October 9, 2006: Javelin accident

[SPUCK]

I'm still trying to figure out how the NFL gets the blue scrimmage line and the yellow first down line on the TV without it going over the player's pictures.

As found on Sportvisions site:
A laser placed in the center of the field is used to collect data on elevation points. That information is used to draw a computer map of the contours of the field, and the map is adjusted and overlaid onto the camera’s view of the actual field. Anywhere from three to five separate broadcast cameras are outfitted with custom Sportvision sensors and encoders to capture camera data so that the 1st and Ten Computers can enhance one camera “live” with the yellow line, and any of the others for use in replay. As cameras pan, tilt and zoom, this data enables the virtual line to follow suit, staying in perspective and getting larger and smaller, as needed.

Drawing the yellow line so that it appears to be painted on field underneath the players is accomplished through a sophisticated process of color keying that allows the operators to tell the computers what colors to draw on (grass, dirt) and what not to draw on (skin, uniforms). And finally, after adding the precise location of the first down marker to the system, Walla … The Yellow Line appears like magic on your TV screen.

I believe they also use 13 computers.

It's hard to do.