虚拟现实中体图形学的研究

本文主要介绍了虚拟现实中体图形学的概况。通过对体图形学的一些算法的阐述，使得我们对体图形学有一些大体的了解及认识。它可生成具有高质量的图形。     

多面体光线跟踪的两种快速算法

本文提出了适用于凸，凹多面体光线跟踪的两种快带算法。     

基于线性八叉树的光线投射体绘制算法改进研究

体视化是地学信息三维可视化研究的前沿技术之一，体绘制算法的效率直接关系到体视化的效果。本文在研究已有光线投射体绘制改进算法的基础上，提出利用线性八叉树数据结构对光线投射体绘制算法进行改进研究，不仅实现了体数据的压缩。而且能对压缩体数据进行直接体视化。在PC机上的实验表明，该方法具有时间复杂度与数据复杂度基本无关的特点．加速效果明显。最后，文章指出了该方法的适用范围。     

Fractal图形学

Fractal图形学是计算机图形学中近年来产生并发展得十分迅速的一个领域,它在复杂自然景象的图形生成方面已经取得明显的效果。本文概述了Fractal图形学的研究对象及其数学基础——Fractal几何学,并着重介绍了Fractal图形学中构造模型的主要目标和几个方法:随机插值模型、粒子系统模型、正规文法模型和迭代函数系统模型。     

基于狭义相对论的新光线跟踪算法

传统计算机图形学绘制算法建立在经典牛顿力学基础上，无法模拟高速运动物体的独特视觉现象．本文按照狭义相对论原理，应用Java面向对象技术，构造了惯性参照系、摄像机、物体、光源、材料和纹理等新的场景对象．通过创建求交、跟踪、照射、测试和阴影等虚拟光线事件，方便地实现了融时空伸缩和多谱勒效应于一体的新光线跟踪算法．揭示了摄像机、物体和光源处于多个不同惯性参照系时的相对论全方位反射、折射和阴影等全新的光照效果．     

一种新的层次包围盒方法

在计算机图形学中，经常碰到这样的问题：给定平面或空间上的一系列景物，判断一条直线是否与这些景物的其中一个相交，或者更进一步地，如果相交的话，它与哪 些景物相交。这个问题在隐茂线消除、隐茂面消除、光线跟踪算法等图形学基本算法中具有普遍意义。     

计算机图形学（续）

(接90年第2期)2.几何变换在计算机图形学中,几何变换是最常使用的方法,它起着十分重要的作用。采用几何变换的方法可以实现图形由一个坐标系统到另一坐标系统的映射。对图形施行几何变     

一种基于光线相关性的快速光线跟踪算法

在分析和比较现有光线跟踪快速求交算法的基础上，基于光线相关性研究和探索了逐步细分光线跟踪算法，以减少光线求交次数。本方法为实时生成真实感图形提供了一条很有潜力的实现途径。     

Sweeping体的离散化原理

本文主要介绍FSMTS中所采用的Sweeping体素的离散化原理。首先讨论了体素离散化的“拓扑有效性”和精度要求,并在此基础上提出了依据主曲率控制离散点密度的方法。其次研究了离散化过程中的三种活动标架,提出了在扫动过程中如何描述截面变化规律的各种策略。最后推导出Sweeping体的合法性检验判据。     

计算机图形学（第一讲）

应广大读者的要求,希望本刊开设计算机图形学讲座,经过一段时间的准备,本期开始第一讲,介绍图形学及其研究对象,重点是图形算法;第二讲着重介绍图形软件标准 GKS和微机绘图软件包 AutoCAD;第三讲着重介绍工程图形数据库及其应用实例。     

Generating a smooth voxel-based model from an irregular polygon mesh

A method for generating a smooth voxelbased model from an arbitrary polygon mesh is presented. It is based on a polygonal subdivision process which takes an irregular polygon mesh as input and creates a finer and smoother mesh. The mesh is recursively refined down to or close to the voxel level, and then voxelized (digitized) into a voxel-based representation. A local subdivision approach has been developed in order to ease the computationally expensive subdivision process. The voxelization of the mesh maintains topological and fidelity requirements which are pre-defined and application dependent.     

