Motion capture has numerous applications. For example, in filmmaking, digital models generated using motion capture can be used as the basis for the motion of computer generated characters or objects. In sports, motion capture can be used by coaches to study an athlete's movements and guide the athlete toward improved body mechanics. In video games or virtual reality applications, motion capture allows a person to interact with a virtual environment in a natural way, e.g., by waving to a character, pointing at an object, or performing an action such as swinging a golf club or baseball bat.
The term “motion capture” refers generally to processes that capture movement of a subject in three-dimensional (3D) space and translate that movement into, for example, a digital model or other representation. Motion capture is typically used with complex subjects that have multiple separately articulating members whose spatial relationships change as the subject moves. For instance, if the subject is a walking person, not only does the whole body move across space, but the positions of arms and legs relative to the person's core or trunk are constantly shifting. Motion capture systems can model this articulation.
Depending on the space being monitored, more than one motion sensor can be deployed. For example, the monitored space can have obstructions that prevent a single motion sensor from “seeing” all relevant activity or it can be desired to monitor a moving object from multiple vantage points. In order to combine images of common or overlapping subject matter from multiple sensors, it is necessary for the sensors to be calibrated to a common coordinate frame of reference. Similar requirements occur in medical imaging applications where more than one imaging modality (e.g., MRI and CT apparatus) is employed to scan the same anatomic region to produce enhanced images in register. In such applications, the reference frames of the imaging devices are aligned with each other and with the geometry of the treatment room using sophisticated laser sighting equipment. Such measures are not practical for many if not most applications involving motion sensing, however—particularly for consumer or gaming applications; in such cases users should be free to move the sensors at will and without inconvenience.