Volumetric methods for the real-time display of natural gaseous phenomena [Elektronische Ressource] / vorgelegt von Stefan Roettger

Sujets

• Informatik

Informations

• Publié par: universitat_stuttgart
• Publié le: 01 janvier 2004
• Nombre de lectures: 7
• Langue: English
• Poids de l'ouvrage: 25 Mo

Extrait

Volumetric Methods for
the Real-Time Display of
Natural Gaseous Phenomena
Von der Fakultat¨ Informatik, Elektrotechnik und
Informationstechnik der Universitat¨ Stuttgart
zur Erlangung der Wurde¨ eines Doktors der
Naturwissenschaften (Dr. rer. nat.) genehmigte Abhandlung
Vorgelegt von
Stefan Roettger
aus Erlangen
Hauptberichter: Prof. Dr. T. Ertl
Mitberichter: Prof. Dr. M. Stamminger
Prof. Dr. W. Heidrich
Tag der mundlichen¨ Prufung:¨ 2. Juni 2004
Institut fur¨ Visualisierung und Interaktive Systeme
der Universitat¨ Stuttgart
20042Contents
1 Motivation and Outline 8
2 The OpenGL Rendering Pipeline 11
2.1 Basic Layout of the Rendering Pipeline . . . . . . . . . . . . . . 11
2.2 Rendering Example . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.3 Lighting and Texturing . . . . . . . . . . . . . . . . . . . . . . . 15
2.3.1 Direct Lighting . . . . . . . . . . . . . . . . . . . . . . . 16
2.3.2 Texture Mapping . . . . . . . . . . . . . . . . . . . . . . 19
2.4 Programmable Graphics Hardware . . . . . . . . . . . . . . . . . 21
2.4.1 Vertex Shaders . . . . . . . . . . . . . . . . . . . . . . . 22
2.4.2 Pixel and Fragment Programs . . . . . . . . . . . 23
3 A Brief History of Terrain Rendering 26
3.1 Data Representation . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.2 TINs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.3 S-LOD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.4 Progressive Meshes . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.5 C-LOD Algorithms . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.5.1 Lindstrom’s Algorithm . . . . . . . . . . . . . . . . . . . 30
3.5.2 Duchaineau’s . . . . . . . . . . . . . . . . . . 33
3.5.3 Roettger’s Algorithm . . . . . . . . . . . . . . . . . . . . 35
3.6 Future Development . . . . . . . . . . . . . . . . . . . . . . . . 39
4 The Terrain Rendering Pipeline 40
4.1 Landscape Data Generation . . . . . . . . . . . . . . . . . . . . . 41
4.2 Real Time Display of the Terrain . . . . . . . . . . . . . . . . . . 41
4.3 Terrain Material . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.4 Terrain Illumination . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.5 Organic Features . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.6 Global Volumetric Effects . . . . . . . . . . . . . . . . . . . . . 43
4.7 Volumetric Effects in Practice . . . . . . . . . . . . . . . . . . . 44
34 CONTENTS
5 Natural Gaseous Phenomena 46
5.1 Sky Dome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.2 OpenGL Fog . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.3 Layered Fog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
5.4 Bounded Layered Fog . . . . . . . . . . . . . . . . . . . . . . . . 51
5.5 Billboards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
5.6 Metaball Methods . . . . . . . . . . . . . . . . . . . . . . . . . . 52
5.7 Impostor Based Methods . . . . . . . . . . . . . . . . . . . . . . 53
6 Volume Rendering: The Basics 57
6.1 Basic Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
6.2 The Rendering Equation . . . . . . . . . . . . . . . . . . . . . . 57
6.3 The Ray Integral . . . . . . . . . . . . . . . . . . . . . . . . . . 59
6.4 Light Scattering in Participating Media . . . . . . . . . . . . . . . 60
6.5 Rendering Solutions for Participating Media . . . . . . . . . . . . 61
7 Direct Volume Rendering 63
7.1 Transfer Functions . . . . . . . . . . . . . . . . . . . . . . . . . 63
7.2 Grid Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
7.3 Ray Casting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
7.4 Slicing via 3D Textures . . . . . . . . . . . . . . . . . . . . . . . 66
8 Pre-Integrated Cell-Projection 68
8.1 Visibility Sorting . . . . . . . . . . . . . . . . . . . . . . . . . . 68
8.2 The Original PT Algorithm . . . . . . . . . . . . . . . . . . . . . 69
8.3 Drawbacks of the Original PT Algorithm . . . . . . . . . . . . . 70
8.4 PT with Accurate Opacity and Color . . . . . . . . . . . . . . . . 71
8.5 A New Approximation for PT . . . . . . . . . . . . . . . . . . . 74
8.6 Prior Work about Isosurfaces . . . . . . . . . . . . . . . . . . . . 75
8.7 Hardware-Accelerated Marching Cells . . . . . . . . . . . . . . . 76
8.8 Flat-Shaded Isosurfaces . . . . . . . . . . . . . . . . . . . . . . . 77
8.9 Smoothly Shaded Isosurfaces . . . . . . . . . . . . . . . . . . . . 79
