摘要
动态地形仿真在虚拟战场中的研究对象主要是地形表面与军事系统之间的交互作用,比如爆炸产生弹坑以及车轮留下痕迹等等。在很大程度上,这些动态地形效果影响着战场仿真过程以及结果的逼真度和可信度。为了满足交互式虚拟战场的仿真需求,本文深入研究了动态地形领域中的相关技术,其具体的研究内容以及创新点如下：
1)在虚拟战场中,爆炸以及车轮的压力会改变地形的拓扑结构以及相关的属性,然后在地形表面产生弹坑以及车痕。为了实现地形的形变操作,本文提出了较为理想的弹坑以及车痕的物理模型弹。其中,弹坑方向的引入使得弹坑的外观更加真实与多样。此外,还采用过程纹理图的方法增强了仿真的视觉逼真度。
2)在大规模地形的可视化研究中,一个主要的问题就是如何用有限的计算机图形处理能力高效的展现大规模地形数据。为了解决这一问题,本文提出了一种改进的Level of Detail (LOD)算法来简化地形模型。该算法结合了Geomipmaping以及Chunked LOD算法的优点,用规则的block以及tile来表示多分辨率的地形网格。并且,我们将tile分割成更小的tilelet,从而引入了GPU缓冲池以及二级视景体裁剪技术,显著提高了实时绘制的效率。此外,我们还引入了动态再细分区域的概念,实现了对地形分辨率的动态扩展,满足了动态地形仿真所需要的细节表达。
3)结合GPU中的framebuffer object (FBO),纹理顶点访问以及shader技术,本文提出了基于GPU的地形形变策略。该策略将地形数据以及地形形变信息转化为GPU存储器中的地形高度纹理图和偏移量纹理图,使得地形形变的所有计算由CPU移植到了GPU中,大大提高了仿真系统的实时效率。
4)在大规模地形的可视化研究中,地形数据的总量很可能会超出系统内存的容量。为了解决海量数据与内存容量之间的矛盾,我们引入了地形分页管理技术。它以离线的方式将地形数据分割成若干页面,并分别保存在外存设备中。在实时运行时,我们只将需要的地形页面从外存调入系统内存,而将超出视域的地形页面从内存中移除。本文结合3)中所提出的策略,改进了静态地形分页管理算法,实现了弹坑以及车痕动态地形中海量数据的管理。该方法的关键在于将极少量地形概要信息以及车痕偏移量数据在内存和外存之间进行双向的传输,从而记录以及恢复地形形变的信息。
为了验证本文提出的方法,我们设计了一个虚拟战场仿真系统,最终实现了弹坑以及车痕的动态地形仿真。因为该系统利用GPU大大减轻了CPU的计算负担,所以得到了较为理想的结果。
Dynamic terrain in virtual battlefield simulation pays attention to interact of dynamic terrain surface and military system, such as the crater of explosion and the ruts of vehicle tires. It influences process and result of combat simulation directly, and it can improves fidelity and credibility of simulation.
To meet the demands of the applications of virtual battlefield, the main contributions of this dissertation are as follows:
1) In virtual battlefield, explosions of ammunition and compression of vehicle tires would change the topology and other features of terrain surface, and then create craters and ruts on the terrain. To simulate the deformation of terrain, we present the physical model of the crater and rut, and crater model has a direction depending on the direction of impacting force. And, we update crater and rut texture with a method of procedural texture.
2) The contradiction between the limited computer processing capacity and complex geographical terrain data representation is a primary problem of the visualization of the large terrain. To solve this problem, we present an improved Level of Detail (LOD) algorithm. Its central idea is to use a regular-grid representation and fixed size blocks/tiles that change in resolution, and use the technology of GPU cache and second level of view frustum culling to render terrain fast. Moreover, to provide the deformation terrain regions with enough detail, we present Dynamically Divisible Regions (DDR) technology, which can dynamically extend the resolution of a region within the terrain mesh with GPU.
3) By means of the features of modern Graphic Processing Unit framebuffer object (FBO), vertex texture fetch and shader technology, we provide a GPU-based strategy for terrain deformation. Our strategy encode the terrain data and deforming information into textures stored in video memory, so that deformation of dynamic terrain can be processed entirely in the GPU, and the efficiency of our strategy is improved.
