| 摘要 |
Real time navigation assistance is provided on multi-level roadways using on-the-fly elevation determinations obtained by measuring the ambient air pressure. Absolute air pressure measurements adjusted to sea level (QNH) are obtained by on-the-fly wireless searches. A navigation device (10) calculates its current elevation above sea level as a function of the measured ambient actual pressure and a selected local QNH reading. This elevation is correlated to a digital map so that the navigation device (10) can be accurately located relative to a multi-level roadway. Elevation readings along any road segment (14) can be transmitted to a map update center for the purpose of updating and improving digital map data.
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