Mark / mark /Marker is a marker that has a special reflective material on the surface. The common shape is spherical, hemispherical, spherical and coded mark. In the motion information acquisition in the field (such as 3D motion capture, three-dimensional gait analysis), usually in the capture object is pasted on the point marked points can reflect the light emitted by the device (usually infrared light), and then the reflection data are received by a device, then the received data processing system. In this way, we can obtain the information of the object / human body movement. Shot in the natural light under the effect of the shooting.