Applications of Evolutionary Computation to Quadrupedal Animal Animation

415 Pages·2011·54.53 MB·English

Applications of Evolutionary
Computation to Quadrupedal
Animal Animation
James E. Murphy
B.Sc. (Hons.)
The thesis is submitted to University College Dublin
for the degree of Ph.D. in the
College of Engineering, Mathematical and Physical Sciences
March 2011
School of Computer Science and Informatics
Head of School
Prof. Joe Carthy
Research Supervisors
Dr. Michael O’Neill
Dr. Hamish Carr
Abstract
As humans are familiar with animal movement, a realistic animal an-
imation must imitate this motion. This thesis explores how observations
of natural evolution and evolutionary computation can be used to pro-
duce realistic quadrupedal animal animations, focusing on the grammar-
based Genetic Programming method of Grammatical Evolution (GE).
A cross-discipline review of animation systems, biological knowledge
and natural computing techniques applicable to animal animation is pre-
sented. Focusing on the horse, the construction of both a kinematic and
physics-based model is described. The origins and representations of the
data used to construct and animate these models are also discussed.
GE is applied to animation problems for the first time. Animat-
ing physics-based models is complex and a GE motion optimisation sys-
tem successfully generates realistic, stable motions. Additionally, simple
grammars with little domain knowledge generate novel movement.
For herd scenes, a GE-based system generates models of varying mor-
phology and automatically optimises motion data for them. GE also
evolves motion adjuster functions that dynamically modify limb move-
ment based on the model’s velocity. These functions are used in a real-
time controllable kinematic animation system, in which a horse model
moveswithanaccurategaitandexecutesgaittransitionswhennecessary.
Overall, the use of GE and natural world observations is found to
facilitate the generation of realistic quadrupedal animal animations.
Acknowledgements
I wish to thank my supervisors Dr. Michael O’Neill and Dr. Hamish
Carr. I would also like to thank the members of the Natural Comput-
ing Research & Applications Group and the Imaging, Visualisation &
Graphics Group for their help and input.
Additionally I would like to acknowledge my university examiners,
Prof. Anthony Brabazon and Dr. Michela Bertolotto, my external ex-
aminer Prof. Simon Lucas and all others who have provided valuable
contributions and opinions.
This research is co-funded by IBM under IRCSET’s Enterprise Part-
nership Scheme and I am hugely grateful for this support.
Finally, I wish to thank my parents for their outstanding support
throughout my time in university and Emily for her great patience and
constant encouragement.
JAMES E. MURPHY
University College Dublin
March 2011
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Contents
List of Figures x
List of Tables xiii
List of Equations xiv
List of Grammars xv
List of Videos xvi
Publications arising xix
1 Introduction 1
1.1 Research aims . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1.1 Research questions . . . . . . . . . . . . . . . . . 4
1.2 Primary contributions . . . . . . . . . . . . . . . . . . . 5
1.3 Research and implementation decisions . . . . . . . . . . 11
1.4 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.5 Secondary contributions . . . . . . . . . . . . . . . . . . 15
1.5.1 Background research . . . . . . . . . . . . . . . . 16
1.5.2 Applications developed . . . . . . . . . . . . . . . 16
1.5.3 Animation techniques and data representations . 18
1.6 Structure of thesis . . . . . . . . . . . . . . . . . . . . . 19
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I Related work 22
2 Animation 24
2.1 History and applications . . . . . . . . . . . . . . . . . . 25
2.2 Kinematic animation . . . . . . . . . . . . . . . . . . . . 26
2.2.1 Hierarchical kinematic modelling . . . . . . . . . 28
2.3 Physics-based animation . . . . . . . . . . . . . . . . . . 32
2.3.1 Open Dynamics Engine . . . . . . . . . . . . . . . 35
2.4 Development of quadrupedal animation . . . . . . . . . . 38
2.4.1 Animation techniques . . . . . . . . . . . . . . . . 38
2.4.2 Gait generation . . . . . . . . . . . . . . . . . . . 46
