Global Positioning Systems
A global positioning system (GPS)19 is a satellite-based system that provides users with accurate and precise location and time information. Using NAVSTAR GPS, you can determine locations on Earth easily within a few meters, and, with more difficulty and expense, within a few centimeters or better. Timing within 40 billionths of a second (40 nanoseconds) is easily obtained. Timing within 10 nanoseconds is possible.
The U.S. Department of Defense operates NAVSTAR GPS in cooperation with the U.S. Department of Transportation. The acronym NAVSTAR stands for NAVigation System Timing And Ranging Global Positioning System.” Informally, it is the Navigation Star.
The Russian GLONASS (Global Navigation Satellite System) operates similarly. Concerns about U.S. control over NAVSTAR led Europe to begin development of its own independent Galileo system in 2002, but it is just now becoming operational. China is developing the BeiDou (Compass) GNSS.
A GPS receiver, which “remembers where it has been,” is becoming a primary method of providing data for GIS. For example, if you drive a van with a GPS antenna on its roof along a highway, recording data every, say, 50 feet, you will develop an accurate and precise map of the location of the highway. The NAVSTAR GPS is discussed in Chapter 5.20