Editing Motion capture (section)

==Non-optical systems==

===Inertial systems===
Inertial motion capture<ref>{{Cite web|url=http://www.xsens.com/images/stories/PDF/MVN_white_paper.pdf|title=Full 6DOF Human Motion Tracking Using Miniature Inertial Sensors|access-date=2013-04-03|archive-date=2013-04-04|archive-url=https://web.archive.org/web/20130404224049/http://www.xsens.com/images/stories/PDF/MVN_white_paper.pdf|url-status=dead}}</ref> technology is based on miniature inertial sensors, biomechanical models and [[sensor fusion]] algorithms.<ref>{{Cite web|url=https://www.xsens.com/fascination-motion-capture/|title=A history of motion capture|website=Xsens 3D motion tracking|language=en-US|access-date=2019-01-22|archive-date=2019-01-22|archive-url=https://web.archive.org/web/20190122195540/https://www.xsens.com/fascination-motion-capture/|url-status=dead}}</ref> The motion data of the inertial sensors ([[inertial guidance system]]) is often transmitted wirelessly to a computer, where the motion is recorded or viewed. Most inertial systems use inertial measurement units (IMUs) containing a combination of gyroscope, magnetometer, and accelerometer, to measure rotational rates. These rotations are translated to a skeleton in the software. Much like optical markers, the more IMU sensors the more natural the data. No external cameras, emitters or markers are needed for relative motions, although they are required to give the absolute position of the user if desired. Inertial motion capture systems capture the full six degrees of freedom body motion of a human in real-time and can give limited direction information if they include a magnetic bearing sensor, although these are much lower resolution and susceptible to electromagnetic noise. Benefits of using Inertial systems include: capturing in a variety of environments including tight spaces, no solving, portability, and large capture areas. Disadvantages include lower positional accuracy and positional drift which can compound over time. These systems are similar to the Wii controllers but are more sensitive and have greater resolution and update rates. They can accurately measure the direction to the ground to within a degree. The popularity of inertial systems is rising amongst game developers,<ref name="Xsens MVN Animate - Products"/> mainly because of the quick and easy setup resulting in a fast pipeline. A range of suits are now available from various manufacturers and base prices range from $1000 to US$80,000.

===Mechanical motion===
Mechanical motion capture systems directly track body joint angles and are often referred to as exoskeleton motion capture systems, due to the way the sensors are attached to the body. A performer 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 from 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 system. Some suits provide limited force feedback or [[Haptic technology|haptic]] input.

===Magnetic systems===
{{Main|Positional tracking#Magnetic tracking}}
Magnetic systems calculate position and orientation by the relative magnetic flux of three orthogonal coils on both the transmitter and each receiver.<ref name="NGen10Mag">{{cite journal|title=Motion Capture: Magnetic Systems|journal=[[Next Generation (magazine)|Next Generation]]|issue=10|publisher=[[Imagine Media]]|date=October 1995|page=51}}</ref> 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. The sensor output is [[six degrees of freedom]] (6DOF), which provides useful results obtained with two-thirds the number of markers required in optical systems; one on upper arm and one on lower arm for elbow position and angle.{{citation needed|date=August 2016}} The markers are vulnerable to magnetic and electrical interference from metal objects in the environment, like rebar (steel reinforcing bars in concrete) or wiring, which affect the magnetic field, and electrical sources such as monitors, lights, cables and computers.

The sensor response is nonlinear, especially toward edges of the capture area. The wiring from the sensors tends to preclude extreme performance movements.<ref name="NGen10Mag"/> With magnetic systems, it is possible to monitor the results of a motion capture session in real time.<ref name="NGen10Mag"/> The capture volumes for magnetic systems are dramatically smaller than they are for optical systems. With the magnetic systems, there is a distinction between [[Alternating current|alternating-current]] (AC) and [[Direct current|direct-current]] (DC) systems: DC system uses square pulses, AC systems use sine waves.

=== Stretch sensors ===
Stretch sensors are flexible parallel plate capacitors that measure either stretch, bend, shear, or pressure and are typically produced from silicone. When the sensor stretches or squeezes its capacitance value changes. This data can be transmitted via Bluetooth or direct input and used to detect minute changes in body motion. Stretch sensors are unaffected by magnetic interference and are free from occlusion. The stretchable nature of the sensors also means they do not suffer from positional drift, which is common with inertial systems. Stretchable sensors, on the other hands, due to the material properties of their substrates and conducting materials, suffer from relatively low [[signal-to-noise ratio]], requiring [[Filter (software)|filtering]] or [[machine learning]] to make them usable for motion capture. These solutions result in higher [[Latency (engineering)|latency]] when compared to alternative sensors.