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 court-line 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.

The paper presents a detailed analysis of precipitation conditions in the West Pomeranian Voivodeship in Poland, covering data from 21 poviats. The basic data consisted of monthly sums of atmospheric precipitation from 49 stations of the Institute of Meteorology and Water Management National Research Institute (Pol.: Instytut Meteorologii i Gospodarki Wodnej Państwowy Instytut Badawczy – IMGW-PIB) in 1991–2020. Variability of precipitation conditions was demonstrated through annual and seasonal totals, the share of seasonal precipitation in annual totals, and the ratios of summer to winter precipitation and autumn and spring precipitation. It was found that area averaged annual totals ranged from below 600 mm in the poviats located in the west of the Voivodeship to more than 800 mm in the poviats located in the north-east. On average, the lowest annual totals were recorded in the area of the Police (550 mm) and Gryfino (565 mm) poviats, and the average highest in the Koszalin (842 mm) poviat. In most poviats, there was a slight, statistically insignificant tendency of increasing annual totals. The contribution of precipitation in spring, summer, autumn, and winter to the annual total in the voivodeship was 21, 33, 24, and 22%, respectively. The greatest year-to-year variability was found for summer (Vs = 28–39%) and winter precipitation totals (Vs = 29–35%). The most statistically significant result of the analysed features was identified for the calendar spring. The most prominent statistically significant changes in precipitation conditions were observed in the Goleniów, Kamień, and Sławno poviats.