Bullet3/pybullet Simulator Contribution

Bullet3/pybullet is very popular physics simulator, widely used for computer graphics.

Now the deep_mimic environment has the support for a popular motion capture dataset, Human3.6M. I’ve contributed an specialized inverse kinematics module to pybullet_env/deep_mimic, so the 3D position data(not necessary needs to be in Human3.6M) can be transformed to quaternions(control parameters), which can be used by the humanoid agent in bullet simulator. See [Bullet3]