Powerful image processing algorithms identify the ball and its position within each camera's viewpoint and calculate via triangulation its position in the goal mouth to within millimetres. The original FIFA specification regarding accuracy was +/- 3 cm, but this has now been halved to +/- 1.5 cm, and both GoalControl and Hawk-Eye confirmed their systems better the revised tolerance level.
The system can work with any pattern, and both companies maintain that the result will be precise even in adverse weather conditions, different lighting positions, mud on the ball, or if there is a maelstrom of players in the goalmouth.
All camera images of every event are stored and can be replayed at any time.
Where there is a difference between the two is how the encrypted signals are transmitted to the officials' specially adapted wristwatches, which are supplied by different companies. At least it is believed the frequencies used are different; neither company would reveal details, citing this as confidential information for security reasons.
In Hawk-Eye's case, the company worked with Adeunis RF, a specialist in supplying RF products for a variety of sports. The watches are guaranteed to be "secure, robust, and interference free," stressed Upshon.
Broichhausen simply said GoalControl, too, worked with another company. However, EE Times can exclusively reveal that the watch being used at the World Cup was specially adapted by researchers at the Fraunhofer Institute for Integrated Circuits near Erlangen, Germany (see below).
So, following the decisions by FIFA and the English Premier League, have we reached a Betamax vs. VHS moment in goal-line technology? Not necessarily.
As already noted, GoalControl 4-D was chosen from a shortlist of four FIFA licensed and independently tested technologies, whittled down from 12 contenders, some of which were based on rather quirky ideas such as putting stickers on the ball or using laser beams on the goal line. The two others in the running were GoalRef and Cairos, both of which use low-frequency magnetic fields in the goal frame to track what is being described as an "intelligent ball."
GoalRef got very close to being selected by FIFA, and its proponents still believe it is the most cost-effective and elegant GLT on offer. Originally a Danish invention, it was further developed by researchers at the Fraunhofer IIS.
Thomas Pellkofer, operations manager for GoalRef at the research group, told EE Times, "Our system is cheaper, more flexible, and more reliable than camera-based options -- it is a closed ecosystem, and there is no need for an operator looking and monitoring screens."
Accurate, real-time tracking of the ball is made possible by a combination of just a few high-precision antennae attached to the goal frame and three coils embedded in the ball, one in each dimension, located between the bladder and the ball synthetics. The coils do not require a power source, and thorough testing has proven that the characteristics and behavior of the ball are completely unaltered, an important consideration for the players.
"Basically, GoalRef works like a bistatic, low-frequency RFID system with 'RFID reader' antennae surrounding the goal that excite the 'RFID transponder' inside the ball," says Pellkofer. The changes in the magnetic field allow precision location.
The Cairos system, also developed in Germany, is a collaboration between Cairos Technologies and sports goods conglomerate Adidas and involves embedding thin cables in the turf of the penalty area behind the goal line. The electric current running through the cables generates the necessary magnetic field. A chip sensor within the ball detects the magnetic field as soon as in range and transmits encrypted data to receivers strategically located behind the goal, which is then instantly sent to a computer. Here the exact location is interpreted, and, as with the GoalRef system, if the entire ball has crossed the line, a signal is sent to match officials.
Fraunhofer's Pellkofer says that, in addition to GoalRef, the group has also developed another potential line of business, the officials' watch, dubbed Watchlink. Since this is FIFA approved, it could be used with all GLT systems. "And certainly, it will be used in conjunction with the GoalControl-4D system in Brazil."
The Watchlink is basically a specially adapted Texas Instruments watch that uses the chip maker's CC430F6137 chipset. "The extremely secure and robust wristwatch uses our patented software and protocol, can work with just one transmitter for the whole stadium, and is remarkably power efficient," says Pellkofer. He added the frequency ranges of the links are 865 to 870 MHz and 915 to 930 MHz, and that the modified devices are assembled by a specialist company in Germany whose identity he would not reveal.
Now that football has embraced technology for goal-line decisions -- and barring any controversial outcomes or computer errors in Brazil during the summer -- the obvious question will be asked whether it could, or more probably if it should, encroach on other parts of the pitch. Many national and international footballing authorities will continue to resist, using the example of other sports such as the rugby union, international cricket, NFL games in the US, and even in tennis, where the flow of play is increasingly disrupted as more and more incidents are subject to video replay.
But the supplier companies and technology developers have other ideas. For instance, a two-year trial is already under way in the Dutch top division in collaboration with Hawk-Eye Innovations.
"The main aim of a video referee is to address issues where television replays almost immediately show a clear and contradictory result to that of the referee," said Upshon. "These are the contentious calls that really influence a match, whether it be an offside call, simulation [by a player to gain an advantage, generally a penalty] or an off-the-ball foul that the officials have missed.
"In many scenarios that we have looked at in Holland, the decision has been made by the video referee within seconds."
Whatever the outcome, referees will continue to rule the roost. Even with GLT, the final decision is theirs, and if the watch vibrates and alerts the official that a goal has been scored, the referee can (and must) still overrule if he has spotted a prior, separate infringement. Nor will the most sophisticated camera or computer ever be able to rule on intent in handball incidents or ugly tackles.
So spectators and TV watchers will still have plenty to argue over, even decades after the event.
— John Walko is a London-based technology writer (who still has not been able to secure tickets for any of England's matches in Brazil).