1. Animating reactive motion using momentum-based inverse kinematics CASA 2005

2. Animating reactive motion using momentum-based inverse kinematics Taku Komura S.L. Ho W.H. Lau Department of Computer Science City University of Hong Kong

3. Outline ○Introduction ○Generating Reactive Motions ○Results and Discussion

4. Introduction ○Motion capture data has become a popular and an effective means of animating human figures. Due to the quality and realism of the result. ○The synthesis of motion capture data is a challenging research problem. Only a limited number of methods consider reactive motions.

5. Introduction ○Interactive generation of reactive motions are very important to many applications. Computer games ○A new method to generate reactive motions for arbitrary external perturbations Pushing, pulling, or hitting vs. standing, walking, or running

7. Motion Database ○Basic standing, walking, and running Primary motion ○Pushed/pulled from eight different directions Front, side, front-side, and back-side

8. Outline ○Introduction ○Generating Reactive Motions ○Results and Discussion

9. Generating Reactive Motions ○Step 1: Adding impact The user specifies the position, amplitude and direction. ○Step 2: Motion search The one minimized the criteria is chosen. ○Step 3: Editing found motion According to the strength of the perturbation ○Step 4: Generating final motion Momentum-based IK

10. Step 1: Adding impact ○The amount of impact, is calculated by subtracting the linear momentum of the body before the impact from that after the impact. ○ p: the position of the impact x g : the position of COM

11. Step 2: Motion Search ○The reactive motion which includes a frame that minimizes the following criteria will be selected from the database. ○It is much simpler than the one used by other graph-based motion stochastic methods.

12. Step 3: Editing found motion ○The positions of the foot steps must be changed according to the amplitude and direction of the impact. ○The velocity of the body is linearly dependent on the displacement of the landing foot onto the ground.

13. Step 3: Editing found motion ○Blends the angular momentum. ○Let the difference at the moment blending starts be.

14. Step 4: Generating final motion ○Once the reactive motion is chosen and edited, this motion will be blended into the primary motion using momentum-based IK.

15. Outline ○Introduction ○Generating Reactive Motions ○Results and Discussion

16. Results

17. Discussion ○Foot sliding can easily happen if the primary motion and the reactive motion is simply interpolated. ○The momentum-based constraints help keep the motion realistic even after editing the motion or adding new constraints. ○The criteria to select the motion in the database is much simpler than previous methods such as in Lee et al., the computation time is much shorter. ○But for offline process, such as Motion Graph, there is no doubt works better.

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