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![Page 1: Sky dome](https://reader033.fdocuments.in/reader033/viewer/2022042816/55993cd81a28abbc038b4758/html5/thumbnails/1.jpg)
An Analytic Model forFull Spectral Sky-Dome Radiance
SIGRAPH 2012
2012/12/05ked
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Authors
Lukas Hosek, Alexander Wilkie
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Outline
Goal Why is the sky blue? Modeling Simulation Results
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Outline
Goal Why is the sky blue? Modeling Simulation Results
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A new sky model is required
Accurate simulation is slow Environment maps are limited Fix the flaws of old model
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A new sky model is required
Accurate simulation is slow Environment maps are limited
Fix the flaws of old model
![Page 7: Sky dome](https://reader033.fdocuments.in/reader033/viewer/2022042816/55993cd81a28abbc038b4758/html5/thumbnails/7.jpg)
A new sky model is required
Accurate simulation is slow Environment maps are limited
Fix the flaws of old model
?
![Page 8: Sky dome](https://reader033.fdocuments.in/reader033/viewer/2022042816/55993cd81a28abbc038b4758/html5/thumbnails/8.jpg)
A new sky model is required
Accurate simulation is slow Environment maps are limited
Fix the flaws of old model Preetham model
Limited turbidity range Fails at some spectrum
![Page 9: Sky dome](https://reader033.fdocuments.in/reader033/viewer/2022042816/55993cd81a28abbc038b4758/html5/thumbnails/9.jpg)
A new sky model is required
Accurate simulation is slow Environment maps are limited
Fix the flaws of old model Preetham model
Limited turbidity range Fails at some spectrum
![Page 10: Sky dome](https://reader033.fdocuments.in/reader033/viewer/2022042816/55993cd81a28abbc038b4758/html5/thumbnails/10.jpg)
A new sky model is required
Demo
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A new sky model is required
Accurate simulation is slow Environment maps are limited
Fix the flaws of old model Preetham model
Limited turbidity range Fails at some spectrum
how?
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Outline
Goal Why is the sky blue? Modeling Simulation Results
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Scattering
http://www.sciencemadesimple.com/sky_blue.html
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Scattering
Effected by Haze: dust particles, water droplets, …. (1859) Air molecules (1899) And finally settle by Einstein (1910)
http://www.sciencemadesimple.com/sky_blue.html
“ 方勵之—天空為什麼是藍色的”
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Scattering – the sky near the horizen
http://www.sciencemadesimple.com/sky_blue.html
http://www.research-in-germany.de/25326/german-countryside-bildergalerie,templateId=popup,currentContentId=25294.html
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The red sunset
http://www.sciencemadesimple.com/sky_blue.html
http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html
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Outline
Goal Why is the sky blue? Modeling Simulation Results
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Luminance model
Perez (1993)
The parameters A to E and Yz are used to tune the luminance distribution.
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Spectral radiance model
Preetham (1999)
CIE xyY color space
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Spectral radiance model
Preetham (1999) The parameters of Perez model (A to E and
Yz) are linear functions of condition, turbidity. Turbidity,
Ratio of the optical thickness to pure air T=2: very clear, Arctic-like sky T=3: clear sky in temperate climate T=6: warm, moist day
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The new model
Hosek (2012) Extend the Perez model
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The new model
Hosek (2012) Extend the Perez model
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The new model
Hosek (2012) Extend the Perez model
![Page 24: Sky dome](https://reader033.fdocuments.in/reader033/viewer/2022042816/55993cd81a28abbc038b4758/html5/thumbnails/24.jpg)
The new model
Hosek (2012) Extend the Perez model
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The parameters
A, B, C, D, E, F, G, H, I, and 10 parameters
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The parameters
A, B, C, D, E, F, G, H, I, and
: control point
: albedo : parameter
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The parameters
John von Neumann “With four parameters I can fit an elephant, and
with five I can make him wiggle his trunk”
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Outline
Goal Why is the sky blue? Modeling Simulation Results
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Scattering models
Molecules: Rayleigh scattering Haze: Mie scattering
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Scattering models
Molecules: Rayleigh scattering Cross section: Density: Phase function:
Haze: Mie scattering Cross section: Density: Phase function:
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Scattering models
Molecules: Rayleigh scattering Cross section: Density: Phase function:
Haze: Mie scattering Cross section: Density: Phase function:
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Scattering models
Molecules: Rayleigh scattering Cross section: Density: decays exponentially with altitude( ) Phase function:
Haze: Mie scattering Cross section Density Phase function:
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Scattering models
Molecules: Rayleigh scattering Cross section: Density: decays exponentially with altitude( ) Phase function:
Angle between outgoing and incoming light directions
Haze: Mie scattering Cross section Density: Phase function:
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Scattering models
Molecules: Rayleigh scattering Cross section: Density: decays exponentially with altitude( ) Phase function:
: angle between outgoing and incoming light directions
Haze: Mie scattering Cross section: pre-calculated tabulated values Density: decays exponentially with altitude( ) Phase function:
g: anisotropy factor
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Scattering models
Phase functions
http://home.comcast.net/~vinelandrobotics/
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Ray tracer100km cover 0.0005%
Lambertian diffuse surface
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Ray tracer100km cover 0.0005%
path tracing
Lambertian diffuse surface
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Ray tracer100km cover 0.0005%
path tracing
ignored
Lambertian diffuse surface
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Ray tracercover 0.0005%
path tracing
ignored
Lambertian diffuse surface
100km
10
720
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Outline
Goal Why is the sky blue? Modeling Reference data generation Results
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Photos vs. simulation
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Turbidity values
Solar elevation = 4o
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Ground albedo
Solar elevation = 40o, T = 4 In high turbidity settings, changing ground albedo
alters the brightness of the whole sky-dome
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New model vs. Perez model
SNR Reference: path tracing results
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Photograph vs. new model
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Feature work
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Reference
為什麼天空是藍的,方勵之 www.sciencemadesimple.com/sky_blue.htm A Practical Analytic Model for Daylight, A.J.
Preetham, P. Shirley, and B. Smits. Unbiased Global Illumination with Participating
Media, M. Raab, D. Seibert, and A. Keller.
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Thx.