一种快速的多边形的线裁剪算法

裁剪算法是计算机图形学的一个基本算法，但大多数算法都是针对矩形窗口或多边形窗口的，已有的凹多边形裁剪主要将其分解为凸多边形处理。此外提出一个任意多边形的快速交点排序线裁剪算法，并将其用于工程图装配的二维消隐。     

一种通用多边形的线裁剪算法研究

提出一个任意多边形的裁剪算法 ,并将其用于工程图装配的二维消隐。     

一种一般多边形窗口的有效线裁剪

在分析已有线裁剪算法优、缺点的基础上提出了一种新算法，该算法通过计算被裁剪线段和多边形各边的真实交点，利用交点将被裁剪线段分成若干子线段，用各子线段的中点来判断是否对它们实施裁剪。裁剪算法对各种情况都能快速、正确地得到结果。     

基于裁剪算法的二维装配图的算法研究

摘要：提出了基于AutoCAD生成装配图的关键技术及解决方案；引入了一种新的轮廓自动识别算法，将内外轮廓识别统一起来。采用线段端点分类及交点排序的策略，快速可靠地解决需要消除的部分。最后给出一个稳定可靠的任意多边形裁剪算法。该方法已成功地应用于机械工程装配图。     

基于四叉树法和波前法的曲面网格剖分算法

提出了一种基于四叉树法和波前法的有限元网格生成算法。该算法首先将裁剪曲线边界离散成多边形,然后使用四叉树法对待划分裁剪参数曲面按细分要求进行递归分解,最终生成规则的栅格点,最后利用波前法的原理生成三角形网格,通过合并处理生成三角形与四边形混合网格。     

基于四叉树法和波前法的曲面网格剖分算法

提出了一种基于四叉树法和波前法的有限元网格生成算法。该算法首先将裁剪曲线边界离散成多边形，然后使用四叉树法对待划分裁剪参数曲面按细分要求进行递归分解，最终生成规则的栅格点，最后利用波前法的原理生成三角形网格，通过合并处理生成三角形与四边形混合网格。     

基于 AUTOCAD 的面向机械装配图的关键技术及其应用

提出了基于ＡＵＴＯＣＡＤ生成装配图的技术关键及解决方案；设计了零件的统一表示模式；引入了一种新的轮廓自动识别算法，将内外轮廓识别统一起来。采用线段端点分类及交点排序的策略，快速可靠地解决需要消除的部分。最后给出一个稳定可靠的任意多边形裁剪算法。上述方法已成功地应用于机械工程装配图。     

一种高效可靠的剖面线参数化绘制技术

剖面线是图形表达的一个重要方面。剖面线算法到现在已经发展得比较成熟,但其主要矛盾仍在于算法的可靠性,由于剖面线算法的核心部分在于裁剪算法,故其可靠性主要取决于裁剪算法的可靠性,本文在一个新的简捷可靠的裁剪算法的基础之上,采用参数化技术,提出了一种高效可靠的参数化剖面线生成算法。     

基于零件图约束信息的装配图重建方法

基于图形多约束的理论,用多约束的方法对零件图进行形状定义,通过树与链表的混合数据结构,实现零件图与装配图的信息共享,在此基础上,巧妙地利用线段之间的不同表达,导出了多边形窗口线段裁剪的最简算法,从而使得零件图中的形状信息自动地被转化为装配图中的形状信息,进而实现了判断、求交和装配可见性测试的一体化。于是,不仅解决了任意复杂度装配图的计算机辅助设计,而且提高了整个机械CAD的水平。     

