The value of GNSS in a stadium environment
At Catapult, data accuracy is of the utmost importance when releasing a new product. This was particularly evident with the engineering of the market-leading OptimEye S5, elite team sport’s first GNSS device.
GNSS refers to Global Navigation Satellite System, which is an umbrella term that covers all satellite-based navigational technologies. Currently the only two available are the US Global Positioning System (GPS) and the Russian Globalnaya Navigazionnaya Sputnikovaya Sistema (GLONASS).
GPS has 32 accessible satellites in the sky, while GLONASS has an additional 24 satellites, meaning GNSS-based tracking technology has greatly increased positional accuracy - and as the playing environment gets more difficult, the more advantageous the additional satellites become. Here is a video on the advantages of GNSS.
Engineered from five generations of satellite-based devices dating back to the invention of the technology by Catapult after the 2000 Sydney Olympics, OptimEye S5 has been independently proven to have the greatest accuracy in sporting stadiums.
Wearable athlete monitoring has become increasingly ubiquitous in elite sport and is now an integral part of elite programs. However, most of these technologies use GPS-based monitoring with various differences in chipsets and antenna design. A commonly recognised problem with GPS is performance in so called ‘urban canyons’, or other difficult GPS environments.
To investigate whether the GNSS and antenna design in our OptimEye S5 leads to improved performance and therefore more reliable data for athlete monitoring when compared with a GPS-based device, we set up an internal validation at a notoriously difficult sporting stadium.
A commercial stadium was chosen over an open field environment because it showed typical GPS challenges that are associated with many elite sports environments.
A well-trained male participant (24 years old), and well-trained female participant (24 years old) ran five laps of a marked 50m square in the middle of the ground.
GPS latitude, longitude and velocity were exported directly from the monitors and the Haversine formula was used to compute distances between successive position solutions. Standard Estimate of Error (SEE) and Bias were calculated using Microsoft Excel.
In addition, position solutions were then exported as a KML file to load into Google earth and plot on a satellite image. The resultant traces were evaluated for positional stability.
OptimEye S5 reported significantly lower SEE and Bias for total distance measured (SEE 1.86% v 12.12%, bias 6.08% v 2.21%).
These results indicate that in challenging satellite navigation environments, GNSS provides a significantly better solution for position and distance parameters and any other parameters derived from this data such as velocity and acceleration.
There is a compelling case to conclude the GNSS engine and antenna technology in newer-generation athlete monitoring devices such as Catapult’s OptimEye S5 is markedly better in environments where GPS is challenged – whether from player congestion, stadiums, or intermittently sparse satellite constellations.
It is important to note that tracking engines provide more information than distance, but this is the most basic of the solutions coming from the engine and its components are used to derive integral parameters such as velocity, acceleration and derivatives thereof such as time and distance spent at high speed.
Elite sporting teams and practitioners require all information that they use in monitoring the performance, health and injury risk of their athletes to be precise, valid and reliable. The present investigation indicates that GNSS provides significantly more accurate data than GPS for tracking athletic performance.
The differences between GNSS and GPS are multiplied in a stadium environment on match day, which will significantly affect a team's collection of valuable data. With the increased allowance of wearable technology in matches, the above test is critical when deciding which wearable technology product to use.