基于分类及环境特征的树木真实感绘制

生成高度真实感的虚拟自然场景一直是图形学研究领域中的一个富有挑战性的难题.作为自然场景的重要组成部分,树木的真实感模拟也得到人们的广泛重视.树木种类繁多,形态各异,复杂的结构使其无论在造形、存储还是在绘制上都存在着相当的困难.针对不同的环境特征和不同类型的树木,根据它们的具体特点需采用不同的绘制手段.对于阔叶树,采用基于OpenGL的深度缓存阴影生成算法;对于针叶树,则采用结合光线跟踪和纹元(texel)绘制的技术;而对于距离视点比较远的树,采用的是体纹理映射(volumetrictexturemapping)的方法.实践证明,这几种绘制技术基本上可以满足各种不同类型场景的树木的绘制要求.     

森林场景的钢笔风格化实时绘制技术*

在大型复杂场景绘制关键技术研究项目中,通过把复杂场景绘制与调度技术,如Slicing、MMI、层次图像缓存和基本布告板等大场景实时加速绘制技术的多层次绘制方法,融合到非真实感绘制技术中,以提高系统面对复杂场景的实时绘制能力。最后实现了对森林等大型场景的钢笔画绘制,借助非真实感绘制技术中基于图像空间的生成方法,利用各种不同大小及形状的笔画实现了艺术化森林场景实时交互绘制。提出了植物多层次钢笔风格化渲染算法。     

基于三维分枝模型的树木模拟

虚拟自然场景的实时生成一直是图形学研究领域中一个富有挑战性的难题,作为自然场景的重要组成部分,树木的模拟也得到了广泛的重视.本文在实际建模中以三维分枝模型为基础,与随机繁衍L系统相结合,对树木模型进行了一些改进.将光源和重力的影响加入枝段的模型中,使生成树木的形态更加逼真;改进了分枝模式,使得生成树木的随机性得到加强;在绘制时根据不同距离选择不同复杂度的树木模型,加快了渲染的速度.     

林木场景漫游系统的研究与实现

由于林木本身结构复杂,因此在模拟中几何模型的面片数多。如何在保证一定的视觉真实感的前提下,尽量简化场景模型,实现林木场景的快速绘制,一直是计算机图形学领域的热点问题。提出了一种适合包含大面积林木的自然场景漫游系统的实现方法,即利用3维建模软件3ds max构建场景模型,然后基于虚拟开发工具Open Scene Graph（OSG）实现场景的实时绘制和漫游。充分利用软件的特点和功能,实现了包含大面积林木的自然场景的漫游,同时还根据相交测试原理实现了漫游过程中的碰撞检测。实验结果表明,此系统具有较高的绘制速度,能满足包含大面积林木的自然场景实时漫游的要求,同时能达到一定的场景真实感。     

基于分形的自然场景绘制

在数据场可视化、计算机仿真及虚拟现实技术中,经常需要实现自然场景的绘制.分形是描述自然景物最好的方法.本文给出了由分形插值曲面生成场景中地形面的具体方法;提出了在同一递归深度取相同随机量的方法解决中点变位法中的裂缝问题,实现了用三角形中点变位法和四边形中点变位法绘制场景中的山形,从而用连续四边形面片构造出了库区山形及河道,用分形曲面构造出了河床,逼真地全景显示了库区自然场景.     

浅谈分形——在计算机游戏领域中的应用

随着计算机图形硬件和CPU性能的飞速发展，人们对PC游戏的场景绘制和人工智能这两方面提出了更高的要求。游戏场景绘制的主要目标是实时性和真实性。当前很多游戏都是以自然景物为背景的，包括蓝天、自云、树木、河流、地表植被、山脉等等。如何才能使这些自然景物更加逼真，使玩家享受身临其境的感觉呢？这是游戏设计制作者面临的新问题。关于自然场景特效生成的方法有很多，比如粒子系统、分形等。这里我们要谈的是分形，因为分形在自然景物绘制方面是独具特色的。     

混合漫游系统

提出一种新颖的场景绘制方法,首先对图像进行处理,用交互的方法区分场景的背景和前景;然后分别建立背景和前景的3D几何模型,采用一种分片绘制的策略,进一步提高了绘制质量．通过将动态网格叠加到几何模型中,在静态图像中产生动态纹理,丰富场景内容,从而建立了一种混合场景表示,实现逼真的场景实时漫游．实验证明,该算法具有较好的普适性,可以处理包含灭点或灭线的不同类型照片、绘画和全景图．     