4) For large terrains models, the amount of mesh data may exceed the amount of available in-core memory. In this situation, paging attempts to resolve the conflict between data size and memory capacity by managing the presence of data in memory. It use spatial partitioning to generate the partitions that are then stored offline. At runtime, viewable partitions are paged into core memory and restored into the data structure as a spatial subunit, creating a sparsely populated entity that uses less memory without affecting the rendered scene. With the method mentioned in3), we present an improved method of paging to manage the large dynamic terrain of craters and tire ruts.
To demonstrate our method, we present a terrain visualization, and then implement the dynamic terrain simulation of craters and tire ruts in a virtual battlefield. And the interactive efficiency of this system is very good.
引文
[1]Liu Xin, Rokne G Jon, Gavrilova L Marina. A novel terrain rendering algorithm based on quasi Delaunay triangulation. The Visual Computer,2010,26(6-8):697-706.
[2]Wang C, Wan T. R, Palmer J. I. Urban flood risk analysis for determining optimal flood protection levels based on digital terrain model and flood spreading model. The Visual Computer,2010,26(11):1369-1381.
[3]Dick Christian, Schneider Jens, Westermann Rudiger. Efficient Geometry Compression for GPU-based Decoding in Realtime Terrain Rendering. Computer Graphics Forum,2009, 28(1):67-83.
[4]Livny Yotam, Kogan Zvi, El-Sana Jihad. Seamless Patches for GPU-based Terrain Rendering. The Visual Computer,2009,25(3):197-208.
[5]Bratkova Margarita, Shirley Peter, Thompson B William. Artistic Rendering of Mountainous Terrain. ACM Transactions on Graphics,2009,28(4):102:1-102:17.
[6]Bruneton Eric, Neyret Fabrice. Real-Time Rendering and Editing of Vector-based Terrains. Computer Graphics Forum,2008,27(2):311-320.
[7]Duchaineau M, Wolinsky M. Roaming terrain:real-time optimally adapting meshes. In Proceedings of IEEE Visualization'97, Los Alamitos CA, USA:IEEE,1997,81-88.
[8]Rottger S. Real-time generation of continuous levels of detail for height fields. In Proceedings of WSCG'98, Citeseer:1998,315-322
[9]Ulrich T. Rendering massive terrain using chunked level of detail control. In Proceedings 29th SIGGRAPH Conf. on Computer graphics and interactive techniques, San Antonio, Texas,2002.
[10]Losasso Frank, Hoppe Hugues. Geometry Clipmaps:Terrain Rendering Using Nested Regular Grids. ACM Transactions on Graphics,2004,23(3):769-776.
[11]Sumner R, O'Brien J. Animating sand, mud and snow. Computer Graphics Forum, 1999,18(1):17-26.
[12]He Yefei, Cremer James, Papelis Yiannis. Real-Time Extendible-Resolution Display of On-line Dynamic Terrain. In Proceddings of the 2002 conference on Graphics Interface, 2002,151-160.
[13]Wang D, Wang C. Real-time GPU-Based Simulation of Dynamic Terrain in Virtual Battlefield. Journal of Computational Information Systems,2011,7(6):1924-1933.
[14]Lindstrom Peter, Pascucci Valerio. Visualization of large terrains made easy. In Proceedings of the 12th conference on Visualization, San Diego, California:IEEE Computer Society,2001,363-371.
[15]Bao Xiahong, Pajarola Renato. LOD-based Clustering Techniques for Optimizing Large Scale Terrain Storage and Visulization. In Proceeding IEEE Visualization,2002, 320-325.
[16]Bhattacharjee S, Patidar S. Real-time Rendering and Manipulation of Large Terrains. Computer Vision, Graphics & Image Processing,2008,551-559.
[17]Finkel R A, Bentley J L. Quad Trees, a Data Structure for Retrieval on Composite Keys. Acta Informatica,1974,4:1-9.
[18]Pritchard M. Direct Access Quadtree Lookup. In Game Programming Gems 2, M. Deloura, Ed. Hingham, Massachusetts:Charles River Media,2001,394-401.
