We told you about who uses data to win and what that data actually is – from the raw to the finest, the Hawkeye data. Today we will talk about how they are collected. The latest episode in our recurring series on tennis and statistics is dedicated to data generators for tennis courts and generally to the understanding of the so-called “constellation” of tools dedicated to the collection of tennis data.
The analysis focuses on data generators installed on tennis courts which can be easily divided into three categories:
– Devices dedicated to refereeing during competitions that offer the following services: supervision of balls landing close to the lines, match statistics, video replays, data analysis for fan engagement and transmission of streaming services;
– Devices specialized in tutoring and training services that offer on-court monitoring of athletes, video analysis, retro analysis (feedback) as well as playful dynamics (gamification);
– Portable devices, flexible enough to perform both refereeing functions as well as the collection of match statistics, while also serving as training tools by means of their application functionalities.
A tennis court is considered a “smartcourt” when a technological component is permanently or semi-permanently installed on the court and it is positioned and secured/protected in order not to interfere with the movements of the athletes or hinder them during a game. This analysis is based on an article published on the Sports Technology blog, which can be found at this link. The most common hardware technology used by these devices is a combination of computer vision cameras. Moreover, there are also radars, sound sensors, lasers, and pressure sensors.
While data collected through the sensors installed in the racquets and the so-called “wearables” are, so to speak, one-dimensional (they are calibrated on the tennis player who uses the tool or wears the sensor itself), those collected through smartcourts possess a two-dimensional component, recording rallies between players involved in official tournaments or training sessions. Therefore, while the first will in the future be used to prevent injuries by being tailored to the person, the second shows an ever-increasing usefulness in the strategic analysis of matches, monitoring the effectiveness of shots against a rival.
Let’s move on to the analysis of the first category of devices, those dedicated to refereeing.
1. Smart referees
Three products may be assigned to this category: FlightScope Tennis, Hawkeye Innovations and Foxtenn, all of which have been approved by the International Tennis Federation (ITF), boasting the status of PAT (Player Analysis Technologies). All ITF-approved products that have PAT status are available at the following link. Therefore, they are used in international tournaments such as the Grand Slams and the WTA and ATP circuits.
FlightScope Tennis
Estimated cost: 35-40 thousand euros per court on a weekly basis
This one has probably the longest history of merging technologies and systems developed over the years, having done so since 1984. Flightscope was founded in South Africa in 1989 and it merged with the Polish company Jagro in 2008 to form Flightscope Tennis at a later date. Today, the main products offered by the company are the live scoring system and the line call system which also include ball and player monitoring.
The live scoring system mainly uses cameras, radars and the Proscorer, which is a tablet for the chair umpire. Therefore, all the collected data are used during a match through visualizations and the distribution to the television media.
The line call system mainly consists of video cameras mounted on each court, with 4 high speed cameras and 8 other specific cameras for line calls. When there is a line call, the data is processed and provides an update to the referee via the official review application. Additional ball tracking data, such as flight parameters and trajectories, plus player tracking data such as motion patterns and heat maps, provide additional interpretations and analysis available to the various stakeholders of the sport in question.
Operation scheme of line calls
Hawk-Eye
Estimated cost: 60-70 thousand euros per court on a weekly basis
The Hawk-Eye system was created in the UK in 1999 and it was used for the first time in cricket (in 2001) in a test match between Pakistan and England. It was then used in the Davis Cup in 2002, then at the Australian Open in 2003, and it became an official tennis refereeing system in 2005. In 2010, Hawk-Eye was acquired by Sony. In competitions it is mainly used for electronic calls during matches, but the system also provides statistics about each player on every shot, service and rally.
Layout and arrangement of cameras
Source: http://www.studiosayers.com/
Essentially, the tracking system is based on the principles of triangulation, using visual images and timing data captured by high-speed cameras installed around the stadium, cameras that are calibrated and synchronized before each event. These are usually positioned high above the courts in such a way that they can capture the trajectory of the balls with minimal obstructions.
Although there has been some controversy regarding the accuracy of the line call, which is able to guarantee a margin of error up to 3.6 mm, the system is generally considered to be reliable and accurate except for a few borderline cases. With regards the heated debates concerning the availability of the data generated by Hawk-Eye for fans, media and third parties external to the ATP and the IT companies appointed by the Slams, we plan to deal extensively with the subject in the next article.
FoxTenn
Estimated cost: less than 50 thousand euros per court on a weekly basis
The latest addition to the industry is FoxTenn, a company founded in 2012 and based in Barcelona, which has developed a technological system to compete with the status quo of line call accuracy.
The system is made up of 40 (ultra) high-speed cameras and 10 high-speed lasers positioned around the court. Each high-speed camera can capture images at 2500 frames per second (FPS), which is over ten times faster than any other system. Another difference compared to Hawk-Eye is the placement, as they are positioned at the far end of the court, and at ground level, rather than above it.
Layout and arrangement of video cameras and lasers on the ground
Foxtenn thinks its ground-level approach avoids many potential errors found in other existing systems. First of all, with the cameras installed above the stands, there is the possibility that the view of the ball can be obstructed by the players or by objects moving between the cameras and the court; ground cameras are so close to the action that there is little or no possibility that this might occur.
Moreover, cameras mounted above the stands can be more sensitive to wind vibrations and even to the movement of fans walking in the stands. Tracking can also be affected if the ball hits the net or if it has a high trajectory – this could lead to a less accurate estimate of where the ball landed.
Foxtenn’s system captures real footage of the bounce and tracking is not affected by the aforementioned situations. Having been approved by all the major tennis federations, FoxTenn could potentially become the most used “Line Calling” technology in major tennis.
