Efficient Rendering of Lightning Taking into Account Scattering Effects due to Clouds and Atmospheric Particles

1
Efficient Rendering of Lightning Taking into
Account Scattering Effects due to Clouds and
Atmospheric Particles
Yoshinori Dobashi
Tsuyoshi Yamamoto
(Hokkaido University)
Tomoyuki Nishita
(The University of Tokyo)
2
Overview

• Introduction

• Effects of Atmospheric Scattering due to
  Lightning

• Clouds Illuminated by Lightning

• Results

• Conclusions

3
Introduction
Previous methods Clear/cloudy days
4
Important Elements
5
Previous Methods

• Methods related to lightning

6
Previous Methods

• Methods related to lightning

7
Previous Methods

• Methods related to lightning

8
Previous Methods

• Methods related to lightning

9
Previous Methods

• Related to clouds and atmospheric scattering

None of these takes into account scattering
effects due to lightning flash.
10
Features of Proposed Method

• Use of Reeds method for modeling

• Use of Reeds method for modeling

• User specifies Color of lightning

• User specifies Color of lightning

• Atmospheric scattering due to flash of
  lightning

• Atmospheric scattering due to flash of
  lightning

• Clouds illuminated by flash of lightning

• Clouds illuminated by flash of lightning

• Efficient rendering of clouds for fly- through
  animations

• Efficient rendering of clouds for fly- through
  animations

11
Features of Proposed Method

• Use of Reeds method for modeling

• User specifies Color of lightning

• Atmospheric scattering due to flash of
  lightning

• Clouds illuminated by flash of lightning

• Efficient rendering of clouds for fly- through
  animations

12
Overview

• Introduction

• Effects of Atmospheric Scattering due to
  Lightning

• Clouds Illuminated by Lightning

• Results

• Conclusions

13
Atmospheric Scattering

• Placing point light sources

clouds
lightning
viewpoint
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Atmospheric Scattering

• Placing point light sources

• Consider a single source k

P
viewpoint V
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Atmospheric Scattering

• Placing point light sources

• Consider a single source k

• No analytical solutions

P
viewpoint
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Atmospheric Scattering

• Placing point light sources

• Consider a single source k

Ik

• No analytical solutions

• Ray tracing

• Computationally expensive

• Use of look-up table

viewpoint
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Efficient Computation Using Look-up Table

• Creating look-up table

• local coordinate uv

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Efficient Computation Using Look-up Table

• function of (ueye, veye , l)

• preparing table by changing values of (ueye,
  veye , l)

• -T lt (ueye, veye) lt T (Tspecified by user)
• l sampled at R, G, B

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Efficient Computation Using Look-up Table

• function of (ueye, veye , l)

• preparing table by changing values of (ueye,
  veye , l)

• Intensity of pixel

Can be computed efficientlyusing look-up table
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Overview

• Introduction

• Effects of Atmospheric Scattering due to
  Lightning

• Clouds Illuminated by Lightning

• Results

• Conclusions

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Intensity Calculation of Clouds

• Density distribution

Dobashi00

• voxels

• metaballs

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Intensity Calculation of Clouds

• Density distribution

Dobashi00

• voxels

• metaballs

• Intensity Calculation

• sum of intensity due to each point source

• use of hardware

• use of LOD

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Intensity Calculation of Clouds

• Density distribution

Dobashi00

• 3D voxels

• metaballs

• Intensity Calculation

• sum of intensity due to each point source

• use of hardware

• use of LOD

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Computing Attenuation Using Hardware

• Attenuation to each metaball

• use of hardware-accelerated splatting
  Dobashi00

• limited to parallel
• sources

• extending to point
• sources

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Computing Attenuation Using Hardware

• Attenuation to each metaball

metaball

• placing a box as 6 screens

point source k
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Computing Attenuation Using Hardware

• Attenuation to each metaball

metaball

• placing a box as 6 screens

point source k
box as six screens
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Computing Attenuation Using Hardware
billboard (square polygon)

• Attenuation to each metaball

• placing a box as 6 screens

• place billboards at centers of metaballs

• project metaballs

• pixel value of the centers

point source k

• Problem

Using LODgrouping metaballs hierarchically
box as six screens
cost ? no. of metaballs
(realistic cloudstens of thousands of metaballs)
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Efficient Computation Using LOD

• Light reaching metaball

metaballj

• inversely proportional to square of distance

point source k
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Efficient Computation Using LOD

• Light reaching metaball

metaball j

• inversely proportional to square of distance

• attenuation due to cloud particles

point source k
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Efficient Computation Using LOD