点云特征型面的边界曲线拟合及曲面裁剪算法

点云特征型面边界曲线的拟合质量直接决定了对应曲面裁剪的质量。以机械零件点云模型为研究对象,针对点云分割型面的边界点识别、排序、拟合和曲面裁剪问题展开研究。基于场力法提取的边界点集,提出了基于最短距离法的边界点集排序和方向夹角阈值限定的边界点集去噪等预处理算法;采用局部二次多项式函数拟合估算边界点集曲率,提出了基于曲率突变点归属性判断的边界点集分段和拟合算法;通过控制点投影变换求取二维裁剪边界,提出了基于特征点集多边形凹凸性的二维边界曲线方向判断法。使用机械零件模型典型型面进行实验,验证了各阶段算法。该算法具有很好的适用性,可进一步扩展应用至复杂曲面边界裁剪。     

星光制导中的凸多边形星图识别算法

提出了以凸多边形为基元、完全不依赖于星等的星图识别算法。首先,构造全部导航星的14°视场模式,共9 176个。然后逐一把这些视场中的导航星投影到像平面,得到一系列的点。依其坐标排序,采用由平面上的点生成凸多边形的算法,就能得到唯一的、以恒星为顶点的凸多边形。在导航星表中以凸多边形为储存单元,其内容为凸多边形的边和顶角。为此,设计了以导航星凸多边形和观测凸多边形之间距离最小为准则的识别算法。针对星光制导的导弹观星时间很短,提出了根据弹道生成弹上导航星表的方法,其导航星表只需存储30颗星的75个凸多边形。仿真结果表明:在任意视场中,基于凸多边形的星图识别成功率高于99%,并具有较强的鲁棒性。     

面向虚拟现实的CAD模型转换研究

应用Pro/E良好的兼容性,通过其接口输出虚拟环境所需的三角面片模型和运用近似凸集分解算法将该三角面片模型转换成凸包模型,生成的凸包模型较之三角面片模型外形更粗糙,数据量程更短,经仿真计算凸包模型较之三角面片模型运算时间更短,所以应选择不同的触觉模型来满足针对虚拟环境中模型对实时性和精确性的不同要求。     

A tool-path generation strategy for wire and arc additive manufacturing

This paper presents an algorithm to automatically generate optimal tool-paths for the wire and arc additive manufacturing (WAAM) process for a large class of geometries. The algorithm firstly decomposes 2D geometries into a set of convex polygons based on a divide-and-conquer strategy. Then, for each convex polygon, an optimal scan direction is identified and a continuous tool-path is generated using a combination of zigzag and contour pattern strategies. Finally, all individual sub-paths are connected to form a closed curve. This tool-path generation strategy fulfils the design requirements of WAAM, including simple implementation, a minimized number of starting-stopping points, and high surface accuracy. Compared with the existing hybrid method, the proposed path planning strategy shows better surface accuracy through experiments on a general 3D component.     

面向工程的优化算法性能实验研究

针对10种工程常用的优化算法进行实验研究,选取12个优化算法Benchmark测试函数进行算法评价,包括连续的和不连续的、凸的和非凸的、单峰的和多峰的、二次的和非二次的、低维的和高维的、有约束的和无约束的测试函数。对实验结果进行分析,从解空间的角度对算法的特性进行分析总结,给出了算法选取的准则。     

一种新的射影变换下平面多边形的识别方法

依据射影不变性提出5个描述多边形拓扑和几何特征的特征向量,以这些特征向量作为约束条件给出在射影变换下两个多边形为类似形的定义;基于类似形原理,提出了一种新的识别平面多边形的方法.用拓扑结构定性分析类似形对图象中的噪声不敏感,用几何特征进行定量分析能反应图象的细小差别.该识别算法不仅能识别不同形状的目标,而且还可以区分形状相同但大小、比例不同的目标.     

Local interference detection and avoidance in five-axis NC machining of sculptured surfaces

The tool interference problem is the most critical problem faced in sculptured surface machining. This paper presents a methodology for interference detection and avoidance in five-axis NC machining of sculptured surfaces with a filleted-end cutter. The surfaces to be machined are divided into convex and non-convex regions. There is no local interference inside the convex regions. For the non-convex regions, based on the analysis of the different local interference, local gouging is first detected and avoided by determining optimal cutter orientations. Rear gouging detection and avoidance algorithms are then proposed for simple smooth surfaces and complex shaped surfaces, respectively. The techniques presented in this paper can be used to generate interference-free tool paths. The realistic results indicate that the proposed method is feasible and reliable .     

