Only three minutes had passed in the opening match of the FIFA World Cup 2022 between host Qatar and Ecuador before the first goal of the tournament was ruled out for offside, reports said.
The headed strike by Ecuador forward Enner Valencia was disallowed because the lower half of his right leg was in an offside position. While such close calls being settled with the help of Video Assistant Referee (VAR) technology is fairly common in modern-day football, the speed with which it was adjudicated surprised fans, explained the Hindu in a report. Before the game resumed, a brief three-dimensional animation of the incident was displayed. The quick decision was made possible by FIFA’s brand new Semi-Automated Offside Technology (SAOT).
Semi-automated offside technology, which was announced in July, has already made an impression at the 2022 FIFA World Cup. The new technology mounts 12 dedicated cameras beneath the stadium roof to track the ball (which also has sensors) and up to 29 data points for each player, 50 times per second, to calculate their exact position on the pitch, providing a support tool for both video match officials and on-field referees. All limbs and extremities relevant for making offside calls are represented by the 29 data points collected, Ken Kerschbaumer wrote for Sports Video Group.
The technology consists of two parts: a sensor inside the match ball (Adidas’ Al Rihla) that is held in place by suspension technology, and existing tracking tools that are part of the VAR system as we know it, the Hindu explained in its report. Kinexon, a German company specialising in sensor networks and computing solutions, has created a small in-ball device that provides precise positional data as well as detects ball movement in three dimensions. When the ball is struck, data is transmitted in real time (at a rate of 500 frames per second) to a network of antennae installed around the playing field. In addition, 12 Hawk-Eye cameras are strategically placed around the turf to shadow both the ball and the players, with up to 29 separate points in the human body tracked. SAOT is the combination of the ball sensor and the Hawk-Eye cameras, which FIFA claims allows for highly accurate and quick decisions. These two data sets are fed into artificial intelligence software, which generates automated offsides alerts for match officials. This takes the place of the manual effort involved in poring over replays for minutes on end.
The accurate and automated detection of the kick-point is one of the most difficult challenges in the development of advanced offside technology. Possible solutions were considered, including tracking data from sensor technology and video data from camera systems, Kerschbaumer said.
A system must also correctly identify which body part places a player on or offside. Human operators tend to pick different body parts for offside lines, according to accuracy tests. There has also been progress in this area, with the automated system providing learning to correctly model a player’s skeleton. In the future, the system’s developed algorithms should be able to automatically identify which body part placed the player offside and by how much.
In the SOAT, an inertial measurement unit (IMU) sensor is placed inside the official match ball, adding another critical component for detecting tight offside incidents. This sensor, located in the centre of the ball, transmits ball data to the video-operation room at a rate of 500 times per second, allowing for extremely precise detection of the kick point.
The new technology, which combines limb- and ball-tracking data and employs artificial intelligence, sends an automated offside alert to video match officials inside the video-operation room whenever the ball is received by an attacker who was in an offside position at the time the ball was played by a teammate. Before informing the on-field referee, the video match officials manually check the automatically selected kick point and the automatically created offside line, which are based on the calculated positions of the players’ limbs. This process takes only a few seconds, allowing offside decisions to be made more quickly and accurately.
The positional data points used to make the decision are generated into a 3D animation that perfectly details the position of the players’ limbs at the moment the ball was played after the decision has been confirmed by the video match officials and the referee on the pitch. The animation, which will always show the best possible perspectives for an offside situation, will be shown on the stadium’s giant screens and made available to FIFA’s broadcast partners in order to inform all spectators as clearly as possible.
The MIT Sports Lab analysed and validated the data collected during online and offline tests, with TRACK at Victoria University scientifically validating the limb-tracking technology. A research team at ETH Zurich provides additional insights into the technological capabilities of such multi-camera tracking systems.
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