• Light reaching metaball

metaball

• inversely proportional to square of distance

• attenuation due to cloud particles

• intensity is small at distant regions, and
  almost uniform.

point source k
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Efficient Computation Using LOD

• Light reaching metaball

metaball

• inversely proportional to square of distance

• attenuation due to cloud particles

• intensity is small at distant regions, and
  almost uniform.

point source k

• Approximation by larger metaballs

• Selecting appropriate metaballs depending on
  distances

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Efficient Computation Using LOD

• Representing metaballs using octree

• Grouping neighboring metaballs

• densityaverage
• radiustwice

• Selecting appropriate levels depending on
  distances

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Efficient Computation Using LOD

• Selection of appropriate levels

• energy received by metaball j

dVj
Ej (light reaching metaball) x (volume)

• condition

( e threshold)
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Efficient Computation Using LOD

• Selection of appropriate levels

• energy received by metaball j

dVj
Ej (light reaching metaball) x (volume)

• condition

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Efficient Computation Using LOD

• Selection of appropriate levels

clouds

• condition

• check metaballs of highest level

point source k
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Efficient Computation Using LOD

• Selection of appropriate levels

clouds

• condition

• check metaballs of highest level

• proceed to metaballs of lower levels

?
point source k
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Efficient Computation Using LOD

• Selection of appropriate levels

clouds
?

• condition

• check metaballs of highest level

• proceed to metaballs of lower levels

point source k
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Efficient Computation Using LOD

• Selection of appropriate levels

clouds
selected metaballs

• condition

• check metaballs of highest level

• proceed to metaballs of lower levels

point source k
Reducing number of metaballs to be processed
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Overview

• Introduction

• Features of Our method

• Effects of Atmospheric Scattering due to
  Lightning

• Clouds Illuminated by Lightning

• Results

• Conclusions

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Results

• Verification using simple example

• Parameter settings

no. of point sources 50
attenuation ratio 0.03
density of atmospheric particles 0.15
threshold e 0.2
no. of metaballs 250,000
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Results
with LOD
without LOD
50 times faster!
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Results
(a) lightning in clouds
(b) multiple lightning
(c) colored lightning (pink)
(d) lightning at sunset
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Example Animation(VIDEO)

• Simulation of lightning under different
  conditions

• Flight simulation

• On animating lightning

• Initial points are determined randomly in clouds.

• Periods from occurrence to the extinction are
  determined randomly, less than 0.5 seconds.

• Intensity is determined randomly.

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Conclusions

• Realistic image synthesis of scenes including
  lightning

• atmospheric scattering due to flash of
  lightning

• clouds illuminated by flash of lightning

• efficient rendering using look-up table and
  idea of LOD

• hierarchical imposters for efficient rendering
  of clouds

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Future Work

• Automatic determination of parameters

• Automatic determination of lightning color

• Further speeding up for real-time simulations

46
Basic Idea
clouds

• Atmospheric scattering

• use of look-up table

• Intensity of clouds

• use of idea of level of detail (LOD)

viewpoint
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Basic Idea

• Atmospheric scattering

• use of look-up table

• Intensity of clouds

• use of idea of level of detail (LOD)

• Efficient rendering of clouds

• use of imposter method

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Rendering of Clouds Using Imposters

• Drawing all metaballs

- increasing rendering time
- use of imposters

• Grouping metaballs

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Rendering of Clouds Using Imposters

• Drawing all metaballs

- increasing rendering time
- use of imposters

• Grouping metaballs

• Placing transparent polygon for each group

• Creating textures by drawing metaballs

clouds (metaball)
viewpoint
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Rendering of Clouds Using Imposters

• Drawing all metaballs

- increasing rendering time
- use of imposters

• Grouping metaballs

• Place transparent polygon for each group

• Create textures by drawing clouds

• Draw texture-mapped polygons

viewpoint
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Rendering of Clouds Using Imposters

• When viewpoint moves

Imposter
texture
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Rendering of Clouds Using Imposters

• When viewpoint moves

Imposter

• Reuse textures

- reducing rendering time

• Conditions for maintaining accuracy

• regions near viewpoint

• distant regions from viewpoint

texture
Grouping metaballs adaptively
viewpoint
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Adaptive Generation of Imposters

• Making use of octree for metaballs

• Selecting appropriate levels depending on
  distance from viewpoint

• Rendering clouds without losing accuracy

viewpoint
clouds
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Results
with imposters
without imposters
7 times faster
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Basic Idea
clouds

• Atmospheric scattering

• use of look-up table

• Intensity of clouds

• use of idea of level of detail (LOD)

viewpoint