How does GPS work?

How does GPS work?

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Getting lost while driving is close to a a lost fine art. With GPS in your car's navigation system, in the portable navigation device on your dashboard, or in your smartphone, it's easy to pull upwards a map and see where y'all are, or get directions to where yous're going. The hardest part may exist speaking or keying in the data if your machine has a clunky interface, or if it doesn't allow y'all enter an address while the car is moving, even if you're driving through a sketchy neighborhood but outside the airport in a rental.

Here's a backgrounder on what GPS is, what it can do for you today in cars, and what'south possible in the near time to come. GPS will brand you safer, route you effectually traffic delays, help you find nearby services, and help merchants attain out to sell you services you may or may not want.

How GPS works (maybe more than you want to know)

Since 1994, ii dozen GPS satellites accept been orbiting the world 13,000 miles up in six groupings, or planes. They are not stationary overhead (geosynchronous), merely move west-to-e at nigh 8,000 mph and orbit the globe (pass over the same spot) twice a 24-hour interval. On lath is an atomic clock. Each satellite continuously reports:

• Pseudorandom code, the ID for each satellite.
• Ephemeris data,the current date and time, and whether the satellite is healthy or unhealthy ("unhealthy" might mean the satellite is being repositioned or re-calibrated; information technology's not always a goner).
• Almanac data,where the satellite should be at any time of the data (also almanac data for every GPS satellite).

The receiver in your GPS captures the time of arrival (TOA) and time of flight (TOF) from satellite to receiver. Given the speed of light (known) and where and when the bespeak was sent, the GPS receiver then calculates where on earth your automobile, PND, hiker's GPS, or smartphone is. Equally your device moves along the highway, it calculates speed, typically a couple miles per hour lower than what the car speedometer shows (trust the GPS speed), and compass heading. Information technology places that information on the navigation organization's moving map. The satellite signal is delayed passing through the ionosphere, the world's upper atmosphere stretching from 40-600 miles altitude; GPS systems use a correction gene.

It takes 3 GPS signals to decide  (triangulate) the receiver'due south position and a fourth to also calculate altitude. If the receiver picks up more than satellites (up to a dozen can exist seen, the other dozen being on the far side of the globe), the quality of the location fix improves. In instance the atomic clock drifts, or some other inaccuracy comes into play, a correction factor is transmitted as well.

The get-go GPS satellite in the organization went up in 1978. Current GPS satellites are good for about x years of operation. They weigh about 2,000 pounds (on the ground) and 17 feet in diameter including the solar panels that power the satellite. The transmitter produces no more than 50 watts output. Replacements are constantly congenital and launched. Other countries have GPS satellites as well.

Newer GPS systems (receivers on world) will be even more accurate, smaller, cheaper, and fifty-fifty work indoors. DARPA has shown a chip smaller than a penny that includes iii gyroscopes, iii accelerometers, and an internal clock (photo above right). Other research is improving the timing and accurateness of satellite clocks. The goal is to get the accurateness of multi-thousand-dollar GPS systems into the head unit of measurement of your machine infotainment system.

How accurate is my GPS receiver?

GPS started life as a armed forces-start satellite system meant to increase the accuracy of aircraft, submarines, and their ordnance. Until 2000, the signal available to civilians was degraded to provide less accuracy. The unencrypted time bespeak sent to non-military users was randomly offset to provide no better than 100-meter accuracy. This was calledselective availability. It meant that a car'due south location might be off by 1 or 2 metropolis blocks, and "take the next right turn" might come up a cake also soon or too late.

The evolution of differential GPStechnology using land-based reference stations corrected the accuracy of the SA signal to near 15 meters (2-3 car lengths) and in best-instance situations to as little as 10 cm or 4 inches, expert enough for surveyors to accurately place a locating stake. At the same fourth dimension, the FAA, Coast Guard and Department of Transportation requested SA be discontinued. President Clinton ordered selective availability removed in 2000. It's gone for expert. The government'due south GPS website says, "The United States has no intent to ever employ selective availability again."

Today, the GPS receiver in a motorcar is authentic to 10-fifteen meters. This is with satellite receiver modules costing only a few dollars. Standalone GPS receivers claim accuracy inside 3 meters (x feet) and higher cost units are adept to a few centimeters. A $25,000 Trimble Full Station GPS system can exist accurate to less than an inch. What does this mean? Variants of high-precision GPS systems tin can remotely control route construction equipment flattening and shaving of the earth to create a roadway.

If you accept an older car navigation system that seems more than accurate than 15 meters, the navigation system plays a picayune trick. If y'all're northbound on the highway and there'due south no other road nearby, the location icon snaps to the roadway  and if it'due south a divided highway, snaps to the northbound side. Navigation can also recalibrate itself if you take a plough or go around a curve. GPS navigation also uses an internal compass, motion sensor, and the speedometer to accurately estimate where you are in a tunnel. (In a tunnel that straddles two states, yous'll see the current position icon cross the state boundary within a auto length or two of perfect accuracy.)

