More and more, people around the world are relying on GPS to go about their daily business. Whether you own a vehicle with an in-dash GPS navigation device, a handheld GPS device, or even a smartphone or tablet, you use this technology all the time. But what do you really know about GPS and how it works beyond pressing the “calculate route” button or checking in at your favorite restaurant via smartphone? Here are ten things you should know about this powerhouse of technology we can’t live without.
GPS stands for Global Positioning System, the 24 satellite constellation with a few extras, referred to as “hot spares,” there to back up the system if one satellite should fail. They were launched into orbit by the US Department of Defense with the purpose of locating either stationary or moving objects on or around the surface of the Earth. Radio signals are sent out from the satellites in space to receivers on the ground which determine velocity, position, and time.
GPS only refers to the constellation of satellites owned by the US. The entire system is referred to as the GNSS, or Global Navigation Satellite System. This includes Russia’s GLONASS as well as systems under development like the EU’s Galileo and China’s COMPASS. France, India, and Japan are all working on their own regional systems.
How Does GNSS Work?
As the satellites orbit the Earth, they are broadcasting information, essentially a time stamp. The receiver, a computer made to gather these signals and perform mathematical equations in order to interpret the data, collects these time stamps from four satellites, comparing them with the time. Based on the location of each of the four satellites and the length of time the signal travels back to Earth, the receiver is able to locate your position.
All GNSS receivers are capable of receiving GNSS signals, converting them into important location information. However, there are three kinds of devices designed for specific uses, all priced differently. As expected, as you up from grade to grade, price and accuracy increase. The categories are recreational/consumer grade, mapping grade, and survey grade. As you may be used to, some receivers place the location on a map contained on the device, determine the direction you are heading, the speed you are traveling, and other types of useful information. All of this data remains on the device unless there is a transmitter, as with a cell phone. GNSS receivers do not communicate with the satellites as the satellites can only broadcast a signal.
GNSS: Afraid of Heights?
Well, not exactly, but GNSS devices are more accurate locating horizontally than vertically. Horizontal accuracy for consumer devices and cell phones is roughly +/- 10 meters, while vertically accuracy is worse, roughly +/- 20 or 30 meters. Why is this? Blame geometry. There are satellites surrounding the Earth, but the device can only gather data from the satellites directly overhead. It would need data from the satellites beneath us on the other side of the Earth to accurately determine elevation.
GNSS: Joining Forces With Other Positioning Technology
GNSS isn’t the only way to find your position on the Earth’s surface. Software developers are hard at work figuring out different ways to pinpoint your GPS location using things like cell phone towers and wi-fi hot spots, the goal being more accurate location information in a variety of places, such as underground or indoors. Hardware developers are working just as hard, creating chips that rely on data gathered from multiple constellations.
The GPS signals from the satellites are really just weak radio signals. As such, interference from man-made and natural signals are common. Natural signals can come from things like solar storms, and man-made signals from anything radio frequency based, including GPS jammers which are illegal in the US.
GPS and the Government
Yes, GPS is owned by the US Department of Defense, but it is also available for use in a wide range of civilian applications such as mappers, surveyors, vacationers, and even geotagging in cell phone pictures and Facebook status check-ins. In the history of the Department of Defense and GPS, they have never denied civilian access at any point in time, anywhere in the world.
GNSS and Navigation
You may have heard GNSS receivers referred to as a “satnav,” a shortened term for “satellite navigation device.” While the device will show your direction and a suggested route towards a user determined destination, the GNSS only gives location information. The device itself contains all of the algorithms and map data directly on the device in the software, or sometimes on a server accessed by the device. The GNSS will only provide location data.
Incorrect GPS Location
For the most part, GPS devices are quite accurate when locating your position on a map. However, sometimes problems can arise. Rather than blame the satellites, it is likely due to bad algorithms, incorrect destination address, or an out-of-date street network. For example, when traveling home from a destination, my GPS tells me to turn in a driveway 8 houses up the street from my actual address. When the maps were made, the street was numbered differently, and the map has yet to be updated. This has happened to a lot of people, and in response to the complaints the US government received, they drafted HYPERLINK “http://www.gps.gov/support/user/mapfix/”an article to aid users in correcting the problem.
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