| 摘要 |
A method and apparatus for determining in a ball game (for example, tennis) the position, relative to a service reference lines (12), of the first contact of the ball (14) with the playing surface. In play, the ball passes through a collimated light beam to intercept light directed at a light sensing array, which comprises many closely spaced sensors (46) arranged in column and row formation. A signal storage means includes one storage device for each of the sensors, so that the position of the ball may be tracked in the storage means as it passes through the light beam. The said position is determined by tracking in the storage means the front of the ball (14F), and for each sensed position of the ball front determining the then height (H) of the top of the ball, at a position displaced rearwardly one half the ball diameter. The detected height of the top of the ball is compared for each position of the ball front with a ball reference height to ascertain the said ball position at the moment the height of the top of the ball equates with the ball reference height. Alternatively, real-time comparisons of detected and reference ball heights may be made by a computer operating on the interrupt principle, thus obviating the need for the storage devices in the making of comparisons.
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