Off-line Adaptation

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Off-line Adaptation
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Motion Editing

• Realistic motion data
• motion capture technology
• commercial library
• Reuse available motion clips
• interactive motion editing
• motion adaptation

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Spacetime Formulation

• Spacetime constraints
• Witkin and Kass 88 Cohen 92 Gleicher 98
• important features of the original motion
• new features to be accomplished
• To find a new motion
• satisfying given constraints
• preserving original characteristics

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Direct Manipulation with Spacetime Constraints
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Basic Idea

• Structure of motion sequences
• Intra-frame relationship
• satisfying constraints
• by inverse kinematics
• Inter-frame relationship
• avoiding jerkiness
• by curve fitting

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Motion Representation

• Configuration of articulated figures
• linear components
• angular components

The position of the root segment
The orientation of the root segment
The orientations of the body segments
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Motion Displacement Mapping

• Bruderlin and Williams 95 Popovic and Witkin
  95

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Motion Displacement Mapping

• Representation of displacement maps
• an array of spline curves
• over a common knot sequence
• Flexibility in representation
• hard to determine knot density
• adaptive refinement is needed

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Adaptive Refinement

• Multilevel or Hierarchical B-splines
• Lee, Wolberg and Shin 97 Forsey and Bartels
  95
• sum of uniform B-spline functions
• coarse-to-fine hierarchy of knot sequences

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Multilevel B-Spline Fitting
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Hierarchical Motion Fitting

• Hierarchy of successively refined motions
• successively finer displacement maps
• at each level in the hierarchy,
• to compute displacements at constrained frames
• to derive a displacement map by curve fitting

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Inverse Kinematics

• A Numerical Approach

Constrained Optimization
Reference configuration
Displacement
Unconstrained version
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Inverse Kinematics

• Hybrid Approach
• one-variable parameterization for arms and legs
• analytic solver for arms and legs

elbow circle Korein and Badler 82
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Knot Spacing

• Direct manipulation
• larger spacing yields wider range of
  deformation
• Precision control
• precision depends on the density of the finest
  knot sequence

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Demonstration
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Summary

• Hierarchical motion fitting
• hierarchical representation
• provides adaptive refinement
• allows to edit motion at any level of detail
• interactive performance
• easy to implement