why do you get the chills with a fever
If you attend a Super Bowl party on Sunday, youÁll probably hear at least one casual football viewer ask, ÁHow do they get that yellow first-down line on the field? Á While ÁmagicÁ is a fine answer in its own right, the real explanation is a bit more technologically intense. LetÁs have a look at the background and mechanics behind every football fanÁs shining beacon: the yellow first-down line. According to Allen St. JohnÁs 2009 book
The Billion Dollar Game: Behind the Scenes of the Greatest Day in American Sport - Super Bowl Sunday, the first-down line actually emerged from the ashes of one of sports broadcastingÁs bigger debacles: the FoxTrax system for hockey, which was designed by a company called Sportvision. Áwhich hockey fans no doubt remember as the much-maligned ÁtechnopuckÁ that debuted in 1996Áemployed a system of cameras and sensors around a hockey rink to place a little blue halo around the puck. FoxTrax wasn't a great fit for NHL broadcasts: Hockey purists hated the intrusion into their game, and casual fans didnÁt flock to hockey just because the puck was suddenly easier to follow. However, the system inspired producers to think of new ways to insert computerized images into live sports broadcasts. The idea of using a line to mark the first down in football was a natural extension, and Sportvision debuted its during ESPNÁs broadcast of a Bengals-Ravens tilt on September 27, 1998.
A couple of months later, rival company Princeton Video Image unveiled its Yellow Down Line system during a Steelers-Lions broadcast on CBS. (Sportvision is still kicking, and ESPN acquired all of PVIÁs intellectual property in December 2010. ) BUT HOW DOES IT WORK? It takes lots of computers, sensors, and smart technicians to make this little yellow line happen. Long before the game begins, technicians make a digital 3D model of the field, including all of the yard lines. While a football field may look flat to the naked eye, itÁs actually subtly curved with a crown in the middle to help rainwater flow away. Each field has its own unique contours, so before the season begins, broadcasters need to get a 3D model of each stadiumÁs field. These models of the field help sidestep the rest of the technological challenges inherent to putting a line on the field. On game day, each camera used in the broadcast contains sensors that record its location, tilt, pan, and zoom and transmit this data to the networkÁs graphics truck in the stadiumÁs parking lot. These readings allow the computers in the truck to process exactly where each camera is within the 3D model and the perspective of each camera. (According to, the computers recalculate the perspective 30 times per second as the camera moves. ) After they get their hands on all of this information, the folks in the graphics truck know where to put the first-down line, but thatÁs only part of the task.
When you watch a football game on television, youÁll notice that the first-down line appears to actually be painted on the field; if a player or official crosses the line, he doesnÁt turn yellow. Instead, it looks like the playerÁs cleat is positioned on top of an actual painted line. This effect is fairly straightforward, but itÁs difficult to achieve. To integrate the line onto the field of play, the technicians and their computers put together two separate color palettes before each game. One palette contains the colorsÁusually greens and brownsÁthat naturally occur on the fieldÁs turf. These colors will automatically be converted into yellow when the line is drawn on to the field. All of the other colors that could show up on the fieldÁthings like uniforms, shoes, footballs, and penalty flagsÁgo into a separate palette. Colors that appear on this second palette are never converted into yellow when the first-down line is drawn. Thus, if a playerÁs foot is situated ÁonÁ the line, everything around his cleat will turn yellow, but the cleat itself will remain black. According to How Stuff Works, this drawing/colorizing process refreshes 60 times per second. All this technologyÁand the people needed to run itÁwasnÁt cheap at first. It could cost broadcasters anywhere from $25,000 to $30,000 per game to put the yellow line on the field.
Sportvision had to deploy a truck and a four-man crew with five racks of equipment. The cost has come down since then, and the process is now less labor-intensive. One technician using one or two computers can run the system, according to Sportvision, and some games can even be done without anyone actually at the venue. Now you can explain it to everyone at your Super Bowl party during one of the less-exciting. Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at. This post originally appeared in 2011. Asked by: Jim Taylor, Spain A fever is when your body increases its internal thermostat, found in the hypothalamus. If you exercise hard or its a hot day, your body temperature might increase, but the thermostat remains at around 36. 8`C. When you feel hot the hypothalamus tries to correct this with sweating and increased blood flow to the skin. With a fever, it is actually the thermostat that has adjusted. This means your body temperature is now below 36. 8`C, so you feel cold and shiver, to try and raise your temperature. The higher body temperature may help fight infection by speeding white blood cell production and slowing bacteria reproduction. Subscribe to for fascinating new Q As every month and follow on Twitter for your daily dose of fun facts.
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