2.5 Chapter summary . . . . . . . . . . . . . . . . . . . . . . 50
3 Natural computing 52
3.1 Biologically inspired algorithms . . . . . . . . . . . . . . 53
3.2 Evolutionary computation . . . . . . . . . . . . . . . . . 55
3.2.1 Evolutionary algorithm overview . . . . . . . . . 56
3.2.2 Evolutionary Programming . . . . . . . . . . . . 58
3.2.3 Evolutionary Strategies . . . . . . . . . . . . . . . 59
3.3 Genetic Algorithms . . . . . . . . . . . . . . . . . . . . . 59
3.3.1 Selection methods . . . . . . . . . . . . . . . . . . 61
3.3.2 Crossover . . . . . . . . . . . . . . . . . . . . . . 64
3.3.3 Mutation . . . . . . . . . . . . . . . . . . . . . . 65
3.3.4 Replacement strategies . . . . . . . . . . . . . . . 67
3.4 Genetic Programming . . . . . . . . . . . . . . . . . . . 68
3.4.1 Initialisation . . . . . . . . . . . . . . . . . . . . . 70
3.4.2 Crossover . . . . . . . . . . . . . . . . . . . . . . 73
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3.4.3 Mutation . . . . . . . . . . . . . . . . . . . . . . 74
3.5 Grammatical Evolution . . . . . . . . . . . . . . . . . . . 76
3.5.1 Implementation details . . . . . . . . . . . . . . . 77
3.5.2 Grammar . . . . . . . . . . . . . . . . . . . . . . 79
3.5.3 Genotype-phenotype mapping . . . . . . . . . . . 81
3.5.4 Initialisation . . . . . . . . . . . . . . . . . . . . . 85
3.5.5 Crossover . . . . . . . . . . . . . . . . . . . . . . 86
3.5.6 Mutation . . . . . . . . . . . . . . . . . . . . . . 89
3.6 Chapter summary . . . . . . . . . . . . . . . . . . . . . . 91
4 Biology 94
4.1 Equine evolution and breeding . . . . . . . . . . . . . . . 96
4.1.1 Natural evolution . . . . . . . . . . . . . . . . . . 96
4.1.2 Breeding . . . . . . . . . . . . . . . . . . . . . . . 98
4.2 Anatomy . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
4.2.1 Tissues involved in locomotion . . . . . . . . . . . 104
4.2.2 Bones and joints . . . . . . . . . . . . . . . . . . 106
4.3 Equine musculoskeletal system . . . . . . . . . . . . . . . 108
4.3.1 Neck and head . . . . . . . . . . . . . . . . . . . 109
4.3.2 Back and tail . . . . . . . . . . . . . . . . . . . . 110
4.3.3 Forelimb . . . . . . . . . . . . . . . . . . . . . . . 110
4.3.4 Hindlimb . . . . . . . . . . . . . . . . . . . . . . 113
4.3.5 Skeletal allometry . . . . . . . . . . . . . . . . . . 115
4.4 Movement . . . . . . . . . . . . . . . . . . . . . . . . . . 118
4.4.1 Gait patterns . . . . . . . . . . . . . . . . . . . . 118
4.4.2 Equine natural gaits . . . . . . . . . . . . . . . . 120
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4.4.3 Neck and back . . . . . . . . . . . . . . . . . . . 124
4.4.4 Transitions . . . . . . . . . . . . . . . . . . . . . 125
4.5 Dynamic similarity . . . . . . . . . . . . . . . . . . . . . 127
4.5.1 Predictions from dynamic similarity . . . . . . . . 129
4.5.2 Discussion and applications . . . . . . . . . . . . 131
4.6 Chapter summary . . . . . . . . . . . . . . . . . . . . . . 132
4.7 Part I summary . . . . . . . . . . . . . . . . . . . . . . . 134
II Model creation and manual gait generation 136
5 Horse model 138
5.1 Data and animation type . . . . . . . . . . . . . . . . . . 139
5.1.1 Origins of data . . . . . . . . . . . . . . . . . . . 140
5.1.2 Skeletal simplifications for animation . . . . . . . 142
5.2 Kinematic model . . . . . . . . . . . . . . . . . . . . . . 145
5.2.1 OpenGL . . . . . . . . . . . . . . . . . . . . . . . 145
5.2.2 Model construction . . . . . . . . . . . . . . . . . 147
5.3 Physics-based model . . . . . . . . . . . . . . . . . . . . 150
5.3.1 Model construction . . . . . . . . . . . . . . . . . 150
5.3.2 Motion . . . . . . . . . . . . . . . . . . . . . . . . 154
5.3.3 Spring-damper system . . . . . . . . . . . . . . . 156
5.4 Chapter summary . . . . . . . . . . . . . . . . . . . . . . 160
6 Gait motion data and representations 161
6.1 Data origins . . . . . . . . . . . . . . . . . . . . . . . . . 162
6.1.1 Photographic . . . . . . . . . . . . . . . . . . . . 162
6.1.2 Motion capture . . . . . . . . . . . . . . . . . . . 165
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6.1.3 Published . . . . . . . . . . . . . . . . . . . . . . 166
6.2 Representations . . . . . . . . . . . . . . . . . . . . . . . 168
6.2.1 Sinusoids for cyclical motion . . . . . . . . . . . . 170
6.2.2 Piecewise for transitional motion . . . . . . . . . 173
