What is GPS?

History of GPS

The Global Positioning System (GPS) network was developed in the 1970's by the US military and was declassified in 1982 for commercial use.

It includes multiple satellites orbiting the earth at a distance of approximately 20,000 miles. The satellites provide detailed time and positioning information. GPS vehicle tracking and fleet management systems use a GPS transmitter/receiver and a small antenna on each vehicle that links it to the GPS network which can then monitor each vehicle's activity 24 X 7 X 365. The vehicle data is then downloaded into the user's master database, providing a permanent history of the entire fleet operation.

GPS-based fleet management systems combine GPS-based tracking data and proprietary software to deliver an informative, cost-effective way to monitor drivers' efficiency and productivity. The systems provide managers with key vehicle data such as start and stop times, number of stops by address per day, time spent at each stop, mileage, speed, idle times, routes traveled and more. The primary goal of GPS-based fleet management systems is to save your business time, money and provide a tool to verify accountability for the employees using your company vehicles. With access to this data, you can better manage drivers' efficiency and productivity, identify "lost time" in vehicle routes and the costs related to engine service, vehicle maintenance, fuel, tires, insurance, customer service, payroll/overtime, etc. There are many ways to customize the data collected to fit any fleet service operation. Special features are easily added that can measure "events." An event feature would track a user-specific activity, such as when a door was opened or closed, or when an onboard compressor was turned on, how long it ran and when it turned off. These readings would capture "real-time" measurements anytime, day or night. Now, you can validate what your vehicle and equipment did, plus when and where it was done

GPS-based fleet management systems can either be "active," providing a real-time link between a monitoring station and each vehicle, or "passive," automatically downloading accumulated information into a base station whenever the vehicle is at it’s “home” base. The difference comes down to needs and cost. To provide real-time data, an “active” system uses a data link, such as a cellular connection, from each vehicle back to the base station. This involves a monthly monitoring fee through a cellular provider. Passive systems require no interaction from a dispatcher or vehicle operator. Information is downloaded automatically whenever the vehicle returns to its home base. Therefore passive systems do not require a monthly monitoring fee. Fleet tracking systems collect information in a database format and then use software to present the information in an easy-to-read report format. The software allows companies to analyze productivity of individual drivers, or the entire fleet, against established benchmarks. Nearly all companies immediately see direct cost benefits. In short, this application of the GPS technology is all about accountability and verification. The value of a GPS fleet tracking system goes beyond managing the vehicles. By having records that can demonstrate the fleet stays within speed limits and determined geographic areas, many users find that their overall cost of fleet insurance is reduced. In summary, the benefits to a company are obvious--including detailed records of vehicle usage, better route management, payroll verification and decreased fuel consumption.

Source: GPS Direct Online http://www.gpsdirectonline.com

What is GPS?

The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense. GPS was originally intended for military applications, but in the 1980s, the government made the system available for civilian use. GPS works in any weather conditions, anywhere in the world, 24 hours a day. There are no subscription fees or setup charges to use GPS.

How it works

GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. GPS receivers take this information and use triangulation to calculate the user's exact location. Essentially, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away the satellite is. Now, with distance measurements from a few more satellites, the receiver can determine the user's position and display it on the unit's electronic map.

A GPS receiver must be locked on to the signal of at least three satellites to calculate a 2D position (latitude and longitude) and track movement. With four or more satellites in view, the receiver can determine the user's 3D position (latitude, longitude and altitude). Once the user's position has been determined, the GPS unit can calculate other information, such as speed, bearing, track, trip distance, distance to destination, sunrise and sunset time and more.

Source: Garmin.com

Basic concept of GPS

A GPS receiver calculates its position by precisely timing the signals sent by the GPS satellites high above the Earth. Each satellite continually transmits messages containing the time the message was sent, precise orbital information (the ephemeris), and the general system health and rough orbits of all GPS satellites (the almanac). The receiver measures the transit time of each message and computes the distance to each satellite. Geometric trilateration is used to combine these distances with the location of the satellites to determine the receiver's location. The position is displayed, perhaps with a moving map display or latitude and longitude; elevation information may be included. Many GPS units also show derived information such as direction and speed, calculated from position changes.

It might seem three satellites are enough to solve for position, since space has three dimensions. However, even a very small clock error multiplied by the very large speed of light[19]—the speed at which satellite signals propagate—results in a large positional error. Therefore receivers use four or more satellites to solve for x, y, z, and t, which is used to correct the receiver's clock. While most GPS applications use the computed location only and effectively hide the very accurately computed time, it is used in a few specialized GPS applications such as time transfer, traffic signal timing, and synchronization of cell phone base stations.

Although four satellites are required for normal operation, fewer apply in special cases. If one variable is already known (for example, a ship or plane may have known elevation), a receiver can determine its position using only three satellites. Some GPS receivers may use additional clues or assumptions (such as reusing the last known altitude, dead reckoning, inertial navigation, or including information from the vehicle computer) to give a degraded position when fewer than four satellites are visible (see [20], Chapters 7 and 8 of [21], and [22]).

Source: Wikipedia