Real-Time Rendering of Planets with Atmospheres

Tobias Schafhitzel, Martin Falk, Thomas ErtlUniversität Stuttgart, Germany

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Motivation

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Outline

Introduction Atmospheric scattering Computation of the scattering texture Rendering Results Conclusion and future work

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Outline

Introduction Atmospheric scattering Computation of the scattering texture Rendering Results Conclusion and future work

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Introduction

Rendering a planet’s atmosphere Physically based computation

color shifts, light attenuation Sunset, sunrise, midday

Combination with terrain rendering Real-time approach

Games CAD Explorative tools (i.e. Google Earth,…)

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Previous Work

Atmospheric Scattering Atmospheric Scattering Effects of the Earth [Nishita et al. 93] Real-Time Atmospheric Scattering [O’Neil 04] Interactive Rendering of atmospheric Scattering Effects using Graphics Hardware [Dobashi et al. 02] Accurate Atmospheric Scattering [O’Neil 05]

Terrain Rendering Real-Time continuous Level of Detail Rendering of Height Field [Lindstrom et al. 96] Real-Time Generation of continuous Level of Detail for Height Fields [Röttger et al. 98]

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Outline

Introduction Atmospheric scattering Computation of the scattering texture Rendering Results Conclusion and future work

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Light scattering equation:

φ

Atmospheric Scattering

Pv

atmosphere

earth

dsPPtPPtKF

II a

P

P

csv

b

a

r )),(),(exp()(

)()(4

Pa

Pb

Pc

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Outline

Introduction Atmospheric scattering Computation of the scattering texture Rendering Results Conclusion and future work

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Parametrization of the 3D scattering texture:

Arbitrary height h = |Pv| For each h Arbitrary view angle θ For each θ an arbitrary angle to the sun φ

θ

Computation of the scattering texture

h

φ

Pv

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Intersection Tests

Camera inside the atmosphere→ use 1st intersection

Camera outside→ no scattering→ move camera to outer boundary→ constant height for parameterization→ use 2nd intersection

Two textures for intersections with Inner sphere Outer sphere Easy to switch when rendering

PV

PV

PV

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Outline

Introduction Atmospheric scattering Computation of the scattering texture Rendering Results Conclusion and future work

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Sky: tessellated sphere View ray Rv

connect vertex Pg with camera Pv

Compute h, θ and φ and map to [0,1] φ is constant (directional light) Fetch the scattering texture (simple lookup)

Rendering the sky

θPv

φ

Pc

Pg

Rv

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Rendering the terrain

More complex Consider structure of the terrain Naive computation fails

Distance too long Terrain color not considered

Solution Compute scattering along PvPb

Subtract contribution along PgPb

Two texture lookups:

PV

Pg

Pb

)exp()exp(

)()()(

4 v

P

P

lv

P

P

lsv ttttKF

IIb

g

b

v

r

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Rendering the terrain II

Considering the terrain color Illumination of the terrain

Incident light is attenuated:

Reflected light is attenuated

Overall light contribution:

dsPPtKF

II cgsgr )),(exp()(

)()(4

PV

Pg

Pc

dsPPtII vgggv )),(exp()cos()(

)()()(* vgvv III

Ig

Igv

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Outline

Introduction Atmospheric scattering Computation of the scattering texture Rendering Results Conclusion and future work

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Results

Earth dataset (2572 x 24 x 12)

Mars dataset (652 x 24 x 12)

Earth Mars

Outside 67.26 83.51

Inside 30.31 56.02

Terrain outside 76.44 102.37

Terrain inside 35.83 61.19

All measurements in fps

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Europe at morning

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Alps at morning

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Alps at midday

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Sunrise

Questions ?