草地场景真实感模拟技术综述

草体作为自然场景的一种重要组成元素,其数量众多、覆盖范围广,因此很难实现实时绘制,大规模草地场景真实感模拟已成为计算机图形学中研究的热点和难点之一.文中对20多年来草地场景真实感模拟技术的发展情况进行综述,分别从绘制技术、LOD表达、动态模拟以及业界现状等几个方面做了比较深入的介绍,分析并比较了一些典型方法的基本原理和优缺点;最后对该领域未来的发展趋势进行了展望.     

视点依赖的温室场景模拟与交互式漫游

为对包含日光温室的农业场景进行实时、逼真的绘制,采用基于视点的连续细节层次（LOD）来减少实际需要绘制的网格数据量,并基于包围盒技术实现了视点的碰撞检测,同时使用可见性剔除算法来加速场景渲染速度。在渲染温室内植物时,通过几何变换实现了大规模植物群体的快速构建,并在场景中使用阴影体算法来渲染阴影,生成了具有真实感的大规模温室农业场景。模拟结果表明该方法能有效地减少渲染的面元数目,大大提高了绘制速率,场景有较高的真实感,能够满足交互式实时漫游的要求。     

雪场景真实感的实时建模与绘制

针对计算机图形学中雪场景的真实感渲染的难题,提出了一种实时绘制高真实感雪景的方法。首先采用类衰减正弦函数模拟雪花运动轨迹,在保证真实性的同时大大提高其实时性;然后基于温度变化与不同地表类型影响,提出了实时积雪-融雪模型,通过计算无损失的热传递积雪方程,提高了交互积雪场景动态渲染的真实性;最后采用GPU图形硬件加速技术提高了整个过程的计算效率,绘制效果逼真。     

自然雪景的构造和绘制

合成高度复杂自然场景一直是计算机图形学中的一个富有挑战性的课题。生成雪景或许更加困难，因为利用常用的造型工具，比如多边形和曲面来表达雪的形状非常不方便。该文介绍一种解决这个问题的方法，这种方法采用位移映射（displacement mapping）来构造近处由多边形构造的物体上的雪块，而体纹理映射（volumetric texture mapping）被用来处理远处的复杂物体，比如树木。绘制结果显示，这种方法能够在较少的内存和计算开销的基础上绘制出高度复杂和真实的雪景。     

Spherical Visibility Sampling

Many 3D scenes (e.g. generated from CAD data) are composed of a multitude of objects that are nested in each other. A showroom, for instance, may contain multiple cars and every car has a gearbox with many gearwheels located inside. Because the objects occlude each other, only few are visible from outside. We present a new technique, Spherical Visibility Sampling (SVS), for real‐time 3D rendering of such – possibly highly complex – scenes. SVS exploits the occlusion and annotates hierarchically structured objects with directional visibility information in a preprocessing step. For different directions, the directional visibility encodes which objects of a scene's region are visible from the outside of the regions' enclosing bounding sphere. Since there is no need to store a separate view space subdivision as in most techniques based on preprocessed visibility, a small memory footprint is achieved. Using the directional visibility information for an interactive walkthrough, the potentially visible objects can be retrieved very efficiently without the need for further visibility tests. Our evaluation shows that using SVS allows to preprocess complex 3D scenes fast and to visualize them in real time (e.g. a Power Plant model and five animated Boeing 777 models with billions of triangles). Because SVS does not require hardware support for occlusion culling during rendering, it is even applicable for rendering large scenes on mobile devices.     

Modelling and Rendering Graphics Scenes Composed of Multiple Volumetric Datasets

This paper presents a method for modelling graphics scenes consisting of multiple volumetric objects. A two-level hierarchical representation is employed, which enables the reduction of the overall storage consumption as well as rendering time. With this approach, different objects can be derived from the same volumetric dataset, and 2D images can be trivially integrated into a scene. The paper also describes an efficient algorithm for rendering such scenes on ordinary workstations, and addresses issues concerning memory requirements and disk swapping.     

