【作者】 李建微；

【导师】 陈崇成；

【作者基本信息】 福州大学 ， 地图学与地理信息系统， 2005， 硕士

【摘要】 森林火灾不仅给国家和人民财产造成巨大的损失,破坏生态系统、降低土壤肥度,而且造成水土流失、泥石流等自然灾害。通过虚拟地理环境技术与林火蔓延模型的集成,研究在不同环境条件下的林火蔓延情况与发展趋势,及多维可视化技术显示蔓延过程,是现代制定最优灭火方案、提高灭火效率的研究趋势,也是本文的主要研究的重点。本文主要研究工作和成果如下: 1) 总结和分析了国内外关于林火模型及其可视化技术的研究进展,综述涵盖了蔓延模型的构建与求解、林火蔓延的多维可视化技术、林火模拟与管理信息系统等方面内容;在对比分析了这些技术的优缺点及研究发展趋势的基础上,结合虚拟地理环境的理论,提出了林火蔓延虚拟地理环境的构建设想。2) 从林火的燃烧原理入手,分析了林火行为及蔓延模型的构建原理。在影响林火蔓延速度的因子分析的基础上,采用Rothermel 地表火蔓延模型为框架,针对福建漳浦林区的特点,通过国内外文献及实地调查、林相图等资料找出燃料床参数的各个取值,并基于惠更斯的蔓延扩散原理,程序实现林火蔓延过程的数学模型构建。3) 对虚拟森林环境的建模技术进行深入探讨,主要内容包括虚拟地形的构建和林木的几何重建技术。在地形方面,对比了GRID 和TIN 技术的优缺点,实现了从geo-tiff 中读取研究区域的高程信息和其它地理信息的方法;GRID 的地形绘制技术及在格网地形上的部分三维空间分析功能。对于林木的几何构建,分别从Billboard 技术和参数化几何建模技术两方面入手,分析了两种方法的优缺点,最终采用Billboard技术实现本文原型系统的虚拟森林场景的绘制。4) 针对森林场景大数据量的带来绘制帧率达不到实时绘制的问题,阐述了场景简化的一些有效算法,包括大地形分块、LOD 技术、层次包围盒结构等算法。综合分析了森林场景数据特点的基础上,作者提出了采用八叉树层次包围盒技术结合线形方程测试的方法,通过提高基于视点的预裁剪率,来解决了大范围森林场景的实时绘制问题。5) 研究了各种林火造型技术和粒子系统的原理,采用面粒子+Billboard 技术,实现了大场景的林火造型模拟。6) 综合以上各种技术解决结果,经过系统分析、模块设计、系统集成等过程实现了林火蔓延虚拟地理环境原型系统的构建,并给出一些典型的应用实例。更多还原

【Abstract】 Forest fire is a kind of tragic nature disaster. It not only can cause tremendous losses of national possessions and people lives, but also can break the balance of ecosystem and reduce the fertilities of soil. Then it can also lead to other nature disaster, such as soil and water losses, debris flow and so on. Therefore based on the techniques of virtual geographic environments, the model of forest-fire spreading and researching on the forest-fire behaviors to forecast the direction and state of fire spreading by multi-dimension visualization techniques, how to find a novel and modern way to improve the efficiency of fire fighting and find a optimization plan to put out the fire is the main aim of this thesis. Our work is as follow: First, we review the development of the model of forest-fire spreading and its visualization. The contents include the way to build and realize the spreading model, the techniques of multi-dimension visualization, the management information system of forest-fire and fire shape simulating. On the base of comparing these methods, discussing the development of forest-fire fighting and combining the theory of virtual geographic environments, we raise the idea to build a virtual geographic environment for forest-fire spreading. After expounding the occur mechanism of the forest-fire and the theory on designing the spreading model and appraising the factors affecting the speed of fire spread, we adopt the Rothermel’s surface fire model(1972) and gain the value of all fuel parameters through the local-investigating data, the relative article and forest mapping. Then we simulate the process of forest-fire spreading on 3D terrain, using the Huygens’theory. We deeply discuss the techniques on geometric modeling. Under the condition of simulating virtual forest landscape, the primary landscapes are terrain and the tree. According to terrain rendering and modeling, we discuss the advantage and disadvantage between GRID and TIN, and in our program, we can read the data by geo-tiff format, which consists the elevation information and other geographic information, render the terrain with GRID data using OpenGL graphic library and realize some functions of special analysis on 3D terrain. In the tree geometric modeling, we adopt two methods (Billboard technique and geometric modeling) to build the virtual forest. The result indicates that Billboard is the best way to simulate large-scale scene, so in our prototype system adapt this method. Aim at the question that how to render large-scale scene, we discuss some methods to real-time rendering it under condition of the hardware level at present. These methods involve tile based rendering, LOD, hierarchical bounding volume. According to the feature of forest scene data, based on Octree hierarchical bounding volume, we adopt linear edge function test to improve the efficiency of pre-clipping to improve the rendering frame. Based on research on all kinds of techniques of fire shape modeling and the principle of particles system deep, we use the face particle and Billboard to simulate large-scale forest-fire. Synthesizing all techniques above expounded, after the process of System Analysis, Modules Design and system integration and so on, we complete a prototype system that realize the forest-fire spreading in a virtual forest environment.更多还原