Motion capture system includes mechanical link, magnetic sensor, optical sensor, acoustic sensor and inertial sensor. Each technology has its own advantages, but no matter which technology, users will be limited.
● Optics uses optical perception to determine the real-time position and direction of an object. Optical equipment mainly includes photosensitive equipment (receiver), light source (emitter) and controller for signal processing. There are all kinds of photosensitive devices, such as ordinary cameras and photodiodes. The light source can be ambient light or structured light. In order to prevent the interference of visible light, infrared light, laser, etc. Usually used as a light source. Due to the fast propagation speed of light, the most obvious advantages of optical equipment are high speed, high update rate and low delay, which is more suitable for real-time occasions and works well in a small range. The working principle of infrared passive optical motion capture: the capture space is composed of multiple cameras, and the near-infrared LEDs on the cameras illuminate the reflection mark points on the target (the surrounding light sources in the above picture are near-infrared light sources). The camera carries out infrared imaging on the landmark point, extracts the two-dimensional information of the landmark point, and calculates the three-dimensional position information of the landmark point through the spatial data fed back by multiple cameras. The motion capture system will complete the continuous shooting, image storage, analysis and processing of performers' actions.
● Inertia formula obtains the position of the tracked object through blind derivation, that is to say, it is completely calculated through the internal motion system. The advantages are no emission source, no fear of shielding, no external interference and unlimited working space. The disadvantage is that the error accumulates quickly.
● Mechanical tracking is an ancient way, which consists of a connecting rod device. It is a system with low price, high precision and short response time. It can measure the whole body motion of an object without delay, and is not interfered by external environment such as sound, light and electromagnetic waves. In addition, it can also be combined with a force feedback device. Disadvantages are heavy, inflexible and inertia. Due to the limitation of mechanical connection, its workspace is also limited to a certain extent, and there is still a central area in the workspace that cannot be entered, commonly known as the dead angle of mechanical system, which leads to the inability of mechanical equipment to enter.
The electromagnetic type uses the strength of the magnetic field to track the position and direction. Generally including transmitter, receiver, interface and computer. The advantage is that there is no occlusion problem, and other objects are allowed between the receiver and the transmitter, which enables the user to walk. Compared with other motion capture devices, it has the advantages of low price, moderate accuracy, high sampling rate (up to 120 times per second) and wide working range (up to 60m), allowing multiple magnetic trackers to track the whole body motion and increasing the tracking range. The disadvantage is that it is easily interfered by electronic equipment and ferromagnetic materials, which may lead to magnetic field deformation and error. The measurement distance increases, the error increases, the delay is large (33ms), and the jitter is small.