Types of Moton Capture Systems

By: The Ant

As motion capture technology developed, several uniquely different types of motion capture systems evolved. The types of motion capture input systems are: mechanical, magnetic, and optical.
Mechanical:
Performer wears a human-shaped set of straight metal pieces (like a very basic skeleton) that is hooked onto the performer's back; as the performer moves, this exoskeleton is forced to move as well and sensors in each joint feel the rotations. What is the apparatus? I t basically a large joystick. And this joystick is attaches to the body of the performer and moves according to the movement of the performer.

Advantage: no interference from light, well that removes the worry of wondering whether there will be a necessity for dim lighting , and from magnetic fields.

Disadvantage:
a)the technology has no awareness of ground, so please no aerobics no jumping, and moreover the data sometimes look like the performer was literally being swept of his/her feet.
b)equipment must be calibrated often
c)unless there is some other type of sensor in place, it does not know which way the performer's body is pointing, resulting in the possibility if the person doing the post production doesn't have the original video there is a great chance the character will end facing the wrong direction and creating many a red face.
d)absolute positions are not known but are calculated from the rotations

Optical:
Performer wears reflective dots that are followed by several cameras and the information is triangulated between them. Markers are either reflective, such as a system manufactured by Vicon or Motion Analysis, or infra-red emitting, many of which have been developed for musical applications (such as conducting). Developed primarily for sports injuries, analysis of athletic performance, games, animation, etc. New developments are allowing for real-time capture and work with animals.

Advantages:
a)performer feels free to move due to no cables connecting body to the equipment
b)larger volumes possible
c)more performers are possible
d)very clean, detailed data

Disadvantages:
a)It is prone to light interference
b)reflective dots can be blocked by performers or other structures, causing loss of data, or occlusion-this can be compensated for with software which estimates the position of a missing dot
c)rotations of body parts must be solved for and are not absolute
d)information has to be post-processed or 'tracked' before viewing so performer cannot see his or her image and so cannot be as creative or identify potential problems (a hand hitting a giant nose, for example)
e)higher cost than magnetic

Magnetic:
Performer wears an array of magnetic receivers which track location with respect to a static magnetic transmitter. Magnetic was used for the military, to track head movements of pilots. This type of motion capture is layered with animation from other input devices.
Advantages:

a)positions are absolute, rotations are measured absolutely; orientation in space can be determined, which is very useful,
b)can be real-time, which allows immediate broadcast as well as the opportunity for performers to puppeteer themselves with instantaneous feedback (more spontaneity in the performance)
c)relatively cheaper than optical

Disadvantages:
a)magnetic distortion occurs as distance increases
b)data can be noisy - it's not as good as optical
c)prone to interference from magnetic fields - cement floors usually contain metal, so stages must be built
d)performers wear cables connecting them to a computer, which limits their freedom
e)sampling speed too low for many sports applications

In conclusion, as modern day motion capture has matured, optical and magnetic systems have proven to be the more popular systems. But the main disadvantage to magnetic systems is that they require wires and transmitter to be placed on the performer, which prevent him to move freely. Optical systems don't have this problem, so they are the choice of most people in the entertainment industry.

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