Markerless outside-in tracking
Positional tracking is an essential component of both virtual reality (VR) and augmented reality (AR), contributing to a greater sense of immersion and presence. It determines the position and orientation of an object within the environment. In VR, this allows for the movements of the user to be translated into the virtual environment, and in AR it is essential for the placement of digital content into real objects or spaces. Markerless outside-in tracking is a composite term that defines a form of positional tracking that uses two specific methods: markerless tracking and outside-in tracking.  
Markerless tracking is a method of motion tracking that avoids the use of markers (also known as fiducial markers). These markers are usually placed in the environment or in the head-mounted displays (HMDs), helping the system determine the users or camera position. The Markerless method uses instead natural features already present in the environment, for tracking purposes.  .
Markerless outside-in tracking is a technology that was used prior to the wide availability of consumer VR devices. Two popular non-VR systems based on this form of tracking are the PlayStation EyeToy, released in October 2003, and the Xbox Kinect, released in November 2010.
With markerless outside-in tracking, cameras are mounted in the environment, such as on top of a television set, and aimed at the user. The user's movements are tracked without requiring any kind of markers or other hardware. The disadvantage of this system is that lacks the fine spacial accuracy and low-latency of marker-based systems.
Advantages of markerless outside-in tracking
Disadvantages of markerless outside-in tracking
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