Animating real-time virtual humans thanks to motion capture Franck - - PowerPoint PPT Presentation

Animating real-time virtual humans thanks to motion capture

Franck Multon

SIAMES project IRISA / INRIA Rennes FRANCE Laboratoire de Physiologie et de l’Exercice Musculaire Université de Rennes 2 FRANCE

Introduction

• Motion re-use

– Interactive environments – Large number of characters – Small database of captured motions

• Applications in videogames, Virtual Reality,

film production, education and training in sports and rehabilitation

Problems (1)

– « Motion retargeting »

• Adapting motion to new characters
• Inverse kinematics/kinetics on each frame [Tsumura 01,

Boulic 03, Glardon 04]

• Inverse kinematics on specific times + filters [Gleicher

98, Lee 99]

Problems (2)

– « Motion blending »

• Merging motions by frame-space interpolation +

dynamic time warping [Guo 96]

• Transitions + distance between motions [Kovar 02,

Arikan 02]

• « Motion Graphs » [Kovar 02, Lee 04]

– Requires a large database + off-line computations

Our approach

• Interactive animation with several actors

– Impossible to use knowledge on the whole motion given that unpredictable events could

• ccur

– Based on [Boulic 97]

• Frame-by-frame adaptation
• Blending with weighted sum of trajectories
• Priorities on body parts for each motion

Architecture

Synchronization Posture Actions User Blending Visualization Mélange Mélange

Retargeting Adaptation

Normalized skeleton

• Adimensional Cartesian and relative

trajectories

• IK for other joints

– Storage of the plan containing the remainding joints – Main joints – Normalized root position – Spline for the trunk

Additionnal constraints

• Continuous constraints :

– Type : distance, position, velocity – 4 times : t1, t2, t3, t4

t1 t2 t3 t4

Time 0 % 100 %

How to adapt motion? (1)

• 1. Placing and orientating the root

– Scaling by new morphological data 2. Scaling normalized data to place main joints – Geometric constraints not verified

How to adapt motion? (2)

• 3. Verifying constraints for the

main joints

– No contact / one-foot / two-feet contacts – Displacing the main joints in the Cartesian space depending on the constraints

How to adapt motion? (2)

• 3. Verifying constraints for the

main joints

– No contact / one-foot / two-feet contacts – Displacing the main joints in the Cartesian space depending on the constraints

How to adapt motion? (3)

–

• Ex. distance contsraints

– Clapping the hands

How to adapt motion? (4)

• 4. Other joints

– Simple inverse kinematics for a two-segments chain

• 5. Computation of quaternions for

visualization

Motion adaptation demo

How to synchronize & blend motions

• Each action associated to

– Priorities for each set of joints (viewed as ressources) – State (start, stop, running, inactive)

• Automatic calculation of weights for each joint j

and motion i kij=f(priorities,states) [Ménardais 04a]

– Ensuring continuity – Intuitive spec. and automatic calculation

2 1 2 1 2 1

, ,

i i i i

k k i P P i S S > ∀ ⇒    > ∀ =

( ) ( )

∑

+ × + × = ∀ ∀

c c i c j i j j i

P S P S k j i ε ε , ,

…

How to synchronize motions

• Dynamic time warping

– Link to events in the original motions: foot- contacts [Ménardais 04b]

Resulting dynamic time warping

Synchronization demo

Conclusion

• More than 200 actors in real-time with few

shared motions

• Only kinematics!

– Dealing with dynamics – Ensuring that biomechanical laws are verified after modification (PCA [Le Gallennec 04] or general rules)