representations and the GD&T errors of the manufactured parts are calculated and compared. The results demonstrate that the modified Steiner format is able to significantly reduce the chordal and profile errors as compared to the STL and AMF formats.     

Program design of STL machine graphics realistic system

This topic is based on Auto CAD graphic input environment.It takes the STL format graphic files as the data exchange interface to do the research of STL interactive 3D realistic graphics displaying content.Through the analysis of the STL file format,in VC++6.0 programming environment,class if stream in the standard IO library was used for object class definition.And get line functions in the string class were called to read and bind STL file line by line.In data processing module,draw triangles in Open GL programming technology was applied to realize the visual display of the STL graphics,with the corresponding 3D entity data generated.Open GL graphics processing technologies were applied to display 3D graphics from STL files input or realistic program module,which contain the graphic transformation,light,materials,et al.Test reports were shared based on the test of the application system.Finally the program design of STL graphics realistic display system was completed based on research work,which has certain theoretical and practical significance in the aspect of engineering application.     

Machine path generation for the SIS process

Because of the differences in the nature of rapid prototyping (RP) processes, there is no standard machine path code for them. Each RP process, based on its characteristics and requirements, uses the standard CAD file format to extract the required data for the process. Selective inhibition of sintering (SIS) is a new layered fabrication method based on powder sintering. Like other RP systems, SIS needs a specialized machine path generator to create an appropriate machine path file. Machine path (i.e., boundary path and hatch path) should produce the printing pattern that enables the SIS machine user to easily remove the fabricated part from the surrounding material. A new machine path algorithm, which generates appropriate boundary and hatch paths for the SIS process is proposed. The new machine path generator provides the ability to process CAD models of any size and complexity, the ability for machine path verification before sending the file to the SIS machine, and the ability to fix the possible STL files disconnection errors. In this system, very large STL files can be processed in a relatively small computer memory. The system has been successfully tested on STL files as large as 200 MB. The generated path files have been used in fabrication of several parts by the SIS process.     

STL file generation from measured point data by segmentation and Delaunay triangulation

For the generation of the models in RP, a laser scanner is currently used a lot due to the fast measuring speed and high precision. Direct generation of STL file from the scanned data has a great advantage in that it can reduce the time and error in modeling process. The reduction of the number of point data is important while generating STL file directly from the measured point data with maintaining their precision.A new approach is addressed to reduce the amount of data by segmentation and Delaunay triangulation. Basic experiments are performed to apply the algorithm developed to real models. Different results are incurred by user-defined criteria, and some dominant output characteristics according to the user input are reviewed and analyzed. The program developed in the research generates an STL files efficiently with automated data reduction. Several criteria are specified in order to maintain the characteristics of the feature and satisfy the needs in real workshops.     

STL数据检验和修复

STL数据文件是快速成型最常用的数据交换文件,STL数据的错误将影响快速成型预处理的进行.本文提出一种STL数据检验和修复算法,它通过对STL数据建立拓扑关系,依据棱与面的关联度快速捕获STL数据的错误.针对不同的STL数据错误采用相应的算法,对STL数据进行有效的修复.     

基于NURBS曲线的STL模型截面轮廓平滑处理技术研究

由于STL文件格式的容易生成且不需要复杂的CAD系统支持，已经发展成为快速成型制造领域数据交换的准标准；但是STL模型的精度与其数据文件的尺寸之间存在严重的矛盾，为了在较小的STL文件下得到较高的轮廓精度，本文提出了一种基于三次NURBS曲线STL模型截面轮廓的重构技术，通过设置直线阈值和转角阈值的方法，分段拟合STL截面轮廓数据，使其截面轮廓具有更好的平滑度和更高的精度。