GPS - How it Works - February 20th, 2007
Made available to the civilian population in the 1980s, the Global Positioning System (GPS) was placed in orbit by the U.S. Department of Defense, originally intended for military applications. As the word “triangulation” suggests, the GPS System establishes the location of a receiver in 2D space (latitude and longitude) by tracking the signal of at least three satellite reference points. When 4 or more signals are locked in, a user’s position in 3D space (longitude, latitude, and altitude) can be determined. The new “turn by turn” navigation service offered on the 2007 Chevrolet Impala is an example of the sophistication available in today’s GPS receivers.
GPS receivers can determine their distance from a satellite by using the travel time of a radio message from the satellite to the receiver. Each GPS satellite is equipped with 4 atomic clocks to assure accurate time. The available technology allows users remarkable accuracy under ideal conditions.
Conditions that adversely affect GPS triangulation include interference from variations in the ionosphere and water vapor in the troposphere. The US Department of Defense imposed a program called Selective Availability which made GPS less accurate for non-military users. With SA in effect, non-military users can expect an accuracy of between 50 and 100 meters. Now that SA has been discontinued, accuracy of GPS triangulation can be as close as 15 meters.
Over the years GPS receivers have decreased in size and cost while becoming more sophisticated and useful. Handheld GPS receivers now cost $100 to $600 and offer features that were only dreamed about a few years ago. For the car, truck, or SUV, a GPS System can provide other travel useful information in addition to position, such as speed, trip distance, distance to destination, and more. Many premium GPS devices, including the receiver available in the 2007 Toyota Camry offer a touch screen, DVD-based navigation system through which you can view satellite signal availability, or determine your location in relation to a chosen target. Coupled with a real-time user interface, you can see exactly where you are within about 1 meter, identify surrounding street names, unaffected by weather or time of day. Use of GPS satellites is free.
Types of GPS Features
On the face of your GPS unit are several buttons which when activated, display a variety of operating interfaces.
Feature Description
Vehicle location: This screen displays present position, elevation, and time of day. If a target destination is selected, the device will also display distance and direction to target.
Cross hair tracking: The screen will display the target in cross hairs and distance and time till interception.
Active Monitoring: As you drive, the device monitors and displays speed and direction. The GPS device shows the distance and bearing to a chosen target. The handy apparatus alerts you when you deviate from the course.
Pull down: By positioning a cursor over a given item on your GPS’ menu, you can change to another operation.
Backtrack: Display a travel history to your target, and view the distance and travel solution to your destination.
Satellite Support: At any given moment, the device notes how many satellites are detected. Having at least 4 satellites online offers the best triangulation for accurate tracking.
Posted on February 20th, 2007 by JP
Filed under: technology |
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