三维船舶模型边界表示转构造表示方法

模型数据表示是CAD几何引擎的基础,边界表示(B-Rep)和构造实体几何(CSG)表示是常用的2种模型数据表示方法,随着混合建模的发展,B-Rep和CSG混合建模开始应用于船舶等模型量大的场景,其中B-Rep与CSG实体的互相转换是一个关键性功能.针对类型多样的基本实体的B-Rep转CSG问题,设计了解析B-Rep几何结构并根据拓扑结构组合为CSG实体的转换流程.针对复杂实体的B-Rep转CSG问题,根据凹凸性将实体划分为不同类型的区域,将区域的边界作为切割环,据此提出了切割环识别算法.基于切割环识别,设计了二叉分解树进行实体分解和CSG树生成流程.对15种基本实体以及4个复杂模型的若干B-Rep实体,测量了其转换为CSG实体的转换误差和转换时间.实验结果表明,模型尺寸归一化后,文中方法可以在0.05%模型尺寸的误差范围内完成B-Rep实体向CSG实体的转换,并已支撑船舶产品设计系统(SPD)的部件小样建模平台的模型轻量化功能.     

路径打孔布尔运算在网页设计实践中的应用

布尔运算是计算机图形学中几何造型技术的基本算法，结合视觉美学理论从路径布尔运算方面，实例论证利用并集、交集、差集等运算规律在Fireworks网页设计软件中可以很好的将平面视觉美学与布尔运算技术融通应用，解决了网页按钮设计中的难点和复杂图形制作问题。     

大一统的时代——统一渲染架构引领未来

Vertex Shader和Pixel Shader长期以来作为GPU的核心处理单元,承载着一个3D图形从程序到画面的重要运算步骤。但是在统一渲染架构中,我们却再难看到VS和PS的身影了。为何要统一?统一渲染架构的意义何在?     

一个基于剖面图的实体布尔运算算法

本文详细介绍了一个基于剖面图的实体布尔算法的构追和原理,并以布尔并运算为例给出了算法的形式语言描述。该算法将实体布尔运算这个三维问题最终变成一个纯二维问题来处理,简单且直观。     

巧用AutoCAD的布尔运算简化复杂实体造型

布尔运算本是布尔代数中的一种运算，现在流行的各种针对光栅图和矢量图的软件（Photoshop、CorelDraw、３Dmax等）几乎无一例外引入布尔运算作为一种辅助绘图手段，AutoCAD中的布尔运算对二维及三维图形都可应用，而且在应用于复杂三维实体造型时比常规方法更显简化。此时可用简单实体构建出复杂的三维实体模型。AutoCAD的布尔运算：并（UNION）、交（INTERSECT）、差（SUBTRACT）。并：UNION命令将两个或两个以上实体合并成单一实体，不论操作对象是否有公共部分；差：SUBTRACT命令将若干被减实体对象减去另外若干要减…     

限定TIN与CSG集成仿真模型生成算法研究

为了有效地组织和管理三维GIS空间数据,实现对三维空间实体高效、完整地表达,提出了限定不规则三角网（TIN）与构造实体几何（CSG）集成的仿真建模算法。采用TIN模型描述地形,CSG模型描述建筑物,通过抽取建筑物地面轮廓线作为地形三角剖分时的限定约束条件,将两种模型有机集成在一起。同时,实现了两类模型可视化渲染操作的同步进行。仿真试验结果表明,算法在保证模拟精度的前提下,能有效地简化建模过程,在一定程度上降低了可视化渲染计算的复杂度。     

支持异种材料体造型的特征布尔运算

针对传统CAD不能提供材料等非几何信息,且无法实现异种材料物体间的布尔运算,提出了一种可应用于构造异种材料物体的特征布尔运算,包含了由材料决定的布尔差和交运算及新的布尔复形并运算,由特征合并和特征抽取两步完成;并给出了该运算的几何实现、实现算法及实例．     

空天三维仿真中空间目标实时渲染算法

近年来,随着载人航天研究的进一步加深,空天任务的复杂性和可靠性要求也日益提高。对海量目标的位置实时解算和场景渲染是空间目标实时渲染的重难点。利用层次细节模型（LOD）在动态渲染中的优势,本文提出一种海量的空间目标实时渲染方法,该算法侧重于把传统的批LOD模型优化成基于R树的LOD模型。在构建基于R树的LOD模型时,会出现索引空间重叠、查询效率低、LOD模型纹理突变等问题。因此,提出基于节点的深度调整策略消除索引空间重叠,采用快速剪枝算法提高查询效率,使用基于Shader的Alpha测试技术实现LOD模型平滑过渡,通过上述3种优化算法的协同处理,优化后的LOD模型在场景渲染时间、空间占有率、帧率等均有所改善。     