[19]Crawfis R A, Max N. Texture splats for 3D scalar and vector field visualization. In Proceedings of the 4th conference on Visualization '93, IEEE Computer society Washington,1993,261-265.
[20]Lefebvre Sylvain, Hoppe Hugues. Appearance-space texture synthesis. In Proc. of SIGGRAPH, ACM Trans.,2006,25(3).
[21]Lefebvre Sylvain, Hornus Samuel, Lasram Anass. By-example Synthesis of Architectural Textures. ACM Transactions on Graphics,2010,29(4):84:1-84:8.
[22]Amara Yacine, Marsault Xavier. A GPU Tile-Load-Map architecture for terrain rendering:theory and applications. The Visual Computer,2009,25(8):805-824.
[23]Hoppe H. Progressive meshes. In Proceedings of the ACM SIGGRAPH Conference on Computer Graphics, ACM Trans.,1996,99-108.
[24]Hoppe H. View-dependent refinement of progressive meshes. In Proceedings of the ACM SIGGRAPH Conference on Computer Graphics, ACM Trans.,1997,189-198.
[25]Hu Liang, Sander Pedro, Hoppe Hugues. Parallel view-dependent refinement of progressive meshes. Symposium on Interactive 3D Graphics and Games,2009,169-176.
[26]Kumler M P. An intensive comparison of triangulated irregular networks (TINs) and digital elevation models (DEMs). Cartographica,1994,31:1-48.
[27]Cheng Wei, Liu Dan. Peer-assisted view-dependent progressive mesh streaming. In MM '09 Proceedings of the 17th ACM international conference on Multimedia, New York, USA:ACM,2009.
[28]Hwa L M, Duchaineau M A, Joy K I. Real-time optimal adaptation for planetary geometry and texture:4-8 tile hierarchies. IEEE Transactions on Visualization and Computer Graphics,2005,11(4):355-368.
[29]Zheng Sheng, Yu Zhanwu, Li Zhongmin. PeerTR:A Peer-to-Peer Terrain Roaming Architecture. In Proceedings of 7th Advanced Parallel Processing Technologies, Guangzhou, China:Springer,2007,292-300.
[30]Lindstrom P, Koller D, Ribarsky W. Real-time continuous level of detail rendering of height fields. In Proceedings of the 23rd annual conference on Computer graphics and interactive techniques, ACM Press,1996,109-118.
[31]Lindstrom P, Pascucci V. Terrain Simplification Simplified:A General Framework for View-Dependent Out-of-Core Visualization. IEEE Transactions on Visualization and Computer Graphics,2002,8:239-254.
[32]Pomeranz A A. ROAM using Surface Traingle Clusters (RUSTiC). In M.S. Thesis Department of Computer Science, University of California, Davis,2000.
[33]Levenberg J. Fast View-Dependent Level-of-Detail Rendering Using Cached Geometry. In Proceedings of the 13th conference on Visualization, IEEE Computer Society Press,2002,259-265.
[34]Cignoni P, Ganovelli F, Gobbetti E. BDAM-Batched Dynamic Adaptive Meshes for High Performance Terrain Visualization. Computer Graphics Forum,2003,22:505-514.
[35]Cignoni P, Ganovelli F, Gobbetti E. Planet-sized Batched Dynamic Adaptive Meshes (P-BDAM). In Proceedings of the 14th conference on Visualization, Seattle, WA, USA: IEEE Computer Society,2003,147-155.
[36]Vanek Juraj, Benes Bedrich, Herout Adam. Large-Scale Physics-Based Terrain Editing Using Adaptive Tiles on the GPU. IEEE Computer Graphics and Applications, 2011,31(6):35-44.
[37]Leitao Ivo, Carmo Maria Beatriz. Block and Quadtree based Simplification in Tiled Blocks Terrain Algorithms. In Proceedings of the Fourth International Conference on Computer Graphics Theory and Applications, Lisboa, Portugal:INSTICC Press,2009, 205-210.
[38]Platings M, Day A M. Compression of Large-Scale Terrain Data for Real-Time Visualization Using a Tiled Quad Tree. Comput Graph Forum,2004,23(4):741-759.
