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[[File:Inside out vs. outside in tracking.png|thumb|Figure 1. Inside-out vs. outside-in tracking (Image: Ishii, 2010)]][[File:F2Ak4iE.jpg|thumbnail|Figure 2. Early [[Lighthouse]] prototype, an inside-out tracking system with QR codes as [[fiducial markers]].]]In [[File:Acer mixed reality headset inside-out.png|thumb|Figure 3. Inside-out tracking]], the tracking camera is placed on the [[device]] being tracked such as an [[HMD]](image: www. The device looks out to the world around it and uses the changing perspectives of the outside world to determine its own position in spacewareable. [[Fiducial markerscom)]] such as QR codes can be placed in the outside world to serve as reference points for the tracking camera.

The opposite ==Introduction==Inside-out tracking is a method of [[positional tracking]] commonly used in [[virtual reality]] (VR) technologies, specifically for tracking the position of [[head-mounted display|head-mounted displays]] (HMDs) and motion controller accessories. It differentiates itself from [[outside-in tracking]] by the location of the cameras or other sensors that are used to determine the object’s position in space (Figure 1). In inside-out positional tracking , the camera or sensors are located on the device being tracked (e.g. HMD) while in outside-out the sensors are placed in a stationary location. <ref name=”1”> Ribo, M., Pinz, A. and Fuhrmann, A.L. (2001). A new optical tracking system for virtual and augmented reality applications. Instrumentation and Measurement Technology Conference Proceedings</ref> <ref name=”2”> 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> <ref name=”3”> Ishii, K. (2010). Augmented Reality: Fundamentals and nuclear related applications. Nuclear Safety and Simulation, 1(1)</ref> A VR device using inside-out tracking looks out to determine how its position changes in relation to the environment. When the headset moves, the sensors readjusts its place in the room and the virtual environment responds accordingly in real time. This type of positional tracking can be achieved with or without markers placed in the environment. The latter is called [[markerless inside-out tracking]]. <ref name=”4”> Langley, H. (2017). Inside-out v Outside-in: How VR tracking works, and how it's going to change. Retrieved from https://www.wareable.com/vr/inside-out-vs-outside-in-vr-tracking-343</ref> The cameras (or any other optical sensors) that are placed on the HMD observe features of the surrounding environment. When using markers, these are designed to be easily detected by the tracking system and placed in a specific area. These [[fiducial markers]] include primitive shapes like points, squares, and circles (Figure 2). QR codes are an example of positional markers that can be placed in the outside world to serve as reference points for the tracking camera. Inside-out positional tracking can also be achieved using infra-red (IR) markers and a camera that is sensitive to this type of light. In case of using markers, the inside-out system works only as long as it can detect the markers. If these are out of its field of view, positional tracking will be affected. <ref name=”2”></ref> <ref name=”3”></ref> <ref name=”5”> Mehling, M. (2006). Implementation of a Low Cost Marker Based Infrared Optical Tracking System. PhD thesis, Fachhochschule Stuttgart</ref> With markerless inside-out tracking - a method based on natural features - uses distinctive characteristics that originally exist in the environment to determine position and orientation. The system’s algorithms identify specific images or shapes and uses them to calculate the device’s position in space. Data from accelerometers and gyroscopes can also be used to increase the precision of positional tracking. <ref name=”3”></ref> <ref name=”6”> Boger, Y. (2014). Overview of positional tracking technologies for virtual reality. Retrieved from http://www.roadtovr.com/overview-of-positional-tracking-technologies-virtual-reality/</ref> With inside-out, the data that is gathered is generally processed by the headset., giving the user an increased mobility within a room. It can also be the case that the sensors are connected to a computer that is carried by the user or the signal is sent wirelessly to a stationary processing unit, but since inside-out tracking aims to provide more freedom of use the optimal solution is the headset providing all the computational power. <ref name=”2”></ref> There is a great deal of interest in inside-out technology. While outside-in solutions are still better for accuracy and latency, there has been big investments in researching and developing inside-out tracking for it to become the leading positional tracking technology. Indeed, it became the big VR trend of 2017, with the potential to make VR more convenient and accessible. <ref name=”4”></ref> <ref name=”7”> Robertson, A. (2017). Self-tracking headsets are 2017’s big VR trend — but they might leave your head spinning. Retrieved from https://www.theverge.com/2017/1/12/14223416/vr-headset-inside-out-tracking-intel-qualcomm-microsoft-ces-2017</ref> High-end VR headsets use external cameras or other sensors to calculate the user’s position in space and translate it to the virtual environment, and mobile VR systems have no positional tracking. Inside-out technology could not only simplify the setup for high-end headsets but also expand the capabilities of mobile VR. <ref name=”7”></ref> Companies are starting to offer interesting inside-out solutions. Microsoft has been investing in this technology for a while, with the [[HoloLens]]and, more recently, with the new line of mixed reality headsets which includes the [[Acer Windows Mixed Reality Headset]] (Figure 3). [[Oculus]] has announced an inside-out prototype called Santa Cruz, and Qualcomm’s 835 reference headset is designed to help other manufacturers build their own systems. Intel has also shown a version of its Project Alloy - a “merged reality” HMD that uses inside-out tracking. Finally, Google has presented an inside-out system named WorldSense intended for use with the VR headsets for the Daydream platform. <ref name=”4”></ref> <ref name=”7”></ref> <ref name=”8”> Lang, B. (2017). Google announces ‘WorldSense’ inside-out tracking for standalone daydream VR headsets. Retrieved from http://www.roadtovr.com/google-announces-worldsense-inside-tracking-standalone-daydream-vr-headsets/</ref> ==Pros and Cons of inside-out positional tracking==The main advantage of inside-out systems is the freedom - the increased mobility - they give to the users. While outside-in systems provide great accuracy, they need external sensors. With inside-out, the computer can calculate the headset’s position based on signals like depth and acceleration, without a fixed point of reference (if it is a markerless system, which is the intended objective of the companies investing in this technology). Another advantage is that inside-out systems may not suffer from occlusion. This occurs in outside-out tracking, when the user gets out of the field of view of the external cameras. On the other hand, having a device that can determine orientation and position independently of external cameras or sensors provides a deeper sense of immersion. Finally, inside-out is essential for augmented and mixed reality since these technologies demand more mobility from the systems. <ref name=”3”></ref> <ref name=”4”></ref> <ref name=”7”></ref> Currently, inside-out tracking systems still lack in accuracy and latency, although improvements are constantly made. It requires good computer vision, that is a bit further behind outside-in solutions. Another disadvantage is that all the computational work must be done by the HMD. <ref name=”4”></ref> ==Future of inside-out tracking==An inside-out system with perfect accuracy is considered the holy grail of positional tracking. While it is expected that the technology will evolve considerably in the future, outside-in will continue to exist as the best solution for high-end VR systems. This specific market will probably be the last to adopt inside-out tracking. The implementation of augmented reality systems will also likely drive the use of inside-out since those systems require great mobility. According to Youssri Helmy, CEO of Eonite, when referring to inside-out said that “It’s got to happen. We think it's crucial. It's like the invention of the mouse with the GUI.” <ref name=”4”></ref> <ref name=”7”></ref>