BRDF Measurement Modelling using Wavelets for Efficient Path Tracing

Physically based rendering needs numerical models from real measurements, or analytical models from material definitions, of the Bidirectional Reflectance Distribution Function (BRDF). However, measured BRDF data sets are too large and provide no functionalities to be practically used in Monte Carlo path tracing algorithms. In this paper, we present a wavelet‐based generic BRDF model suitable for both physical analysis and path tracing. The model is based on the separation of spectral and geometrical aspect of the BRDF and allows a compact and efficient representation of isotropic, anisotropic and/or spectral BRDFs. After a brief survey of BRDF and wavelet theory, we present our software architecture for generic wavelet transform and how to use it to model BRDFs. Then, modelling results are presented on real and virtual BRDF measurements. Finally, we show how to exploit the multiresolution property of the wavelet encoding to reduce the variance by importance sampling in a path tracing algorithm. ACM CSS: I.3.7 Computer Graphics—Three‐Dimensional Graphics and Realism     

Global stabilization and asymptotic tracking for a class of nonlinear systems by means of time‐varying feedback

A simple backstepping design scheme is proposed and sufficient conditions for non‐uniform in time global stabilization for parameterized systems by means of time‐varying feedback are established. Our methodology is applicable to a special class of systems that in general cannot be stabilized by static feedback and includes non‐holonomic systems in chained form. For this class of systems the main results on feedback stabilization enable us to derive sufficient conditions for the solvability of the tracking problem. Copyright © 2003 John Wiley & Sons, Ltd.     

使用体渲染进行的快速全局照明

提出了一种基于体渲染的快速全局照明方法，用于实时计算复杂的直接照明和间接照明。该方法使用一系列预先计算的图像数据来表示照明在特定空间中的分布，在实时渲染时通过对这些空间数据的重组来得到给定位置处的光强。计算过程分为预处理和实时渲染两部分：首先，针对每一个物体计算出该物体对周围空间辐照度的影响，并存储在体数据结构中；然后，在实时渲染过程中，利用已有的体数据重建出给定点的辐照度，实现照明。该方法可以计算任意形式的光源照明以及间接漫射。     

一种新的网络入侵模式提取算法及其应用

该文在分析国内外现有入侵检测技术和系统的基础上,提出了一种基于实时入侵时态知识模型和可变滑动窗口的实时模式提取算法,并在此基础上,实现了基于规则的、层次化的智能入侵检测原型系统(RIDES)。实验结果表明:该系统不仅能快速检测网络入侵,而且具有一定的学习能力,能够适应不同的网络应用环境。     

汽车照明防眩的新技术

文章介绍了一种新颖的汽车照明防眩技术，这是汽车前照灯的脉冲化照明所带来全新功能之一。通过利用高速频闪的脉冲氙灯，配合高速液晶电光开关制成的挡光板，让对方照明效果光透过，而挡去大部进入眼睛的外部眩光，从而达到防止眩光的目的。本文详细论述了这种新颖的防眩控制技术，并给出了在实用中多车交会时的处理方法。     

Least possible time paths in stochastic, time-varying networks

In this paper, two computationally efficient algorithms are presented for determining the least possible time paths for all origins to a single destination in networks where the arc weights are discrete random variables whose probability distribution functions vary with time. The first algorithm determines the least possible time path from each node for each departure time interval, the least possible travel time and a lower bound on the associated probability of the occurrence of this travel time. The second algorithm determines up to k least possible time paths, the associated travel times and the corresponding probabilities of occurrence of the travel times (or a lower bound on this probability). No such efficient algorithms for determining least time paths in stochastic, time-varying networks exist in the literature.     

自然山区大气景观模拟显示方法初探

提出了一个模拟大气、云雾等自然环境的照明模型，对视线距离较大，视野开阔的自然景物造型，如山体造型，更具有真实感效果，可获得模拟云、雾等天气特征的三维地形风景图。实验效果令人满意，并具有简单实用之特点。     

关于变系数线性微分方程的稳定性*

本文用矩阵测度和比较定量给出了变系数线性微分方程稳定性的一个简单判据，对周期系数的线性微分方程给出了较为精确的渐近稳定判据，推广和改进了文［１］的工作。     

面光源的蒙特卡洛模拟

本文从点光源出发,讨论了面光源的蒙特卡洛模拟的方法,提出了模拟的公式和原则.然后以圆柱面光源为例,给出了模拟光源、标准光源和实际的卤钨灯L7386A通过自由曲面反射器后获得的照度图,比较了它们的结果,并简要分析了原因.     

道路照明的数字化仿真研究

道路照明的数字化仿真是在虚拟环境中判断路面的明亮程度、均匀度、眩光情况、环境亮度等合适与否,并可以显示出随着时间推延,光源流明维持系数和灯具维护系数等的变化,从而使照明效果发生变化,也可显示出相应的照明的属性数据,使所设计的照明方案从现在到未来的演变过程生动地、直观地、定量地再现,使照明设计人员和管理者在交互的虚拟场景中进行实时的图、数操作和可视化分析.