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N T R O D U C T I O N
EG99 Tutorial
Level-of-Detail in
Surface and Volume Modeling
Leila De Floriani, Enrico Puppo
University of Genova Genova (Italy)
Paolo Cignoni, Roberto Scopigno
National Research Council Pisa (Italy)
I N T R O D U C T I O N
Outline
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Introduction
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Surface Approximation with Triangle Meshes
o
Simplification Algorithms
o
LOD Models
mPart one: a comprehensive framework for multiresolution
mPart two: overview of LOD models
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N T R O D U C T I O N
EG99 Tutorial
Motivations
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High complexity of 3D scenes
mautomatic acquisition of the surface of solid objects Grange scanners -- 3D scanners
Gresolution supported: ~ 10 facets / mm2
mstandard solid modeling tools (CAD) Gcomplex 3D object defined by # faces > 100K
mdigital terrain models Gmillions of faces
mtessellation of implicit surfaces
I N T R O D U C T I O N
...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 )
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N T R O D U C T I O N
EG99 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
I N T R O D U C T I O N
View Frustum Culling
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an example of view frustum culling
(images by SGI, OpenGL Optimizer)
view frustum
culling OFF culling ON
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N T R O D U C T I O N
EG99 Tutorial
Visibility Culling
o
an example of occlusion/visibility culling
(images by SGI, OpenGL Optimizer)
I N T R O D U C T I O N
Level of Detail:
Approximating surfaces with triangle meshes
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Assumption:
maccuracy of the approximation is proportional to the number of triangles
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Objective:
malways produce the simplest mesh that satisfies the accuracy required by the application
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N T R O D U C T I O N
EG99 Tutorial
…Approximating Surfaces...
o
On-the-fly simplification:
extract from raw data a mesh of minimal size whose accuracy is sufficient for application needsGonly raw data and the simplified mesh are stored Gsimplification is usually an expensive task
I N T R O D U C T I O N
…Approximating Surfaces...
o
LOD / multiresolution model:
build a model off-line that encompasses many different representations and that can be queried efficientlyGmore expensive in terms of space
Gmore efficient: support to real-time operations
