Rendering of Clouds Scattering/absorption due to cloud

Rendering of Clouds

Intensity of clouds
atmosphereparticles
 Multiple scattering Atmospheric effects

Rendering of Clouds Single scattering & atmospheric effects

sunbackgroundcolor

two-pass splatting approach for clouds
 volume rendering for atmosphere Multiple scattering

viewpoint

precomputation-based approach for multiplescattering Monte Carlo methodsinglescattering

cloudsmultiplescattering

Computationally expensiveSingle Scattering

Single Scattering Two-pass splatting approach Two-pass splatting approachRepresenting clouds using metaballs

pass1: render clouds viewed from the sunsunmetaballs

billboard
virtualscreenproject andmultiply attenuation

Single Scattering

Single Scattering Two-pass splatting approach Result

pass2: render clouds viewed from viewoint
project andaccumulate intensity

viewpoint

billboard

Atmospheric Effects

Examplessunclouds

spherical
shellsxV(texture mapping)vertices

intensity due to atmosphereshafts of light (daytime)

simulation: 0.5 [sec]shafts of light (evening)

rendering: 15 [sec]voxel size: 256x256x20 image size: 640x480(PentiumIII 733Mhz, NVIDIA GeForce256)

Multiple Scattering

Examples Precomputation-based approach

prorpcesssimulation: 0.3 [sec]rendering: 10 [sec]voxel size: 256x256x10 image size: 640x480(PentiumIII 733Mhz, NVIDIA GeForce256)

compute shading of clouds with different lighting
conditions
store the results in a database after compressing
them by orthogonal basis functions (sphericalharmonics or wavelets)

real-time process

extract shading corresponding to the current lighting
condition
render imageMultiple Scattering

Clouds illuminated by lightning

 Precomputation-based approach Arbitrary shapes of lightning Anisotropic multiple scattering Consisting of preprocess and real-timeprocess
 Use of wavelet transform for drasticallyaccelerating intensity calculation
 Assumption: Static clouds

cloud illuminated by lightning

dynamic clouds (periodical)
14/45

Clouds illuminated by lightning

Clouds illuminated by lightning
 Preprocess䠖computation of basis

 Two separate grids

intensities

saveclouds
grid for clouds

simulation
space

grid forsimulation
space

intensity calculation
taking into accountmultiple scattering

virtual point source(intensity = 1.0)

Clouds illuminated by lightning

Clouds illuminated by lightning

 Preprocess䠖computation of basis

 Preprocess䠖computation of basis

intensities

intensities

Clouds illuminated by lightning

Clouds illuminated by lightning

 Preprocess䠖computation of basis

 Real-time process䠖rendering of clouds

intensities

basis intensities

Repeating for
all grid points

multiplication
intensity ofvirtual point
sourcesbasis intensities
㽢accumulation

㽢6

㽢㽢

generating
lightning Fast but cost proportional to number of grid points
23/45by using wavelets
 Further acceleration

Animation

Examples

24/45

25/45

Dynamic Clouds

Dynamic Clouds Real-time rendering of endless cloud Precomputation

animation
 volume data for clouds is generated at runtime
 real-time rendering of clouds illuminatedby sunlight and skylight with single andmultiple scattering GPU implementation

shading
data

䞉䞉䞉

Basic
VolumeData䞉䞉䞉Dynamic Clouds

Dynamic Clouds

 Rendering process Rendering process

shadingdatashadingdata

BasicVolumeData

BasicVolumeDatastate transition䞉䞉䞉䞉䞉䞉+Results

Multiple Scattring Monte Carlo Method

Out-of-core renderingmovie Large-scale clouds

0.7 km

10 km

150 km

600 km