Tool-path generation for pockets with freeform curves using Bezier convex hulls

The objective of this paper is to generate tool paths for pockets with freeform curves, i.e. Bezier curves or B-spline curves. Time efficiency and overcut avoidance are two of the most important factors in NC machining. A method, based on the convex hull property of Bezier curves, is thus developed so that the portion of the boundary defined by a Bezier curve is replaced by parts of its convex hull on the cavity side. Therefore, the new pocket boundary, redefined by only segments of straight lines, can be solved efficiently based on current algorithms without overcuts. Cutting tool paths can be generated for pockets with islands avoiding computation of higher degree curve/curve intersections. Furthermore, recursive subdivisions on Bezier curves are used to improve the accuracy of the cut with an allowance criterion based on sizes of convex hulls.The portion of the boundary defined by a B-Spline curve is transformed into piecewise Bezier curves. The tool-path generation for pockets with B-spline curves can thus be solved by reducing the problem to one of pockets with Bezier curves.     

Optimal positioning of irregular shapes in stamping die strip

The nesting of two-dimensional shapes is a common problem, where raw material has to be economically cut. As for the single-pass single-row strip layout, several algorithms, based on established methods, have been proposed. Moreover, it should be noticed that the optimum layout should also consider a few constraints, like grain orientation for subsequent forming operation, correct bridge width, and the commercial roll of metal width in order to make solutions applicable in real industrial environments. Most of the procedures until now shown in literature are quite complex and often ignore these real constraints. They usually make use of sliding techniques and are not able to effectively work with relatively multiple-connected figures. In particular, most of the different proposed procedures are based on the No Fit Polygon (NFP) computation of non-convex polygons, which often generates holes. This work is a proposal for a more efficient method, which can be used in heuristic procedures. In order to overcome some faults of most of the former methods presented in literature, in this paper a new geometric entity called ??No Fit Path?? (NFPh) of non-convex polygons is applied. It allows researchers to find solutions of nesting problems even when there are NFP faults due to degenerate solutions. Moreover, the No Fit Path allows researchers to easily read, modify, or share their results, overcoming all those problems arising from the usual large amount of information and from the different origins and formats of the obtained data. Given two non-convex polygons, the algorithm is able to calculate their NFPh very quickly and without any approximation by a polygon clipping method. In this paper a totally automated procedure has been developed. This procedure firstly obtains the ??No Fit Path?? (NFPh); secondly, between all the existing positions on the NFPh, the algorithm searches the optimal one, minimizing the global waste. The proposed approach also allows designers to set an optimal orientation of the shapes on the roll of metal, taking account of the grain orientation in order to obtain the best mechanical characteristics for the cut pieces.     

Evaluation of circularity from coordinate and form data using computational geometric techniques

Data for evaluating circularity error can be obtained from coordinate measuring machines or form measuring instruments. In this article, appropriate methods based on computational geometric techniques have been developed to deal with coordinate measurement data and form data. The computational geometric concepts of convex hulls are used, and a new heuristic algorithm is suggested to arrive at the inner hull. Equi-Distant (Voronoi) and newly proposed Equi-Angular diagrams are employed for establishing the assessment features under different conditions. The algorithms developed in this article are implemented and validated with the simulated data and the data available in the literature.     

显微视觉检测的几何量测量算法研究

为了提高微小型结构件视觉测量结果的准确度,研究了微小型结构件的圆、直线等几何要素的测量方法,并指出不同的测量方法对测量结果的准确度影响较大,在进行尺寸、形状和位置误差测量时,应选取不同的测量方法。提出一种直线和圆最小包容区域及最小外接圆的快速搜索算法,该算法利用凸包原理,排除不相关的运算数据点,可减小运算量。试验结果表明,该检测算法可大幅度提高检测速度。