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why do we still even have umpires or referees or line judges, etc etc? why haven't they all been replaced by computers and electronic sensors and whatever newfangled technological doodads that can ensure 99.99999999% accuracy?
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mostly because that kind of accuracy hasn't been achieved yet. There is this sort of technology in research and development. Some has been used in Japan, namely bases that light up when touched. I don't know much more in the way of specifics, but you are not the first person to think of this.
Also, there is currently a computerized system locating pitches. At this point it is only used for umpire evaluation, and not for calling the games.
link
By the way that camera out in centerfield that makes the umpire look two feet taller than the batter doesn't give the viewer at home much of a perspective of where a particular pitch was. "K Zone" is a little better, but it doesn't take into account the fact that the strike zone is three-dimensional. The area over home plate, the bottom boundary being the hollow below the knee-cap and the upper boundary being an imaginary line half-way between the shoulders and the waistline, when the batter is prepared to swing. Any part of the ball touches any part of the strike zone, and by rule the pitch is a strike. Obviously the "K-Zone" has limitations in this area.