6.3 Chapter summary . . . . . . . . . . . . . . . . . . . . . . 178
7 Manual motion data optimisation 180
7.1 Kinematic CMA . . . . . . . . . . . . . . . . . . . . . . . 181
7.1.1 Interaction . . . . . . . . . . . . . . . . . . . . . . 182
7.1.2 Visualisations . . . . . . . . . . . . . . . . . . . . 183
7.1.3 Applications . . . . . . . . . . . . . . . . . . . . . 186
7.2 Physics-based MDDE . . . . . . . . . . . . . . . . . . . . 186
7.2.1 Interface . . . . . . . . . . . . . . . . . . . . . . . 188
7.2.2 Animation and motion data editing . . . . . . . . 189
7.2.3 Visualisation and verification . . . . . . . . . . . 194
7.2.4 Applications . . . . . . . . . . . . . . . . . . . . . 196
7.3 Chapter summary . . . . . . . . . . . . . . . . . . . . . . 201
7.4 Part II summary . . . . . . . . . . . . . . . . . . . . . . 202
III Experiments with GE 204
8 Automatic physics-based motion data optimisation 206
8.1 GE system overview . . . . . . . . . . . . . . . . . . . . 208
8.1.1 Grammars . . . . . . . . . . . . . . . . . . . . . . 210
8.1.2 Physics-based simulation fitness function . . . . . 213
8.2 Motion data optimisation experiments . . . . . . . . . . 220
8.2.1 Seed data grammar . . . . . . . . . . . . . . . . . 220
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8.2.2 Free grammar . . . . . . . . . . . . . . . . . . . . 224
8.2.3 Sinusoidal grammar . . . . . . . . . . . . . . . . . 227
8.2.4 Motion data optimisation conclusions . . . . . . . 231
8.3 Evolution rate experiments . . . . . . . . . . . . . . . . . 233
8.3.1 Dynamic fitness function . . . . . . . . . . . . . . 234
8.3.2 Generational joint freedom . . . . . . . . . . . . . 236
8.4 Uneven terrain experiment . . . . . . . . . . . . . . . . . 237
8.4.1 Results . . . . . . . . . . . . . . . . . . . . . . . . 241
8.5 Chapter summary . . . . . . . . . . . . . . . . . . . . . . 243
9 Variable morphologies 244
9.1 Interspecies motion retargeting . . . . . . . . . . . . . . 245
9.1.1 Discrete model system . . . . . . . . . . . . . . . 247
9.1.2 Continuous model system . . . . . . . . . . . . . 251
9.1.3 Retargeting summary . . . . . . . . . . . . . . . . 254
9.2 Multiple models . . . . . . . . . . . . . . . . . . . . . . . 255
9.2.1 Allometric measurements . . . . . . . . . . . . . . 256
9.2.2 Variable Morphologies System overview . . . . . . 257
9.2.3 Spring-damper coefficient experiments . . . . . . 260
9.2.4 Comparison . . . . . . . . . . . . . . . . . . . . . 267
9.2.5 Animation results . . . . . . . . . . . . . . . . . . 268
9.3 Chapter summary . . . . . . . . . . . . . . . . . . . . . . 270
10 Kinematic gait and transition animation system 272
10.1 Animation system overview . . . . . . . . . . . . . . . . 274
10.2 Gait adjusters . . . . . . . . . . . . . . . . . . . . . . . . 274
10.2.1 Extensions to the CMA . . . . . . . . . . . . . . 276
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10.2.2 GE system . . . . . . . . . . . . . . . . . . . . . . 278
10.3 Kinematic Gait Transition System . . . . . . . . . . . . . 281
10.3.1 Transitions . . . . . . . . . . . . . . . . . . . . . 283
10.3.2 MIDI control . . . . . . . . . . . . . . . . . . . . 285
10.4 Animation results . . . . . . . . . . . . . . . . . . . . . . 287
10.4.1 Transition phase data . . . . . . . . . . . . . . . . 288
10.4.2 Bone rotation data . . . . . . . . . . . . . . . . . 289
10.4.3 Aesthetic realism . . . . . . . . . . . . . . . . . . 290
10.5 Chapter summary . . . . . . . . . . . . . . . . . . . . . . 293
10.6 Part III summary . . . . . . . . . . . . . . . . . . . . . . 293
IV Conclusions 294
11 Conclusions and future work 295
11.1 Thesis summary . . . . . . . . . . . . . . . . . . . . . . . 295
11.1.1 Contributions . . . . . . . . . . . . . . . . . . . . 296
11.1.2 Research and implementation decisions . . . . . . 302
11.2 Future research directions . . . . . . . . . . . . . . . . . 308
Glossary 313
A 319
A.1 Genetics overview . . . . . . . . . . . . . . . . . . . . . . 320
A.1.1 Genetic terminology . . . . . . . . . . . . . . . . 320
A.1.2 Evolutionary processes . . . . . . . . . . . . . . . 326
A.2 Horse conformation . . . . . . . . . . . . . . . . . . . . . 332
A.3 Terminology for anatomical location . . . . . . . . . . . . 334
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