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Shape Deformations . Wolfram von Funck / Holger Theisel / Hans-Peter Seidel. MPI Informatik. ACMSIGGRAPH 2006. Computer Graphics Lab.. SoHyeon Jeong. 2007/04/16. Contents. Introduction . Constructing the vector field . ID: 259012

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## Presentations text content in Vector Field Based

Vector Field Based

Shape Deformations

Wolfram von Funck / Holger Theisel / Hans-Peter SeidelMPI Informatik

ACMSIGGRAPH 2006

Computer Graphics Lab.SoHyeon Jeong2007/04/16

Slide2Contents

Introduction Constructing the vector field Modeling metaphors Implementational DetailsEvalutation and Comparison

2

Slide31. Introduction

3

Slide4Shape Deformation

Original shape

New Deformed shape

Performance

Detail & Feature preservation

Volume preservation

Avoidance of self-intersections

Deformation metapor

Transformation with Constraints

4

Slide5Deformation Metaphors

Free movement of certain handlesSingh and Fiume 1998Bendels and Klein 2003Pauly et al. 2003 9-dof object Botsch and Kobbelt 2004

Two Handed metaphorLlamas et al. 2003New Metaphor Implicit tools

?

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Slide6Modeling Metaphors: Implicit Tools

IdeaUse simple implicit objects as deformation tools

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Slide7Deformation Approaches

Mapping problemFinding a mapping transformation between the original and the new deformed shapeFinding path problemFinding continous path that certain point should follow

7

Slide8Finding Paths Problem

Integration of vector field at time T Similar to “flow of fluid” [Foster and Fedkiw 2001]

scaling

Translation

Rotation

8

Slide9The Main Idea to Solve

Constructing vector fields that produce useful deformation Computing deformation by integrating using vector fieldsFlexibleVariety of different deformationsTranslations & rotationsSimple Fast computation Interactivity & large mesh deformation

9

Slide10Properties of Vector Fields

Simple local properties of vector

Global and local properties of shape deformation

Divergence-free C1 continuity Time-dependent path integration

Volume preservation[Davis 1967] Smooth deformation No self-interaction[Theisel et al. 2005]

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Slide112. Constructing the Vector Fields v

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Slide12Piecewise Region Field

Inner regionWell-defined regionOuter regionNo deformationIntermediate regionBlending between Inner & Outer regionDivergence-freeC1 continuity

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Slide13Piecewise Region Field

Region Field :

Inner region Intermediate region Outer region

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4

4

4

4

4444433333334432222234432111234432101234432111234432222234433333334444444444

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Slide14Terms

Scalar field Gradient Co-gradient Divergence

2D 3D

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Slide15Constructing the Deformation Vector Field V

Constructing a divergence-free vector field 2D Co-gradient field of a scalar field [Davis 1967] :3D Cross product of gradients of two scalar fields

15

Slide16Constructing the Deformation Vector Field V (3D)

Define scalar field in terms of region fieldConstruct divergence-free field using defined scalar fields

: Berstein polynomials

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Slide17Blending intermediate region

Inner & outer region should be connected smoothly It requires C1 continuity Scalar fields : C2 continuity Vector field : C1 continuity

e(

x

)

0

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Slide18Blending: 2D Example

inner region

v

constant

outer region

v

= 0

intermediate

region

1

0

-1

1

0

-1

1

0

-1

1

0

-1

1

0

-1

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Slide192D Example

Region Field

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Slide20Special Deformations - Translation

Translation vector field : A constant vector fieldThe center point c : to determine DOF

: The center point

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Slide21Special Deformation - Rotation

Rotation vector field : linear vector field v and rA center point : An Axis :Ristrected as a cylinder

21

Slide22Vector Field

Translation

Rotation

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Slide233. Modeling Metaphor

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Slide24Deformation Cycle

Usually r(x) : the distance to a certain point c : the center of the inner region u, w, a : determined by interactive input device(mouse)IntegrationIf tool moves , the integration inside the inner region moves the points by The step size of the path line integration is chosen so that the path line follows the path of the tool

