## 6 Localization Systems
### Outdoor Localization Systems  
The leading technologies employed for localization in outdoor applications are based on GNSS or video analysis performed with multiple camera recording systems. The latter method is also widely used to support the referees in specific action evaluations. In addition, recent studies show that these proposed sensor fusion methods can give good precision in the order of meter level in outdoor positioning and centimeter level for indoor [190; 191; 192]. Wearable Navigation Systems  
GNSS is widely used in sports to study the position, intensity, volume, and nature of athletes' movements, especially in sports where considerable activity occurs in an open environment. They are widely used, for example, in football and similar sports, to study the specificities of players' movements in various game roles or to quantify the kinematic variables of a canoe. Since the last decade, numerous studies have been conducted using GNSS on footballers. The analysis of the examined studies showed that athletes' competition loads, positions, movement patterns, heart rate, and speed data are the parameters mainly investigated [193; 194; 195; 196]. Thus far, there are six satellite positioning systems (GNSS) in orbit: the Global Positioning System (GPS) by the United States, the Global Navigation Satellite System (GLONASS) by the Russian Federation, the European Galileo System by European Global Navigation Satellite Systems Agency, the Chinese BeiDou, the Indian Regional Navigation Satellite System (IRNSS) by India, and the Japanese Quasi-Zenith Satellite System (QZSS). The latest GNSS receivers are designed to support multi-constellation (most, if not all, of the available satellite constellations) and multi-frequency signals. These features aim to exploit satellite redundancy and, using some high-performant processing algorithms, fulfill localization error mitigation, allowing different sensor family integration. Moreover, thanks to the availability of several low-cost devices, and since these systems can retrieve the actual position with high reliability, accuracy, and continuity, the number of applications using GNSS is continuously growing [197; 198]. However, these systems have limitations regarding kinematic analysis to detect vertical motions in any condition. For a better assessment of these movements, GNSS is often integrated using accelerometers or video analysis [199]. Studies to validate the use of a GNSS with an accelerometer unit (GNSS-Acc) were conducted to quantify the kinematic variables of the canoe. The analysis examined eight canoe and kayak sprint races, including 200 and 500 m distances [200]. A digital camera was positioned on the side for data collection, tracking the kayak's bow or canoe throughout each race. Simultaneously, a GNSS-Acc unit recorded relevant data such as the boat's position, speed, and acceleration. This comprehensive approach provided valuable insights into the performance and dynamics of the races. The GNSS-Acc unit data was analyzed using a self-developed routine. The agreement between the video and the GNSS-Acc analysis was measured, and no differences were found between the two methodologies, except for the time and speed at the first 50 m, thus suggesting an agreement between the analysis methods. The GNSS-Acc unit is suitable for quickly and accurately measuring kinematic variables, mainly boat speed and ride rate. However, video analysis is required for a detailed examination of the paddling technique when a more comprehensive understanding is  
Figure 8: An example of a hockey UWB system for localization of a player in the field. desired [201]. Some systems that integrate GNSS, video analysis, and strain gauges are used to evaluate the efficiency of the interaction among the members of a flat-water sprint kayak crew [108]. In particular, the latest multi-channel wireless systems include a high-frequency GNSS receiver, an IMU, and two force channels for the paddle and foot brace.