January 21, 2003 Multiresolution (ECS 289L) - Winter 2003 1

visualization and graphics research group

CIPIC

Dynamic View-Dependent Simplification for Polygonal

Models

By Julie C. Xia and Amitabh Varshney

Presented byJaya Sreevalsan Nair and Christopher Co

January 21, 2003 Multiresolution (ECS 289L) - Winter 2003 2

visualization and graphics research group

CIPIC

Introduction

Problem:

Meshes too large

AND

Simplified mesh not necessarily visually accurate

Desire:

Visual accuracy of fine meshes with the efficiency of coarse representation

Image from Xia96

January 21, 2003 Multiresolution (ECS 289L) - Winter 2003 3

visualization and graphics research group

CIPIC

Previous Work (1/2)

• Level-of-Detail (LOD) Representations for Mesh Simplification

– Statically generated• Vertex deletion (Schroeder et al) ,Vertex collapse (Rossignac and

Borrel) , Edge collapse (Hoppe et al), Wavelet Decomposition (Gross et al), etc.

• Curvature-guided simplification, proposed by Hamann and Turk• Change in tolerance volume (Gueziec)

– Dynamically generated• Progressive Meshes (Hoppe)

– ( M0, { split0, split1, split2, … splitk-1} )

– selective refinement– Continuous LOD

January 21, 2003 Multiresolution (ECS 289L) - Winter 2003 4

visualization and graphics research group

CIPIC

Previous Work (2/2)

• Issues not addressed by Progressive Mesh Representation

– Non-optimal series of edge collapses (distance metric driven)

– Linear time complexity for accessing node

– No efficient updating of frame-to-frame selective refinements

January 21, 2003 Multiresolution (ECS 289L) - Winter 2003 5

visualization and graphics research group

CIPIC

Guidelines for Image-Space Simplification

• Local Illumination

• Screen-Space Projections

• Visibility Culling

• Silhouette boundaries

January 21, 2003 Multiresolution (ECS 289L) - Winter 2003 6

visualization and graphics research group

CIPIC

Overview of the Method

• Hierarchy Construction– Preprocessing– Static

• Hierarchy Traversal– Run time– Dynamic

January 21, 2003 Multiresolution (ECS 289L) - Winter 2003 7

visualization and graphics research group

CIPIC

Construction

• Merge tree (binary tree)– Edge collapse– Parent – child relationships– Euclidean distance stored (“upswitch” and “downswitch”)

• Region of Influence

• Termination– User specified minimum number of vertices– No more legal edge collapses

• Dependencies

January 21, 2003 Multiresolution (ECS 289L) - Winter 2003 8

visualization and graphics research group

CIPIC

Example for dependencies

Image from Xia96

January 21, 2003 Multiresolution (ECS 289L) - Winter 2003 9

visualization and graphics research group

CIPIC

Traversal

• Choosing display vertices– Check Upswitch / Downswitch distances

• T > U : Vertex marked “inactive” for display

• T < D : More refinement needed

– Check dependencies• To select final list of display vertices

– Frame-to-frame coherence• Display vertex list for the next frame

• Choosing display triangles– Interleaved with display vertex selection

• Immediate deletion and addition of triangles

January 21, 2003 Multiresolution (ECS 289L) - Winter 2003 10

visualization and graphics research group

CIPIC

Results(1/2)

Image from Xia96

January 21, 2003 Multiresolution (ECS 289L) - Winter 2003 11

visualization and graphics research group

CIPIC

Results(2/2)

Image from Xia96

January 21, 2003 Multiresolution (ECS 289L) - Winter 2003 12

visualization and graphics research group

CIPIC

Conclusion (Pros vs. Cons)

Contribution• Data structure (merge tree) for efficient mesh update for

continuous LOD representation

Advantages• Continuous LOD• Incremental update between frames• Avoids illegal edge collapses efficiently• Logarithmic vertex lookup

Disadvantages• What should T be?• In core• Storage overhead (linear)

January 21, 2003 Multiresolution (ECS 289L) - Winter 2003 13

visualization and graphics research group

CIPIC

Outside Reading

• H. Hoppe. Progressive Meshes. Computer Graphics Proceedings, Annual Conference Series, ACM SIGGRAPH, 1996.

• J. Xia, J. El-Sana, and A. Varshney. Adaptive Real-Time Level-of-detail-based Rendering for Polygonal Models. IEEE Transactions on Visualization and Computer Graphics. Vol. 3, No. 2, June 1997, pp 171 - 183