BiomechanicallyInspired Motion Path Editing Noah Lockwood and Karan

Biomechanically-Inspired Motion Path Editing Noah Lockwood and Karan Singh University of Toronto

Goals • Fast editing of single motions • High-level spatial direction • Flexible to motion content

Related Work • Path-based approaches – Motion graphs, motion doodles, deformable models • Path-based motion editing – Kinematic, limited to walking or simple locomotion – Multi-character synchronized motion [Kim 2009]

Algorithm • • Motion Preprocessing Interactive Path Deformation Pose Adjustment Timewarping

Terminology • Keys: full body pose, position, and time • Path: sequence of skeleton root positions

Algorithm • • Motion Preprocessing Interactive Path Deformation Pose Adjustment Timewarping

Motion Preprocessing • Real motion changes are constrained • Identify deformation handles • Must correspond to potential motion changes

Motion Preprocessing • • Real motion changes are constrained Identify deformation handles Must correspond to potential motion changes Character exertion at path vertical minima

Motion Preprocessing • • • Real motion changes are constrained Identify deformation handles Must correspond to potential motion changes Character exertion at path vertical minima Many local minima though:

Path Deformation Handles • Filter based on locally maximal # of contacts:

Algorithm • • Motion Preprocessing Interactive Path Deformation Pose Adjustment Timewarping

Interactive Path Deformation • As-rigid-as-possible-deformation [Igarashi 2005] – Adjustments for curves instead of triangle meshes • Sharpness artifacts in large deformations:

ARAP Modifications • Automatic pre-scaling factor:

Algorithm • • Motion Preprocessing Interactive Path Deformation Pose Adjustment Timewarping

Pose Adjustment • Body rotation with path tangent • Foot path deformation and IK

Algorithm • • Motion Preprocessing Interactive Path Deformation Pose Adjustment Timewarping

Timewarping • Unmodified timing can look unnatural:

Froude Number • Used to evaluate dynamic similarity

Froude Number • Used to evaluate dynamic similarity • Relative stride length vs. Froude number:

Froude Timewarping • Velocity and stride length ratios:

Froude Timewarping • Velocity and stride length ratios: • Target velocities and deformed path overconstrain new key times

Timewarping results

Algorithm • • Motion Preprocessing Interactive Path Deformation Pose Adjustment Timewarping

Algorithm • • Motion Preprocessing Interactive Path Deformation Pose Adjustment Timewarping • Limited to simple edits of simple motion

Algorithm • • Motion Preprocessing Interactive Path Deformation Pose Adjustment Timewarping • Limited to simple edits of simple motion • Each stage modified based on components of motion

Vertical Motion • ARAP deformation is 2 D – Apply twice, from top and side

Vertical Motion • ARAP deformation is 2 D – Apply twice, from top and side • Local coordinate system produces rotations:

Vertical Motion • ARAP deformation is 2 D – Apply twice, from top and side • Local/global coordinate system produces shears:

Vertical Motion Editing Results

Ballistic Motion • Unrealistic deformation of airborne motion:

Ballistic Motion • Unrealistic deformation of airborne motion: • Constrained to stretch only, no bending:

Ballistic Motion Editing Results • Acceleration-based timewarping:

Ballistic Motion Editing Variety

Turns • Realistic turning paths, but motion is too fast:

Curvature and Velocity • One-third power law which relates curvature and velocity:

Curvature and Velocity • One-third power law which relates curvature and velocity: • Path curvature from curvature-continuous overall path

Path Curvature • Overall path: handle-interpolating cubic spline

Turn Timewarping • Curvature and velocity ratios:

Combined Timewarping • Two target velocities from Froude and curvature rules:

Combined Timewarping • Two target velocities from Froude and curvature rules: • Multiplicative combination:

Combined Timewarp Results

Mixed Motion Editing

Non-human Characters

Simulation Editing

Conclusion and Discussion • Our system: –Uses biomechanical models and observations –Accommodates many motion types –Automatically adjusts motion timing • Limitations: –Acrobatic maneuvers –Range of plausible timings –Full-body editing

Thanks! • Questions? • Acknowledgements: – Jacobo Bibliowicz, Patrick Coleman, Martin de Lasa, John Hancock, Ryan Schmidt, Patricio Simari – – SCA 2011 reviewers CMU Motion Capture Database Centroid Motion Capture Autodesk

Pose Adjustment • Rigid transformation of footsteps: