光线追踪在空间目标与地球场景渲染中的研究与实现
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摘要
随着航天技术的发展和计算机图形学的进步,人们对空间任务仿真可视化的效果需求越来越高。光线追踪是一种基于几何光学原理生成真实感图形的通用技术,它采用一种统一的模型来模拟光源和环境入射光在物体表面产生的漫反射、镜面反射和散射、介质中产生的透射、折射和衰减等光学现象,实现场景消隐、阴影生成、水面波动、大气效果等复杂特效的渲染。将光线追踪算法引入到空间场景的渲染中,不仅可以较真实的展现可见光波段的空间科学任务,而且可以应用到不具备光谱特性的科学数据的可视化中。
本文研究了如何将场景信息进行组织以形成适合于光线追踪算法加速的数据形式,同时解决了如何将3DS格式模型转化为本系统的基本图元。
为了生成更为真实的图像,本文引入了Mersenne Twister随机扰动来对漫反射光线进行追踪,同时使用比耳定律来模拟光线在半透明物体中的衰减以及根据Monte Carlo理论来生成软阴影,形成了非常逼真的渲染效果。
在大气效果绘制方面,对Nishita单散射模型的建立过程进行了详细介绍,并指出了O'Neil大气散射绘制的不足,将其改造为光线追踪模式融入到本文所建立的渲染系统中。
最后,本文采用模块化的方式基于分层组织的思想设计了一个通用、可扩展的光线追踪系统,为以后空间任务的可视化提供了一个基础框架。
With the development of space technology and advances in computer graphics, the expected effects of the space mission simulation and visualization have been growing. Ray tracing is a generic technology based on geometrical optics to generate realistic images, which uses a uniform model to simulate optical phenomena such as diffuse reflection, specular reflection and scattering at surface and transmission, refraction and attenuation at medium, to achieve complex special effects rendering such as scene blanking, shadow generation, water fluctuations and atmospheric effects. The ray tracing algorithm is introduced to render the space scene, not only can factually show the space science missions with visible light, but also can be applied to visualize scientific data with no spectral characteristics.
This article studies how to organize scene data to form a special data format for accelerating ray tracing algorithm, and discusses how to change 3DS format model into basic element supported by the system.
In order to generate more realistic images, this paper introduces the Mersenne Twister random perturbation to track the diffuse light, and use Beer's law to simulate the light attenuation in the semi-transparent objects and generate soft shadows according to Monte Carlo theory. Finally, it formed very realistic rendering effects.
In terms of drawing atmospheric effects, this paper describes the process of Nishita single scattering model in detail, points out the lack of drawing atmospheric scattering by O'Neil, and transforms it into ray tracing mode for this rendering system.
Finally, this article designs a generic, distensible ray tracing system with modular approach based on ideas of hierarchical organization and provides a basis framework for future visualization space missions.
本文研究了如何将场景信息进行组织以形成适合于光线追踪算法加速的数据形式,同时解决了如何将3DS格式模型转化为本系统的基本图元。
为了生成更为真实的图像,本文引入了Mersenne Twister随机扰动来对漫反射光线进行追踪,同时使用比耳定律来模拟光线在半透明物体中的衰减以及根据Monte Carlo理论来生成软阴影,形成了非常逼真的渲染效果。
在大气效果绘制方面,对Nishita单散射模型的建立过程进行了详细介绍,并指出了O'Neil大气散射绘制的不足,将其改造为光线追踪模式融入到本文所建立的渲染系统中。
最后,本文采用模块化的方式基于分层组织的思想设计了一个通用、可扩展的光线追踪系统,为以后空间任务的可视化提供了一个基础框架。
With the development of space technology and advances in computer graphics, the expected effects of the space mission simulation and visualization have been growing. Ray tracing is a generic technology based on geometrical optics to generate realistic images, which uses a uniform model to simulate optical phenomena such as diffuse reflection, specular reflection and scattering at surface and transmission, refraction and attenuation at medium, to achieve complex special effects rendering such as scene blanking, shadow generation, water fluctuations and atmospheric effects. The ray tracing algorithm is introduced to render the space scene, not only can factually show the space science missions with visible light, but also can be applied to visualize scientific data with no spectral characteristics.
This article studies how to organize scene data to form a special data format for accelerating ray tracing algorithm, and discusses how to change 3DS format model into basic element supported by the system.
In order to generate more realistic images, this paper introduces the Mersenne Twister random perturbation to track the diffuse light, and use Beer's law to simulate the light attenuation in the semi-transparent objects and generate soft shadows according to Monte Carlo theory. Finally, it formed very realistic rendering effects.
