How does GPS Work?

Posted By BrokenClaw on October 8, 2007

The Global Positioning System, abbreviated and more commonly known as GPS, is a tracking system that allows a GPS device on earth, called a receiver, to determine its precise location by measuring microwave signals from orbiting satellites. Since it uses extremely accurate clocks and makes this determination essentially instantaneously, it can use a series of readings to calculate direction and speed of the receiver as well.

The satellites used for GPS were originally intended for exclusive use by the US Department of Defense, but in 1983, President Reagan declared that the system should be available to the general public. There are currently more than 30 GPS satellites in service, maintained by the US Air Force.

The theory behind GPS is an extension of triangulation, whereby a surveyor can measure distance based on the angle from two different known points. In the case of GPS, its location on earth can be determined by trilateration from three satellites. Today’s more advanced GPS systems use eight or more satellites to improve reliability and accuracy. In order to receive a signal, the receiver, or at least the antenna, must be outside within view of the sky, just like satellite radio.

Obviously, GPS is an important tool for military, scientific, and aviation purposes, but for the consumer, GPS generally takes on one of the following applications:

  • Automobile navigation
  • Marine navigation
  • Wilderness navigation
  • Personal navigation

TomTom GPSAutomobile navigation via GPS is always integrated with a highway mapping program. The GPS receiver may be installed into the dashboard of the vehicle, or it may be a portable device that you can move from one vehicle to another. Some models also include a digital voice feature, so the GPS device can speak to you and give directions in real time. Marine navigation is essentially the same as automobile, when combined with nautical charts.

Stand-alone GPS receivers have become a must-have tool for wilderness travelers, whether they are hikers, hunters, mountain bikers, off-road drivers, white-water rafters, etc. Garmin portable GPSThe GPS device can be used to set waypoints and direct the traveler to them. For example, a hunter who plans to wander about an unfamiliar mountain forest can set a waypoint when he leaves his vehicle, and no matter where he roams, he can follow the directions of the GPS back to his vehicle. A hiker can set waypoints along the trail, or wander off the trail, and follow the GPS to backtrack the same path.

Like most other electronic technologies, GPS receivers are getting smaller and lighter. A hand-held GPS receiver is sometimes called a personal navigation device, abbreviated PND. They can also be embedded into other devices, such as cell phones, PDAs, and laptop computers. Any such device that is connected to the Internet or to a cell phone network can have software that enables reverse GPS. In other words, it can send the location information from the receiver to a remote station, so that someone else can track the movements of the PND-carrying person. Reverse GPS is touted as a safety measure for parents and children and as an advanced business practice for employers. However, this ability for others to track your location, whether you realize it not, becomes another privacy issue to be considered.

When reviewing or purchasing portable devices, it’s important to differentiate GPS from GPS-like navigation. For instance, cell phones can use triangulation from cell towers to give an approximate location, but they are not nearly as accurate as GPS. Cell phone triangulation is active in most cell phones, which allows emergency services to approximate the origin location of emergency calls.

The accuracy of GPS receivers depends on many natural conditions, but in normal circumstances, consumer devices are usually accurate to within a few feet, which makes them useful for such things as determining distances on a golf course. And because they operate at light speed, GPS can be used to track vehicles in high-speed racing. At the highest level of performance, GPS can be accurate to within a few inches.

There are many different manufacturers of GPS receivers, and the models vary greatly in features and price. Some examples of manufacturers of consumer products are:

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