GPS - What It Is and How It Works

By Michael Russell

A GPS unit can be purchased in stores for anywhere between $100-$1000 dollars and allows a user to know their location anywhere in the world. Unlike the GPS receiver the actual global positioning system is composed of approximately 30 satellites, which orbit the earth.
Furthermore, at any time of the day, anywhere in the world, there must be at least 3 GPS satellites visible for a receiver (unit) to function properly. By using radio frequencies to contact the GPS network of satellites a receiver can pin-point a users location via a process called three dimensional trilateration.

Originally the GPS system was developed by the United States Department of Defense, as a new means of tracking navigation. Ironically, GPS is free for civilians; anyone can pick up a unit at a local store and begin to know his or her location immediately. In fact GPS has become so popular as a means to aiding navigation that map makers, surveyors, businesses and scientists use it as part of everyday operations. A very useful feature of GPS is that it provides a precise time stamp allowing users to make calculations of their velocities as well as track their changes in locations.

There are minor errors with GPS; in fact certain problems can occur if a user is next to large objects such as buildings, canyons, tunnels, etc. The cause being that radio waves bounce off of large objects, giving the impression that key satellites are father away than in reality. Originally users in large cities with skyscrapers experienced these problems rather frequently. In order to solve these problems differential GPS (DGPS) was developed as a means of providing more accurate information. By sending out more frequencies, DGPS receivers could receive more accurate information instantly resulting in fewer errors and transmission problems. In addition, DGPS units could reports latitudes, longitudes and altitudes of current locations and included this data into maps, which were stored within the unit. Currently, you can use maps stored in a DGPS unit, you can download new maps, or connect your unit to a computer to allow you to find your way more accurately.

The newest GPS receivers typically have the following features; display how far you have traveled, how long you’ve been traveling, current speed, average speed, a trail showing you where on the map you have traveled and can even display estimated times of arrival given current speeds. The technology has grown so much that many consumer products have been fitted with GPS units. New cell phones, cars, rentals, boats and government vehicles have been fitted with positioning units; making travel safer and more reliable. In addition GPS is believed to have contributed to lower crime rates and in certain countries greater compliance with speed limits.

Currently, according to the retailer Amazon.com, the top vehicle GPS units are: the Garmin Nuvi, Street pilot, Pocket Navigator, TomTom One and Magellan Maestro. On the other hand, for handheld units the most popular are: Garmin Forerunner, Lowrance iWay, Via Michelin and the Magellan Explorist. If you’re interested in purchasing a unit, be sure to check consumer reports to determine the right GPS unit for your needs.
Michael RussellYour Independent guide to GPS