TECH TUESDAY: How goal-line technology works


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Photo by Michael Makmur |

This year marks the 18th birthday of overlaid graphics on sports broadcasts, which have been used to help viewers see where players and sporting equipment are at any point in time during a game, like using lines to indicate first downs in football.


September marks the beginning of many sports seasons at once, from the National Football League (NFL) regular season to the group stages of the Union of European Football Associations Champions League (CL). With this, technology in sports will once again make an appearance.

Technology can be found in many areas of sports, including goal-line technology in soccer to determine if a goal was scored, sensors in football helmets to determine if a concussion may be present, and cameras to track player and ball movements in basketball, according to SportTechie.

Among all of these pieces of technology, perhaps one of the most famous examples is the “yellow line” shown during football games, denoting the first down marker. The technology made its television debut 18 years ago today, according to mentalfloss.com.

The technology used for the yellow line was created following the introduction of a system that highlighted the movement and position of a hockey puck during hockey games, called FoxTrax. The system was abandoned, but it introduced the potential for technology to be used in sports, according to the site.

The line was designed by a company called Sportvision, founded by a group of people with the specific plan of applying technology to sports media, according to Sports Illustrated.

Sportvision made the line by first creating a model of the playing surface. Sensors were placed at the 20 yard lines and midfield, measuring every camera movement up to 30 times each second, according to the site.

Football fields are curved, with the center being higher than the edges so water can drain during inclement weather. Measurements had to be taken at every stadium, as each stadium has its own curvature that must be accounted for, according to the site.

To ensure the line shows up in the right place, exact shades of green had to be determined, accounting for shadows and different lighting. This is important so only green grass has a line produced over it, instead of green jerseys, according to the site.

Swatches of color would be taken before and during the game to update the hues of green the system would replace. The team took their own television truck to every game to produce the line for the broadcast, according to the site.

Other issues include ensuring that the line is in the right place, it does not move around and actually looks like it is on the field instead of floating in air, according to the site.

This technology was in the works for months and shown to different broadcasters. The high price of $25,000 made many networks reject the idea, but eventually it was picked up and applied for the 1998 season opening game, according to the site.

Another application of technology in sports is goal line technology in soccer, first introduced in the 2013-2014 English Premier League (EPL) season, which makes it possible to definitively know whether the ball crossed the goal line, according to SportTechie.

Similar technology has been implemented in tennis, where it is used to decide whether the ball landed inside or outside of the line, according to the site.

There were many competitors attempting to have their product used by the EPL, including CAIROS, Hawk-Eye, GoalControl and GoalRef, according to the site.

CAIROS worked by creating a magnetic field so receivers around the field could track sensors in the soccer ball. It was promised to be quick, but was found to have slow and inaccurate results, according to the site.

GoalRef also created a magnetic field, but used electromagnetic antennas around the goalpost. It looked for disturbances in the field on and inside the goal line, sending a message to referee whether the ball was in or not, according to the site.

Hawk-Eye relies on six cameras placed around the field that follow the ball’s every move, creating an exact location of the ball at all times. The cameras are very precise and increase in precision when the goal nets are black, according to the site. This was used by the EPL.

This technology was also used in the Fédération Internationale de Football Association (FIFA) World Cup in 2014, but was implemented by GoalControl. GoalControl works similarly to Hawk-Eye, but uses 14 cameras instead of six, according to the site.

Each camera must be placed in an exact location to ensure precise calculations of the ball’s position. The cameras take about 500 pictures each second, updating location data constantly and precisely, according to the site.

Technology has had a massive influence on sports, and will only continue to shape the sporting world, according to SportTechie.


Harshel Patel is a School of Arts and Sciences sophomore majoring in molecular biology and biochemistry. He is the digital editor of The Daily Targum. He can be found on Twitter @harshel_p.


Harshel Patel

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