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The use of technology in sports has increased in recent years. One of the most influential of these technologies is referee support systems. Team sports such as volleyball require accurate and robust tracking systems that do not affect either the players or the court. This paper introduces the application of intrinsic and extrinsic camera calibration in a 12-camera volleyball referee system. Intrinsic parameters are calculated by using the classic pinhole model and Zhang's method. To perform extrinsic calibration in real time, the volleyball court is treated as a global calibration artifact. Calibration keypoints are defined as courtline intersections. In addition, a new keypoint detection algorithm is proposed. It enables achievement of an accurate camera pose in regard to the court. With all 12 cameras calibrated in a common coordinate system, a dynamic camera stereo pair creation is possible. Therefore, with known ball 2D image coordinates, the 3D real ball coordinates can be reconstructed and the ball trajectory can be estimated. The performance of the proposed method is tested on a synthetic data set, including 3Ds Max rendering and real data scenarios. The mean camera pose error calculated for data biased with keypoint detection errors is approximately equal to 0.013% of the measurement volume. For the real data experiment with a human hand phantom, it is possible to determine the presence of the human phantom on the basis of the ball reflection attitude.

This paper proposes a method for offline accurate ball tracking for short volleyball actions in sport halls. Our aim is to detect block touches on the ball and to determinate accurate trajectory and impact positions of the ball to support referees. The proposed method is divided into two stages, namely training and ball tracking, and is based on background subtraction. Application of the Gaussian mixture model has been used to estimate a background, and a high-speed camera with a capture rate of 180 frames per second and a resolution of 1920 × 1080 are used for motion capture. In sport halls significant differences in light intensity occur between each sequence frame. To minimize the influence of these light changes, an additional model is created and template matching is used for accurate determination of ball positions when the ball contour in the foreground image is distorted. We show that this algorithm is more accurate than other methods used in similar systems. Our light intensity change model eliminates almost all pixels added to images of moving objects owing to sudden changes in intensity. The average accuracy achieved in the validation process is of 0.57 pixel. Our algorithm accurately determined 99.8% of all ball positions from 2000 test frames, with 25.4 ms being the average time for a single frame analysis. The algorithm presented in this paper is the first stage of referee support using a system of many cameras and 3D trajectories.

Purpose. The main aim of this article was to show that Cracow’s Christmas Market is an attractive tourism product, type-event. Method. The study was carried out with the diagnostic poll method. The author's questionnaire, which was prepared in cooperation with the Congregation of Merchants and the Institute of Tourism, was used. The simple random sample, which was selected from visitors who came for a Christmas Market, was constituted by 518 Poles and 56 foreigner tourists. Findings. The subjects had clearly indicated that Christmas Market is an attractive tourism product. This is confirmed by the fact that: 96.3% of them recommend the Christmas Market to their friends and 61% of them claim that the Christmas Market is the most attractive trade event in the centre of Cracow. The results also showed some lacks in the area of promotion and organization. However, this did not result in a low rating of the event itself. Research and conclusions limitations. The study was carried out on a simple, random sample. Due to the lack of previous research on this event, it is difficult to reference previous editions. Cyclical repetition of research with the use of the same methodology would allow deeper investigation of the phenomenon in the future. Practical implications. The research is a valuable contribution to the development of the Cracow Christmas Market. Visitors’ feedback gave organizers a chance to focus on elimination of weaker parts and to work on highlighting the most interesting elements and to improve the event in subsequent years. Originality. This is the first publication on the Christmas Market in Cracow as a tourism product. Type of paper. Original work, demonstrating the results of empirical research.