Automatic Golf Ball Trajectory Reconstruction and Visualization Tadej Zupanˇ ciˇ c and Aleˇ s Jakliˇ c University of Ljubljana, Faculty of Computer and Information Science, Computer Vision Laboratory, Trˇ zaˇ ska 25, 1000 Ljubljana, Slovenia {tadej.zupancic,ales.jaklic}@fri.uni-lj.si Abstract. The article presents the steps required to reconstruct a 3D trajectory of a golf ball flight, bounces and roll in short game. Two video cameras were used to capture the last parts of the trajectories including the bounces and roll. Each video sequence is processed and the ball is detected and tracked until is stops. Detected positions from both video sequences are then matched and 3D trajectory is obtained and presented as an X3D model. Key words: tracking, golf, stereo, trajectory, 3D, video 1 Introduction Video analysis is nowadays an important tool not only for professional athletes but also for amateurs in various sports. It gives them visual information of what they are doing and can help them improve by seeing their (not perfect) moves and the consequences, that they cause. There are a lot of golf accessories on the market, probably more than in any other sport. On the other hand, golf ball tracking articles are not so common. To detect and display the trajectory of the golf ball, usually some expensive equipment like radars is used. While there is no doubt, that the trajectory obtained that way is accurate, its price tag is out of the range of the average user. In the area of golf video tracking there has been a research of golf club tracking during the swing [1] and tracking of the position of the golf club and the ball using markers [2]. Ball tracking in tennis [3, 4], on the other hand, has been studied extensively and the successful results can be seen on the television during the tennis broadcasts. There are also quite a lot of articles about soccer ball detection [5, 6], but these are not as widely used in practice as the ones from tennis. 2 Motivation Golf is a sport full of variety. Because of different course condition, flag position, weather and tactics, every shot is different. The player is faced with the choice