sky dome
DESCRIPTION
A summary of the Siggraph paper, "An Analytic Model for Full Sky-Dome Radiance."TRANSCRIPT
An Analytic Model forFull Spectral Sky-Dome Radiance
SIGRAPH 2012
2012/12/05ked
Authors
Lukas Hosek, Alexander Wilkie
Outline
Goal Why is the sky blue? Modeling Simulation Results
Outline
Goal Why is the sky blue? Modeling Simulation Results
A new sky model is required
Accurate simulation is slow Environment maps are limited Fix the flaws of old model
A new sky model is required
Accurate simulation is slow Environment maps are limited
Fix the flaws of old model
A new sky model is required
Accurate simulation is slow Environment maps are limited
Fix the flaws of old model
?
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
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
A new sky model is required
Demo
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?
Outline
Goal Why is the sky blue? Modeling Simulation Results
Scattering
http://www.sciencemadesimple.com/sky_blue.html
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”
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
The red sunset
http://www.sciencemadesimple.com/sky_blue.html
http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html
Outline
Goal Why is the sky blue? Modeling Simulation Results
Luminance model
Perez (1993)
The parameters A to E and Yz are used to tune the luminance distribution.
Spectral radiance model
Preetham (1999)
CIE xyY color space
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
The new model
Hosek (2012) Extend the Perez model
The new model
Hosek (2012) Extend the Perez model
The new model
Hosek (2012) Extend the Perez model
The new model
Hosek (2012) Extend the Perez model
The parameters
A, B, C, D, E, F, G, H, I, and 10 parameters
The parameters
A, B, C, D, E, F, G, H, I, and
: control point
: albedo : parameter
The parameters
John von Neumann “With four parameters I can fit an elephant, and
with five I can make him wiggle his trunk”
Outline
Goal Why is the sky blue? Modeling Simulation Results
Scattering models
Molecules: Rayleigh scattering Haze: Mie scattering
Scattering models
Molecules: Rayleigh scattering Cross section: Density: Phase function:
Haze: Mie scattering Cross section: Density: Phase function:
Scattering models
Molecules: Rayleigh scattering Cross section: Density: Phase function:
Haze: Mie scattering Cross section: Density: Phase function:
Scattering models
Molecules: Rayleigh scattering Cross section: Density: decays exponentially with altitude( ) Phase function:
Haze: Mie scattering Cross section Density Phase function:
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:
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
Scattering models
Phase functions
http://home.comcast.net/~vinelandrobotics/
Ray tracer100km cover 0.0005%
Lambertian diffuse surface
Ray tracer100km cover 0.0005%
path tracing
Lambertian diffuse surface
Ray tracer100km cover 0.0005%
path tracing
ignored
Lambertian diffuse surface
Ray tracercover 0.0005%
path tracing
ignored
Lambertian diffuse surface
100km
10
720
Outline
Goal Why is the sky blue? Modeling Reference data generation Results
Photos vs. simulation
Turbidity values
Solar elevation = 4o
Ground albedo
Solar elevation = 40o, T = 4 In high turbidity settings, changing ground albedo
alters the brightness of the whole sky-dome
New model vs. Perez model
SNR Reference: path tracing results
Photograph vs. new model
Feature work
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.
Thx.