[curious]

I noticed that they paint a yellow stripe on the field to show where the first down line is. HOw do they do that so fast?

[pavyracer]

They use lasers from a satellite.

[curious]

They use lasers from a satellite.

Okay, I can buy that. But then how do they erase it? Do they paint over it with green?

[tacomax]

Classic thread.

[Doug]

Bigfoot secretly sub-contracts the job !

[pavyracer]

Okay, I can buy that. But then how do they erase it? Do they paint over it with green?

They change the cartridge in the laser beam from yellow to green. Duh!

[m3vr6]

I noticed that they paint a yellow stripe on the field to show where the first down line is. HOw do they do that so fast?

i don't know how they do it either!, but i think on artificial surface they have a glowing lights underneath the fields.

[curious]

i don't know how they do it either!, but i think on artificial surface they have a glowing lights underneath the fields.

That's crazy. THe satellite theory makes much more sense. LOL

[pavyracer]

That's crazy. THe satellite theory makes much more sense. LOL

I hate to spoil all the suspense but here is how they do it.

http://entertainment.howstuffworks.c...down-line1.htm

[curious]

I hate to spoil all the suspense but here is how they do it.

http://entertainment.howstuffworks.c...down-line1.htm

WAIT just a #$(*& minute. You mean that the yellow stripe is only in the VIDEO? The people at the stadium don't see the yellow stripe? How do the players know when they are near a first down? How do the referees know if the ball is over the first down?

You guys made up that wicki page just to fool us.

[Matt Rain]

I can't tell if this thread is serious.

You can often see bits of yellow go over players' and referees' limbs. Of course it's only in the video.

[20Four7]

I can't tell if this thread is serious.

You can often see bits of yellow go over players' and referees' limbs. Of course it's only in the video.

Unfortunately I believe it's serious. The yellow stripe is only on the TV portion. The players, referees are expected to know where the 1st down is. There is also something called the chains which is located on the sideline which shows where the first down mark is. That's what they bring out to determine if where the ball is spotted actually got to the first down mark.

[VegasDave]

You guys are stupid!

The lasers don't come from satellites, they come from the first down markers! They beam across to each other in super bright yellow.

I believe a player in I-AA recently had to leave the game with retinal damage because he wasn't used to the yellow laser and looked right into it!

[imgv94]

Wow how sad.

[Dark Horse]

It's computer generated. Doh. Here's how it works:

The idea to paint a first-down line across the field on people's TV screens sounds so simple. As it turns out, implementing this is incredibly complex. It takes a tractor-trailer rig of equipment, including eight computers and at least four people, to accomplish this task!

Here are some of the problems that have to be solved in order for this system to work:

* 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.

This is not an easy process!

A key piece of hardware used in the system is a special camera mount that holds the television cameras. This mount encodes all of the camera's movement (such as tilt, pan, zoom and focus). This data enables the computers to understand exactly what each camera is doing in real-time.

Another key piece is a computerized 3-D model of the field. The computers know exactly where the cameras are located in the 3-D model and can orient the virtual first-down line on the field accordingly. The model also accounts for things like the crest of the field and the location of the yard lines on the field.

The color palettes are also critical to the system. The computers must be able to distinguish between grass, on which the line should be painted, and everything else (players, referees, the ball, etc.), on which it should not. Color palettes solve this problem. You can see the palettes at work in this frame:


Photo courtesy SporTVision
Players seem to run over SporTVision's "1st and Ten" line.

The player does not have the line painted over his jersey because of the color palettes.

All counted, there are eight computers used in the system:

* Four SGI computers
* One PC
* Three special computers used in conjunction with the television cameras

These special computers' sole task is to record aspects of each camera's movement 30 times per second from the camera mount, and then send that data back to the production truck for analysis and use.

Drawing the Line
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.

[curious]

No one answered my question:
Can the people in the stands and the referees see the yellow stripe?

I just don't think the first downs can be accurate unless the referees can see the stripe.

[Matt Rain]

No one answered my question:
Can the people in the stands and the referees see the yellow stripe?

NO! Jeez.

[Dark Horse]

Just a matter of time before they put a little chip in each ball to show if it got to the 1st down marker.

That'll give Belichick a whole new electronic utopia to mess with.