Define region field r(x) with ri, ro and c

Define scalar field e(x), f(x)with orthogonal vector u, w, a center c and an axis a

Update v

Integrate point of the shape with v

24

Slide25Implicit Tools

Point toolsPoints in the inner regionat the beginning followthe movement of the toolOther points never enter the inner region no self-intersectionLine tools

25

Slide26Deformation Paint

The tool is moved along a path on the surface : the location of the point on the shape at a certain time , = choosen interactively

26

Slide27Moving Point Sets

Multiple isolated point set the shape : Smooth approximated distance function to this point set , : interactively choosen : Barycenter of all points

27

Slide28Collision Tools

An arbitrary closed tool shape for which a repeated collistion detection with the deformed shapeFind collision region using Bounding box hierarchy Setting Collision detected points :r = smooth approximated distance function along with ri = 0Inner region is constant It follows the path of the input device

6

5

4

3322543221143211003210011210112210122331012344

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Slide29Collision Tools : Example 1

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Slide30Collision Tools : Example 2

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Slide31Twisting & Bending

Linear and quadratic vector fieldTwsiting : linear : direction of the twisting axis : on the twising axis

31

Slide32Twisting & Bending

BendingUsing a rotation ,

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Slide33Twisting & Bending

twisting

bending

33

Slide34Feature Preservation

Details on the surface are preserved during deformation

34

Slide354. Implementation

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Slide36Integration with adaptive stepsize

Best tradeoff between speed and accuracy [Nielson et al. 1997]4th order Runge-Kutta integration with adaptive stepsize

36

Slide37Remeshing

Large deformation causes unpleasing artifactsUndersample Volume changingIdeaRemeshing both the original and deformed objectNew vertices undergo same deformation as the original vertices

It Requires

remeshing

37

Slide38Remeshing

M : original mesh, M’ : deformed mesh, P : deformation path M and P are storedAll edges of the M’ are tested for refinementlength(edge) > thresholdAngle between the normals of the end-vertices is large Edge split on both M and M’New vertices of M are deformed using PDiffusion of the vertices Guarantee a uniform distribution of the verticesVertices moves to the barycenter of its 1-ringVertex is projected back onto the surface of the undiffused mesh Repeated a fixed number of stepsDecimation steplength(edge) < thresholdSmall anglePerform step 3 again for collapsed points

collapsed

38

Slide395. Evaluation and Comparision

39

Slide40Visual Quality

The twisting of a box

[Yu et al 2004]

[Proposed]

[Lipman et al. 2005]

[Zhou et al. 2005]

40

Slide41Visual Quality

Bending a sylinder

[Proposed]

[Laplacian surface]

[Poisson Mesh]

[Zhou et al. 2005]

[Botsch and Kobbelt 2004]

41

Slide42Speed

FactorsVertex # in inner, intermediate regionVertex # in intermediate effects more than vertex # of inner region Modeling metaphorRegion field r Simple r gives a higher performanceCollision detection step in shape stampingDeformation is highly parallelizable using GPU4th order Runge-Kutta path line integration of points Read-back of the computed points drops performces But still 10 times faster than CPU

42

Slide43Speed

Implementation EnvironmentAMD Opteron 152(2.6 GHz) 2GB RAM GeForce 6800 GT GPU

43

Slide44Accuracy

Accuracy in volume Discrete surface points produces slight changes of the vlumeBut is tolerable

44

Slide456. Conclusion and Future Work

45

Slide46Conclusion

Alternative approach to shape deformation Time-dependent divergence-free vector field volume-preservingSelf-intersection Sharp features Realtime deformationAccuracy in volume preserving is high

46

Slide47Future Work

Preformance can futher be increased Multi-processor parallelization of the integration Integration of vertices is carried out independentlyApplcation to point-based shape representationDoes not rely on any connectivity information of the meshModeling metaphor can be extendedFull and zero deformation can be marked explicitly on the surfaces

47

Slide48Slide49