The Basics: GPS Devices
The Global Positioning System, or GPS, consists of three different segments: a space segment, a control segment and a user segment. The space segment includes a minimum of 24 satellites in orbit 12,000 miles above the earth, the control segment handles tracking the flight path of these satellites, and the user segment involves handheld receivers that process the signals from these satellites.
The GPS, also known as NAVSTAR GPS, was developed by the U.S. Department of Defense, but in 1996 it was decided that civilians could benefit from GPS access as well. In 2000, the Selective Ability of the GPS which watered down the civilian signals was eliminated, giving consumers access to extremely accurate tracking signals.
At any given time, at least six satellites are in view and are broadcasting time, velocity, and position information. The GPS can be utilized with a receiver colloquially known as a GPS device, which usually contains a visual map to display an accurate position within less than 20 meters (or even more precise if it's a WAAS, or Wide Area Augmentation System, receiver). A GPS receiver has multiple channels (up to 20) that can each monitor a separate satellite. With three satellites observed, the GPS device can present a 2D location based on latitude and longitude. With four or more satellites observed, the GPS can offer a 3D location with altitude thrown in as well.
Most consumer GPS devices include street maps and allow users to plot a course from one location to another. Accessing the GPS signals is free, although some vendors charge for additional services such as real-time traffic conditions.
When consumer GPS devices first debuted a little over a decade ago, they were rather primitive, offering latitude and longitude locations in text or maybe displaying a crude grayscale map. Today's GPS devices contain 3D color maps that mirror your driving perspective, provide voice directions, and include Points of Interest (POIs) on the map so you can easily find a gas station or hotel when you need one.
The color screens usually range from 3.5 inches to 4.3 inches in size, and they're touch sensitive, letting you manipulate the on-screen interface easily.
Purchasing a GPS device for your car used to be an expensive prospect, and you can still expect to spend at least $500 extra to have a built-in GPS system as part of your new vehicle purchase. But some of the major vendors--including Magellan, Garmin, TomTom, and others--are starting to sell stand-alone GPS devices with vehicle mounting kits priced at less than $200. These kits usually include a dashboard or windshield mount and a car adapter so you can keep your GPS device powered during long road trips (most GPS devices ship with rechargeable batteries, but battery life is usually only a couple of hours).
Even basic GPS devices will include pre-installed maps of the 48 contiguous United States. The higher-end models will often include Canada and Puerto Rico as well. And you can download additional maps with new locations or greater detail, although there may be an additional charge. You can download or purchase topographical and trail maps for off-road hiking, biking, or snowmobiling.
GPS devices come with built-in storage, but this is often filled with the pre-installed maps. Some GPS devices offer a Secure Digital or other media card slot, so you can add more storage room--and more maps. Some of the more advanced GPS devices even play music or let you view photos.
GPS devices can be used for entertainment as well. Many users will hide objects at specific latitude and longitude locations, called waypoints, and then other users try and find them in a sort of high-tech scavenger hunt.
Five Questions
1) How do GPS devices work?
GPS devices include receivers that process signals from satellites in orbits. These receivers can use the signals from three or more satellites to triangulate your position on the ground. This position is then displayed on a 2D or 3D map.
2) How much does it cost for a GPS device?
GPS devices start at under $200 and range upwards of $500 or more. The basic GPS device will include a color touchscreen, preloaded maps, and mapping and direction software. More expensive GPS devices may have a larger screen or more features or both.
3) How much does it cost for the GPS service?
It is free to access the GPS satellite signals, although some GPS vendors charge for extra services such as road-side assistance or real-time traffic updates.
4) What kind of features do GPS devices offer?
A standard GPS device will usually include a color map that lets you see your position on streets and roads. Most GPS devices offer voice instructions, telling you to turn right at the next intersection, for example. The higher-end models include text-to-speech capabilities, so they can give you exact street names. A few of the newer models even include MP3 players and image viewers, so you can pop in the Secure Digital card from your digital camera and see your pictures without a PC.
5) Where can I use a GPS device?
Although most GPS devices are used in automobiles, they're handy to use on foot or in other vehicles as well. You can often download hiking or marine maps to your GPS device so you can use them "off road". Most GPS devices need a clear signal to the sky however, so they're of limited use indoors or for spelunking.
How to Shop
GPS devices range widely in price. You can get a basic GPS receiver for less than $200, but you want to make sure that it will do everything you want it to. Make sure that the screen is large enough for your use, and that the GPS device offers any extra features you want. Some new GPS devices feature widescreen displays, so shop around to see which screen will work the best for you.
Most users can get by without a built-in MP3 player or image viewer, but having text-to-speech capabilities so your GPS device can read street names can be a valuable asset for travelers in unfamiliar locations. Some GPS devices also have Bluetooth connectivity, letting you connect your cell phone and make hands-free calls via the GPS device speaker. And a few of the newer models have voice command capabilities, so you can map directions to a new location without taking your hands from the steering wheel.
Most new GPS devices feature the WAAS receivers that better pinpoint your location, but check the specifications on the bargain-priced models just to be sure. The POI (Points of Interest) database can vary quite widely from one GPS device to another. Some number in the thousands while others number in the millions, so if it's important to you to be able to find a restaurant or gas station quickly when you're on the road, check out the details of this feature.
Most GPS devices work in a similar fashion: you plug in an address or cross-street and the GPS will map the best route there. But the "best route" is subject to interpretation. Most GPS devices let you decide between fastest and shortest in terms of route parameters, and some let you adjust the route to include most or least use of freeways as well. If you have a chance, play around with a GPS device and its interface at your local brick-and-mortar electronics store, even if you're buying online (where you can usually get the best deal).
If you'll be using your GPS device in a boat or while hiking, you might also consider one of the waterproof models that many vendors offer.
Many new PDAs (Personal Digital Assistants) and smartphones offer GPS capabilities as well, so if you're in the market for a new PDA, you can address two needs at once with one of these convergence devices.
