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Layered Acting for Character Animation

Layered Acting for Character Animation. By Mira Dontcheva Gary Yngve Zoran Popović. SIGGRAPH 2003. presented by Danny House. Editing Motion. Keyframing: positions and tangents Physical Simulation: initial conditions Motion Graphs: splicing Texturing. Layered Editing.

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Layered Acting for Character Animation

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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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