GPS System

Global Positioning System (GPS)

GPS is a precise satellite-based navigation and location system. It was developed for U.S. military use to enable all elements of the military (planes, ships, submarines, tanks and ground forces) to know their position precisely and instantaneously, anytime and anywhere on the earth's surface. With a GPS receiver you can quickly and accurately determine the latitude, longitude and altitude of a point on or above Earth's surface. A single GPS receiver can find its own position in seconds from GPS satellite signals.

The GPS system consists of more than 24 communication satellites constantly orbiting the earth at an average altitude of 20,000 kilometers. They are scattered on 6 equally spaced orbital planes. They transmit signals globally around the clock. As a result, at least three satellites are always visible at anytime from anyplace on the surface of the earth. Each satellite emits a coded signal, which contains essential GPS Navigation/GPS Location information - like its position and the exact timing of the signal emission to earth. Therefore, only a simple receiver is needed to measure the elapsed time between emission and reception of the signal. The satellite to station distance is simply calculated from this travel time.

Three different measurements made on three different satellites give the three distances needed to determine the three coordinates of the location of the receiver; latitude, longitude, and altitude. This type of measurement is known as "pseudo-range" measurements in GPS jargon. Every satellite emits two types of pseudo-ranges: A precise code (P code) which enables a position precision of around 10 meters and a coarse code (C/A code) which allows a precision of around 100 meters. The precise code is encrypted and restricted to the U.S. military receivers. Civilian applications are based on the pseudo-ranges measurements is this of the C/A code. However, even using the C/A, incredibly precise location positions are possible for every day use.

GPS Navigation Systems

There are three main types of GPS devices available for consumer and commercial use:

• GPS Navigation
• GPS Tracking
• GPS Location.

1. GPS Navigation is used to help you see where YOU are right now, and to help you get from Point A to Point B. There are numerous devices made for GPS Navigation, from hand-held units, to those that are installed in cars and commercial vehicles. These are basically mapping systems that offer integrated cartographic databases (also known as base maps), allowing users to locate a point on a map and define it as a waypoint. Some GPS systems intended for automobile navigation can generate a suggested driving route between two waypoints, based on the cartographic database. As one drives along the route, the system indicates the driver's current location and gives advance notice of upcoming turns. The best of these systems can take into account traffic restrictions such as one-way streets and intersections where left or right turns are prohibited when computing the suggested driving route.

2. GPS Tracking is used to precisely record a log of all vehicle (or personal) activity and travel over an extended period of time. GPS Tracking is useful in eliminating time-consuming and poor quality vehicle use logs; as well as, increase productivity, and accountability, by maximizing business use of your vehicles, while decreasing or eliminating personal use. They are also great to keep track of where the kids have been. The best units provide second by second tracking for the highest accuracy of position AND speed traveled, while having built-in motion sensors so data is only collected during actual travel allowing for much longer recording.

3. GPS Location is used to provide Real-Time positioning of a vehicle or the GPS device, so you know where it is right now. These usually provide minimal tracking capability or none at all, and are not a replacement for GPS Tracking. GPS Location is mostly used for fleet vehicles, emergency location positioning, or as an aid in recovery of a vehicle or asset. GPS Location involves "Pinging" the device via satellite or by cell phone, and having it "phone" home with its current position via satellite cellular technology. This means that there is a recurring cost for GPS Location that does not usually apply to GPS Tracking.