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Layered Techniques for Character Animation: Insights from SIGGRAPH 2003

Explore innovative layered acting methods for character animation as presented by Mira Dontcheva, Gary Yngve, and Zoran Popović at SIGGRAPH 2003. Learn about key concepts such as motion graphs, physical simulations, and layered editing to create nuanced character movements. This presentation delves into rigging, articulation layers, and the integration of user interaction, while also addressing advanced feature mapping techniques for enhanced animation precision. Gain insights into the hardware and software required for sophisticated character animation and simulation.

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Layered Techniques for Character Animation: Insights from SIGGRAPH 2003

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  1. Layered Acting for Character Animation By Mira Dontcheva Gary Yngve Zoran Popović SIGGRAPH 2003 presented by Danny House

  2. Editing Motion • Keyframing: positions and tangents • Physical Simulation: initial conditions • Motion Graphs: splicing • Texturing

  3. Layered Editing Start with Broad Outline Top Down Construction

  4. Dimensions for Layering • Accuracy • Scale • Articulation

  5. Layers of Articulated Movement • Torso • Limbs to Fingers • Head to Face to Eyes • Secondary Motion

  6. Interaction via Acting • Correspondence of Movement and Time • Not Quite Puppetry • Motion Capture

  7. Imitation • Imitating the User • Imitating the Animated Character

  8. System Overview • Hardware • Space and Time Interaction • Character Interaction • Synthesis and Editing With Layers

  9. Hardware • 8 camera optical motion capture • wireless mouse • wall display screen • various animation widgets

  10. Space and Time Interaction • Camera View and Studio Correspondence • Distance to Object Affects Gain on Controls • Ground Calibration • Speed and Interval of Playback • Anticipation Guides • Predictive Ghost Renderings • Projections of Trajectory Streamers

  11. Character Interaction • User Features • position and orientation of widgets • Character Features • Correspondence Between Character and User Features

  12. Character Features • Must be prespecified in the character model. • May include • joints • points on the body • DOFs • IK handles

  13. Correspondence Between Character and User Features • Explicit selection by User • Implicit selection via acting • Absolute, trajectory-relative, or additive

  14. Synthesis and Editing with Layers • Select One or More Character Features • Map them to a Widget • Act with the Widget while Watching Playback • Repeat

  15. Definitions for Feature Mapping • X0: initial position of widget • X(t): position of widget at time t • C´: rotational component of transform from studio to camara coordinates • Y0: initial position of character feature • Y(t): position of character feature at time t • Y ´(t): character feature’s position after edit • XR0, XR(t), etc, are the corresponding rotations

  16. Absolute Feature Mapping • Used for top level rough sketch of motion • Good for contact with ground • the system supports snapping to the ground • Useful for body parts that interact with in the scene • Could be useful with physical props

  17. Equations of Absolute Feature Mapping • Y ´(t) = Y0 + C´(X(t) - X0) • Y R´(t) = C´XR(t)(XR0)-1YR0

  18. Trajectory-Relative Mapping • Useful for animating a feature relative to an existing parent motion. • K(t) is the product of the matrices in the parent hierarchy of the feature being edited. • Y ´(t) = Y0 + K(t)C´(X(t) - X0)

  19. Additive Mapping • Useful for adding detail or personality while preserving the underlying motion • Y ´(t) = Y(t)+ C´(X(t) - X(t-dt))

  20. Equations of Trajectory-Relative Mapping • K(t) is the change in the widget’s translation over [0,t] • Y ´(t) = Y0 + K(t)C´(X(t) - X0)

  21. Implicit Editing • The user selects the features to edit by imitating their behavior. • The system discovers the relevant features using a statistical technique called “Canonical Correlation Analysis” or CCA. • CCA is applied to each user/character feature pair. • Heuristics are used to choose the best pairs. They are non-robust but effective in practice.

  22. Physically Based Motion Transformation • By Popović, Z. and Witkin, A. P. • SIGGRAPH 99 • Sophisticated retargeting of motion data.

  23. Preparation for Editing • Character Simplification • manual elimination of many details • Spacetime Motion Fitting • manual capture of pose and mechanical constraints, addition of muscles, assumes optimality

  24. Editing • Tweak the Constraints • change a pose, alter flexibility of a joint, introduce obstacles, alter gravity • Motion Reconstruction • automtic

  25. Interactive Manipulation of Rigid Body Simulations • Popović, J., Seitz, S. M., Erdmann, M., Popović, Z., and Witkin, A. P. • SIGGRAPH 2000 • Allows goal oriented editing of physical simulations.

  26. User specifies waypoints and velocities in simulation. • Will alter initial conditions if permitted. • Obtains extra DOFs by tweaking surface normals, elasticity. • Small changes in these parameters are not noticed by audience.

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