Semi-globalization of stochastic spectral synthesis

This paper describes a new approach to stochastic modeling for natural objects that provides a unified model for describing terrains, clouds, sea waves and many other shapes. The geometrical data of the model can be created or modified without undue computational time, simply by specifying several parameters. In addition, these parameters have intuitive meanings, which make it easy to control the model's geometry. Then the models for different natural objects can be effectively combined through some functional operations, which makes the method more flexible for acquiring realistic images of complex three-dimensional scenes.     

A fast rendering method for clouds illuminated by lightning taking into account multiple scattering

Methods for rendering natural scenes are used in many applications such as virtual reality, computer games, and flight simulators. In this paper, we focus on the rendering of outdoor scenes that include clouds and lightning. In such scenes, the intensity at a point in the clouds has to be calculated by taking into account the illumination due to lightning. The multiple scattering of light inside clouds is an important factor when creating realistic images. However, the computation of multiple scattering is very time-consuming. To address this problem, this paper proposes a fast method for rendering clouds that are illuminated by lightning. The proposed method consists of two processes. First, basis intensities are prepared in a preprocess step. The basis intensities are the intensities at points in the clouds that are illuminated by a set of point light sources. In this precomputation, both the direct light and also indirect light (i.e., multiple scattering) are taken into account. In the rendering process, the intensities of clouds are calculated in real-time by using the weighted sum of the basis intensities. A further increase in speed is achieved by using a wavelet transformation. Our method achieves the real-time rendering of realistic clouds illuminated by lightning.     

Computer graphics for water modeling and rendering: a survey

A key topic in computer graphics is the realistic representation of natural phenomena. Among the natural objects, one of the most interesting (and most difficult to deal with) is water. Its inherent complexity, far beyond that of most artificial objects, represents an irresistible challenge for the computer graphics world. Thus, during the last two decades we have witnessed an increasing number of papers addressing this problem from several points of view. However, the computer graphics community still lacks a survey classifying the vast literature on this topic, which is certainly unorganized and dispersed and hence, difficult to follow. This paper aims to fill this gap by offering a historical survey on the most relevant computer graphics techniques developed during the 1980s and 1990s for realistic modeling, rendering and animation of water.     

大规模复杂场景交互绘制技术综述

大规模复杂场景的快速绘制是虚拟现实、实时仿真和三维交互设计等许多重要应用的底层支撑技术,也是诸多研究领域面临的一个基本问题.随着近几年三维扫描和建模技术的飞速发展,三维场景的规模和复杂度不断增大,大规模复杂场景的交互绘制受到了国内外研究者越来越多的重视并取得了一系列研究成果.首先简要回顾了大规模复杂场景交互绘制的研究进展情况;然后通过对其中涉及的主要关键技术进行总结分析,并对国内外典型的绘制系统进行比较和分类,阐述了大规模复杂场景交互绘制的主要研究内容,给出了大规模复杂场景交互绘制系统所应包含的基本组成部分和一般框架;最后对今后的发展方向做出了展望.     

大规模复杂场景的可见性问题研究

大规模复杂场景的快速绘制技术是虚拟现实、实时仿真以及三维交互设计等许多重要应用的底层支撑技术，也是诸多研究领域面临的一个基本问题．作为其中一个技术解决手段，可见性问题在近年来得到了高度重视并取得了一系列研究成果．通过对相关可见性算法进行分析与总结，阐述了可见性问题的研究内容，提出了方法的优劣判别标准，给出了可见性判断算法所应包含的基本组成部分和步骤，最后指出未来仍然需要重点研究的若干关键问题．     

Fast Estimation and Rendering of Indirect Highlights

This paper proposes a method for efficiently rendering indirect highlights. Indirect highlights are caused by the primary light source reflecting off two or more glossy surfaces. Accurately simulating such highlights is important to convey the realistic appearance of materials such as chrome and shiny metal. Our method models the glossy BRDF at a surface point as a directional distribution, using a spherical von Mises‐Fisher (vMF) distribution. As our main contribution, we merge multiple vMFs into a combined multimodal distribution. This effectively creates a filtered radiance response function, allowing us to efficiently estimate indirect highlights. We demonstrate our method in a near‐interactive application for rendering scenes with highly glossy objects. Our results produce realistic reflections under both local and environment lighting.