grapp, lisbon, february 2009 university of ioannina skeleton-based rigid skinning for character...
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![Page 1: GRAPP, Lisbon, February 2009 University of Ioannina Skeleton-based Rigid Skinning for Character Animation Andreas Vasilakis and Ioannis Fudos Department](https://reader038.vdocument.in/reader038/viewer/2022110205/56649c7d5503460f94932689/html5/thumbnails/1.jpg)
GRAPP, Lisbon, February 2009University of Ioannina
Skeleton-based Rigid Skinning for Character Animation
Andreas Vasilakis and Ioannis Fudos
Department of Computer Science University of Ioannina, Greece
{abasilak,fudos}@cs.uoi.gr
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GRAPP, Lisbon, February 2009University of Ioannina
Abstract
A new skeletal animation framework:• Addresses vertex weighting • Works on a single mesh• Produces refined skeleton extraction• Derives robust rigid skinning with blending
patches
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GRAPP, Lisbon, February 2009University of Ioannina
Talk Structure
• Introduction
• Skeletonization
• Improved Rigid Skinning
• Results
• Summary
• Future Work
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GRAPP, Lisbon, February 2009University of Ioannina
Introduction
• Realistic mesh animation in Movie/Game industry
• Skeletal animation• Rigid Skinning
• self-intersections• Linear Blend Skinning - LBS
• volume loss• vertex weighting• training pose set• over-fitting
collapsing jointcandy wrapper
Rigid Skinning LBS
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GRAPP, Lisbon, February 2009University of Ioannina
Related Work
• Skeletonization• Geometric Methods
• Reeb graphs• Volumetric Methods
• Field functions • Other Methods
• Training pose set • Mesh contraction• Mesh decomposition
• Skinning• Geometric Methods
• Simple/Dual quaternions• Spherical blending
• Example-based Methods• Skeletal-Subspace Deformation• Multi-weight Enveloping• Animation Space
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GRAPP, Lisbon, February 2009University of Ioannina
Skeletonization
o Centroid - Principal Axis Methods *o Approximate refinements using local and neighbor
featureso Improve skeleton orientationo Global alignment of OBBs (for skinning)
(*): Lien J.M., Keyser, J. and Amato N.M., “Simultaneous shape decomposition and skeletonization”. In proceeding of 2006 ACM symposium on Solid and Physical Modeling.
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GRAPP, Lisbon, February 2009University of Ioannina
Opening Method
• Opening centroid - OC• Boundary: common joint
points between neighbor components
• Skeletal segments intersect component borders
• Addresses previous flaws• Kernel's centroid• Lacks topological
information
Centroid Method
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GRAPP, Lisbon, February 2009University of Ioannina
Principal Axis Method
• Algorithm:1) through centroid of kernel
and resides within component
2) subdivision with OC projections
3) sort OCs4) grouping algorithm5) connecting algorithm
• Slightly slower than previous• High quality skeleton morphs
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GRAPP, Lisbon, February 2009University of Ioannina
Grouping Algorithm
F1: Normalized Merging Function between OCs:• average of distances of OCs to PA
• ratio of non utilized PA length
F2: Normalized Separating Function between 2 groups:• average of distances of OCs to PA
• complement of ratio of generated PA length
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GRAPP, Lisbon, February 2009University of Ioannina
Connecting Algorithm
• OCs -> 1 link point and is close to1) PA's centroid 2) PA's end point
• OCs -> k>1 link points and are close to1) PA's centroid2) PA's end point
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GRAPP, Lisbon, February 2009University of Ioannina
Skeleton Refinements
• PCA is limited on cuboid and spherical shapes • Approximate slight modifications • Perfection of PA orientation by 2 novel methods:
• Local Refinement• Hierarchical Refinement
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GRAPP, Lisbon, February 2009University of Ioannina
Local Refinement
• OC = 1: match closest PD with vector• OC > 1: weighted vector alignment with
• angle = a * weight• a = angle between vector and closest PD• weight = 1 / (|OC|+1)
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GRAPP, Lisbon, February 2009University of Ioannina
Hierarchical Refinement
• Skeletal uniformity• Algorithm:
1) Align closest parent PD with child PA 2) Align the closest pair of remaining child-parent PDs
• Limitation : Initial PD orientation of root node
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GRAPP, Lisbon, February 2009University of Ioannina
Advanced Rigid Skinning
• Our skinning algorithm1) Removing vertices2) Adding vertices3) Blending mesh 4) Computing mesh normal vectors
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GRAPP, Lisbon, February 2009University of Ioannina
Removing Vertices
• Detect which points are inside neighbor's OBBs• Optimal cut due to previous refinements• Vector Classes
• Boundary• Replaced• In-Between
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GRAPP, Lisbon, February 2009University of Ioannina
Adding Vertices - FBPC
o Boundary points -> circular arc o interpolation between before - after rotationo QLERP
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GRAPP, Lisbon, February 2009University of Ioannina
Adding Vertices - RBPC
• Triplet• In-Between, child-parent Replaced sets • min {dihedral angle of planes}• Rational Bezier arc• Replace In-Between with Vm
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GRAPP, Lisbon, February 2009University of Ioannina
Blending Mesh
• Tight Cocone algorithm *
Computing normals
• Patch Normal = average { new + old normal faces }
(*): Dey T.K and Goswami S.. “Tight cocone: a water-tight surface reconstructor”. In proceeding of 2003 ACM symposium on Solid Modeling and Applications.
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GRAPP, Lisbon, February 2009University of Ioannina
Results - Skeletonization
Human Model:
Dinosaur Model:
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GRAPP, Lisbon, February 2009University of Ioannina
Results - Skinning
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GRAPP, Lisbon, February 2009University of Ioannina
Conclusions
• Refined skeleton extraction technique
• Robust rigid skinning without using weights
Future work
• Skeletonization• Local refinement: optimization method
• Skinning • GPU implementation
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GRAPP, Lisbon, February 2009University of Ioannina
Thank You
Questions ???