基于圆柱体轴向包围盒检测的巷道相交建模

针对岩土工程中三维巷道相交建模复杂、运算时间长的问题,根据巷道的几何特性,提出了一种圆柱体-轴向包围盒的双层包围盒检测方法。该方法能够快速查找出可能相交的三角形单元,结合三维实体布尔运算实现了一种不规则三角形网(TIN)巷道曲面相交的快速构建方法。详细讲述了圆柱体-轴向包围盒(AABB)双层包围盒碰撞检测的基本原理以及实体相交布尔运算中的关键技术,对生成的实体网格提出优化方案。通过工程实例验证,在巷道曲面相交建模中,相比于层次有向包围盒(OBB)算法,圆柱体-AABB双层包围盒在包围盒生成方面效率提高近50%,具有建模简单、检测时间短、顶层检测准确度高等特点。     

新一代显卡的性能标杆--3DMark05全解析

在下一代Pixel Shader(像素着色)和Vertex Shader(顶点着色)规格——SM(Shader Model渲染模式)4．0出现之前, 游戏开发者仍需要考虑如何利用现在的Shader Model创造更佳的游戏画面效果。然而目前支持S M 2．0图形的核心管线仅拥有 10条指令,已经不能快速执行更复杂的渲染效果。因此,业界需要扩展S M 2的性能、推出新的标准而不用像硬件那样全面改变API架构。正是鉴于这种趋势,Shader Model 2．0a, Shader Model2．0b和Shader Model3．0陆续现身。     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.     

Editorial: Special issue on recent advances in hybrid control theory and applications

正The demands of a rapidly advancing technology for faster and more accurate controllers have always had a strong influence on the progress of automatic control theory.In recent years control problems have been arising with increasing frequency in widely different areas,which cannot be addressed using conventional control techniques.The principal reason for this is the fact that a highly competitive economy is forcing systems to operate in regimes where     

Information for Authors

正Aim The Journals of Zhejiang University-SCIENCE(A/B/C)areedited by the international board of distinguished Chinese andforeign scientists,and are aimed to present the latest devel-opments and achievements in scientific research in China andoverseas to the world’s scientific circles,especially to stimulateand promote academic exchange between Chinese and for-eign scientists everywhere.     

Enhancing a leaf radiative transfer model to estimate concentrations and in vivo specific absorption coefficients of total carotenoids and chlorophylls a and b from single-needle reflectance and transmittance

The relative concentrations of different pigments within a leaf have significant physiological and spectral consequences. Photosynthesis, light use efficiency, mass and energy exchange, and stress response are dependent on relationships among an ensemble of pigments. This ensemble also determines the visible characteristics of a leaf, which can be measured remotely and used to quantify leaf biochemistry and structure. But current remote sensing approaches are limited in their ability to resolve individual pigments. This paper focuses on the incorporation of three pigments—chlorophyll a, chlorophyll b, and total carotenoids—into the LIBERTY leaf radiative transfer model to better understand relationships between leaf biochemical, biophysical, and spectral properties.Pinus ponderosa and Pinus jeffreyi needles were collected from three sites in the California Sierra Nevada. Hemispheric single-leaf visible reflectance and transmittance and concentrations of chlorophylls a and b and total carotenoids of fresh needles were measured. These data were input to the enhanced LIBERTY model to estimate optical and biochemical properties of pine needles. The enhanced model successfully estimated reflectance (RMSE = 0.0255, BIAS = 0.00477, RMS%E = 16.7%), had variable success estimating transmittance (RMSE = 0.0442, BIAS = 0.0294, RMS%E = 181%), and generated very good estimates of carotenoid concentrations (RMSE = 2.48 µg/cm², BIAS = 0.143 µg/cm², RMS%E = 20.4%), good estimates of chlorophyll a concentrations (RMSE = 10.7 µg/cm², BIAS = − 0.992 µg/cm², RMS%E = 21.1%), and fair estimates of chlorophyll b concentrations (RMSE = 7.49 µg/cm², BIAS = − 2.12 µg/cm², RMS%E = 43.7%). Overall root mean squared errors of reflectance, transmittance, and pigment concentration estimates were lower for the three-pigment model than for the single-pigment model. The algorithm to estimate three in vivo specific absorption coefficients is robust, although estimated values are distorted by inconsistencies in model biophysics. The capacity to invert the model from single-leaf reflectance and transmittance was added to the model so it could be coupled with vegetation canopy models to estimate canopy biochemistry from remotely sensed data.     

Mr. Twinn’s bombes

This article discusses the history and design of the special versions of the bombe key-finding machines used by Britain’s Government Code & Cypher School (GC&CS) during World War II to attack the Enigma traffic of the Abwehr (the German military intelligence service). These special bombes were based on the design of their more numerous counterparts used against the traffic of the German armed services, but differed from them in important ways that highlight the adaptability of the British bombe design, and the power and flexibility of the diagonal board. Also discussed are the changes in the Abwehr indicating system that drove the development of these machines, the ingenious ways in which they were used, and some related developments involving the bombes used by the U.S. Navy’s cryptanalytic unit (OP-20-G).