Land-based navigation using on-the-fly elevation assessments

Abstract

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.

1 . A method for providing real-time navigation assistance on land-based vehicular roadways using on-the-fly elevation determinations, said method comprising the steps of:
 providing a digital road map having a representation of a road network corresponding to a plurality of roads in reality, each road in reality having a measurable elevation above sea level at any given geo-position there along;   providing a mobile navigation device interactive with the digital map, the navigation device capable of determining its instantaneous geo-position in the digital road network relative to the road in reality;   transporting the navigation device along a road in reality while simultaneously updating its corresponding geo-position in the digital road network;   conducting an on-the-fly search for local absolute atmospheric pressure readings (QNH) via wireless transmission;   selecting a reliable local absolute atmospheric pressure reading (QNH);   measuring the actual ambient atmospheric pressure;   calculating a current road elevation as a function of the measured actual and selected absolute (QNH) pressures; and   associating the calculated current road elevation with the corresponding instantaneous geo-position of the navigation device.   
     
     
         2 . The method according to  claim 1  further including the step of updating the on-board digital map with the calculated elevation at the corresponding geo-position. 
     
     
         3 . The method according to  claim 1  further comprising:
 transmitting the calculated elevation at the corresponding geo-position to a map update center. 
 
     
     
         4 . The method according to  claim 1  wherein said selecting step includes computing the distance between the instantaneous geo-position of the navigation device and the geo-location of the local absolute atmospheric pressure reading (QNH). 
     
     
         5 . The method according to  claim 1  wherein said step of selecting a reliable local absolute atmospheric pressure reading (QNH) includes comparing a plurality of available readings and choosing the closest in geo-position and time to the instantaneous geo-position of the navigation device. 
     
     
         6 . The method according to  claim 1  wherein said step of selecting a reliable local absolute atmospheric pressure reading (QNH) includes linearly approximating the gradient of the air pressure field between the location of the local absolute atmospheric pressure reading and the instantaneous geo-position of the navigation device. 
     
     
         7 . The method according to  claim 1  wherein said step of selecting a reliable local absolute atmospheric pressure reading (QNH) includes computing an average local absolute atmospheric pressure reading (QNH) from a plurality of data sources. 
     
     
         8 . The method according to  claim 1  wherein said step of measuring the ambient atmospheric pressure includes making regular periodic passive samplings. 
     
     
         9 . The method according  claim 1  wherein said step of calculating a current road elevation includes applying the formula:
   current elevation (in meters)=(selected absolute pressure (in mbar)−measured ambient pressure (mbar))/0.12.
 
 
     
     
         10 . The method according to  claim 1  wherein said step of conducting an on-the-fly search includes searching the internet. 
     
     
         11 . The method according to  claim 1  further including the step of continuously updating the instantaneous geo-position of the navigation device in the digital road network relative to the road in reality based on data transmitted from a constellation of satellites. 
     
     
         12 . The method according to  claim 1  further including the step of providing navigation assistance based on the calculated current road elevation. 
     
     
         13 . The method according to  claim 1  wherein at least one road in reality overlies another road in reality but at an offset elevation, said step of associating the calculated current road elevation with the corresponding instantaneous geo-position of the navigation device includes associating the navigation device with a specific one of the two offset roads in reality; and providing navigation assistance based on the calculated current road elevation, said navigation assistance including mapping the navigation device to a specific one of the two offset roads in reality based, at least in part, on the calculated current elevation of the navigation device. 
     
     
         14 . A method for providing real-time navigation assistance on multi-level overlapping roadways using on-the-fly elevation determinations, said method comprising the steps of:
 providing a digital road map having a representation of a road network corresponding to a plurality of roads in reality, each road in reality having a fixed and measurable elevation above sea level at any given geo-position there along; at least one road in reality overlying another road in reality but at an offset elevation;   providing a mobile navigation device interactive with the digital map, the navigation device configured to determine its instantaneous geo-position in the digital road network relative to the road in reality based on data transmitted from a constellation of satellites;   transporting the navigation device along a road in reality while simultaneously updating its corresponding geo-position in the digital road network;   simultaneously with said transporting step, conducting an on-the-fly search for local absolute atmospheric pressure (QNH) readings via wireless transmission;   selecting a reliable local absolute atmospheric pressure reading (QNH) relatively near in geo-position and time to the instantaneous geo-position of the navigation device;   measuring the ambient actual atmospheric pressure;   calculating a current elevation of the navigation device above sea level as a function of the measured ambient actual and selected absolute (QNH) pressures;   associating the calculated current road elevation with the corresponding instantaneous geo-position of the navigation device;   mapping the navigation device to a specific one of the two overlying roads in reality at least partially based on the calculated current elevation of the navigation device;   providing navigation assistance based on the calculated current road elevation;   updating the on-board digital map with the calculated elevation at the corresponding geo-position by saving the calculated elevation as an attribute; and   transmitting the calculated elevation at the corresponding geo-position to a map update center.   
     
     
         15 . A navigation device configured to perform the method of  claim 1 .