二维线段的矩形窗口逐边裁剪算法研究

本文详细介绍了一种二维线段的矩形窗口逐边裁剪算法。该算法充分利用了矩形窗口的凸性和窗口边界平行于坐标轴的特点，通过对二维线段与窗口边界的各种相对位置关系进行详细分类，以减少裁剪求交的次数，从而减少了算法的算术运算量，达到快速裁剪线段的目的。该算法原理简单，便于理解和实现，且运算速度较快。     

二维线段裁剪的概率模型

相对于矩形窗口的二维线段裁剪是计算机图形学中的基本操作之一,已有多种裁剪算法.由于这些算法在不同情况下各具优劣,一般只能分不同情况比较算法的性能,无法比较算法的平均性能.本文首先分析了线段与窗口之间位置关系的概率分布,从而得到二维线段裁剪的概率模型.接着使用该模型计算出一些常用算法的平均运算次数,并对算法的平均性能进行比较.该模型也纠正了一些论文中关于线段与窗口之间位置关系的概率分布的错误观点.     

具有最少算术运算量的二维线裁剪算法

本文在分析现有二维线裁剪算法的基础上,提出了具最少算术运算量的算法.新算法充分利用了矩形裁剪窗口的凸性和窗口边界线平行于坐标轴的特性,沿两组平行的窗口边界线对线段进行裁剪.通过将被裁剪线段定义为有向线段、确定窗口边界的进出边,避免了不必要的求交计算.实际算例表明,这一算法比当前国际上最快的线裁剪算法省时约一年.     

一种新的线段裁剪算法—四区域裁剪算法

本算法按裁剪窗口将整个图形区域划分为四个区 ,不仅提高了线段裁剪算法的效率 ,而且克服了一些算法要求裁剪窗口为矩形和对被裁剪线段端点进行编码的缺陷。     

-种新的线段裁剪算法-四区域裁剪算法

本算法按裁剪窗口将整个图形区域划分为四个区不仅提高了线段裁剪算法的效率,而且克服了一些算法要求裁剪窗口为矩形和对被裁剪线段端点进行编码的缺陷.     

一种新的线段裁剪算法一四区域裁剪算法

本算法按裁产针整个图形区域划分为四个区,不仅提高了线段裁剪算法的效率,而且克服了一些算法要求裁剪窗口为矩形和对被裁剪线段端点进行编码的缺陷。＋     

二维有向直线段常用裁剪算法裁剪效率比较

二维有向直线段剪效率的高低,直接影响到整个图形系统效率的高低。对二维有向直线段进行裁剪,较常用的算法有Ｓｕｔｈｅｒｌａｎｄ－ｃｏｈｅｎ算法,中点分割算法及梁友栋－Ｂａｒｓｋｙ算法。本文介绍一个测试上述三种算法裁剪二级有向直线段裁剪效率的程度,通过该程序的运行,以三种不同方式计算不同算法裁剪二维有向直线段所用的时间,从而比较出不同算法裁剪效率的高低。     

一种快速的二维线段裁剪算法

本文在分析了传统的二维线段裁剪算法的基础上，提出了一种新的二维线段裁剪算法。与传统的算法相比，该算法既不需要计算区域编码信息，也不依赖于直线的参数表示形式，而且算法简单，运算速度快。     

多边形裁剪及布尔运算的新方法

1.引言 多边形裁剪是指任意多边形经裁剪以后落在裁剪窗口内的一系列可见线段,正确地连接成一个或数个封闭的多边形,所谓正确连接是指落在窗口边界上的点之间如何选取部分窗口边界把裁剪后的多边形封闭起来,这里必然会遇到窗口边界角点的取舍问题,从国内外发表的多边形裁剪算法看,大都采用分区编码法,即以矩形裁剪窗口的四条边界及     

二维线段裁剪算法的分析与探索

线段裁剪是计算机图形学需要解决的基本问题之一。在对常见的线段裁剪算法分析的基础上，针对Cohen-Sotherland算法的改进进行了探索。利用合理构造分割窗口的辅助线，实现线段和窗口间位置关系的更精确判断，避免了无效交点的计算，提高了裁剪算法的整体效率。改进思路也同样适用于其他的裁剪算法。     

Determination of camera location from 2-D to 3-D line and pointcorrespondences

A method for the determination of camera location from two-dimensional (2-D) to three-dimensional (3-D) straight line or point correspondences is presented. With this method, the computations of the rotation matrix and the translation vector of the camera are separable. First, the rotation matrix is found by a linear algorithm using eight or more line correspondences, or by a nonlinear algorithm using three or more line correspondences, where the line correspondences are either given or derived from point correspondences. Then, the translation vector is obtained by solving a set of linear equations based on three or more line correspondences, or two or more point correspondences. Eight 2-D to 3-D line correspondences or six 2-D to 3-D point correspondences are needed for the linear approach; three 2-D to 3-D line or point correspondences for the nonlinear approach. Good results can be obtained in the presence of noise if more than the minimum required number of correspondences are used     