立体可视化——新兴的灵境技术

立体可视化是９０年出现的可视化及计算机图形学的一个重要领域。立体可视化质变计算机图形学带来了一场革命,并在其众多的应用领域中取得了突破性进展,不仅容易实现图形演示的虚拟真实性（灵境）,而且可以将视野深入至复杂物体的内部世界,文语文介绍立体可视化技术的原理,立体数据的生成,处理及演示。     

Fast and simple hardware accelerated voxelizations using simplicial coverings

Voxelization of solids, that is the representation of a solid by a set of voxels that approximates it, is an operation with important applications in fields like solid modeling, physical simulation or volume graphics. Moreover, the new generation of affordable 3D raster displays has renewed the interest on fast voxelization algorithms, as the scan-conversion of a solid is a basic operation on these devices. In this paper a hardware accelerated method for computing a voxelization of a polyhedron is presented. The algorithm is simple, efficient, robust and handles any kind of polyhedron (self-intersecting, with or without holes, manifold or non-manifold). Three different implementations are described in detail. The first is a conventional implementation in the CPU, the second is a hardware accelerated implementation that uses standard OpenGL primitives, and the third exploits the capabilities of modern GPUs by using vertex programs.     

—体视技术在铸造充型过程流场模拟中的应用

铸造充型过程流场模拟会产生数以万计的数据，如温度、压力等标量，速度等矢量，这些数据场的显示是铸造充型过程流场模拟的关键问题之一，也是计算机图形学的研究热点。文中采用体视技术显示铸件的充型过程，其图形清晰生动，既能体现铸件的整体感，又能显示流场的内部细节。     

矢量图形编辑系统的数据模型及其实现

以电力行业为实际应用背景，本文提出了一组基于SVG的矢量图形编辑系统的数据模型，主要包括类结构、图元描述模型和SVG解析模型；同时，以该模型为基础设计和实现了一个独立于具体应用的矢量图形编辑系统，讨论了该系统的设计思想和体系结构，并对各部分功能进行了分析。     

超级计算机图形学和可视化

近两年,超级计算机、计算机图形学和科学可视化是三个引人注目的论题。今天,大量的计算机应用问题是运用超级计算机以及图形系统和科学可视化来解决的。本文介绍了超级计算机图形学产生和发展的背景,着重阐述了更高级的图形学及其应用的研究与发展,总结了超级计算机可视化的研究现状和发展趋势。最后,本文指出,基于超级计算机图形学的可视化时代已经到来。     

Efficient CPU‐based Volume Ray Tracing Techniques

Recent research on high‐performance ray tracing has achieved real‐time performance even for highly complex surface models already on a single PC. In this report, we provide an overview of techniques for extending real‐time ray tracing also to interactive volume rendering. We review fast rendering techniques for different volume representations and rendering modes in a variety of computing environments. The physically‐based rendering approach of ray tracing enables high image quality and allows for easily mixing surface, volume and other primitives in a scene, while fully accounting for all of their optical interactions. We present optimized implementations and discuss the use of upcoming high‐performance processors for volume ray tracing.     

Normal estimation in 3 D discrete space

Three-dimensional voxel-based objects are inherently discrete and do not maintain any notion of a continuous surface or normal values, which are crucial for the simulation of light behavior. Thus, in volume rendering, the normal vector of the displayed surfaces must be estimated prior to rendering. We survey several methods for normal estimation and analyze their performance. One unique method, the context-sensitive approach, employs segmentation and segment-bounded operators that are based on object and slope discontinuities in order to achieve high fidelity normal estimation for rendering volumetric objects.     

Volume seeds: A volume exploration technique

Ray-traced volume rendering has been shown to be an effective method for visualizing 3D scalar data. However, with currently available workstation technology, interactive volume exploration using conventional volume rendering is still too slow to be attractive. This paper describes an enhanced volume rendering method which allows interactive changes of rendering parameters such as colour and opacity maps. An innovative technique is provided which allows the user to plant a ‘seed’ in the volume to rapidly modify local shading parameters. For a fixed viewing position, the user can interactively explore specific regions of interest. Furthermore, a virtual cutting technique with the exploratory seed allows the user to remove surfaces and see the internal structure of the volume. Examples demonstrate these techniques as an attractive option in many applications.     

A distance template for octree traversal in CPU-based volume ray casting

Several optimization techniques have been proposed to improve the speed of direct volume rendering. A hierarchical representation formed by an octree is a data structure to skip over transparent regions while requiring little preprocessing and data storage. However, in order to skip over an octant estimated to be transparent (a transparent octant), the distance from a boundary to another boundary of the octant should be calculated. Because the distance computation is expensive, we propose a precomputed data structure, the distance template, which stores direction and distance values from one boundary voxel on a face to all the boundary voxels on the remaining five faces. In the rendering step, if a ray reaches a transparent octant, it leaps over the octant by referring to the stored distance value.