8.10 Colored and Multiple Isosurfaces . . . . . . . . . . . . . . . . . . 80
8.11 Mixing Isosurfaces with Projected Volumes . . . . . . . . . . . . 81
8.12 Performance Comparison . . . . . . . . . . . . . . . . . . . . . . 83
8.13 Heaviside Excursion . . . . . . . . . . . . . . . . . . . . . . . . 84
8.14 Pre- vs. Post-Classification . . . . . . . . . . . . . . . . . . . . . 85
9 Unstructured Volume Rendering on the PC 88
9.1 High Resolution Ray Integral . . . . . . . . . . . . . . . . . . . . 88
9.1.1 Opacity Reconstruction . . . . . . . . . . . . . . . . . . . 88CONTENTS 5
9.1.2 Chromaticity Reconstruction . . . . . . . . . . . . . . . . 90
9.2 Hardware Accelerated Pre-Integration . . . . . . . . . . . . . . . 91
9.3 Performance Measurements . . . . . . . . . . . . . . . . . . . . . 95
10 Ground Fog Rendering 98
10.1 Theoretical Performance . . . . . . . . . . . . . . . . . . . . . . 99
10.2 Practical Analysis . . . . . . . . . . . . . . . . . . . 99
10.3 Projected Convex Polyhedra Algorithm (PCP) . . . . . . . . . . . 100
10.4 Applications of the PCP Method . . . . . . . . . . . . . . . . . . 102
11 Cloud Rendering 106
11.1 View-Dependent Rendering . . . . . . . . . . . . . . . . . . . . . 106
11.2 C-LOD Rendering . . . . . . . . . . . . . . . . . . . . . . . . . 107
11.3 Generating Continuous Levels of Detail . . . . . . . . . . . . . . 107
11.3.1 Hierarchical Volume Representation . . . . . . . . . . . . 107
11.3.2 View-Dependent Mesh Simplification . . . . . . . . . . . 107
11.3.3 Building a Conforming Mesh . . . . . . . . . . . . . . . 109
11.3.4 Hierarchical Error Propagation . . . . . . . . . . . . . . . 109
11.4 Volumetric Morphing . . . . . . . . . . . . . . . . . . . . . . . . 110
11.5 Cell Projection . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
11.6 Non-Photorealistic Cloud Rendering . . . . . . . . . . . . . . . . 113
11.6.1 Modified PT Algorithm . . . . . . . . . . . . . . . . . . 114
11.6.2 Non-Photorealistic Lighting . . . . . . . . . . . . . . . . 114
11.7 Performance Measurements . . . . . . . . . . . . . . . . . . . . . 115
11.8 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
12 Summary 118
12.1 Decision Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
12.2 Availability and Licensing . . . . . . . . . . . . . . . . . . . . . 121
13 Zusammenfassung 140Acknowledgements
...I’ll just lie back and think pleasant thoughts. Chicken
pot pie... Chocolate covered RAIsins... EEGlazed
Hammmmm... They think I’m crazy... But I know
better... It is not I who am crazy... It is I who am MAD!...
Didn’t you hear ’em? Didn’t you see the crowds?!! Oh
my beloved ice cream bar... How I love to lick your
creamy center... eeyaaarghruch... eeyaarghrunch...
eeyaarghrunch... And your oh-so-nutty chocolate
covering... You’re not like the others... You like the same
things I do... Wax paper... Boiled football leather... Dog
breath... WE’RE NOT HITCHHIKING ANYMORE...
WE’RE RIDING...
Ren Hoek’¨ s insane ravings in “Space Madness”
First of all I would like to thank Martin Kraus of VIS, Stefan Guthe of WSI/GRIS,
and Ingo Frick of Massive Development for the great teamwork and all others
from the computer graphics labs in Erlangen, Tubingen,¨ and Stuttgart for their
support. They all have been a great help in writing this thesis.
On 7th February of 2002 I was lucky to become the father of my daughter Leonie.
I have to say the warmest thanks to my girl friend who so much cared about her
while I was busy writing, so this thesis is dedicated to my dear Leonie and Petra!
Stuttgart / Erlangen, 9th September 2004
Stefan Rottger¨
6Abstract
Blaise Pascal: The last thing one knows
in constructing a work
is what to put first.
Compared to the nineties where fast 3D graphics was the domain of expensive
workstations, in the last few years the development of ever faster 3D graphics
hardware was mainly driven by the gaming industry. The upcoming of pro-
grammable PC graphics hardware has opened the field for new graphics algo-
rithms which allow unprecedented realism in real time applications. Nevertheless,
one area of application is persistently resisting most efforts to achieve sufficient
rendering performance: This is the area of volume rendering. Because of the huge
amounts of data that have to be processed to obtain a three-dimensional visualiza-
tion, it is very challenging to achieve real time performance for large volumetric
data sets.
In this thesis we try to tackle this problem in one specific application field.
We devise algorithms that are suitable for the real time display of natural gaseous
phenomena. In particular our goal is to render clouds and fog in real time. In
principle, the problem reduces to solving the