“Graphical Modeling and Animation of Brittle Fracture” by James F. O’Brien and Jessica K. Hodgins, Georgia Institute of Technology

“A Morphable Model for the Synthesis of 3D Faces” by Volker Blanz and Thomas Vetter, Max-Planck-Institut für Biologische Kybernetik

“Teddy: A Sketching Interface for 3D Freeform Design” by Takeo Igarashi and Hidehiko Tanaka, University of Tokyo, and Satoshi Matsuoka, Tokyo Institute of Technology

CHAOS Meeting!Bill White will present an overview of three papers that were presented at this year’s SIGGRAPH. These papers were selected as being expected to have the greatest overall impact on computer graphics and interactive techniques.

WednesdaySeptember 8, 1999

4:30 - 5:30 PMPeck Hall 2304

“Graphical Modeling and Animation of Brittle Fracture”

James F. O’Brien and Jessica K. Hodgins

Georgia Institute of Technology

Previous work in modeling breaking objects either:

•simulated material deformations , generating a fracture whenever the distance between originally close nodes exceeded a certain size, or

•used virtual springs to connect masses together until the springs were pulled too far apart.

The two main drawbacks to these techniques:

•the exact location and orientation of the fractures is unknown, and

•the fracture surfaces are limited to the boundaries of the original mesh structure.

This work remedies these two problems by structuring the breakable objects as a 3-D mesh of tetrahedra, each of which can be split into multiple tetrahedra after being fractured.

An adobe wall struck by a wrecking ball. The wall is attached to the ground.

The same adobe wall struck by a wrecking ball with 50 times the original wrecking ball’s mass.

(a) The initial mesh used to generate the face of the adobe wall that is struck by the wrecking ball.

(b) The (reassembled) mesh after being struck by the wrecking ball.

(c) Same as (b), with cracks emphasized.

(d) Internal fractures shown as a wireframe.

A simple object and its

tetrahedron mesh.

Opening Mode

In-Plane Shear Mode

Out-Of-Plane Shear Mode

The force modesthat could make the object open further.

(a) The original tetrahedral element.

Splitting a Tetrahedral Element with a Fracture Plane

(b) The splitting node and fracture plane.

(c) The element is split into polyhedra that are decomposed into tetrahedra.

Comparison of a Real-World Event and a Simulation

A physical ceramic bowl dropped from one meter

onto a hard surface.

A simulation matching the initial conditions of

the physical bowl.

“A Morphable Model for the Synthesis of 3D Faces”Volker Blanz and Thomas Vetter

Max-Planck-Institut für Biologische Kybernetik

A data set of A data set of prototypical of 3D facial prototypical of 3D facial

scans is used...scans is used...

……along with a 2D along with a 2D image of a face...image of a face...

……to produce a parameterization of to produce a parameterization of the 2D face as a linear combination the 2D face as a linear combination

of the faces in the database...of the faces in the database...

……that can be that can be manipulated to manipulated to

have a new have a new orientation, orientation, expression, expression,

etc.etc.

Making New Faces from Old Ones

Halfway between the average and

the prototype

The “Anti-Face”- As far from

the average as the prototype,

but in the opposite way!

TheOriginal

The 3DModel

TheColor Map

The 3DReconstruction

Reorientations

“Teddy: A Sketching Interface for 3D Freeform Design”

Takeo Igarashi & Hidehiko Tanaka, University of Tokyo

Satoshi Matsuoka, Tokyo Institute of Technology

Creating a 3D object with a 2D

input stroke.

Painting on the surface of the 3D object with a 2D input stroke.

Creating an extrusion from the 3D object with a closed stroke, followed by a rotation, and then an extrusion stroke.

Cutting off part of the 3D object with a 2D input

stroke.

Adding an extrusion after cutting the object.

Scribbling to

erase a feature.

Scribbling to smooth off a surface.

Creating the 3D Object

Original Polygon

Triangulation into Terminal, Sleeve,

and Junction Triangles

Chordal Axis

Retriangulation into Fans

Spine

Final Retriangulatio

n

Spines are elevated,

quarter ovals are generated,

and then triangulated as

a 3D mesh.