Animation of Clouds Realistic motion

complex dynamics of cloud formation
 phase transition effects
Animation of Clouds

procedural simulation(cellular automata)

Procedural animation
 Basic idea

Procedural animation
hum : humidity
act : activation
cld : cloudtime tiphysically-based simulation(fluid simulation)

time ti+1

 Three logical variables at each cell‘hum·: there is enough vapor‘act·: phase transition is ready to occur‘cld·: clouds exist or not Basic idea

time tihum : humidity
act : activation
cld : cloudtime ti+1 Status of variables: 0 or 1
 Simple transition rules by Boolean operations- cloud growth- cloud extinction- advection by wind

Procedural animation

Procedural animation

 Rules for cloud growth [Nagel92]

 Rules for cloud extinction

time ti+1

time ti

hum
cld
actzx

act=0
act=1

act=0
act=1

y

hum=0
hum=1

phase transition effects

humid active/humid cloudpropagation of activation
variablesz(cloud growth)yx
act 䠖activationhum 䠖humidity:cld=0cld 䠖cloud
cld=1

supply ‘KXP·& ‘act ‘

hum=0
hum=1

cld=0cld=1

empty

Formation and extinction occur repeatedlyProcedural animation

Procedural animation

 Controlling distribution of clouds

 Controlling distribution of clouds

1 humid area(spheres/elipsoids in 3D)

1 humid area(spheres/elipsoids in 3D)

2 change ‘KXP· & ‘DFW·
from 0 to 1

2 change ‘KXP· & ‘DFW·
from 0 to 1
3 clouds are formed
4 change ‘cld·IURPWR
Controlling red area
Controlling cloud shapes & motion

Procedural animation

Procedural animation

 Advection by wind

 demo

Shifting variables toward the wind direction
cldhumactwind direction

Procedural animation

Procedural animation

 Creation of continuous distribution

 Example

q center density
fieldfunction

metaballReffective
radiusmetaball• radius: specified by user ( cell width x 1.5 in our case)• center density: filtered valueModeling of Clouds

Cloud Formation

 Image-based modeling Required physical quantities

Use of 2D images to synthesize density
distribution of 3D clouds

 Procedural animation
Cellular automata: simple rules to compute
motions of clouds

 Physically-based simulation

Velocity, water vapor, water droplet (cloud),temperature of atmosphere Phase transition between vapor and droplet
Generation/extinction of clouds



Cloud growth to higher region

Numerical simulation of atmospheric fluiddynamics

Overview of Cloud Formation Process
Ground is heated by the sun.

Overview of Cloud Formation Process
Air parcels start to move upward.

air parcels

Overview of Cloud Formation Process
Temperature of air parcels decreases.

buoyancyforce

Overview of Cloud Formation Process
Clouds are generated due to phase transition
phase transition

adiabaticexpansion/cooling(vaporcloud)Overview of Cloud Formation Processlatent heat isliberated due tophase transition

phase transition(vaporcloud)Overview of Cloud Formation Process

Overview of Cloud Formation Processlatent heat isliberated due tophase transition

phase transition(vaporadditional buoyancycloud)Equations for cloud simulation
 Velocity of atmosphere

latent heat isliberated due tophase transition
additional buoyancy

phase transition(vaporcloud)Navier-Stokes equation + buoyancy force

 Temperature of atmosphere

adiabatic cooling, latent heat, heat from ground Cloud formation/extinction

further cloud growth

Numerical Simulation

phase transition between vapor and droplets

Simulation Results Cumulus clouds

Velocity of atmosphere

Temperature of atmosphere

Number of grids : 150㽢
㽢120㽢50
Water vapor and water droplet

Computational time: 4 sec./stepcomputer : Pentium III 1.2GHz

VideoSimulation Results Cumulonimbus

VIDEO

Number of grids : 150㽢
㽢120㽢100
Computational time: 8 sec./stepcomputer: Pentium III 1.2GHz

Control of Cloud Formation

Control of Cloud Formation

 User draws contour line of the desired shape.

 User draws contour line of the desired shape.
 System controls simulation and generates realistic clouds

Overview of Cloud Formation Process

nt heat islatent
ated duliberated
due toe transition
trans
phase

Feedback Control
 Latent heat controller Water vapor supplierphase transition

target shape((vapor cloud)l d)additional buoyancy
uoo The cloud growth is controlled byadjusting the amount of latent heatfurther cloudd growththHtargetHc / Htarget
Hcsimulated clouds

Feedback Control

Feedback Control

 Latent heat controller Water vapor supplier Latent heat controller Water vapor suppliertarget shapeHtarget

target shape

simulated clouds

simulated clouds

Hc / Htarget

Hc / Htarget
increase latent heat

Hclatent heat controller

latent heat controller

Feedback Control

Feedback Control

 Latent heat controller Water vapor supplier Latent heat controller Water vapor supplierwater vapor supplierwater vapor supplier
add water vapor

target shape
simulated clouds

Hc / Htarget

increase latent heat

latent heat controller

ExampleTypical cloud shapes

No. of grid points : 320㽢80㽢100– Comp. time : 7.6 sec. per single time step–simulated clouds

 Generation of clouds
Hc / Htarget
 Cloud development

increase latent heattarget shapelatent heat controller

Example using Photograph Creating target shape from real photographNo. of grid points : 320㽢80㽢100– Comp. time : 7.6 sec. per single time step–

Unnatural Clouds

Creating holes inside clouds to form skull-shapedclouds––

No. of grid points : 240㽢80㽢100Comp. time : 5.6 sec. per single time step