The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL Adrian Ilie Realistic Avatar Movement Using Combined Trackers

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL Adrian Ilie Project goal Take some steps towards more convincing, believable avatars.

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL Adrian Ilie Project focus: motion We want a realistic animation of the avatar. We don’t want to use full-body tracking. Solution? Use just a few trackers and Inverse Kinematics instead.

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL Adrian Ilie Combining different trackers HiBall has 2 trackers, Fastrack has another 4. Fastrack’s sensor is fixed, and its position in HiBall space is known. The combination? Transform everything in HiBall coordinates.

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL Adrian Ilie Tracker layout

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL Adrian Ilie Changing the pose To preserve bone lengths, bones are only rotated so that they point in the direction indicated by the trackers. Cal3D has local (incremental) coordinate systems for each bone, so absolute rotations don’t always yield the desired result.

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL Adrian Ilie Problems with tracking Magnetic trackers drift a lot, and have variable accuracy. “Solution?” Calibration: choose the best estimate of the Fastrack’s sensor position in HiBall coordinates for each user.

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL Adrian Ilie Inverse Kinematics Many complex ways to compute. Simple Cyclic Coordinate Descent:

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL Adrian Ilie Problems with IK Unconstrained CCD gives noisy solutions for sharp angles. Cal3D has no structure to implement constraints. Making the model adopt a pose corresponding to an IK solution does not always give the expected results in Cal3D.

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL Adrian Ilie Future work Implement efector rotation (hands). Implement movement constraints for IK in Cal3D.

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL Adrian Ilie Conclusions Combined trackers work well only if their accuracy is comparable and constant. Unconstrained IK is not appropriate for avatar limbs animation (sharp angles are problematic), but works well for the spine.