In terms of drawing atmospheric effects, this paper describes the process of Nishita single scattering model in detail, points out the lack of drawing atmospheric scattering by O'Neil, and transforms it into ray tracing mode for this rendering system.
Finally, this article designs a generic, distensible ray tracing system with modular approach based on ideas of hierarchical organization and provides a basis framework for future visualization space missions.
引文
[1] Donald Hearn,M.Pauline Baker著,蔡士杰,宋继强,蔡敏译.计算机图形学(第三版)[M],北京:电子工业出版社,2005.6,PP.1-25.
[2]孙家广.计算机图形学(第三版)[M].北京:清华大学出版社,2003,PP.529-546.
[3]黄文均,鲍虎军.计算机真实感图形的算法基础[M].北京:科学出版社,2002,PP.127-131.
[4] Andrew Glassner. An Introduction to Ray Tracing[J]. Morgan Kaufmann,1989. ISBN 0-12286-160-4.
[5] Autodesk Ltd. 3D Studio File Format Document Revision 0.93[S]. January 1997.
[6] D. Green, D. Hatch. Fast Polygon-Cube Intersection Testing[J]. Alan Paeth, ed., Graphics Gems V, AP Professional, Boston, pp.375-379, 1995. http://www.graphicsgems.org/
[7] Tomas Akenine-M?oller. Fast 3D Triangle-Box Overlap Testing[J]. Department of Computer Engineering,Chalmers University of Technology. March 2001, updated June 2001.
[8] Eberly, David.3D Game Engine Design: A Practical Approach to Real-Time Computer Graphics[M]. Morgan Kaufmann Publishers Inc., San Fran-cisco, 2000. http://www.magic-software.com/
[9] M?oller, Tomas, Eric Haines. Real-Time Rendering[J], AK Peters Ltd.,Natick, MA, 1999. http://www.realtimerendering.com/
[10] J. Amanatides, A. Woo. A faster voxel traversal algorithm for ray tracing[J].
[11] Vlastimil Havran. Heuristic Ray Shooting Algorithms.Ph.d. thesis[D]. Department of Computer Science and Engineering, Faculty of Electrical Engineering, Czech Technical University in Prague, November 2000.
[12] Frank D.Luna著,段菲译. DirectX9.0 3D游戏开发编程基础[M].北京:清华大学出版社,2007.4,PP.193-205.
[13] Barycentric Coordinates , http://mathworld.wolfram.com/BarycentricCoordinates.html
[14] T M?LLER, B TRUMBORE. Fast, minimum storage ray/triangle intersectuion[J]. Journal of Graphics Tools 2, 1(1997), 21–28.
[15] Jeff Arenberg. Ray/Triangle Intersection with BarycentricCoordinates[J]. Ray Tracing News, edited by Eric Haines,Vol.1,No.11,November 4,1988, http:://www.acm.org/tog/resources/RTNews/.
[16] Steve Renals. Nearest neighbours and the kD-tree[J]. Informatics 2B,Learning Note 6(v1.0), January 2007.
[17] Laszlo Szecsi. An effective implementation of the k-D tree[J]. Charles River Media, Inc., 2003,PP.315–326.
[18] V Havran, J Bittner. On improving kd tree for ray shooting[C]. Proceedings of the WSCG’2002 Conference. Plzen,Czech Republic, 2002:209-216.
[19]范文山,王斌.启发式探查最佳分割平面的快速KD-Tree构建方法[J].计算机学报.2009年2月第32卷,第2期.
[20] Wald, V. Havran. On building fast kd-trees for ray tracing, and on doing that in O(nlogn)[J]. In Proc. IEEE Symp.Interactive Ray Tracing, pages 61–69, 2006.
[21] V. Havran. Heuristic Ray Shooting Algorithms[M]. Ph.d.thesis, Department of Computer Science and Engineering, Faculty of Electrical Engineering, Czech Technical University in Prague, November 2000. http://www.cgg.cvut.cz/ havran/phdthesis.html.
[22] Alexander Reshetov. On building good KD-Trees in the Intel Multi-Level Ray Tracing System[J]. Personal Communication, 2005.
[23] M. Shevtsov, A. Soupikov, A. Kapustin. Highly parallel fast kd-tree construction for interactive ray tracing of dynamic scenes[J]. Computer Graphics Forum, 2007,26(3):395-404.
[24] T. Whitted. An Improved Illumination Model for Shaded Display [J]. Comm.ACM Vol.23,No.6,1980.
[25]陈家新,周纬杰.一种改进的Phong光照模型及光线跟踪实现[J].系统仿真学报,2002.12第14卷第12期.
