Participating Media

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Participating Media
CICyT TIC98-0973-C03-03 Zaragoza meeting Nov 2000
Frederic Pérez GGG-IIiA/UdGGirona, Spain
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Outline

• Participating media Quick review
• Two Pass algorithm Link Probabilities
• LDI approach

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Participating Media Transport Equation
being
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Participating Media Phase functions
Linear-anisotropic phase function
Rayleigh scattering
Hazy atmosphere Mie approximation
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Participating Media Solving the problem
1. Source radiance
2. Integral transport equation
? Two pass methods
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Link Probabilities Overview

• 1st Pass Radiance Clustering
• Produces Hierarchical Links
• Coarse solution not for rendering
• 2nd Pass Monte Carlo Path Tracing
• Improved Importance Sampling with Link
  Probabilities
• Use links arriving at leaves as a representation
  of the irradiance

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Radiance Clustering Results
Isotropic
Backward
Forward
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Link Probabilities Basic Algorithm

• Importance Sampling in a random walk step

for each bounce at point x
x
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Link Probabilities

• PDF accuracy and visibility Example

S1
l1
S2
l2
R
Finite elements pass ? two links arriving at
leaf R
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Link Probabilities

• PDF accuracy and visibility

Solution Adaptive PDFs
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Link Probabilities Results w/o media
16 samples
128 samples
64 samples
NEE
806s
1613s
201s
LP
1273s
2434s
409s
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Current Work New Two Pass Method

• New code Getting rid of BRIGHT SIR
• New code using the new SIR
• New 1st pass particle tracing based
• Same requirements as previous 1st pass
• Obtain quickly a coarse solution to guide a 2nd
  pass
• Maintaining the 2nd pass using the Link
  Probabilities
• Reimplementing and finishing it

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Current Work New 1st Pass

• Extended Hierarchical Monte Carlo Radiosity ?
  Link hierarchy
• Bekaert et al. Hierarchical Monte Carlo
  Radiosity. In Rendering Techniques 98
• Adaptively refined mesh and (implicit) link
  structure ? but storing links for the 2nd pass
• Extended for anisotropic participating media and
  glossy surfaces ? by means of Illumination Samples

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Current Work First Results
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Link Probabilities Near Future Work

• Extension for isotropic participating media
• Account for links arriving to leaf clusters with
  media and sample directions as for surfaces
• Addition of anisotropic participating media and
  glossy surfaces
• Account for phase function/BRDF
• Use of Link Probabilities in BPT
• Eye paths as presented
• Light paths similarly using importance

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LDI Approach Idea

• 1st Pass Photon tracing
• Produces a photon map
• From photon map ? Grid or set of photons w/
  in a special LDI
• 2nd Pass Computing the eye radiance
• Just by using the estimated

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LDI Approach Idea
Spherical Harmonics
Infinite series able to represent functions
defined over a sphere
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The end