二维直方图准分的Renyi熵快速图像阈值分割

针对传统二维Renyi熵(RE)分割法分割结果不够准确和计算复杂度高的问题,提出一种快速的二维RE准分法。首先,用与主对角线平行的四条斜线将直方图分成内点区、边界点区和噪声点区,并对噪声点区进行去噪处理以便获得更好的分割性能。然后,对内点区与边界点区在RE公式中的对应量准确取值使阈值选取更准确。最后,提出二维RE准分法的一般递推算法,并在此算法的基础上利用RE在二维直方图上的计算特性和两个公式导出快速的二维RE阈值选取算法来降低计算复杂度。实验结果表明,与对比方法相比,文中方法不仅分割更准确和抗噪性更强,而且其运行时间少,与二维RE斜分法运行时间相近。     

矩不变调整的二维Shannon嫡图像分割及其快速实现

为了克服二维Shannon熵阈值法的缺陷,提出了一种使用矩不变法来调整二维直方图斜分Shannon熵的阈值分割方法。首先将二维直方图斜分原理运用到两种Shannon熵阈值法中,然后利用矩不变法从两种熵阈值法获取的阈值中选择最佳阈值,并提出二维直方图斜分Shannon熵阈值法的一般递推算法,最后将二维直方图分布特性与这种算法有机结合得到新型快速的递推算法。实验结果表明,提出的方法不仅分割效果优于当前的二维直方图斜分的最大熵阈值法,而且运行速度更快,约快4倍。     

一种相贯线的展开算法

介绍了一种应用于数控钣金加工中相贯线的展开算法,使复杂的三维相贯线变成了二维曲线,利用直线逼近曲线的方法进行数控编程,实现了数控技术对复杂曲线的加工,为类似的数控加工拓展了一种思路。     

基于离线训练的二维灰度特征向量快速目标搜索算法

本文以运动图像中的目标搜索为背景,根据模式识别和图像处理的基本理论,提出了一种基于离线训练的二维灰度特征向量模式匹配的快速目标搜索算法.首先离线在样本图像中对二维灰度特征向量模式进行训练,然后在线对运动图像提取二维灰度特征向量,进行模式匹配,搜索运动目标.     

Efficiently computing and representing aspect graphs of polyhedralobjects

An efficient algorithm and a data structure for computing and representing the aspect graph of polyhedral objects under orthographic projection are presented. The aspect graph is an approach to representing 3-D objects by a set of 2-D views, for the purpose of object recognition. In this approach the viewpoint space is partitioned into regions such that in each region the qualitative structure of the line drawing does not change. The viewing data of an object is the partition of the viewpoint space together with a representative view in each region. The algorithm computes the viewing data for line drawings of polyhedral objects under orthographic projection     

Tracking 3-D motion from straight lines with trifocal tensors

We present a novel approach to track the position and orientation of a stereo camera using line features in the images. The method combines the strengths of trifocal tensors and Bayesian filtering. The trifocal tensor provides a geometric constraint to lock line features among every three frames. It eliminates the explicit reconstruction of the scene even if the 3-D scene structure is not known. Such a trifocal constraint thus makes the algorithm fast and robust. The twist motion model is applied to further improve its computation efficiency. Another major contribution is that our approach can obtain the 3-D camera motion using as little as 2 line correspondences instead of 13 in the traditional approaches. This makes the approach attractive for realistic applications. The performance of the proposed method has been evaluated using both synthetic and real data with encouraging results. Our algorithm is able to estimate 3-D camera motion in real scenarios accurately having little drifting from an image sequence longer than a 1,000 frames.     

Perceptual grouping of line features in 3-D space: a model-based framework

In this paper, we propose a novel model-based perceptual grouping algorithm for the line features of 3-D polyhedral objects. Given a 3-D polyhedral model, perceptual grouping is performed to extract a set of 3-D line segments which are geometrically consistent with the 3-D model. Unlike the conventional approaches, grouping is done in 3-D space in a model-based framework. In our unique approach, a decision tree classifier is employed for encoding and retrieving the geometric information of the 3-D model. A Gestalt graph is constructed by classifying input instances into proper Gestalt relations using the decision tree. The Gestalt graph is then decomposed into a few subgraphs, yielding appropriate groups of features. As an application, we suggest a 3-D object recognition system which can be accomplished by selecting a best-matched group. In order to evaluate the performance of the proposed algorithm, experiments are carried out on both synthetic and real scenes.     

二维自适应有限元网格生成

自适应有限元网格生成是基于误差估计，自动进行有限元网格优化的一种策略。本文提出了一种基于单元误差估计的二维自适应有限元网格生成算法，并讨论了其实现过程。     

基于几何特征的血管快速重建算法

针对X光造影图像中血管三维重建的特殊性，提出了基于血管几何特征的快速重建算法。该算法依据双目视觉的重构原理，按照一定的顺序，选择并匹配具有分叉，转折，末梢等几何特征的点作控制点。使得连接控制点的血管可以简化成一条具有一定宽度的线段。提取并生成各个控制点的三维信息，然后采用“化曲为直，多线逼近”的方法进行三维绘制。达到了快速、简便、数据量小、精度可控性高的效果。非常适合成像质量有限的X光造影图像中血管这类线形几何体的重建。最后在微机平台上，通过实际测试验证了上述优点。