Camera Hawk

Camera Hawk

How accurate is the system "for Hawkeye Tennis Online Requests

We know and have seen how video analysis can used to analyze performance in tennis players, but can also be used in real time or near real time to track the ball and even make calls to close line. Of course I am speaking of La Mancha "Shot" or the Hawk-Eye system.

If you've seen any tennis Mayor since 2006, you will know exactly Hawk-Eye what it is. The Hawk-Eye is used to make decisions about line calls that are challenged by the tennis player. Each player (or team if you play doubles) can challenge a line call at any point. They get a maximum of two incorrect challenges in each set. If the set is going to break a tie is an extra challenge allowed. Basically the challenge Hawk-Eye allows tennis players to use technology to challenge line calls they believe are incorrect.

The technology used by Hawk-Eye system is Video Analysis. That's how it works.

1. Multiple cameras are placed around the pitch and players. These cameras are usually placed at the top, so there is less likelihood that a player is blocking the ball from the point of view camera.
2. Multiple cameras are used to ensure accurate tracking of the ball and to account for possible occlusion (the ball is hidden in view of the camera body players …)
3. The system uses at least four high-speed cameras video, with a catch rate of a presumption 500 frames per second.
4. The camera position is calibrated to determine its position in space and in relation to the other cameras in the system. The lines on the court also used in the calibration and to compensate for any camera movement.
5. The center of the ball is tracked 2D for each camera. The ball is therefore a marker or a point of reflection on the body. Using information from all cameras, the system eye hawk then triangulate the 3D position of the ball.
6. This process is performed for each captured frame so that the trajectory of the ball may be created and then superimposed on an animated background that contains the lines of the tennis court.
7. Finally, the compression paddle and the ball is measured by examining position and trajectory of the ball before the bounce and their position and trajectory after bouncing. In this way you can determine how long the ball was on the floor and how it skidded on the ground.
8. Hawk-Eye system is said to have an accuracy of 3.6 mm.

I think the use of technology video in this way is very good for the sport of tennis and the players' piece of mind and enjoyment of the viewer. However, we have seen a number of calls with the controversial "hawkeye the system. Take a look at the video of two of the greatest here.

In this first video we see a call very Mikhail Youzhny hard for over Rafael Nadal in Dubai in 2007.

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This second video is the final Wimbledon in 2007. Rafael Nadal benefit from a very close over Roger Federer.

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In both cases would have to say that the ball can judge looked at the lines that made the call. In both cases, the player is probably just a challenge the call because it is a crucial point (Yozhny vs Nadal – Set point, Nadal vs Federer – Break point). The system Hawk-Eye suggests that in both cases, these calls measured as 1 mm to be in, which means the ball was 1 mm to be out. Can Hawk-Eye have been wrong in one or both of these calls and what it means 2-3 mm of accuracy, but may suggest that the ball was in only 1 mm? Here are some points that may affect the accuracy of the system.

1. The type of camera captures 500 pictures per second can be too slow to play strong tennis today. Andy Roddick has been a rapid service to 155 miles per hour and earthworks are often hit with a similar speed. Assuming a capture rate of 500 frames per second or one frame every 0.002 seconds, the ball has moved about 139 mm for each video frame. This may not be sufficient data to determine the position of the ball to the nearest 1 mm.
2. The cameras used the greater the possibility to follow the ball and the higher the accuracy. However, there are possibilities of occlusion by the players, tennis rackets and network This will lead to reduced accuracy.
3. High speed video capture also has an excellent lighting. We discussed the importance of lighting for capturing high speed in a previous pos t . Therefore the system work better under a roof with artificial bright light and possibly have a problem tracking outdoor activities ball, especially when there is no coverage of clouds as it gets later in the evening.
4. Assuming everything is perfect for fishing, the center of the ball has to be identified as precisely as possible too. If a camera sees the ball in a funny angle or partially occluded the center can not be properly defined by this camera one and the position of the ball will inaccurate.
5. The skid and compression of the ball is being estimated and extrapolated based on the trajectory of the ball before and after the rebound. Any inaccuracy in monitoring the position and trajectory of the ball will be bigger on an extrapolation (motion estimation).

The system of Hawk-Eye can not be perfect, but it is definitely a step up from the sight of one eye lineman, especially when the ball moves at high speed. We have improved Hawk-Eye line calls in tennis and this is great for players and spectators alike. However, it still leaves room to discuss the interesting points and close matches. U.S. Experience Tennis Open and hopefully we will not see any controversy "Hawkeye calls.

About the Author

Dudley Tabakin is Co-Founder of Sadaka, LLC http://videosportsanalysis.blogspot.com, a motion capture and biomechanics consultancy. Clients include FootJoy, Titleist, Warrior Hockey, Vicon Motion Systems, Innovision Systems Inc. and other Sports and Motion capture and biomechanics software companies

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