Magnetic Motion Capture
		Motion Capture  ·  What is it?  ·  Why use it?  ·  Recording vs. real-time  ·  Magnetic ·  Optical ·  Electro-mechanical  ·  Workflow  ·  Specialized tools ·  Who uses it?	Products  ·  Motion Captor  ·  Gypsy  ·  Datagloves  ·  Cybergloves  ·  Face Trackers  ·  MotionBuilder

Motion capture is typically accomplished by any of three technologies: Optical, Magnetic and Electro Mechanical. While each technology has its strengths, there is not a single motion capture technology that is perfect for every possible use.

Magnetic Motion Capture Systems:

Magnetic motion capture systems utilize sensors placed on the body to measure the low-frequency magnetic field generated by a transmitter source. The sensors and source are cabled to an electronic control unit that correlates their reported locations within the field. The electronic control units are networked with a host computer that uses a software driver to represent these positions and rotations in 3D space.

Magnetic systems use 6 to 11 or more sensors per person to record body joint motion. The sensors report position and rotational information. Inverse kinematics (IK) is used to solve the angles for the various body joints, and compensate for the fact that the sensors are offset from the actual joint's center of rotation. The IK approach produces passable results from 6 sensor systems, but IK generally adds system overhead that can cause latency in real-time feedback. Although 6 sensor systems are less expensive, they are more likely to produce 'joint popping' since the IK solution needs to guess about a lot of the information it is receiving. The markers tend to move a bit during capture sessions, and require repeated readjustment and recalibration. Since each sensor requires its own (fairly thick) shielded cable, the tether used by magnetic systems can be quite cumbersome.

DC Magnetic systems have issues with azimuth. If an actor is doing a push-up type posture, the system will get confused. Multiple actor magnetic setups also have problems with two or more actors in close proximity. Sensors from the different actors will interfere with each other, providing distorted results.

continued next page