Pioneer AVIC-U250 Owner's Manual - Page 68

Appendix Appendix Positioning technology Positioning by GPS The Global Positioning System (GPS) uses a network of satellites orbiting the Earth. Each of the satellites, which orbit at a height of 68 900 000 feet (21 000 km), continually broadcasts radio signals giving time and position information. This ensures that signals from at least three can be picked up from any open area on the ground's surface. The accuracy of the GPS information depends on how good the reception is. When the signals are strong and reception is good, GPS can determine latitude, longitude and altitude for accurate positioning in three dimensions. But if signal quality is poor, only two dimensions, latitude and longitude, can be obtained and positioning errors are somewhat greater. Handling large errors Positioning errors are kept to a minimum by combining GPS, dead reckoning and map matching. However, in some situations, these functions may not work properly, and the error may become bigger. When positioning by GPS is impossible ! GPS positioning is disabled if signals cannot be received from more than two GPS satellites. ! In some driving conditions, signals from GPS satellites may not reach your vehicle. In this case, it is impossible for the system to use GPS positioning. In tunnels or enclosed parking garages Under elevated roads or similar structures When driving among high buildings When driving through a dense forest or tall trees ! If a car phone or cellular phone is used near the GPS antenna, GPS reception may be lost temporarily. ! Do not cover the GPS antenna with spray paint or car wax, because this may block the reception of GPS signals. Snow buildup can also degrade the signals, so keep the antenna clear. p If a GPS signal has not been received for a long time, your vehicle's actual position and the current position mark on the map may diverge considerably or may not be updated. In such case, once GPS reception is restored, accuracy will be recovered. Conditions likely to cause noticeable positioning errors For various reasons, such as the state of the road you are traveling on and the reception status of the GPS signal, the actual position of your vehicle may differ from the position displayed on the map screen. 68 En