[39]Reuter Hannes Isaak, Nelson Andrew, Mehl Wolfgang. A First Assessment of Aster GDEM Tiles for Absolute Accuracy, Relative Accuracy and Terrain Parameters. In Proceedings of IEEE International Geoscience Remote Sensing Symposium, University of Cape Town, Cape Town, South Africa:IEEE,2009,240-243.
[40]Yin Ping, Jiang Xiaohong, Shi Jiaoying. Multi-screen Tiled Displayed, Parallel Rendering System for a Large Terrain Dataset. IJVR,2006,5(4):47-54.
[41]Bishop L, Eberly D, Whitted T. Designing a PC Game Engine. IEEE Computer Graphics and Applications,1998,18:46-53.
[42]Yoo Byounghyun, Brutzman P. Donald. X3D earth terrain-tile production chain for georeferenced simulation. In Proceeding of the 14th International Conference on 3D Web Technology, Darmstadt, Germany:ACM,2009,159-166.
[43]Sun Chih Hao, Tsao You Ming, Chien Shao Yi. High-Quality Mipmapping Texture Compression With Alpha Maps for Graphics Processing Units. IEEE Transactions on Multimedia,2009,11(4):589-599.
[44]Toksvig Michael. Mipmapping Normal Maps. Journal of Graphics Tools,2005,10(3): 65-71.
[45]Asirvatham A, Hoppe H. Terrain Rendering using GPU-based Geometry Clipmaps. In GPU Gems 2, M. Pharr and R. Fernando, Addision-Wesley,2005.
[46]Li X, Moshell J M. Modeling soil:realtime dynamic models for soil slippage and manipulation. In Proceedings of the 20th annual conference on Computer graphics and interactive techniques, ACM Press,1993.
[47]Chanclou B, Luciani A, Habibi A. Physical Models of Loose Soils Dynamically Marked by a Moving Object. In Proceedings of Computer Animation, Geneva, Switzerland:IEEE Computer Society,1996,27-35.
[48]Onoue K, Nishita T. Virtual Sandbox. In 11th Pacific Graphics Conference on Computer Graphics, Canmore, Canada:IEEE Computer Society,2003,252-.
[49]Onoue K, Nishita T. An Interactive Deformation System for Granular Material. Computer Graphics Forum,2005,24(1):51-60.
[50]Yi Hehe, Zhang Wei, Ma Zhi. Dynamical modeling and controller design of four wheels driven intelligent vehicle on three-dimensional terrain. IEEE International Conference on Automation and Logistics, Chongqing, China:IEEE,2011,229-232.
[51]Boo Montserrat, Amor Margarita. Dynamic hybrid terrain representation based on convexity limits identification. International Journal of Geographical Information Science, 2009,23(4):417-439.
[52]Ellis Christopher, Babenko Pavel. Dynamic Terrain for Multiuser Real-Time Environments. IEEE Computer Graphics and Applications,2010,30(1):80-84.
[53]Cai X Q, Li F X. Research of Dynamic Terrain in Complex Battlefield Environments. Edutainment,2006,3942:903-912.
[54]Chen G, Zhang J. Dynamic Terrain LOD with Region Preservation in 3D Game Engine. Edutainment,2006,3942:711-715.
[55]Goral C M, Torrance K E. Modeling the interaction of light between diffuse surfaces. In Proceedings of the 11th annual conference on Computer graphics and interactive techniques, ACM Press,1984.
[56]Whitted T. An Improved Illumination Model for Shaded Display. Communications of the ACM,1980,23:343-349.
[57]Hoffman N, Mitchell K. Real-Time Photorealistic Terrain Lighting. In Proceedings of the 2001 Game Developers Conference,2001.
[58]Stewart A J. Fast Horizon Computation at All Points of a Terrain With Visibility and Shading Applications. IEEE Transactions on Visualization and Computer Graphics,1998, 4:82-93.
[59]Williams L. Casting curved shadows on curved surfaces. In Proceedings of the 5th annual conference on Computer graphics and interactive techniques, ACM Press,1978.
