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Published Oct. 27, 2008

Ever wonder how Fox can instantly follow the flight of a pitch to determine if it's a strike?

The St. Petersburg Times asked Sportvision, the creator of Fox's Pitchf/x technology, to explain how the system works.

You can watch the technology in action during Fox broadcasts of the World Series.

Starts with 2 cameras

Calculations are based on two black-and-white, high-resolution cameras, with constant views of the pitcher's mound and home plate, according to Sportvision technical operations producer Andrew Lorenz.

One camera is positioned high above home plate; the other is near the first-base dugout.

Before a game, engineers create reference points in each camera shot, learning precise distances between points.

Eventually, a computer builds a virtual field that engineers place over the actual field. (You never see it.)

In the batter's box

For each batter, engineers create a strike zone based on baseball rules: the midpoint between the shoulders and the top of the pants and the bottom of the knees.

As with an umpire, the strike zone is altered for each player.

Here comes the pitch

The cameras relay the pitch to a computer, which is trained to look for white pixels (the baseball) moving across the screen.

Using the virtual field, the computer follows the ball's path as it crosses home plate.

That information is then relayed to the centerfield camera. It's the view you see most often while watching the game.

The system can also track the speed and break of a pitch.

Every pitch

The system is tracking every pitch of the World Series, and the information is available to teams. Umpires don't use it during the game, though Major League Baseball does use a similar system to grade umpires' performances.

What pitches Fox broadcasts the technology on is the network's call.