一个有效的多边形窗口的线裁剪算法

在已有的一般多边形窗口的线裁剪算法的基础上提出了一个新算法,该算法通过内包围盒的方法,排除大量不与裁剪线段相交的多边形的边,从而降低了求交中复杂度极高的乘除法运算量,保证了算法的快速、高效.     

基于点区域分布的多边形窗口线裁剪算法

通过判断多边形窗口顶点相对于裁剪线段所在直线的区域分布,明确窗口的哪些边与裁剪线段所在直线相交;再通过判断裁剪线段两端点相对于这些多边形窗口相交边的区域分布,最后确定裁剪线段与多边形窗口的实际交点.避免大量不必要的求交运算和其他复杂的辅助操作.实验结果表明:新算法提高了裁剪效率,对各种情况都能快速、正确地得到结果.     

基于叉积法的凸多边形窗口裁剪算法

提出了一种建立在矢量叉积分析基础上的线段对凸多边形窗口进行二维裁剪的新算法．这种算法的基本思想是从多边形的某一边开始．沿多边形寻找线段所在直线与多边形的两个交点．然后用文中提出的判断准则找出线段的可见部分．使用本算法，可以不必求出多边形各边界边的单位内法线矢量；在绝大多数情况下．只有一部分边界边参与运算；参与运算的边界边中．除了被线段穿过的那两条之外．余者均可通过简单的运算与判断予以迅速排除．与现行算法相比．本算法浮点运算次数显著减少．裁剪速度明显提高．     

一种快速的多边形裁剪算法

提出并实现了一种有效的基于任意窗口的任意多边形裁剪算法．通过简单的预处理和有效的数学方法,不需要做复杂的“内点’”、“外点”以及“进点”、“出点”的讨论就可准确地确定裁剪线段或折线．建立了简单且有效的数据结构,使得匹配这些有效线段和有效折线的过程十分简洁,从而可快速输出裁剪结果．     

一种处理交点退化现象的高效多边形裁剪算法

针对复杂多边形裁剪中出现的多边形彼此间重点和重边现象,提出了一种能够处理交点退化现象的高效多边形裁剪算法.该算法利用单向链表实现多边形的存储,同时基于单调链的平面扫描法求解多边形间的交点,减少了多边形顶点的遍历次数和求交次数;对于重点和重边现象,通过交点关联的线段间的方向关系判别交点的进出性;最后更新多边形顶点序列,获取裁剪结果.实验结果表明,该算法能够完成对含内环多边形的裁剪,在交点退化情况下也能获得准确的裁剪结果.且该算法裁剪效率较Greiner-Hormann算法大幅提高,具有很高的执行效率和实用性.     

对Cohen-Sutherland裁剪算法的改进

Cohen-Sutherland裁剪算法对不与边框相交的线段进行裁剪时效率较高,而对与窗口边界有交点的线段裁剪效率低.而且很多的时候,被裁剪线段仅与窗口边界延长线相交,求交点到最后是无效的操作,因为线段可能完全被丢弃;并且被裁剪线段与窗口边界相交时交点的取得比较复杂.本文就这两个问题,利用点与直线位置的关系性质,提出基于Cohen-Sutherland算法的图形裁剪新思路.     

论文摘编

论文摘编任意多边形对线段的裁剪傅百文（北京联合大学电子自动化工程学院，北京１００００９）本文利用参数方程法，提出了一个任意多边形裁剪线段的简捷而有效的方法，该方法不受多边形凸性等的限制，具有通用性。１参数方程设Ａ、Ｂ两点的坐标分别为Ａ（ｘＡ，ｙＡ），...     

计算机图学的一种裁剪法

图形的裁剪法已有多种并且均用得很成功，主要目的之一是减少计算量，根据一个点位于一条 段的左或右方的判定可导出一种较简单的算法．本文据此提出一种计算量较少的线段和多边形间 的裁剪法，有关多边形既有凸的也有凹的，同时提供了已用计算机执行过的两个例子。     

对Cohen-sutherland线段裁剪算法的分析及改进

研究分析了cohen-sutherland线段裁剪算法,针对cohen-sutherland线段裁剪算法不能有效地判断出所有完全位于窗口之外线段的情况,通过添加判断条件,能够判断出所有完全位于裁剪窗口之外的线段,从而减少了求交点的次数,提高了算法的运算效率.     

对Cohen-Sutherland裁剪算法的分析与改进

在矩形窗口的二维裁减中,Cohen-Sutherland线段裁剪算法既不能有效地判断出线段是否完全在窗口外又可能求解出无效交点,因此本文提出一种基于Cohen-Sutherland线段裁剪算法的改进算法,给定一个线段,由计算剪裁窗口顶点到线段的有向距离符号来判断线段与窗口相对位置关系,避免求取无效交点的操作。改进算法可以迅速判断哪些线段与裁剪窗口有真正的交点,再通过距离大小的比较,确定直线与窗口的哪条边相交,最终将被裁剪线段快速、准确输出。实验表明,改进的Cohen-Sutherland算法比原算法有更高的执行效率。     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the     

An affordable accurate evaluation of the binding conformations predicted by molecular docking studies in bio-system

Franck-Condon factors bridge the gap between theoretical modeling and experimental observations for molecular electronic spectroscopy and electron transfer.Under the displaced harmonic oscillator approximation,multidimensional Franck-Condon factors are decomposed into a product of many one-dimensional(1D)Franck-Condon(FC)factors,and each 1D-FC factor is associated with one Huang-Rhys factor that determines the leading contribution of     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with     

Journal of Donghua University ( English Edition) Contents of Volume 31

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