Global Positioning System (GPS) or more correctly Navstar GPS is a global navigation satellite system that provides location and time information continuously anywhere on the earth. A receiver is capable of calculating its current location when there is an unobstructed line of sight to four or more GPS satellites. The satellite network is maintained by the United States government and is freely accessible by anyone with a GPS receiver.

 

 

Navstar GPS was created and realized by the U.S. Department of Defense and was originally run with 24 satellites. It was established in 1973 to overcome the limitations of previous navigation systems.

 

 

 

GPS has become widely used in both commercial and scientific applications. The accurate timing of GPS facilitates everyday activities such as banking, mobile phone operations, and even the control of power grids. Farmers, surveyors, geologists and countless other groups perform their work more efficiently, safely, economically, and accurately.

 

 

 

A less known system is the russian GLONASS which was created by the former Soviet Union, after a period of disrepair, the Russian government committed in 2001 to the restoration of the system, which was completed in 2010.

 

 

 

A current project within the European Union and European Space Agency (ESA) creates an alternative system called Galileo.

Galileo is intended to provide more precise measurements than available through GPS or GLONASS including the altitude above sea level, and better positioning services at high latitudes. The driving forces behind the Galileo system is political since Russia or the USA could prevent use of their systems by others. Galileo shall become a positioning system upon which European nations can rely even in times of war or political disagreement,

Like the american GPS, use of basic (low-accuracy) Galileo services will be free and open to everyone. However, the high-accuracy capabilities will be restricted to military use and paying commercial users.

.