Realistic Avatar Movement

1
Realistic Avatar Movement

• Using Combined Trackers

2
Project goal
Take some steps towards more convincing,
believable avatars.
3
Project focus motion

• We want a realistic animation of the avatar.
• We dont want to use full-body tracking.
• Solution? Use just a few trackers and Inverse
  Kinematics instead.

4
Combining different trackers

• HiBall has 2 trackers, Fastrack has another 4.
• Fastracks sensor is fixed, and its position in
  HiBall space is known.
• The combination? Transform everything in HiBall
  coordinates.

5
Tracker layout
6
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 dont always
  yield the desired result.

7
Problems with tracking

• Magnetic trackers drift a lot, and have variable
  accuracy.
• Solution? Calibration choose the best estimate
  of the Fastracks sensor position in HiBall
  coordinates for each user.

8
Inverse Kinematics

• Many complex ways to compute.
• Simple Cyclic Coordinate Descent

9
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.

10
Future work

• Implement efector rotation (hands).
• Implement movement constraints for IK in Cal3D.

11
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.