|
篇章阅读21：汽车系统 Navigation computers, now sold by most car-makers, cost $2,000 and up. No surprise, then, that they are most often found in luxury cars, like Lexus,BMW and Audi. But it is a developing technology-meaning prices should eventually drop-and the market does seem to be growing. Even at current prices, a navigation computer is impressive. It can guide you from point to point in most major cities with precise turn-by-turn directions-spoken by a clear human-sounding voice. and written on a screen in front of the driver. The computer works with an antenna that takes signals from no fewer than three or the 24, global positioning system satellites. By measuring the time required for a signal to travel between the satellites and the antenna. the cars location can be pinned down within l00 meters. The satellite signals. along with inputs on speed from a wheel-speed sensor and direction from a meter, determine the car s position even as it moves. This information is combined with a map database. Streets, landmarks and points of interest are included. Most systems are basically identical. The differences come in hardware-the way the computer accepts the drivers request for directions and the way it presents the driving instructions. On most systems, a driver enters a desired address, motorway junction or point of interest via a touch screen or disc. But the Lexus screen goes a step further: you can point to any spot on the map screen and get directions to it. | 
