Tracking the use of optics in sports
If you have watched a game of American football on TV, you’ll have noticed a yellow line superimposed across the field. The line, only viewable to those watching the broadcast, is a visual representation of where the offensive team must advance the ball to reach a first down and retain possession of the ball.
While not an exact match to the actual line, which is measured by a chain that stretches 10 yards, it does give the viewer at home a good indication of the yards needed by the offense. Where the ball gets placed in relation to this line after a player is tackled has been a source of controversy in games as, currently, this placement relies on a human referee’s visual judgment of where the ball was when the ball carrier was tackled. The National Football League (NFL) may have a solution.
The NFL will test optical tracking technology during the 2024 preseason to assist with line-to-gain rulings. A system of high-speed cameras will track the ball to gather exact placement information after each play. This system uses pre-programmed points to determine the distance of one tracked object from other objects or points. The NFL’s exploration of this technology is the most recent effort to integrate optical tracking technology in sports worldwide. While it is unlikely that this change will be fully implemented for the NFL’s 2024 regular season, the NFL’s tests mark an increasing reliance on optical tracking to benefit officials and fans alike.
A wide range of cameras is already used at sporting events around the world to enhance the viewing experience for fans and to help officials make a variety of decisions. In the US, Major League Baseball (MLB), Major League Soccer (MLS), the National Basketball Association (NBA), the National Hockey League (NHL), and the Professional Golfers’ Association of America (PGA) all use optical tracking for different purposes.
For example, some organizations use optical tracking to enhance TV viewers’ experience, such as the PGA using ball tracking to show fans the flight path of golf balls. Other sports leagues use more advanced tracking systems to help officials make potentially game-deciding calls, such as the tracking systems used in major tennis to determine whether a ball is out of bounds.
The accuracy of optical tracking systems depends on the calibration used for the system. Each camera must be calibrated to detect people and objects—baseballs, baseball bats, footballs, soccer balls, etc.—entering and leaving the calibration area, and the cameras must also track the objects as they move within the calibration area.
“A camera system is only as good as the information you give it,” says Kyle Wait, ground truth specialist at the Sports Science Laboratory (SSL) at Washington State University. “You need to have a very accurate way to tell the system that this point in space is exactly x inches or feet from another point in space. For example, one of our systems uses over 200 different calibration points to create a 3D model of the area. We can then relate objects tracked within the field of view to actual distances or reference points.”
As a ground truth specialist, Wait provides stakeholders like sports teams, equipment manufacturers, and sporting leagues accurate and precise 3D positional data on moving objects.
The SSL, then, is very familiar with calibrating optical tracking systems. Using high-speed cameras, including monochrome and 2k cameras, the lab can achieve precise calibrations with errors of less than one-sixteenth of an inch at frame rates exceeding 4,500 fps. Each camera type has a unique function and can be synced to monitor a large area with incredible accuracy. Monochrome cameras have lower resolution but they allow for easy data storage, taking up less data storage space than high-resolution video. When the SSL captures live actions or events, higher resolution
2k cameras are used to track multiple areas in a single video.
Minor league baseball is testing "robot umpires." Photo credit: Kyle Wait, Washington State University.
When trying to calibrate a new capture area, the SSL team inputs known values, for example, the length of a football field. Using multiple cameras, they are able to use stereovision and epipolar geometry to establish a 3D grid that determines lengths and distances. “The points are extremely accurate in their position from one another. This gives us frame-by-frame ability to either manually or automatically track the object of interest in another software program. Software programs that automatically track objects do this by creating search parameters—usually size, pixel color, etc., and blacking out the rest of the screen as it focuses on those parameters set,” says Wait.
The SSL has partnered with bat manufacturers, amateur baseball and softball leagues, and even the MLB. They use the lab’s cameras and other equipment to observe high-speed bat and ball collisions and ensure that new bats from manufacturers meet NCAA, USA Softball, and USA Baseball compliance standards. Much of their work with the MLB consists of motion analysis. Their system allows for accurate measurements of the ball’s position within the strike zone, including the spin and speed of the ball as it crosses home plate, and the entire trajectory of the pitch.
To apply this technology to strike zone calls, Minor League Baseball (MiLB), is testing their potential to be “robot umpires.” A new rule adopted for the 2023 and 2024 MiLB seasons allows batters, catchers, and pitchers to challenge whether a pitch is inside or outside the strike zone. While this system is not refined enough to implement in the MLB, and is being continuously tweaked and tested, it is certain that optical tracking systems have the potential to play a pivotal role in baseball..
In addition to making judgement or rule-based calls, these optical tracking systems are also used to provide data for players, coaches, and fans alike. These include tools that use multiple cameras and advanced tracking algorithms to monitor, among other things, the spin rate of the baseball coming out of a pitcher’s hand. This, along with other metrics recorded, can help a pitcher find ways to improve their delivery, a hitter to better understand the ball’s movement, or provide a fan with another data point to better understand the game.
Systems like those used in the MLB have made their way into youth and amateur levels of the sport. Companies like Rapsodo have developed mobile systems that track speed, location, and other metrics.
The SSL is not only focused on baseball, they are also working on improving the understanding of biomechanics and equipment interactions in ice hockey, badminton, soccer, cricket, golf, taekwondo, and even pickleball. They are working to make sports safer and improve equipment.
“I believe our goal is to provide the most accurate 3D motion analysis data possible. We do this in a flexible way that allows us to travel anywhere in the country and set up a capture system to precisely measure objects moving at high speeds. In all, our lab provides a diverse working environment that looks to better understand all the different components and interactions between all types of sports and sporting equipment,” says Wait.
In the last 10 years, optical tracking systems have been adopted across all levels of sports, from youth leagues to professional organizations. The ongoing advancements in optical tracking technology enhance training capabilities and assist officials in making critical game-changing decisions. As these systems continue to improve, they are becoming indispensable to modern sports and are anticipated to further integrate themselves in the sporting landscape.
Jakab Terpstra is the 2024 SPIE Communications Intern and a former collegiate baseball player.
