Global positioning and navigation systems are being used for an increasing number of scientific and industrial endeavors as well as for private, civilian use. The devices most people think of when they think of GPS are those designed and marketed for consumer use, like automotive navigation systems and handheld systems for use by outdoor enthusiasts. However, industrial use is so large that many large GPS companies have separate divisions for professional and consumer users.
The Global Positioning System is a product of the US Department of Defense and is not alone in Earth orbit. Russia has a system called GloNaSS and the European Union has a system that will be completed in 2008 called GALILEO. Collectively, these systems are called Global Navigation Satellite Systems, or GNSSs. There are other systems in place called Satellite Based Augmentation Systems (SBASs) that improve the function and accuracy of GNSSs as a whole.
A GNSS is set up so that a receiver on the ground will be able to make contact with at least four overhead satellites at any given time and at any point on Earth. The contacts are used to geometrically locate the receiver (and therefore the person operating it). The system can also be used to determine elevation as well as position. One quirk of the system is that it does not (at least for basic civilian use) register altitudes below average sea level.
Making Use of Global Positioning Systems
GPS receivers, for whatever uses, all operate in basically the same way and will be more or less accurate and reliable based on individual design and construction. The most accurate consumer models utilize differential GPS (DGPS), dual frequencies, and kinematic (or On-The-Fly) real-time signal processing. These systems can also use signal encrypting (known as Y-code) and have a host of other specialized features, the list of which is too long to enumerate here.
