1. Motion Capture
CSE 3541
Matt Boggus

2. MoCap Technologies
Instrument the talent to facilitate tracking feature points on the human figure
Need some kind of sense-able markers from which positional and possibly rotational status can be recorded

3. “Traditional” MoCap Technologies
Optical – uses video capture
passive – markers just reflect light
active – markers emit light
Magnetic – active sensors sense their position and orientation in magnetic field
Electro-Mechanical – rotors connected to limb-aligned rods record their status – for hands, optical sensors used sometimes

4. Optical - Passive

5. Newer MoCap Technologies
Inertial systems (similar to Wii technology)
Make-up (fluorescent powder)
Semi-passive imperceptible markers (emit light and observe changes ; Kinect uses infrared)
Markerless systems (video tracking)

6. Markerless Organic Motion www.organicmotion.com/
Image Metrics (facial)

7. Kinect – skeleton tracking, depth, audio
Using the Kinect in Unity

8. Passive Optical

9. Motion capture lab Multiple markers - e.g., 20-40
Multiple cameras - e.g., 8-14 high-res, high-speed
Constrained, conditioned space - 20x20 non-reflective
Multiple lights - synced w/ cameras
Vicon

10. Motion capture lab

11. Processing the Images PROCESSING STEPS Extract markers from video
Track markers over time in video
Marker cleanup
3D marker position reconstruction
Joint position reconstruction
Joint angle reconstruction

12. Extract markers from video
Basic image processing aided by constrained environment:
High contrast markers
Special illumination
Non-reflective environment

13. Practice problem - algorithm to extract markers from image
Image source:

14. Marker tracking Given frames each with recognized markers
Associate markers over multiple frames
Temporal coherence using:
Position
Frame rate
Velocity

15. Marker Clean-up

18. Camera calibration Project known 3-space points to camera’s image
Six degrees of freedom - use that many known point-pairs

19. Projecting from 2D image out to 3-space

20. 3D – image plane projection
Projecting marker onto image plane

21. Reconstructing a 3D marker

22. Working with Mocap Sample files
Tools
MotionBuilder
Maya
3DSMax

23. Example BVH file
See ACCAD files

24. Constructing a hierarchical character for a BVH file
Example on board

25. Manipulating the mocap data
Next steps:
Manipulating the mocap data
Frequency deconstruction & manipulation
Transitioning between two motions – Blending
How to map a motion onto a figure with different geometry – Retargeting
Finding motion clips to create behavior – motion graphs

26. Additional and Cut slides

27. Mocap hardware tech

28. Optical - Active

29. Ex: Ascension technology
Magnetic

30. Ex: Metamotion
Electro-Mechanical

31. Reconstructing the data

32. Fitting to the skeleton
Locate joints relative to markers
Markers
Joint

33. Reconstructing angles