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MOTION CAPTURE

CONTENTS Introduction Related Work Motion Capture-Driven Simulations Controllers and Tracking System Evaluation Pushing People Around Physically Based Grasping Conclusion Reference

INTRODUCTION The interactive approach of character animation requires sophisticated motion synthesis algorithms to generate poses and motion for unpredictable events.Traditional animation techniques used alone cannot produce the needed degree of realism or the degree of controllability required for virtual characters. Motion capture techniques and the physical simulation of characters, when combined offer the potential to produce realistic motions while still maintaining a high level of control.

Related Work Complimenting motion capture and Physics is an interdisciplinary field of research applying knowledge of areas from robotics,biomechanics,computer graphics and artificial intelligence. The following sections give an overview of the related work. Motion Capture Editing Physically Based Characters Combination of motion capture and Physics

Motion Capture Editing Editing motion capture data is a method, which consists of modifying motions without re-recording them. It allows to generalize the data and reuse it effectively. The method creates smooth deformations that preserve the fine structure of the original motion.Adapting the motions to new characters is called retargeting.

Motion graphs clustering frames into groups

Physically Based Characters In the topic of animating human athletic is detailed and a method presented to animate human athletics in respect to the physically laws.Running, gymnastics, and diving motions are generated by using hand-tuned, state machine-driven controllers.To produce physically realistic, periodic walking and running motions lazlo presented an approach with a limit cycle control. Designing physically-based controllers for individual behaviors is one solution, but combining several controllers is a better approach to generate more complex motions.

Combination of Motion Capture and Physics To produce a variety of modifications of motion data physical models are used to constrain possible solutions.To generate efficient motion transitions Rose proposed a method using space-time constraints they used an inverse dynamics model to transition between motion sequences by finding a minimum energy solution.A response motion of a character is animated reacting to a mass being dropped on the characters back.

Motion Capture-Driven Simulations The following sections describes the behaviour modeling approach of Motion Capture-Driven Simulations. Behavior modeling Controllers and Tracking System Evaluation

Behaviour Modeling Several different animation methods exist,such as hand-keyed animation, forward /inverse kinamtics, human motion capturing, motion graphs, or procedural animation, such as physically-based simulation. Motion capturing is a wide used technique but has its limitations.Not everything is recordable and some motions are dangerous for the motion actors to perform.Motions such as boxing where the impact would be too great to be performed by an actor cannot be recorded.

Combination of different Animation Technique

The behavioral transition diagram

Controllers and Tracking System The tracking system uses raw motion data and converts it to desired joint angles which are then fed into the tracking controller that computes the torques for the dynamic model. Also the balancing controller feeds torques into the dynamics simulation.

Overview over the system with tracking controller, dynamic model, collision handler, task controller and balance controller

Influence values control the mix of the different techniques

Parellelism of controller threads

Evaluation To evaluate the method it is important to compared the synthesized motion side - by side with recorded video material.The robustness of the physical simulation must be reduces to achieve time . Dividing the character into two parts,i.e. The upper and lower body ,is one way, and also removing parts of the bodywith a low mass can help to cut the computation cost and lower the numerical stiffness of the overall system

Side-by-side comparison of recorded live video footage and the simulation

PUSHING PEOPLE AROUND The pushing people around paper introduces an oracle which is explained in this section. The oracle recognizes visually realistic motions. Motion deformation with different parameters yielding unrealistic poses

PHYSICALLY – BASED GRASPING When animating human characters it is important to capture even small movements for example, interactions with the environment using the hands. Motion capture techniques deliver realistic motions but when contact with the environment or other subtle interactions are involved it becomes difficult to edit and retarget the motions.

The collision model for the hand and an example of a generated handshake

State diagram of the hand actions

CONCLUSION A higher-level behavioral graph is important instead of more low –level approaches such as motion graphs when it comes to realistic character animation. Combining motion capture techniques and dynamic simulation offers an interesting solution to maintain realism to ultimately achieve controllable characters for interactive virtual environments.

Reference 1. Witkin, A., Popovic, Z.: Motion Warping. In: Proceedings of SIGGRAPH 95, ACM SIGGRAPH,pp. 105–108 (1995) 2. Gleicher, M.: Retargeting Motion to New Characters. In: Proceedings of SIGGRAPH ’98,ACM SIGGRAPH, pp. 33–42. (1998) 3. Choi, K.J., Park, S.H., Ko, H.S.: Processing Motion Capture Data to Achieve Positional Accuracy. Graphical models and image processing: GMIP 61, 5, pp. 260–273 (1999)

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