[26] Ingo Wald. Realtime Ray Tracing and Interactive Global Illumination[M]. PhD thesis, Computer Graphics Group, Saarland University, 2004. http://www.mpi-sb.mpg.de/_wald/PhD/.
[27] Mersenne twister. http://en.wikipedia.org/wiki/Mersenne_twister.
[28] Eric Weisstein’s World of Physics, Snell’s Law[S].http://scienceworld.wolfram.com
[29] Bram de Greve. Reflections and Refractions in Ray Tracing[J]. 2004.10.10.
[30] Beer’s Law. http://en.wikipedia.org/wiki/Beer%E2%80%93Lambert_law.
[31] Vlastimil Havran. Heuristic Ray Shooting Algorithms[J]. http://www.cgg.cvut.cz/~havran/phdthesis.html
[32]程剑.实时动态阴影算法的研究与实现[D].硕士学位论文,2005.
[33] C. Benthin. Real time ray tracing on current CPU architectures[D]. Ph.D dissertation. Saarland University, Sarrbrucken, German,2006.
[34]贺欢.空间环境可视化关键技术研究[D].博士学位论文. 2009.
[35]钱徽,朱淼良.大气效果的绘制技术综述[J].计算机辅助设计与图形学学报,Vol.14,No.5 May,2002.
[36]吴春明,钱徽,朱淼良.大气效果绘制的若干问题研究[J].电子学报,Vol.33.No.8 Aug.2005.
[37] Ralf Stokholm Nielsen. Real Time Rendering of Atmospheric Scattering Effects for Flight[J].
[38] T. Nishita, T. Sirai, K. Tadamura, E. Nakamae. Display of the Earth Taking into Account Atmospheric Scattering[J]. In proceedings of SIGGRAPH, 1993,PP.175-182.
[39] O’Neil Sean. Real-Time Atmospheric Scattering[J]. GameDev.net. 2004.
[40] N. Hoffman, A.J.Preetham. Rendering Outdoor Scattering in Real Time[J]. ATI Coporation. 2002.
[41]宫正.基于物理的大气现象真实感建模与绘制[D].硕士学位论文,2006.
[42]王长波,王章野,周麒等.海市蜃楼现象的真实感绘制[J].计算机学报,2006年12月第29卷第12期.
[43] T Binzoni, T S Leung, A H Gandjbakhche. The use of the Henyey–Greenstein phase function in Monte Carlo simulations in biomedical optics[J]. PHYSICS IN MEDICINE AND BIOLOGY, 51 (2006) N313–N322
[2]孙家广.计算机图形学(第三版)[M].北京:清华大学出版社,2003,PP.529-546.
[3]黄文均,鲍虎军.计算机真实感图形的算法基础[M].北京:科学出版社,2002,PP.127-131.
[4] Andrew Glassner. An Introduction to Ray Tracing[J]. Morgan Kaufmann,1989. ISBN 0-12286-160-4.
[5] Autodesk Ltd. 3D Studio File Format Document Revision 0.93[S]. January 1997.
[6] D. Green, D. Hatch. Fast Polygon-Cube Intersection Testing[J]. Alan Paeth, ed., Graphics Gems V, AP Professional, Boston, pp.375-379, 1995. http://www.graphicsgems.org/
[7] Tomas Akenine-M?oller. Fast 3D Triangle-Box Overlap Testing[J]. Department of Computer Engineering,Chalmers University of Technology. March 2001, updated June 2001.
[8] Eberly, David.3D Game Engine Design: A Practical Approach to Real-Time Computer Graphics[M]. Morgan Kaufmann Publishers Inc., San Fran-cisco, 2000. http://www.magic-software.com/
[9] M?oller, Tomas, Eric Haines. Real-Time Rendering[J], AK Peters Ltd.,Natick, MA, 1999. http://www.realtimerendering.com/
[10] J. Amanatides, A. Woo. A faster voxel traversal algorithm for ray tracing[J].
[11] Vlastimil Havran. Heuristic Ray Shooting Algorithms.Ph.d. thesis[D]. Department of Computer Science and Engineering, Faculty of Electrical Engineering, Czech Technical University in Prague, November 2000.
[12] Frank D.Luna著,段菲译. DirectX9.0 3D游戏开发编程基础[M].北京:清华大学出版社,2007.4,PP.193-205.
[13] Barycentric Coordinates , http://mathworld.wolfram.com/BarycentricCoordinates.html
[14] T M?LLER, B TRUMBORE. Fast, minimum storage ray/triangle intersectuion[J]. Journal of Graphics Tools 2, 1(1997), 21–28.
