Hawk-Eye is a complex computer system employed formally in several sports such as cricket, tennis, Gaelic football, hurling and association football, to visually follow the trajectory of the ball and display a record of its most statistically probable path as a moving image.
Hawk-Eye was built in the United Kingdom by Dr Paul Hawkins. The system was initially implemented in 2001 for television uses in cricket. The system works via six (sometimes seven) high-performance cameras, usually placed on the underside of the stadium roof, which track the ball from different angles.
The video from the six cameras is then triangulated and combined to generate a three-dimensional representation of the trajectory of the ball. Hawk-Eye is not perfect and is accurate to within 5 millimeters (0.19 inch) but is normally trusted as an neutral second opinion in sports.