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An actor's movement is translated into a 3d model

Motion Capture


Motion capture or motion tracking, describes the process of using technology to record and translate movement into a digital model. It is used in many industries, including the entertainment industry, military applications, medical technologies, and sports coverage. In film it is used to record actors and recreate them in digitally animated characters using computer animation. Motion capture can be detailed enough to capture and recognize facial expressions, individual finger movements, and multiple objects.






Description


Optical Systems

The traditional method for motion capture relies on actors in a plain environment, sometimes in front of blue/green screens with various cameras stationed around the stage. The actor must wear a form-fitting outfit lined with special sensors the cameras are able to detect in 3 degrees of movement. The sensors are often placed on joints and appendages to make a virtual skeleton with which the animators can create a model.

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Passive Markers-Passive optical system use markers coated with a retroreflective material to reflect light back that is generated near the cameras lens. The camera's threshold can be adjusted so only the bright reflective markers will be sampled, ignoring skin and fabric.

Active Markers-Active optical systems triangulate positions by illuminating one LED at a time very quickly or multiple LEDs with software to identify them by their relative positions, somewhat akin to celestial navigation. Rather than reflecting light back that is generated externally, the markers themselves are powered to emit their own light.
Example: The TV series ("Stargate SG1") episode was produced using an active optical system for the VFX. The actor had to walk around props that would make motion capture difficult for other non-active optical systems.


Time Modulated Active Marker- Active marker systems can further be refined by strobing one marker on at a time, or tracking multiple markers over time and modulating the amplitude or pulse width to provide marker ID.

Semi-Passive Imperceptible Marker-One can reverse the traditional approach based on high speed cameras. Systems such as Prakash use inexpensive multi-LED high speed projectors. The specially built multi-LED IR projectors optically encode the space. Instead of retro-reflective or active light emitting diode (LED) markers, the system uses photosensitive marker tags to decode the optical signals. By attaching tags with photo sensors to scene points, the tags can compute not only their own locations of each point, but also their own orientation, incident illumination, and reflectance.

Markerless-Emerging techniques and research in computer vision are leading to the rapid development of the markerless approach to motion capture. Markerless systems such as those developed at Stanford, MIT, and Max Planck Institute, do not require subjects to wear special equipment for tracking. Special computer algorithms are designed to allow the system to analyze multiple streams of optical input and identify human forms, breaking them down into constituent parts for tracking. Applications of this technology extend deeply into popular imagination about the future of computing technology. Several commercial solutions for markerless motion capture have also been introduced.


Non-Optical Systems
The Gypsy(Gyro) IGS-190
The Gypsy(Gyro) IGS-190

Inertial Systems: Inertial gyroscopes which measure, record and transmit movement or rotations of the subject to a computer where the data is applied to a skeletal puppet.

Mechanical Motion- Mechanical motion capture systems directly track body joint angles and are often referred to as exo-skeleton motion capture systems, due to the way the sensors are attached to the body. Performers attaches the skeletal-like structure to their body and as they move so do the articulated mechanical parts, measuring the performer’s relative motion. Mechanical motion capture systems are real-time, relatively low-cost, free-of-occlusion, and wireless (untethered) systems that have unlimited capture volume. Typically, they are rigid structures of jointed, straight metal or plastic rods linked together with potentiometers that articulate at the joints of the body. These suits tend to be in the $25,000 to $75,000 range plus an external absolute positioning

Magnetic Systems-Magnetic systems calculate position and orientation by the relative magnetic flux of three orthogonal coils on both the transmitter and each receiver. The relative intensity of the voltage or current of the three coils allows these systems to calculate both range and orientation by meticulously mapping the tracking volume.



Applications


Military
Motion Capturing was originally used for military tracking purposes. It was also used to study and analyze ballistics. Military simulators have improved and benefited greatly from motion capture technology. The military uses various motion capturing techniques to develop simulators for fighter jet and helicopter pilots, open field combat, and stinger missile training.


Entertainment
The film industry uses Prosthetic(electromechanical) and electromagnetic Motion Capture to enhance our view of certain filmmakers imaginations. An actor will put on a plastic exoskeleton, equipped with Potentiometers; or several receivers are attached to their body. The movement of the actor is measured by these sensors, recorded and translated into the context of the movies action.

The use of Motion Capturing in the entertainment industry has changed immensely from it's start in the 1970s. A method developed in the early 1900s called "Rotoscoping" made it possible to successfully imitate human movement in animation. Rotoscoping is a method where animators draw over motion captured live-action film. The first use of Rotoscoping was seen in the Out of the Inkwell, by Max Fleischer in 1915. He invented the technique to make his character, Koko the Clown, more realistic. Starting in the seventies, the Rotoscoping method was adapted so it was able to be used with computer animation, giving birth to the new age of Motion Capturing.





Sports
Motion capture is used by athletes to improve their technique. Most sports related motion capture programs will concentrate on joint angles, body alignment, velocities, and power flows. Athletes ranging from runners to tennis players to cricket bowlers have used motion capturing to improve and hone their skills. Innovative Sports Training has developed The MotionMonitor to assist in your golf swing, among other helpful applications. external image MMSGolfSwing.jpg

Video Games
Motion Capturing has been used in the development of video games by having people acting out what is supposed to be in the game. In sports games, athletes are used so that game can be authentic by having player's real batting stances or pitching motions and other things.
Toronto's Maurice Edu during a motion capturing session for FIFA Soccer '09
Toronto's Maurice Edu during a motion capturing session for FIFA Soccer '09


Motion capturing doesn't only affect the way video games are made but also how they are played. Wii uses a motion sensing controller and lets the person playing the game take a more active role in the gameplay. Project Natal for Xbox promises to eliminate the need for the game-controller altogether, or more accurately, the player's body will be the controller.

Project Natal
Project Natal


Medicine
Medical students have used Motion Capturing to help them learn more about the body and how it works. This also gives them more insight of the body when the body is moving. Use of motion capture also helps medical students quantify the improvement over time of their rehabilitation or surgical efforts. Motion Capturing also is used with physical therapy and can be used to help with injury prevention with not only sports related activities but with day-to-day actions that we all do.
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A person using "The Lift Trainer"
Motion and Gait Analysis
Motion and Gait Analysis



Research
Motion capture research labs all over the country are working to find new ways to use the technology. Ohio State University’s Advanced Computing Center for the Arts and Design (ACCAD) is one of those labs. The ACCAD captures human, animal, and other motion in order to collect data for various purposes.

The Ford Motor Company has recently started using motion capture to research and study how people actually move while they are in a car. Ford’s system is called the Human Occupant Package Simulator (HOPS). The human test subject is equipped with 50 motion capturing sensors and performs various everyday movements such as reaching for their seat belt. The goal of HOPS is to provide data to help produce more ergonomic and safer cars.

Motion Capture Technology is used in research like National Geographic's Fight Science.

This scenario displayed that the impact of a Muay Thai knee kick produced an effect equivalent to that of a car going 35 mph
This scenario displayed that the impact of a Muay Thai knee kick produced an effect equivalent to that of a car going 35 mph




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