Dynamics-based analysis and synthesis of human locomotion

Abstract

One of the best ways to synthesize realistic human motions is to animate characters from captured motion data that inherently respect motion laws. Retargeting and interpolation methods are often used to adapt these motions to different representations of the character and to various environmental constraints but they may introduce physical inaccuracies, although the synthesized motions are natural looking. This paper presents a method for evaluating the physical correctness of retargeted and interpolated locomotions using an inverse dynamics analysis. Furthermore, we propose to improve an initial database with analysed motions that are synthesized again by using a forward dynamics approach. The analysis algorithm consists in determining the resulting forces and torques at joints. With this intention, we develop an automatic creation process of the mass/inertia model of the character. Then using support phase recognition, we compute resulting forces and torques by an inverse dynamics method. The retargeting and the interpolation methods change the physics of the motions. This change is evaluated by using the results of our analysis on artificial and real motions and by using literature results and experimental data from force plates. The evaluation relies on the study of several retargeting and interpolation parameters such as the global size of the character or the structure of the model. The output of this evaluation, the resulting forces and torques at joints, are used to produce physically valid motions by using forward dynamics simulation. With this purpose, we introduce forces and torques normalizations, and finally the synthesized motions may improve the initial database.