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Saturday, February 26, 2011

Hawk-Eye : How does it work?

It’s the cricket world cup season! So, all the fans are getting anxious, and the game is getting hot. Cricket is a game where win or loss defined by a thing margin. Recently, a lot of money involved in the game and lot of spectators waiting to see a favorable result for their team. Therefore not to mention the responsibility of the players to win games and play without mistakes. But all the thing in a cricket match defined by the decisions of the umpires.



Umpires are also human. So the errors may occur when they taking the decision. To support umpires taking the correct decision, lot of new technical utilities are used. This is going to be about one of those technical advancements of the sport; Hawk-eye.

Hawk-Eye is basically a complex computer system used in cricket, tennis and some other sports to visually track the path of the ball used in the game. After detecting the path the system is capable of projecting the path (most statistically likely path ) of the ball as a video clip. In cricket those predictions are used to visualize the path of the ball and aid the umpire to determine what could have happened by predicting the future moments.

This technology was developed by engineers at Roke Manor Research Limited of United Kingdom, in 2001. Later this initiative technology developed into a separate new company, Hawk-Eye Innovations Ltd.

The term “Hawk-Eye” was coined by cricket commentators, but later it was adopted into Tennis, Snooker and Coaching. From then on, this technology has become a necessary requirement for the sport.

How does it work?

Hawk-eye consists of image processing technologies, 3D modeling technologies and laws of physics. There should be at least four high speed cameras placed at different locations of the stadium covering the whole play in different angles. During each frame of the video captured by those cameras, computer system identifies the group of pixels which corresponds to the actual ball. Usually the cameras used in hawk-eye system record the action at 60 frames a second, which is about double the speed of standard commercial TV cameras. The following image shows the positions of the cameras while covering a tennis match.

Camera positions at a tennis game (Click to enlarge)


After that, the three dimensional position of the ball is calculated by comparing the position against at least two other cameras (at least three cameras in total). Then those derived 3D location data are stored in a predefined model of the playing area (stadium). This process is called as ‘triangulation’.

Even though it calculates the three dimensional location, it’s more likely a "four-dimensional" technology, because the time is also added to the triangulation process. So that places the ball in space, are synchronized with the time. Accuracy of the position is pretty impressive as it gives the location with a precision in millimeters.



Using those location data, system can calculate the next movements of the ball by applying laws of physics. System is capable of calculating where the ball will interact with any of the playing area features already programmed into the database.  Furthermore Hawkeye can be taught about the game rules so it can take more sophisticated decisions for human umpires.

Finally to give the visual out come system generates a real time graphic image of the ball path and playing area, which can be used for the benefits of umpires, television viewers or coaching staff.

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