GPS, or Global Positioning System, got its start in 1978 when the Defense Department began launching 24 satellites into space. The satellites, which circle the Earth twice a day in a precise synchronous orbit, emit signals that can be picked up by GPSreaders on board ships, planes, tanks and now pocket-size gadgets. You can use a GPS device to pick up the satellite's signals to, say, find your way back to that spot on the river where you landed that trophy brook trout last summer. GPS devices work by tracking the signals of at least three satellites at once. The device calculates its position via triangulation and displays the coordinates on the screen. On some units the information is then combined with a topographical or regional map built into the device. Most units run on batteries and will let you upload or download coordinates from desktop map software. As you move, the device records "waypoints"-markers that create a trail of where you've been. They also track your speed, time until destination and altitude.Īnd you don't have to be an avid backpacker or traveler to enjoy one of these. You can join Web GPS communities like Geocaching, which challenges its members to go on GPS treasure hunts in their area. Here's our assessment, from best to worst, of the latest in portable GPS. This silvery GPS unit from Garmin is hitting retailers' shelves now, and it's the best one we've seen. It has rich, detailed preprogrammed maps of North and South America that include all state and federal highways. The rugged device works on two AA batteries and weighs 5.3 ounces. We found the interface intuitive, so getting started was easy. Features include an electronic compass, an altimeter that is accurate to within ten feet, 24 megabytes of memory and a backlit screen for use in the dark. The only downside is that with all the information packed onto this gadget, the screen, which offers a crisp resolution of 160-by-288 pixels, should be bigger. For less than half the price, you can buy Vista's predecessor, the Etrex, which lacks preprogrammed maps but has most of the Vista's other features. While the Map 330 looks like a piece of electronic equipment from the 1950s, it is robust. It weighs 7 ounces, has a wrap-around rubber grip and, like other good outdoor GPS devices, will float. Despite its antiquated look, the Map 330 comes packed with features, including a detailed built-in roadmap of North America. We took it on a drive from New York to Philadelphia and it kept us from missing a single turn. The unit comes with 8MB of memory for its database of maps and another 8MB of flash memory, 12 parallel channels and a quadrifilar antenna, which allows it to lock onto a GPS satellite's signal even in thick woods or other harsh environments. The biggest drawback is that this device is not intuitive: You'll need to slog through the user manual.
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