[pavyracer]

The funny thing is that they still use chains to measure the 10 yards! Can't they put the coordinates of the stadium in a GPS device then put a chip in the ball and have the ref read the yardage from his portable GPS? This will speed up the game by at least half an hour. The problem is they use 100 footballs per game!

[cartay]

The funny thing is that they still use chains to measure the 10 yards! Can't they put the coordinates of the stadium in a GPS device then put a chip in the ball and have the ref read the yardage from it's portable GPS? This will speed up the game by at least half an hour. The problem is they use 100 footballs per game!

Hilarious thread! But in all serious, you would think that nowadays we're close to being able to do something more high-tech. Would take the guesswork out of it (but I guess the question is whether it's worth it)

[Bluehorseshoe]

The funny thing is that they still use chains to measure the 10 yards! Can't they put the coordinates of the stadium in a GPS device then put a chip in the ball and have the ref read the yardage from it's portable GPS? This will speed up the game by at least half an hour. The problem is they use 100 footballs per game!

That is the most unnecessary thing I've ever heard.

[NapoleonEli]

The funny thing is that they still use chains to measure the 10 yards! Can't they put the coordinates of the stadium in a GPS device then put a chip in the ball and have the ref read the yardage from it's portable GPS? This will speed up the game by at least half an hour. The problem is they use 100 footballs per game!

LOL. .. .2 THUMBS UP FOR GPS .. OHH an wtf is with 100 balls per game???

[seaborneq]

Well, now I see why you think a 20X rollover is easy. Do you even watch the games? The yellow line has been on the field for nearly 10 years. Curious, you can't be serious about this? Don't you think you would have seen the elves and Smurfs running across the field with their paint buckets by now. I see them all the time, they are really fast.........and tiny........and smart.

[curious]

Where's Ganch when you need him? We need one of his 18 page Ph.D. dissertations on the physics of the yellow stripe. Ganch, help us out on this please!

[the2ofspades]

I noticed that they paint a yellow stripe on the field to show where the first down line is. HOw do they do that so fast?

that's good

[ritehook]

Of course, the whole thread is a "curious" put on.

Congrats to those posters who saw thru it.

If it had come from someone with less than 10 posts you might give it a tiny shred of credibility.

I think Fox began it some 8 or 10 years ago, and now everyone does. It was, intially, done by Fox employees on the field (giving the co-oridinates to the computer people, not painting a line LOL - curious stuff, that!)

[curious]

Of course, the whole thread is a "curious" put on.

Congrats to those posters who saw thru it.

If it had come from someone with less than 10 posts you might give it a tiny shred of credibility.

I think Fox began it some 8 or 10 years ago, and now everyone does. It was, intially, done by Fox employees on the field (giving the co-oridinates to the computer people, not painting a line LOL - curious stuff, that!)

You mean you think this post is similar to the post where I miscalculated a parlay payoff and thought i was going to get paid $1,000,000?

[raiders72002]

How do they paint the yellow stripe on the field so fast?
I noticed that they paint a yellow stripe on the field to show where the first down line is. HOw do they do that so fast?

Good question, these guys are quick that paint those lines. They have tryouts for the painters and have to run a sub 4.4 40 to get the job. When it snows a few of them have slipped and hurt themselves but the NFL has good insurance.

[curious]

Okay, I can get that they use lasers put into the big sticks that the people hold on either side of the field, what are they called "First down poles?". Anyway, how do they paint the down and yardage arrow on the field so fast? That can't be coming from the lasers in the first down poles. Explain THAT one.

[raiders72002]

Only David Copperfield could figure that one out.

[Reverse]

LOL this thread is hilarious. Can fans and players see the stripe...LMAO

[OrionSky]

ok, now when the players are in the red zone, can they see the last 20 yards turn red?

[pavyracer]

I think you guys miss the most obvious question. How is the blue line generated? It's easy to pound the old yellow line in this thread. But does anyone actually care about the pour blue line?

[curious]

I think you guys miss the most obvious question. How is the blue line generated? It's easy to pound the old yellow line in this thread. But does anyone actually care about the pour blue line?

There are SOOOO Many questions.

How do they paint the blue line so fast?
How do they paint the entire end zone red so fast?
How do they paint the down and yards arrow so fast?

So many questions.

[dwaechte]

I can't believe people took this seriously lol. Or atleast seemed to. Maybe they weren't and I'm the idiot for thinking they were.