Here's a look at early attempts at implementing goal line technology in various sports (by FIFA and others) and the system that, so far, is keeping everything running smoothly in Brazil.

Apparatus for Monitoring a Boundary Line - U.S. Patent No. 4,375,289 (1983)

A German company, Precitec, began trying to solve a similar problem at least as early as the 1970s. They received a U.S. Patent for their efforts in 1983.

There's a lot going on in this diagram, but here are the important parts: transmitting lines 1 and 2 each have alternating current provided by generator 5, coordinated so that at any given moment, their currents are running in opposite directions from each other. Receiving line 3 "defines a boundary area which is to be monitored to ascertain whether it is cut by a ball 19" (i.e. 3 is the goal line). Either one of these currents would deliver a voltage to line 3, which would produce a detectable signal, but the effects of the two currents cancel each other out, so no signal is detected.

The ball 19 contains a oscillatory circuit 4, which has the same frequency as generator 5. Assuming line 2 is facing the field of play, once the circuit comes between lines 2 and 3, the circuit is excited by the electromagnetic field of line 2, and in turn delivers a voltage to line 3. This voltage isn't canceled out by anything, and results in a detectable signal.

It was a valiant and ahead-of-its-time effort. Maybe too ahead of its time, as Precitec doesn't seem to exist anymore. However, a similar system, GoalRef, would later be considered by FIFA for the current World Cup (more on that later).

Electronic Method of Locating a Football - U.S. Patent No. 4,675,816 (1987)

This invention tracks the ball all over the field, not just at a goal line. While the above figure looks like a ball shortly before being vaporized by death rays, what's actually shown is:

In FIG. 1, a portable transmitter, 11, is shown positioned at the point of a football, 10. A pure carrier signal is being emitted from the transmitter. This signal is being received by antennas, 12, which are mounted on poles or other structures at the ends of a football field, 9.

Based on the angle from at least two antennas to the transmitter in the ball, the location of the ball can be determined. The inventors focused entirely on the use of this system to determine if a first down was achieved, and not if the ball crossed the plane of the goal line, though.

Electronic Goal Detector - U.S. Patent No. 5,748,073 (1998)

This patent, obviously, covered the use of goal line technology in hockey (or "ice football" as it's called over in Europe). They didn't address the specific type of technology being used, other than to broadly refer to "sensors" embedded in the playing surface, the crossbar, and/or the goalposts. The puck can, but doesn't have to, have "pick up means" embedded therein. It also introduced an automatic shutoff (40 in Figure 1, above) so as not to register the puck's crossing the plane if the goal itself was knocked out of position.

Instead of adapting one of these available options to work in a soccer game, FIFA decided to go with the product of a young upstart, the Adidas Smartball, in its first foray into goal line technology at the 2005 World Under-17 Championship in Peru, The plan was to use it at the 2006 World Cup if all went well.

This picture shows a slightly later iteration than that used in Peru, but the idea is the same. The pictured animatronic orange cut-in-half ball reveals a core held in the center, containing a microchip. Sensors either on the goalposts or to the side of the goal are placed so as to be triggered by the microchip when the entire ball crosses the goal line. According to FIFA's desired specifications, when the sensors detect a goal, a signal is automatically sent to a referee's wristwatch within one second.

Even though the smartball system didn't get used in any borderline goal line situations, the feedback was great:

The "smartball" being used at FIFA's Under-17 world championship in Peru is proving accurate and popular, officials have confirmed.

The ball – which contains a microchip designed to help the referee determine if it has crossed the goal line – had worked well.

"Cairos and Adidas are pleased with the performance of the chip and construction of the ball," Guenter Pfau, Adidas AG's manager for relations with FIFA, told Reuters.

"The feedback from the referees is forward-looking, positive – they are taking it as a tool," he added.

So, that cleared the way to use the system at the World Cup, right? Nope:

FIFA has ruled out using "smartball" technology at the 2006 World Cup in Germany, saying the system needs more testing to prove its reliability.

"We consider the technology is not yet ready," FIFA general secretary Urs Linsi said on Monday.

They didn't go into much more detail on exactly why it wasn't ready, other than to suggest it wasn't quite robust enough for the rigors of soccer:

"I think that after the first experiment, the system as a system and the idea as an idea was positively received (by International Board members)" Linsi said.

"(But) the players don't just touch the ball, they hit it, and the ball goes on to hit the bar. The chip must stay in the middle of the ball and give a signal to a watch in a second.

"This is more complicated than people think. The technology must be sophisticated and reliable. They are the two challenges."

We're left to suppose that they were concerned about the ball - particularly the core - being impact resistant. A loose microchip rattling around the inside of a smartball wouldn't do much for the system's accuracy, and if a bunch of 16-year-olds could break it, imagine what the Azzurri could do. A few years later, FIFA president Sepp Blatter would end testing of the Adidas system, insisting that it was only 95% accurate, and therefore unusable.

On a related note, skip to about 33:15 of this video of the France v. South Korea match from the 2006 World Cup group stage, to see a French should-have-been goal refereed with 0% accuracy:

The video is in Russian because this "save," for some reason, isn't in FIFA's official English language highlights. France should have gone up 2-0 on the header; the game ended in a 1-1 tie.

