The winning GoalControl-4D system being deployed in all the stadia in Brazil works with seven cameras trained on each goal capable of taking full-frame, color pictures at 500 frames per second. They are strategically located around the stadium and focused on the goal mouths.
The cameras are connected to a powerful image processing system that tracks the movement of all objects on the field and filters out the players and officials and everything but the ball. The system then calculates its three-dimensional x-, y-, and z- position to within a few millimeters in the coordinate system of the pitch. If and when the ball has completely crossed the line, the central analysis unit transmits within one second an encrypted signal to a specially adapted wristwatch worn by the referee, alerting him both optically and via vibrations that a goal can be awarded.
All camera images of every event are stored and can be replayed at any time.