Validity of the Catapult ClearSky T6 Local Positioning System for Team Sports Specific Drills, in Indoor Conditions

Abstract

Aim: The aim of the present study was to determine the validity of position, distance traveled and instantaneous speed of team sport players as measured by a commercially available local positioning system (LPS) during indoor use. In addition, the study investigated how the placement of the field of play relative to the anchor nodes and walls of the building affected the validity of the system.Method: The LPS (Catapult ClearSky T6, Catapult Sports, Australia) and the reference system [Qualisys Oqus, Qualisys AB, Sweden, (infra-red camera system)] were installed around the field of play to capture the athletes' motion. Athletes completed five tasks, all designed to imitate team-sports movements. The same protocol was completed in two sessions, one with an assumed optimal geometrical setup of the LPS (optimal condition), and once with a sub-optimal geometrical setup of the LPS (sub-optimal condition). Raw two-dimensional position data were extracted from both the LPS and the reference system for accuracy assessment. Position, distance and speed were compared.Results: The mean difference between the LPS and reference system for all position estimations was 0.21 ± 0.13 m (n = 30,166) in the optimal setup, and 1.79 ± 7.61 m (n = 22,799) in the sub-optimal setup. The average difference in distance was below 2% for all tasks in the optimal condition, while it was below 30% in the sub-optimal condition. Instantaneous speed showed the largest differences between the LPS and reference system of all variables, both in the optimal (≥35%) and sub-optimal condition (≥74%). The differences between the LPS and reference system in instantaneous speed were speed dependent, showing increased differences with increasing speed.Discussion: Measures of position, distance, and average speed from the LPS show low errors, and can be used confidently in time-motion analyses for indoor team sports. The calculation of instantaneous speed from LPS raw data is not valid. To enhance instantaneous speed calculation the application of appropriate filtering techniques to enhance the validity of such data should be investigated. For all measures, the placement of anchor nodes and the field of play relative to the walls of the building influence LPS output to a large degree.

Football-specific validity of TRACAB’s optical video tracking systems

“…Otherwise, no conclusions can be drawn as to whether the observed deviations result from the system's measurement inaccuracy or merely from differing data-processing decisions. In addition, the raw position might be the most unaffected variable and should be used as the primary variable to compare measurements between different positioning systems' acquisition technology [21]. It is for this reason that we decided to apply the very same data processing steps to both VICON's and TRACAB's raw data.…”

“…Accordingly, analysis of validity and reliability of EPTS has been subject to extensive research in recent years. While a large and ever-increasing number of GNSS and LPS validation studies can be found [7,8,[18][19][20][21][22], only a few studies are available that validated the measurement accuracy of football-specific video tracking systems. To date, two studies fulfil this criterion.…”

“…Since tracking systems differ significantly in terms of the applied camera setup, sampling rates and data processing steps, validation results of one system cannot be extended to others [27]. Instead, individual validation of each system is required [21,25]. A secondary aim of the study was to assess whether there is a difference between the Gen4 and the Gen5 system.…”

Accuracy and Inter-Unit Reliability of Ultra-Wide-Band Tracking System in Indoor Exercise

“…A different method should be used to evaluate the accuracy of the position of players on the court or to estimate instantaneous velocities (real-time analysis). Only three studies have evaluated position data, and these studies used LPS-based technology with video analysis as a reference [5,18,19]. LPS and video analysis are costly and complex to use.…”

“…In particular, the reference system is based on fixed cameras and can therefore only acquire data in restricted areas [20]. In this sense, no studies have been found that have evaluated the accuracy of a tracking system in a complete field of play, where instead they only exist in confined and controlled spaces [3,5,18,19,21]. The capture volume is dependent on the maximum number of cameras and the field of view of each camera.…”