After heroically holding out for a little longer against the twin forces of "technology" and "widespread support," FIFA finally relented in 2010, agreeing to give goal line technology another shot. They got so serious that they eventually produced a 45-page manual, detailing the specifications and necessary testing for any goal line technology to receive the FIFA seal of approval. Included is a helpful representation of what is and is not a goal:

a diagram of testing shots, both into the goal and into the top/sides of the net:

and an impressive list of adverse conditions that must be tested for, for various types of goal line technology, including smoke, snow, laser pointers, power lines, bluetooth devices, and garage door openers. If you clicked through to the manual, you may have noticed this, and giggled:

Oh, grow up. That's not what they mea-

They don't even make the goalkeeper wear pants. Maybe that is what they meant. Let's move on.

GoalRef, Hawk-Eye and GoalControl systems

Tests of ten different systems were conducted under FIFA's guidance in 2011, in an effort to figure out which technology to use. One, interestingly, was the Cairos GLT system, which was a newer version of Adidas' smartball system. This system failed phase one of testing. From the initial ten, two frontrunners for Brazil emerged: GoalRef and Hawk-Eye.

GoalRef requires a weak magnetic field created at and behind the plane of the goal and a ball with a passive circuit embedded as an interior layer. When the ball completely crosses the plane, a change in the magnetic field is detected, indicating that a goal has been scored. As in the original Adidas system, an encrypted signal is then sent to a referee's wristwatch within one second. Here's a video put out by FIFA in 2012 to demonstrate the system:

Hawk-Eye, on the other hand, doesn't require any specialized equipment at ground level. There's no modified ball, and no Star Trek-looking force field across the goal. It's a camera based system, and one you're probably familiar with if you watch tennis:

Hawk-Eye uses several high-speed cameras placed around the top of the stadium to triangulate the position of a ball (soccer, tennis, or cricket, among others) within about 5 millimeters. You wouldn't be able to tell by the disgust evident on Roger Federer's face, but it's generally well-regarded.

In case you thought the system got its name because it watched the action on the court/field/pitch like a hawk, the first patent application related to this technology was filed back in 1999 by David Sherry and Paul Hawkins. To be fair, there's a good chance they got the name "Hawk-Eye" from Paul's name anyway, but it makes you wonder if Paul would have come up with this system if his last name was "Sparrowkins" or "Common-Ostrichkins". The pictures from the later-filed international application make clear that the system was designed with cricket in mind:

This schematic obviously isn't to scale, or it'd be some sort of Orwellian interrogation booth. The principle is evident, though, and applies to more sports than just cricket: multiple cameras track the ball, and data from at least two cameras is combined to determine its exact position. Having data from more cameras makes the determined position more accurate. Additionally, the system can be used to predict where the ball is going to go; it's easy to imagine using this system to determine, say, if a tennis player has a tendency to return balls along the baseline that would have otherwise gone out of bounds. This predictive capability is used for in-game review in cricket.

Hawk-Eye was considered the front-runner for selection for Brazil, despite being about twice as expensive to install and operate compared to GoalRef. It seemingly couldn't have hurt its chances that Sony, a major FIFA partner, purchased Hawk-Eye in 2011. Paying \$25-\$50 million per year to FIFA should get your system picked, right? Not so much.

Last April, FIFA surprisingly picked GoalControl, a German company, to provide the goal line technology at the World Cup, despite having approved their system for testing only a month earlier. GoalControl claimed it would cost about \$270,000 per Brazilian stadium to install (less than the \$678,000 figure cited by the German Bundesliga in rejecting installation of either Hawk-Eye or GoalControl in its stadiums). Cost wasn't the only issue, according to FIFA:

"While all four companies had previously met the stringent technical requirements of the Fifa quality programme, the final decision was based on criteria relating more specifically to the tournaments in Brazil, including the company's ability to adapt to local conditions and the compatibility of each GLT system in relation to Fifa match operations," read a statement from the governing body. "The respective bids were also judged on cost and project management factors such as staffing and time schedules for installation.

Since the unassailable bastion of integrity that is FIFA was involved, we can be sure that everything was above-board in the selection process. Presumably, the project management factors played a large role, because it's not actually clear what GoalControl's system offers, function-wise, that Hawk-Eye doesn't. GoalControl's website explains how its GoalControl-4D system works:

The GoalControl-4D system works with 14 high-speed cameras (7 per goal) around the pitch at the stadium roof/catwalk. The cameras are connected to a powerful image processing computer system which tracks the movement of all objects on the pitch and filters out the players, referees and all disturbing objects. The remaining object is the ball and the system knows its three dimensional x-, y- and z-position with a precision of a few millimeters in the coordinate system of the pitch. When the ball passes the goal line, the system sends a vibration- and optical signal to the officals´watches.

Everything in that paragraph applies to the Hawk-Eye system. This year, GoalControl actually had an international patent application published showing a more complicated goal line technology system, featuring two groups of high-speed cameras. The first is made of the same rafters- or roof-mounted cameras as used in Hawk-Eye or GoalControl-4D. The second group is mounted on or in the goal frame: