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Principal-Ordinates Propagation for Real-Time Rendering of Participating Media
@ Computers and Graphics (CaG) 2014


Oskar Elek1,2      Tobias Ritschel1,2      Carsten Dachsbacher3      Hans-Peter Seidel1     
1MPI Informatik      2MMCI / Saarland University      3Karlsruhe Institute of Technology     

2014
We extend our previous work on Principal Ordinate Propagation by splitting the main transport stage in two parts: anisotropic and isotropic propagation. We heuristically estimate the number of anisotropic iterations that need to be executed; after that, we assume the directional radiance distribution to be isotropic. As a consequence the residual radiance can be propagated in a single domain without even keeping track of its directionality, resulting in much higher simulation speeds. The figure above shows both the anisotropic and the isotropic portions of the propagated energy for two different illumination conditions and two opposing camera positions.


Abstract

Efficient light transport simulation in participating media is challenging in general, but especially if the medium is heterogeneous and exhibits significant multiple anisotropic scattering. We present Principal-Ordinates Propagation, a novel finite-element method that achieves real-time rendering speeds on modern GPUs without imposing any significant restrictions on the rendered participated medium. We achieve this by dynamically decomposing all illumination into directional and point light sources, and propagating the light from these virtual sources in independent discrete propagation domains. These are individually aligned with approximate principal directions of light propagation from the respective light sources. Such decomposition allows us to use a very simple and computationally efficient unimodal basis for representing the propagated radiance, instead of using a general basis such as spherical harmonics. The resulting approach is biased but physically plausible, and largely reduces the rendering artifacts inherent to existing finite-element methods. At the same time it allows for virtually arbitrary scattering anisotropy, albedo, and other properties of the simulated medium, without requiring any precomputation.

Downloads


2014 CaG Article
(20.7 MB)
2014 Supplement
(0.2 MB)

Citation

2014 Oskar Elek, Tobias Ritschel, Carsten Dachsbacher, Hans-Peter Seidel
Principal-Ordinates Propagation for Real-Time Rendering of Participating Media
Computers and Graphics 45, December 2014
(Extended version)
@article{ElekCAG2014,
  author = {Oskar Elek and Tobias Ritschel and Carsten Dachsbacher and Hans-Peter Seidel},
  title = {Principal-Ordinates Propagation for Real-Time Rendering of Participating Media},
  journal = {Computers \& Graphics},
  volume = {45},
  doi = {10.1016/j.cag.2014.08.003},
  publisher = {Pergamon Press, Inc.},
  year = {2014}
}
	


Interactive Light Scattering with Principal-Ordinate Propagation
Best Student Paper @ Graphics Interface (GI) 2014


Oskar Elek1,2      Tobias Ritschel1,2      Carsten Dachsbacher3      Hans-Peter Seidel1     
1MPI Informatik      2MMCI / Saarland University      3Karlsruhe Institute of Technology     

2014
Our method's pipeline. The surface portion of the light transport is obtained from a Reflective Shadow Map (RSM), attenuated by the medium. Importance-sampling the RSM yields a set of Virtual Point Lights (VPLs). These are then used to calculate 1st-bounce global illumination, as well as indirect multiple scattering from surfaces (using a separate propagation grid for each VPL). Scattering from environment illumination is obtained similarly from VPLs generated by importance-sampling the environment map. Combining these partial solutions with the light directly scattered from light sources produces the final solution.


Abstract

Efficient light transport simulation in participating media is challenging in general, but especially if the medium is heterogeneous and exhibits significant multiple anisotropic scattering. We present a novel finite-element method that achieves interactive rendering speeds on modern GPUs without imposing any significant restrictions on the rendered participated medium. We achieve this by dynamically decomposing all illumination into directional and point light sources, and propagating the light from these virtual sources in independent discrete propagation volumes. These are individually aligned with approximate principal directions of light propagation from the respective light sources. Such decomposition allows us to use a very simple and computationally efficient unimodal basis for representing the propagated radiance, instead of using a general basis such as Spherical Harmonics. The presented approach is biased but physically plausible, and largely reduces rendering artifacts inherent to standard finite-element methods while allowing for virtually arbitrary scattering anisotropy and other properties of the simulated medium, without requiring any precomputation.

Downloads


2014 GI Paper
(15.8 MB)
2014 Supplement
(0.2 MB)
2014 Video
(60 MB)
2014 Slides
(67 MB)
2014 Slides
(3.1 MB)

Video


The video demonstrates several scenes corresponding to some of the figures in the paper (running elephant, train smoke/steam, clouds). It was captured online at cca. 10 FPS on NVidia GTX 485 Mobile GPU. All settings used in the video are identical to the ones used to generate the corresponding figures. For more details see the youtube page.

Citation

2014 Oskar Elek, Tobias Ritschel, Carsten Dachsbacher, Hans-Peter Seidel
Interactive Light Scattering with Principal-Ordinate Propagation
Proc. Graphics Interface, Motreal/Quebec/Canada, May 2014
(Michael A. J. Sweeney Award 2014: Best Student Paper)
@inproceedings{ElekGI2014,
  author = {Oskar Elek and Tobias Ritschel and Carsten Dachsbacher and Hans-Peter Seidel},
  title = {Interactive Light Scattering with Principal-Ordinate Propagation},
  booktitle = {Proceedings of Graphics Interface},
  address = {Montreal/Quebec/Canada},
  year = {2014}
}