First and Ten

I am not a sports fan (Except for six-year-olds and Soccer!), but here is something that I always wondered about that I found the answer to today.




The first and ten line, how do they do it?
The following is pasted from the source that explained it to me: (Don't have a byline or whatnot, but who needs credit for something they probably stole anyway.)

First introduced in 1998, the virtual yellow line also known as the
"First and Ten" line, is a computer-generated tool to help television
viewers distinguish how many yards a team needs to go to get a first
down. While it may seem like a simple detail, the "First and Ten" line
system is vastly sophisticated, requiring eight computers, three sets of
special encoders and abundant wiring, dedicated to generating the
virtual first down line in video format.

Here's how it works:

* Each field-side camera must have a very sensitive encoder
attached to it that reads the camera's angle, tilt and zoom and sends
that information to the system.

* The system uses a complex 3-D model of the field so that it
knows where each yard line is. By integrating the tilt, pan and zoom
information with the 3-D model, the system can calculate where the line
should go.

* Then the system uses color palettes to identify objects on the
field, like players and referees, to recognize whether it is looking at
the field or something else. This way, only the field gets painted - not
the football or the players.

Pretty darn impressive.