Modeling of Clouds
 Procedural approach

fractals, noise functions, etc.

 Difficult to create realistic shapes

fractals/noises are useful for small-scaledetails
 overall shapes need to be specified by the user

Modeling of Clouds[[Gardner 1985][Nishita 1996][Schpok 2003]

Image-based Modeling

3D clouds from satellite images

 Use of a single photograph Density distribution using metaballs

 Not to reconstruct the same clouds Optimizing parameters of metaballs

 Using the photo as a guide to synthesize

similar clouds

positionradiuscenterdensity
Large-scale clouds
using satellite images

Cloud from a single
photographsatellite image

field
function

metaball

3D clouds from satellite images

3D clouds from satellite images

 Density distribution using metaballs

 Density distribution using metaballs

 Optimizing parameters of metaballs

 Optimizing parameters of metaballs

position

metaballs

positionradiuscenterdensitysatellite image

radiuscenterdensityfieldfunction

metaballsatellite image

field
function

metaball3D clouds from satellite images

3D clouds from satellite images

 Objective function

 Optimization processintensityy of pixel k of input satellite image

1. Create new metaball
2. Determine center position
3. Determine radius and density

cumulative ddensity of metaballs overlapping at pixel kf

4. Calculate error
5. If error < H then stop, otherwise go to 1

F = 6
6
metaballExamplesExamplessatellite image

synthesized clouds

No. of metaballs:

different viewpoint

8506

Computation time:

13 sec.

Rendering time:

3.7 min.
computer: SGI Indigo2 MAXIMUM IMPACT(195 MHz MIPS R10000)
video

Clouds from a single photograph

Overview of Our Method Three types of clouds

cirruscirrusaltocumulus

altocumulus

cumuluscumulusCalculation of cloud image

Modeling of cirrus

videoModeling of Cirrus

Modeling of Cirrus

 Cirrus cloudsThin and no self-shadows Two-dimensional textureUse of cloud image as 2D texture

Removing effect of perspective transformation byspecifying cloud plane
input image
cloud image
cloud planecirrus cloud texture

input photograph

Overview of Our Method

Modeling of Altocumulus
 Altocumulus

Thin but with self-shadows are observed
 Using Metaballs to define three-dimensional
density distributioncirrusmetaballmetaballaltocumulus

positionradiusModeling of altocumulus
cumuluscenterdensityfieldfunction

input photo

Optimizing Metaball Density

Specifying Cloud Plane Example

 Interactive specification

Orientation of cloud plane and viewing angle

cloud plane

cloud image

cumulative density image

Projecting Metaballs

Overview of Our Method

Projecting metaball center onto cloud plane Scaling metaball radius in proportion todistance from viewpoint

cloud plane
2D metaballs
viewpoint

cirrusaltocumulus
cumuluscumulus

Modeling of Cumulus

Computing Surface Shape Cumulus

 Converting cloud image into binary image

Generating surface shape Calculating densities inside surface shapecloud image

surface shape

3D density
distribution

cloud image

binary image

Computing Surface Shape

Computing Surface Shape Distance transform of binary image

 Use distance at medial axis as thickness of Extracting medial axes


Pixels where distances are local maxima
medial axis

binary image

distance image
distanceimage

clouds Propagate thickness by optimization
medial axis

cloud image

thickness image
colorization by optimization [Levin 04]

Computing Surface ShapeComputing Density Distribution

 Constructing surface shape Calculating bounding box of surface shapeAssuming symmetric shape with respect toimage plane

front view

 Subdividing bounding box into grid
 Calculating density at each grid pointside view

Results

Results

 Computer Cirrus

CPU: Intel Corei7 (3.33 GHz)
 Main memory: 4GB
 GPU: NVIDIA GeForce GTX 295
 Computation time

input image

cloud texture

input image

cloud texture

within 10 seconds

Results

Results

 Altocumulus

 Cumulus

input

input

synthesized

input

input

synthesizedsynthesizedsynthesizedResults

Results

 Modeling process A cloud scene