What GPS does for your auto besides moving maps

Obviously, GPS in your machine provides the blinking dot on the map that shows where your car is. There'south more. Here are some examples:

• Automatic crash notification. In an blow, if your car is equipped with telematics such as GM'due south OnStar, the car automatically reports your location to the telematics call center, which then calls the nearest PSAP (public prophylactic answering indicate), or 911 number. Starting with Ford and Sync, the call could also be made exist a Bluetooth continued cellphone. Commonly a passing motorist likewise calls 911, but that might be five minutes after on a lightly traveled route, and if you become downward an embankment and out of sight of passing cars, that might be never if the cops didn't know where to look. Enhanced ACN adds additional not-GPS information such as the location and severity of the crash, if occupants were belted in, and if the automobile rolled over. BMW and GM are working on algorithms that would predict the odds an occupant is seriously injured; they believe the algorithms are accurate enough to warrant letting them tell rubber officials when to acceleration a medical evacuation helicopter ($5,000-$15,000). All of this wouldn't be possible without the GPS indicate.
• Predictive headlamps.First there were headlamps, and then skillful headlamps (xenon, LED, laser), then steerable headlamps that aim to the correct when you plow the wheel right, and now headlamps that start turning to the right just before the plough (photo to a higher place). They utilise the GPS signal to start turning the headlamps at the time you commencement looking into the corner for deer, pedestrians or disabled vehicles, a 2nd or two earlier the wheels turn. Ford is piloting GPS-aimed headlamps.
• Longer range hybrids, EVs. The car wants to go along some battery power in reserve for an actress boost of ability, or then the storage battery doesn't get run downwardly. Say your Toyota Prius is proficient for a mile of threescore mph driving on the highway with a slight uphill incline. If the map data plus your current GPS location plus the car'due south current recharging abilities knew the uphill was followed past a 2.5 mile downhill, it could tell the car to travel the next uphill mile on battery power knowing the downhill run would get the battery recharged.
• Services.When yous search for the nearest Burger King not McDonald'southward (peradventure your kids call back BK prizes are improve), that requires GPS. Some of the kinks are nevertheless being worked out. Many third party apps, equally well as the databases in auto navigation systems, don't nevertheless take into business relationship that y'all probably want services ahead of you, non backside, and not xx miles off to the side.
• Smartphone apps.If your car has embedded telematics, it has a smartphone app with a number of features such as remote start and remote door unlock. There'southward also a GPS-based locator app that guides you to your car when your forgot its location at the stadium or in the mall.
• Smart garage door opener. Many cars take HomeLink garage door openers. Rather than clutter the automobile with more buttons past the  windshield mirror, or virtual buttons on the LCD, Tesla masks them for view. When GPS senses the car is about a half-mile from dwelling, the buttons pop up in the right corner of the center stack display.
• Calibrate your speedometer.Federal regulations require the speedometer to never understate your speed regardless of which canonical tire size is on the car. You don't want to become a 78-in-a-65-zone ticket when you thought y'all were simply doing 75; instead, you're probably driving 72 or 73 mph. The integrated GPS could calibrate your speedometer to the absolutely right speed for this set of tires at this inflation. It could. It doesn't. If yous have a portable navigation device, that typically shows your speed.
• Best lane advice. Today, practiced navigation systems have exit-lane views showing which are through-traffic lanes, exit lanes, and the lane that can be either one. Ever-more than-accurate GPS could sense when you need to move over a lane to exit.

GPS and the self-driving car

Self-driving cars rely on optical (also radar) sensors and 3D maps to empathize precisely where they are and where the hazards are. GPS could play a larger role when it's authentic to the inch, not the meter or v meters. That'due south coming. At the least, the car needs to eye itself in a 12-pes lane and not waver more than a pes off center. A car with mirrors is 6-7 feet wide. Add a human foot for allowable drift from exact center and you're left with a safety margin of i.5-2.0 feet on each side. That tin can be handled best today by optical systems that track the car's position relative to lane markings.

With hyper-accurate GPS, it could human action every bit an independent auditor of the car'south sensors — for instance, if it believed LDW was no longer performing perfectly. In rainy or mildly snowy conditions where optical systems dethrone, or the lane markings are partially obscured, the combination might assistance the automobile maintain lane-centering a bit longer. Eventually it would close downward.

A snowplow could still venture out in crappy weather condition and forge ahead at least at moderate speed with GPS either guiding the steering cycle, or alert the driver that the plow is off-grade and drifting off the road. What'due south not possible at 60 mph in the side by side five years might be workable at 30 mph.

Ownership advice

The start embedded auto navigation arrangement in the mid-1990s on the BMW seven Series price nearly $2,500 ($4,000 in 2015 dollars). At present few nav systems cost more $1,000, many are $500 or less, and they're oft standard on $50,000-plus cars, since having a color LCD in the center stack is pretty much mandatory already. The primary advantages of embedded navigation are the big screen (7 to ten inches diagonal), secondary navigation displays in the instrument panel or the head-up display, and (usually) larger control knobs and buttons than on a PND or smartphone. The rooftop shark fin antenna may become a quicker position fix when starting up. Motorcar navigation systems are almost never stolen, and there are no unsightly wires showing.

Smartphones typically accept ameliorate voice recognition ("Siri, requite me directions to Mile High Stadium"), the apps are cheaper or gratuitous, and updates are free. Car navigation updates may be $100-$200.

Apple CarPlay and Google'south Android Auto combine superior aspects of both: You get an embedded mapping app you already know and like (Apple tree Maps on iOS, Google Maps on Android devices), displayed on the car's LCD display, and using some of the car's buttons and knobs.

If y'all practise purchase in-car GPS navigation, do it knowing it has a half-life, significant it may exist better than a portable device today, but over fourth dimension it may exist surpassed by portable units. So far, automakers take non offered caput unit of measurement or GPS module updates. If y'all want the most current GPS at all times in your auto, charter — don't buy.

Bank check out our ExtremeTech Explains serial for more in-depth coverage.

Source: https://www.extremetech.com/extreme/210893-extremetech-explains-how-does-gps-work

Posted by: humphreyhunty1956.blogspot.com

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