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Remove patently-false claims. I hate this paragraph, but removing the patently-false claims meant I had to reword it.
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{{see also|Markerless outside-in tracking|Positional tracking}}
==Introduction==
[[File:Outside in tracking.png|thumb|Figure 1. Outside-in tracking (Image: www.wareable.com)]]
Outside-in VR tracking uses cameras or other sensors placed in a stationary location and oriented towards the tracked object (e.g. a headset) that moves freely around a designated area defined by the intersecting visual ranges of the cameras (Figure 1). The object is therefore observed from outside by the fixed tracking device. Usually, the tracked object has a known set of markers that are essential for the calculation of its position relative to the sensors. Also, while this type of positional tracking can be achieved using the visible light spectrum, it is common to use infra-red (IR) markers and cameras that can detect that type of light. <ref name=”1”></ref> <ref name=”2”> Mehling, M. (2006). Implementation of a Low Cost Marker Based Infrared Optical Tracking System. PhD thesis, Fachhochschule Stuttgart</ref> <ref name=”3”> Boger, Y. (2014). Positional tracking: "Outside-in" vs. "Inside-out.” Retrieved from http://vrguy.blogspot.pt/2014/08/positional-tracking-outside-in-vs.html</ref>
Outside-in tracking using markers is a well-developed and researched technology. Indeed, a group of researchers (Pustka et al., 2012) built a positional tracking system of this kind using only unmodified off-the-shelf mobile phones. Also, an early two-camera tracking system was described by Madritsch and Gervautz in 1996, and a system that used synchronized IR cameras, able to distinguish 6D targets, was described by Dorfmüller in 1999. <ref name=”5”> Pustka, D., Hülb, J.P., Willneff, J., Pankratz, F., Huber, M. and Klinker, G. (2012). Optical Outside-In Tracking using Unmodified Mobile Phones. IEEE International Symposium on Mixed and Augmented Reality</ref>
The outside-in tracking system needs room calibration after the cameras or sensors are placed, and the data acquired by the system is processed on a computer. <ref name=”3”></ref> <ref name=”5”></ref> Besides its application in VR, this type of tracking is used in motion capturing, as in the case of the film industry. <ref name=”2”></ref>
Outside-in tracking functions as the inverse of [[inside-out tracking]] (Figure 2). While the former places the sensors in a stationary location to track the VR goggle, in the latter the sensors are placed on the goggles and the markers in stationary locations. <ref name=”3”></ref> <ref name=”7”> Ishii, K. (2010). Augmented Reality: Fundamentals and nuclear related applications. Nuclear Safety and Simulation, 1(1)</ref>
==Devices using outside-in tracking==
'''[[Oculus Rift|Rift]]''' (including [[Oculus Rift DK2|Rift development kit]])
'''[[PlayStation VR]]'''
