Interactive control of physically-valid aerial motion: application to VR training system for gymnasts

ABSTRACT

This paper aims at proposing a new method to animate aerial motions in interactive environments while taking dynamics into account. Classical approaches are based on spacetime constraints and require a complete knowledge of the motion. However, in Virtual Reality, the user's actions are unpredictable so that such techniques cannot be used. In this paper, we deal with the simulation of gymnastic aerial motions in virtual reality. A user can directly interact with the virtual gymnast thanks to a real-time motion capture system. The user's arm motions are blended to the original aerial motions in order to verify their consequences on the virtual gymnast's performance. Hence, a user can select an initial motion, an initial velocity vector, an initial angular momentum, and a virtual character. Each of these choices has a direct influence on mechanical values such as the linear and angular momentum. We thus have developed an original method to adapt the character's poses at each time step in order to make these values compatible with mechanical laws: the angular momentum is constant during the aerial phase and the linear one is determined at take-off. Our method enables to animate up to 16 characters at 30hz on a common PC. To sum-up, our method enables to solve kinematic constraints, to retarget motion and to correct it to satisfy mechanical laws. The virtual gymnast application described in this paper is very promising to help sports-men getting some ideas which postures are better during the aerial phase for better performance.

References

1. Abe, Y., Liu, C., and Popovic, Z. 2004. Momentum-based prameterization of dynamic character motion. In Proceedings of ACM SIGGRPAH/Eurographics Symposium on Computer Animation, 173 -- 182.
2. Boulic, R., Becheiraz, P., Emering, L., and Thalmann, D. 1997. Integration of motion control techniques for virtual human and avatar real-time animation. In Proceedings of the ACM symposium on Virtual reality software and technology, ACM Press, 111--118.
3. Fang, A., and Pollard, N. 2003. Efficient synthesis of physically valid human motion. ACM Trans. on Graphics 22, 3, 417--426.
4. Gleicher, M., and Litwinowicz, P. 1998. Constraint-based motion adaptation. Journal of Visualization and Computer Animation 9, 2, 65--94.
5. Kulpa, R., Multon, F., and Arnaldi, B. 2005. Morphologyindependent representation of motions for interactive human-like animation. Computer Graphics Forum, Eurographics 2005 special issue 24, 3, 343--352.
6. Liu, C., and Popović, Z. 2002. Synthesis of complex dynamic character motion from simple animations. ACM Transaction on Graphics 21, 3 (July), 408--416.
7. Pollard, N., and Behmaram-Mosavat, F. 2000. Forcebased motion editing for locomotion tasks. In Proceedings of IEEE international conference on Robotics and Automation.
8. Safonova, A., and Hodgins, J. 2005. Analyzing the physical correctness of interpolated human motion. In SCA '05: Proceedings of the 2005 ACM SIGGRAPH/Eurographics symposium on Computer animation, ACM Press, 171--180.
9. Safonova, A., Hodgins, J., and Pollard, N. 2004. Synthesizing physically realistic human motion in low-dimensional, behavior-specific spaces. In Proceedings of ACM SIGGRAPH.
10. Shin, H., Kovar, L., and Gleicher, M. 2003. Physical touchup of human motions. In Proceedings of Pacific Graphics.
11. Sulejmanpasic, A., and Popovic, J. 2005. Adaptation of performed ballistic motion. ACM Trans. on Graphics 24, 1 (January), 165--179.
12. Yeadon, M. 1993. The biomechanics of twisting somersaults. part iii: Aerial twist. Journal of Sports Sciences 11, 209--218.
13. Zordan, V., Majkowska, A., Chiu, B., and Fast, M. 2005. Dynamic response for motion capture animation. ACM Trans. Graph. 24, 3, 697--701.

Index Terms

• Computing methodologies

  • Computer graphics

    • Animation

    • Graphics systems and interfaces

      • Virtual reality