Alpine NVE-N872A Hardware Manual - Page 6

Preface Preface Navigation systems This navigation system uses three different sensing devices to determine the present location and to track the progress of the vehicle. These three devices are: a GPS (Global Positioning System) receiver which receives digital signals from the GPS satellites to determine the current position of the vehicle, a gyroscope which determines which direction the vehicle turns, and a speedometer pulse sensor which determine how far the vehicle has travelled. Because this system incorporates a gyroscope and a speed sensor, the system will be able to display the vehicle's position and track the vehicle's progress even in areas where the GPS signal may be blocked. All map data is contained on a removable DVD ROM (sold separately). This system integrates this unique map database with the sensing devices to automatically plot out a route when a destination is entered. While driving, the navigation system guides you along the route with pictorial displays and verbal prompts. Note: Altitude display accuracy can vary widely since the system uses only GPS signals for determining altitude approximations. Unlike altitude measurement, map matching accuracy is much more precise due to calculation methods that utilize three inputs: 1) GPS signals, 2) vehicle speed signals, and 3) the system's built-in electronic gyro signals. GPS (Global Positioning System) This system receives signals from 3 or more GPS satellites (operated by the United States Department of Defense) orbiting at an altitude of 13,100 miles (21,000 kilometers) and measures the present car position using the same principles as triangulation. There may be a delay before the actual vehicle's position is dis- played Determination of the present vehicle's position starts when the ignition key is turned to the ACC or ON positions and ends when the key is turned OFF. When the key is first turned to the ACC or ON positions, there is a slight delay of approximately one to two minutes before the present vehicle's position can be displayed. The error from the actual position of the vehicle When GPS signals can be received from 4 or more satellites, 3 dimensional positioning (the altitude, latitude, and longitude) of the vehicle can be determined. In this case, the error from the actual position of the vehicle is in the range of 100 to 655 feet (30 to 200 meters). When GPS signals can only be received from 3 satellites, only two dimensional positioning (latitude and longitude) can be determined, resulting in a slightly increased error. When GPS signals can only be received from less than three satellites, positioning of the vehicle through GPS is not possible. In addition to the inherent errors from GPS, the error rate can also be increased if the United States Department of Defense deliberately changes the accuracy rate. 6