1 INTRODUCTIONINTRODUCTION VIS98 Tutorial Level-of-Detail in Surface and Volume Modeling Leila De Floriani University of Genova Genova (Italy) Enrico Puppo National Research Council Genova (Italy) Roberto Scopigno National Research Council Pisa (Italy)

2 INTRODUCTIONINTRODUCTION VIS98 Tutorial Outline o Introduction o Surface Approximation with Triangle Meshes o Simplification Algorithms o LOD Models mPart one: a comprehensive framework for multiresolution mPart two: overview of LOD models mAnalysis and comparison o Applications mGraphics and virtual reality mGIS and flight simulation mVolume visualization

3 INTRODUCTIONINTRODUCTION VIS98 Tutorial 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 INTRODUCTIONINTRODUCTION VIS98 Tutorial...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: KB/sec local, KB/sec remote Gcommercial/home users: 56Kb/sec (in Italy) graphics file size: G24 byte/vertex ( if binary, >> if ascii )

5 INTRODUCTIONINTRODUCTION VIS98 Tutorial 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 INTRODUCTIONINTRODUCTION VIS98 Tutorial View Frustum Culling o an example of view frustum culling (images by SGI, OpenGL Optimizer) view frustum culling OFFculling ON

7 INTRODUCTIONINTRODUCTION VIS98 Tutorial Visibility Culling o an example of occlusion/visibility culling (images by SGI, OpenGL Optimizer)

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 VIS98 Tutorial

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 INTRODUCTIONINTRODUCTION VIS98 Tutorial …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