GPS: Information Provider or Controller?

A GPS receiver is one of the most accurate clocks in the world, if it has continual access to the satellites. The forte of a clock in a tracking device is short-term accuracy, not long-term consistency. People who really want to know exactly what time it is can set up a base station over a known point and analyze GPS signals for time instead of position. GPS time does differ from UTC time by an integer number of seconds, less than 20 for the near future. There are many applications for which coordinated time is vital. Examples: making the telephone system, the banking system, and the Internet, on which the World Wide Web is based, run smoothly.

There will be an increasing number of applications in which GPS signals control equipment directly, rather than going through a human “middle-man.” In such joint GPS/GIS uses as fertilizer or pesticide application, the automated system may steer the tractor while the farmer rides along simply for reasons of safety. Carving out roadways or laying pavement may be conducted in similar fashion. The Center for Mapping at Ohio State University boasts a system that can put a bulldozer blade in the correct position with an accuracy approaching one centimeter.

At sea, or flying over unlit bodies of land at night, captains and pilots used methods that provided absolute coordinates. One’s position, within a few miles, can be found by “shooting the stars” for a short time with devices such as sextants or octants. So the GPS concept–finding an earthly position from bodies in space–is not an entirely new idea. But the ability to do so during the day, almost regardless of weather, with high accuracy and almost instantaneously, makes a major qualitative difference. As a parallel, consider that a human can move by foot or by jet plane. They are both methods of locomotion, but there the similarity ends. GPS, then, gives people an easy method for both assigning and using absolute coordinates. Now, humans can know their positions (i.e., the coordinates that specify where they are); combined with map and/or GIS data they can know their locations (i.e., where they are with respect to objects around them). I hope that, by the time you’ve completed this text and experimented with a GPS receiver, you will agree that NAVSTAR constitutes an astounding leap forward.

While this is a text on how to use GPS tracking device in GIS–and hence is primarily concerned with positional issues, it would not be complete without mentioning what may, for the average person, be the most important facet of GPS: providing Earth with a universal, exceedingly accurate time source. Allowing any person or piece of equipment to know the exact time has tremendous implications for things we depend on every day (like getting information across the Internet, like synchronizing the electric power grid and the telephone network). Further, human knowledge is enhanced by research projects that depend on knowing the exact time in different parts of the world. For example, it is now possible to track seismic waves created by earthquakes, from one side of the earth, through its center, to the other side, since the exact time2 may be known worldwide.

More GPS tracking solutions at http://www.jimilab.com/ .