Document Type : Research Paper

Author

• Abbasali Salehabadi

Abstract

Considering the advancements in GPS technology and applications of this important tool in the world, having a knowledge of the different ways of positioning by this system seems essential. The high precision of this system and its universality are reasons for utilization of this system in all surveying, geodetic, hydrographic, imagery (photo) and other works. As an introduction, we will first review the GPS and N.N.S.S positioning systems, and then discuss the mathematical equations and observations of the GPS system in full.
Generally, space-based positioning was begun by NASA since 1960's using the Doppler system. However, it’s time-consuming process and lack of precision caused the US Department of Defense (DOD) in 1974 to declare its need for a comprehensive and global positioning system for its military purposes. This led to the creation of GPS (Global Positioning System), and in 1983, the launch of the first GPS satellite was an effective step in the history of surveying. With the rise of the GPS system all previous systems, including ballistic cameras, Doppler (N.N.S.S.), the LONG-C, OMEGA and SECOR gradually disappeared.