How GPS works
How GPS functions? What is the technology they use? Nothing more than the satellites! They synchronize with the 24 operational satellites and fix up some errors arising out of the obstacles which are either man made or natural. Find more below…
GPS is short for Global Positioning System, and that captures well what it does: it indicates your position on the globe. The way GPS operates is a fascinating tale that doesn’t require advanced mathematics to understand.
Before looking into the details of how navigation systems work, it’s helpful to have some general knowledge of how certain positions on earth are specified. The classic view provides one that’s easy to visualize.
Imagine a simple grid that wraps the globe ‘vertically’ originating at the earth’s North Pole and stretching out over to the South Pole. Then add ‘horizontal’ lines that cross the globe at right angles to the vertical lines. That grid is the familiar longitude and latitude ‘mesh’ that can be found on every school room globe and map. Each line of lat and long is divided in degrees that specify how far along a line you are located.
Now, what does the ‘mesh’ have to do with the GPS system?
The U.S. Air Force maintains 24 different operational GPS satellites (with 3 spares). Each satellite has the electronics and software installed to calculate its own location, most importantly the distance to the Earth. It does that by sending a radio beam out and registering the time needed to hit the Earth where the signal is picked up by ground stations.
A simple formula is: distance = velocity * time, and that describes it pretty straightforward. Radio waves travel at the speed of light (~186,00 mph or ~300,000 kph) and the electronics measure the delay from when the beam is sent to when it hits the target.
Satellites (and ground stations) can measure that delay accurately because they have computers synchronized by atomic clocks that are able to measure time incredibly accuracte. GPS Receivers don’t have atomic clocks included but perform some tricks to compensate.
Also because of variations in the atmosphere, the motion of the satellites, reflections from buildings and other imperfections GPS have to make up for small calculation errors in order to get the precision needed to locate your receiver to within a few meters.
Distance provides only one important factor in GPS. Imagine you’re told you are 600 miles east of Los Angeles. That puts you in the center of a circle of radius 600 miles, with LA somewhere on the circumference (the rim). But you don’t know exactly where. Now you’re told you are also few hundred miles north of Las Vegas and another circle is created. Those two circles intersect at two points. A third intersecting circle will place you at exactly one unique point (to within measurement accuracy).
Since the GPS system is dependent on satellites in space that interact with ground stations, it operates in three dimensions, not just the two provided by the surface of the Earth. So, the Global Positioning System works with spheres rather than circles. The calculations are more complex, but the idea is the same. Where the surfaces of four spheres intersect they calculate a certain point, the location point of the GPS device.
Your GPS receiver is designed to ‘listen’ for the signals from four of those satellites, and uses the info provided to determine your latitude and longitude. It overlays that unique point onto a map that resembles your surrounding area to help you to navigate your way to anywhere in the world.