# Evaluation of the SteamVR Motion Tracking System with a Custom-Made Tracker
## 1 Introduction  
Virtual reality (VR) systems have been gaining popularity in recent years due to the development of virtual technologies. They have become cheaper, the image visualisation possibilities have increased, and motion controllers more accurately transfer the user's actual actions to the virtual world. All this means that the use of virtual reality systems for applications much more advanced than those commonly associated with entertainment is being considered more often [1, 2, 3]. To name but a few industries, virtual reality is used in medicine [4, 5], sport [6], and in military applications [7], where the typical use is for shooting simulators [8, 9]. Some simulators display the image on a large screen but, in immersive solutions, the virtual world image is shown on a head-mounted display (HMD). Proper training in a virtual environment ensures cost reductions, increased training safety, as well as the possibility of creating many training scenarios. The usefulness of a given training system, including a virtual one, is primarily determined by the transfer value, which means the possibility of applying the knowledge and skills acquired during training to a real environment and situations where they are used and needed [10]. The transfer value of virtual training simulators is influenced by several factors, such as immersion, i.e., the impression of being present in the virtual world, fidelity of the real-world representation, and the level of user acceptance of a given simulator [11, 12, 13]. For immersive shooting simulators, all these factors largely depend on the accuracy with which the application is able to reproduce the weapon's real movements. Therefore, it is extremely important to choose the right motion tracking system. Such a system provides real-time data on the position (coordinates x, y, z) and orientation (angles \(\alpha\), \(\beta\), \(\gamma\)) of the tracked object. It is essential that this data is continuously measured and delivered to the application without significant delays (below 20 ms [14]). It is equally important that the measurement is characterised by high precision (low random error value) and trueness (low systematic error value). There are several types of motion tracking systems available on the market, the most popular of which are marker optoelectronic solutions, characterised by their highaccuracy [15; 16; 17]. In this respect, multi-camera systems are the best solution, [18] but their use entails the complicated installation and calibration of cameras and, above all, a high price. Single-camera systems are much simpler and cheaper [19], however they do not provide sufficient accuracy and, moreover, there may be problems with the camera's visibility of the tracked object, causing interruptions in tracking. An alternative approach to the systems considered above is the lighthouse solution [20; 21], in which base stations located in the room are stationary, and the tracked object is equipped with a set of detectors. An example of this type of system is SteamVR (the full name is SteamVR Tracking), developed by Valve, which is used in commercial devices such as the HTC VIVE virtual reality set. SteamVR is an open system and can be used by other companies implementing it to track the devices they manufacture. Hardware development kits provided by Triad Semiconductors and Virtual Builds are helpful in implementing this technology [22]. This system was used in the developed PIORUN [23] shooting simulator (Polish MANPADS missile system). Initially, a commercial product from HTC VIVE was used as a tracked device (tracker). The SteamVR system operating with this tracker was tested [24], which proved the accuracy of the motion tracking was sufficient, but there were some problems with maintaining uninterrupted tracking of the launcher model. Accordingly, a proprietary design for the tracking device was developed, which was able to ensure continuous measurement of an object with dimensions as large as the PIORUN missile launcher.