155.

All X are based on the principles of triangulation using the visual images and timing data provided by at least four high-speed video cameras located at different locations and angles around the area. The system rapidly processes the video feeds by a high-speed video processor and Y tracker. A data store contains a predefined model of the playing area and includes data on the rules.

In each frame sent from each camera, the system identifies the group of pixels which corresponds to the image of the Y. It then calculates for each frame the 3D position of the Y by comparing its position on at least two of the physically separate cameras at the same instant in time. A succession of frames builds up a record of the path along which the Y has travelled. It also "predicts" the future flight path of the Y and where it will interact with any of the playing area features already programmed into the database. The system can also interpret these interactions to decide infringements of the rules of the game.

The system generates a graphic image of the Y path and playing area, which means that information can be provided to judges, television viewers or coaching staff in near real time.