# Evaluation of the SteamVR Motion Tracking System with a Custom-Made Tracker
## 2 Tracker and Measurement Setup  
The subject of the research was the SteamVR system tracker equipped with a set of sensors (a photodetector with a signal conditioning system) receiving a predetermined sequence of signals from the base stations. By analysing these signals, the SteamVR system is able to determine the position and orientation of the tracker. The predicted random error of the measurement is inversely proportional to the distance between the sensors. The tracker structure was designed using the CAD program; simulation software included in the SteamVR Hardware Development Kit (SteamVR HDK version 04558546), as well as analytical and simulation programs prepared by the author. The project was optimised so that the designed device was characterised by a high accuracy of the position and orientation measurements in the range of 0-360\({}^{\circ}\) azimuth and 0-60\({}^{\circ}\) elevation angles for the 2 \(\times\) 2 m working area, which means:  
1. High precision, expressed by the standard deviation (\(SD\)) of the measurement results for each of the vector components: \(\bullet\) position (\(SD_{X}\), \(SD_{Y}\), \(SD_{Z}\)) below 1 mm; \(\bullet\) orientation (\(SD_{A}\), \(SD_{B}\), \(SD_{\Gamma}\)) below 0.1\({}^{\circ}\). 2. High trueness, which translates into the difference (\(\Delta\)) between the mean measured value and the real value of the measured quantity: \(\bullet\) each of the position components (\(\Delta_{X}\), \(\Delta_{Y}\), \(\Delta_{Z}\)) below 10 mm; \(\bullet\) orientation (\(\Delta_{orientation}\)) below 1\({}^{\circ}\). The result of the design work was a model equipped with 24 sensors, which at the simulation stage had better parameters than commercial devices available on the market. Based on the model, a prototype of the device was made using 3D printing. Photos of the model and prototype are shown in Figure 1.  
The prototype was tested, which confirmed that the simulation program's predictions about the number of visible sensors were correct. Therefore, further tests were started, the aim of which were to determine the tracker's parameters in conditions typical for a shooting simulator. A measuring setup was prepared in a laboratory room with dimensions of 3.6 by 4.5 m and a height of 1.98 to 2.15 m. Strong light sources and reflective elements that could distort the measurements were removed from the room. Two base stations (BS1 and BS2) of the SteamVR system were placed in opposite corners of the room at heights of 2.09 and 1.89 m. Their orientations were chosen so that they faced the centre of the room, and the inclination was set at 30\({}^{\circ}\) from the vertical. This is the minimum suggested value associated with the lower than recommended mounting height of the base stations. The distance between the base stations was over 5 m, which is more than the maximum distance for correct optical synchronisation. Therefore, wire synchronisation was used, which guaranteed uninterrupted work during the measurements. On the floor, in the centre of the room, nine measurement points were marked out, within a square with sides of 2 m. The distance between the points was 1 m. The distribution scheme for the measurement points is shown in Figure 2.  
Figure 1: The lower part of the tracker model prepared for printing: with electronic components (**a**); a photo of the tracker prototype (**b**); and its dimensions (units—mm) (**c**). At each of the nine points marked with the symbol \"x\", a tripod with a mounted launcher was placed sequentially. The tests were carried out for the launcher at a height of 1.6 m, which corresponds to the average height of a human arm. The geared tripod head Manfrotto 405 allowed the desired orientation of the launcher to be set. The tests were performed for the angles \(\varphi=0\)-360\({}^{\circ}\) (azimuth) in steps of 30\({}^{\circ}\) and \(\theta=0\)-80\({}^{\circ}\) (elevation) in steps of 20\({}^{\circ}\).