1. 1 INTRODUCTIONINTRODUCTION Multiresolution Meshes in Surface Modeling Leila De Floriani DISI - University of Genova (Italy) and UMIACS Joint work with Paola Magillo and Enrico Puppo (DISI - University of Genova)

2. 2 INTRODUCTIONINTRODUCTION Outline o Introduction: motivations and background o LOD Models: layered versus multiresolution models o A general framework for multiresolution models: the Multi- Triangulation o Classification of Multiresolution Models: tree-like and evolutionary models o Tree-like Models: nested models based on regular or irregular subdivisions o Evolutionary Models: construction strategies and encoding structures o A taxonomy for multiresolution models

3. 3 INTRODUCTIONINTRODUCTION Motivations o High complexity of 3D scenes mautomatic acquisition of the surface of solid objects Grange scanners -- 3D scanners Gresolution supported: ~ 10 facets / mm 2 mstandard solid modeling tools (CAD) Gcomplex 3D object defined by # faces > 100K mdigital terrain models Gmillions of faces mtesselation of implicit surfaces

4. 4 INTRODUCTIONINTRODUCTION...Motivations... o 3D graphics is a limited, valuable resource mgraphics throughput of low level ws / pc : ~100K faces/sec minteractivity requires multiple frames per second mweb graphics (VRML) needs trasmission of data on low bandwidth networks Gscientific users: 300-500KB/sec local, 10 - 100KB/sec remote Gcommercial/home users: 56Kb/sec (in Italy) graphics file size: G24 byte/vertex ( if binary, >> if ascii )

5. 5 INTRODUCTIONINTRODUCTION Reducing Graphics Costs o Visualization Stage: mculling back faces mview frustum culling mvisibility culling o Modeling Stage: mtessellate surfaces with triangle meshes msimplify meshes mconstruct a LOD model

6. 6 INTRODUCTIONINTRODUCTION View Frustum Culling o an example of view frustum culling (images by SGI, OpenGL Optimizer) view frustum culling OFFculling ON

7. 7 INTRODUCTIONINTRODUCTION Visibility Culling o an example of occlusion/visibility culling (images by SGI, OpenGL Optimizer)

8. 8 INTRODUCTIONINTRODUCTION Level of Detail: Approximating surfaces with triangle meshes o Assumption: maccuracy of the approximation is proportional to the number of triangles o Objective: malways produce the simplest mesh that satisfies the accuracy required by the application

9. 9 INTRODUCTIONINTRODUCTION …Approximating Surfaces... o On-the-fly simplification: extract from raw data a mesh of minimal size whose accuracy is sufficient for application needs Gonly raw data and the simplified mesh are stored Gsimplification is usually an expensive task

10. 10 INTRODUCTIONINTRODUCTION …Approximating Surfaces... o LOD / multiresolution model: build a model off-line that encompasses many different representations and that can be queried efficiently Gmore expensive in terms of space Gmore efficient: support to real-time operations LOD model