Do you know it takes 8, count 'em, 8 computers and four employees working and crunching simultaneously together to project the first down line marker that football fans have grown to depend on and take for granted?

Here is a little tidbit from How Stuff Works.com on how SporTVision projects the first down marker for ESPN, ABC's and Fox's football games.

The system, which is known as "1st and Ten", first debuted a few years ago on ESPN.

Here are the engineering/computing issues that the computers have to solve to correctly place the line.

The system has to know the orientation of the field with respect to the camera so that it can paint the first-down line with the correct perspective from that camera's point of view.

The system has to know, in that same perspective framework, exactly where every yard line is.

Given that the cameraperson can move the camera, the system has to be able to sense the camera's movement (tilt, pan, zoom, focus) and understand the perspective change that results from the movement.

Given that the camera can pan while viewing the field, the system has to be able to recalculate the perspective at a rate of 30 frames per second as the camera moves.

A football field is not flat -- it crests very gently in the middle to help rainwater run off. So the line calculated by the system has to appropriately follow the curve of the field.

A football game is filmed by multiple cameras at different places in the stadium, so the system has to do all of this work for several cameras.

The system has to be able to sense when players, referees or the ball cross over the first-down line so it does not paint the line right on top of them.

The system also has to be aware of superimposed graphics that the network might overlay on the scene.

So it takes a total of eight computers, and four operators to help solve all of these issues.

In order to determine where the line should go, a central computer utilizes several pieces of information: The virtual field modeled from measurements of the field (done before the game), and the data from the camera mounts showing what each camera's range of view is

The raw video feed from the camera that is currently on-air (which is determined by a separate computer in the Sportvision production truck)

Two distinct color palettes, one representing the on-field colors that should be changed to yellow, and another representing those colors that should not be changed (like colors in the players' and officials' uniforms -- this allows a player to appear to "obscure" the line, making the line appear as if it were really painted on the field)
Once the computer determines exactly which pixels should be colored yellow, this information, along with the raw video feed of the tallied (on-air) camera, is sent to a computer whose job it is to draw the yellow line 60 times per second. The line is then sent to a linear keyer to superimpose the yellow line onto the program video. Since it takes time for all this to occur, the program video is sent through several frame delays so that the generated yellow line and delayed program video can be synchronized and turned into what you see on your TV screen.

On game day, it takes four people to run the system:

A spotter and an operator work together to manually input the correct yard line into the system. The spotter is in the press box and the operator is in the production truck physically keying in the correct number.
Two other Sportvision operators are on hand to make any adjustments or corrections necessary during the course of the game. These adjustments might include adding colors to the color palettes due to changing field conditions, such as snow or mud.

Amazing what we take for granted isn't it?