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The American TV network Fox Sports thinks viewers will enjoy sport more if
they can still see a computer-generated image of a ball when it disappears
behind a scrum of players or goes behind a billboard (WO 98/32287). An infrared
camera tracks the ball by sensing the light reflected off it. At the same time,
the camera keeps an eye on at least one of several fixed infrared sources
positioned around the stadium. This information is used to map the position and
trajectory of the ball. If it disappears from view, a video graphics generator
places a virtual image of the ball on the screen.