[60]Crow F C. Shadow algorithms for computer graphics. In Proceedings of the 4th annual conference on Computer graphics and interactive techniques, San Jose, California: ACM Press,1977.
[61]Nordman Bruce, Granderson Jessica. Standardization of user interfaces for lighting controls. Computer Standards & Interfaces,2012,34(2):273-279.
[62]Lafont Ugo, Zeijl Henk van. Increasing the reliability of solid state lighting systems via self-healing approaches:A review. Microelectronics Reliability,2012,52(1):71-89.
[63]Bekker M G Introduction to Terrain—Vehicle Systems [M]. Michigan:The University of Michigan Press,1969.
[64]周彦,戴剑伟.HLA仿真程序设计,电子工业出版社,2002.
[65]张亚崇,孙国基,严海蓉,钟联炯.RTI中时间推进机制的研究[J],计算机应用研究,2005,3：104-107.
[66]翟永翠,程健庆.基于HLA的实时仿真研究[J],系统仿真学报,2004,16(9)：1966-1969.
[67]孙世岩,刘健.基于HLA时间管理的仿真程序实现[J],计算机工程与应用,2004,2：109-111.
[68]韩林,刘步权,姚益平,王怀民.符合EIEE1516规范的HLA/RTI时间管理[J],计算机仿真,2003,20(6)：14-17.
[69]黄树彩,李为民,刘兴堂.高层体系结构的时间管理技术[J],空军工程大学学报(自然科学版),2000,1(2)：64-68.
[70]梁彦刚,唐国金,王锋.基于HLA仿真系统的实时性改进策略研究[J],系统仿真学报,2005,17(2)：361-363.
[71]刘步权,王怀民,姚益平.基于HLA的时间同步技术[J],计算机工程与科学,2004,26：96-99.
[72]黄健,黄柯棣.HLA中的时间管理[J],计算机仿真,2000,17：69-74.
[73]欧阳伶俐,宋星,卿杜政.HLA时间管理与PDES仿真算法研究[J],系统仿真学报,2000,12：237-240.
[74]张亚崇,严海蓉.HLA/RTI中的时间管理机制分析[J],计算机应用研究,2003,7：105-107.
[75]Lefebvre Sylvain, Hornus Samuel, Neyret Fabrice. Texture sprites:Texture elements splatted on surfaces. Proceedings of the Symposium on Interactive 3D Graphics, Proceedings-I3D 2005:ACM SIGGRAPH Symposium on Interactive 3D Graphics and Games,2005,163-170.
[76]Amara Y, Meunier S, Marsault X. A GPU framework for the visualization and on-the-fly amplification of real terrains. In Proceedings of ISVC 2007, Part I. LNCS,2007, 4841:586-597.
[77]Blanchet J, Modeles Markoviens. Extensions pour la classification de donnees complexes. Ph.D. of Universite Joseph-Fourier Grenoble I, France,2007.
[78]Livny Y, Kogan Z, El-Sana J. Seamless patches for GPU-based terrain rendering. Vis.Comput.,2008,25(3):197-208.
[79]Pajarola R, Gobbetti E. Survey of semi-regular multiresolution models for interactive terrain rendering. Vis.Comput.2007,23(8):583-605.
[80]Schneider J, Westermann R. GPU-friendly high-quality terrain rendering. J. WSCG, 2006,14(1-3):49-56.
[81]Schneider J, Boldte T, Westermann R. Real-time editing, synthesis and rendering of infinite landscapes on GPUs. In 11th Workshop on Vision, Modeling and Visualization, 2006.
[82]Seoane A, Taibo J, Fernandez L. Hardware-independent clipmapping. In Proceedings of WSCG2007, International Conference in Central Europe on Computer Graphics, Czech Republic,2007.
[83]刘洁,邹北骥,周洁琼.基于海浪谱的Gerstner波浪模拟,计算机工程与科学,2006,2：41-44.
[84]Yacine Amara, Xavier Marsault. A GPU Tile-Load-Map architecture for terrain rendering:theory and applications. Vis Comput,2009,25:805-824.
[85]Hans Kohling Pedersen. A framework for interactive texturing on curved surfaces. In Proceedings of SIGGRAPH,1996,295-302.