[15] Jeff Arenberg. Ray/Triangle Intersection with BarycentricCoordinates[J]. Ray Tracing News, edited by Eric Haines,Vol.1,No.11,November 4,1988, http:://www.acm.org/tog/resources/RTNews/.
[16] Steve Renals. Nearest neighbours and the kD-tree[J]. Informatics 2B,Learning Note 6(v1.0), January 2007.
[17] Laszlo Szecsi. An effective implementation of the k-D tree[J]. Charles River Media, Inc., 2003,PP.315–326.
[18] V Havran, J Bittner. On improving kd tree for ray shooting[C]. Proceedings of the WSCG’2002 Conference. Plzen,Czech Republic, 2002:209-216.
[19]范文山,王斌.启发式探查最佳分割平面的快速KD-Tree构建方法[J].计算机学报.2009年2月第32卷,第2期.
[20] Wald, V. Havran. On building fast kd-trees for ray tracing, and on doing that in O(nlogn)[J]. In Proc. IEEE Symp.Interactive Ray Tracing, pages 61–69, 2006.
[21] V. Havran. Heuristic Ray Shooting Algorithms[M]. Ph.d.thesis, Department of Computer Science and Engineering, Faculty of Electrical Engineering, Czech Technical University in Prague, November 2000. http://www.cgg.cvut.cz/ havran/phdthesis.html.
[22] Alexander Reshetov. On building good KD-Trees in the Intel Multi-Level Ray Tracing System[J]. Personal Communication, 2005.
[23] M. Shevtsov, A. Soupikov, A. Kapustin. Highly parallel fast kd-tree construction for interactive ray tracing of dynamic scenes[J]. Computer Graphics Forum, 2007,26(3):395-404.
[24] T. Whitted. An Improved Illumination Model for Shaded Display [J]. Comm.ACM Vol.23,No.6,1980.
[25]陈家新,周纬杰.一种改进的Phong光照模型及光线跟踪实现[J].系统仿真学报,2002.12第14卷第12期.
[26] Ingo Wald. Realtime Ray Tracing and Interactive Global Illumination[M]. PhD thesis, Computer Graphics Group, Saarland University, 2004. http://www.mpi-sb.mpg.de/_wald/PhD/.
[27] Mersenne twister. http://en.wikipedia.org/wiki/Mersenne_twister.
[28] Eric Weisstein’s World of Physics, Snell’s Law[S].http://scienceworld.wolfram.com
[29] Bram de Greve. Reflections and Refractions in Ray Tracing[J]. 2004.10.10.
[30] Beer’s Law. http://en.wikipedia.org/wiki/Beer%E2%80%93Lambert_law.
[31] Vlastimil Havran. Heuristic Ray Shooting Algorithms[J]. http://www.cgg.cvut.cz/~havran/phdthesis.html
[32]程剑.实时动态阴影算法的研究与实现[D].硕士学位论文,2005.
[33] C. Benthin. Real time ray tracing on current CPU architectures[D]. Ph.D dissertation. Saarland University, Sarrbrucken, German,2006.
[34]贺欢.空间环境可视化关键技术研究[D].博士学位论文. 2009.
[35]钱徽,朱淼良.大气效果的绘制技术综述[J].计算机辅助设计与图形学学报,Vol.14,No.5 May,2002.
[36]吴春明,钱徽,朱淼良.大气效果绘制的若干问题研究[J].电子学报,Vol.33.No.8 Aug.2005.
[37] Ralf Stokholm Nielsen. Real Time Rendering of Atmospheric Scattering Effects for Flight[J].
[38] T. Nishita, T. Sirai, K. Tadamura, E. Nakamae. Display of the Earth Taking into Account Atmospheric Scattering[J]. In proceedings of SIGGRAPH, 1993,PP.175-182.
[39] O’Neil Sean. Real-Time Atmospheric Scattering[J]. GameDev.net. 2004.
[40] N. Hoffman, A.J.Preetham. Rendering Outdoor Scattering in Real Time[J]. ATI Coporation. 2002.
[41]宫正.基于物理的大气现象真实感建模与绘制[D].硕士学位论文,2006.
[42]王长波,王章野,周麒等.海市蜃楼现象的真实感绘制[J].计算机学报,2006年12月第29卷第12期.
[43] T Binzoni, T S Leung, A H Gandjbakhche. The use of the Henyey–Greenstein phase function in Monte Carlo simulations in biomedical optics[J]. PHYSICS IN MEDICINE AND BIOLOGY, 51 (2006) N313–N322