Accuracy of the LPM tracking system considering dynamic position changes

Abstract

This study investigates the accuracy of the tracking system LPM (local position measurement). The goal was to determine detailed error values of the system in the context of sports performance analyses. Six moderately trained male soccer players (amateur level) performed 276 runs on three different courses at six different speeds. Additionally, ten small-sided game plays were carried out. All runs and game plays were recorded with the LPM tracking system and the motion capture system VICON simultaneously. VICON served as the reference system. The absolute error of all LPM position estimations was on average 23.4±20.7 cm. The estimation for average velocities varied between 0.01 km h(-1) and 0.23 km h(-1), the maximum speed estimations differed by up to 2.71 km h(-1). In addition, the results showed that the accuracy of the LPM system is highly dependent on the instantaneous dynamics of the player and decreases in the margins of the observation field. These dependencies were quantified. Considering commonly used applications of position tracking systems in sports (Leser, Ogris, & Baca, 2011), the accuracy of LPM is acceptable for position and velocity estimations. The system provides valuable results for average velocities but seems to be far less reliable when dealing with high dynamic movements and measuring instantaneous velocities.

Measuring Acceleration and Deceleration in Soccer-Specific Movements Using a Local Position Measurement (LPM) System

“…Considering only the straight and 90° changeof-direction movements, the average and maximal errors of LPM average speed in our study (0.1% and 2.0%, respectively) were less than in the study of Frencken et al 15 (-2.8% and -3.9%, respectively). Furthermore, our results indicated that peak speed estimation of LPM differed between -4% and 3% (0.6% on average) from the gold standard, which is considerably less than the average relative difference of 10% found by Ogris et al 18 One of the reasons for the lower average-and peak-speed error estimation of LPM in our study compared with other studies, apart from differences in protocol, can be the newer version of the LPM system used in the current study. As already indicated by Ogris et al, 18 this newer version has improved filter algorithms, including Kalman filtering, which probably reduces position-estimation error, thereby improving the tracking of the dynamics.…”

“…Furthermore, our results indicated that peak speed estimation of LPM differed between -4% and 3% (0.6% on average) from the gold standard, which is considerably less than the average relative difference of 10% found by Ogris et al 18 One of the reasons for the lower average-and peak-speed error estimation of LPM in our study compared with other studies, apart from differences in protocol, can be the newer version of the LPM system used in the current study. As already indicated by Ogris et al, 18 this newer version has improved filter algorithms, including Kalman filtering, which probably reduces position-estimation error, thereby improving the tracking of the dynamics. A Kalman filter is an algorithm that predicts data based on a weighting of the dynamics of previous data combined with the current measurement.…”

“…19 Moreover, data on acceleration or deceleration were not reported. In discussing their study's limitations, Ogris et al 18 specifically indicated that they expect that the newer versions of the LPM system in combination with the latest filtering techniques could positively influence the estimation of the dynamics.…”

“…[15][16][17] Recently, Ogris et al 18 compared a local position measurement (LPM) system with Vicon, a 3-dimensional motion-capture system, under realistic, dynamic conditions. However, despite the use of a gold standard and a wide range of movement intensities and movements involving accelerations, the participants in the Ogris et al study performed neither movements at maximal acceleration and deceleration nor movements involving a 180° change of direction, as occur frequently during soccer.…”

The validity and reliability of a novel indoor player tracking system for use within wheelchair court sports

“…Radio-frequency tracking systems have emerged, which gather similar data to GPS, with both the Local Position Measurement (LPM) system (Frencken, Lemmink, & Delleman, 2010;Ogris et al, 2012) and the Wireless Ad-hoc System for Positioning (WASP) (Hedley et al, 2010;Sathyan, Shuttleworth, Hedley, & Davids, 2011) currently available. These systems rely on distance measurements between known fixed base stations and mobile tags worn by the athlete (Leser, Baca, & Ogris, 2011).…”