The invention relates to a position determination method operating by means of adjustment of a position determined by dead reckoning with the aid of a digital road map, and to a navigation device.
Patent specification U.S. Pat. No. 4,796,191 discloses correcting a position determined by dead reckoning by comparison with roads of a digital road map. For this purpose, a comparison is carried out between a direction traveled by a vehicle and the direction of roads of a digital road map. As a result of adjusting with the aid of the digital road map, a summation of the measurement errors occurring in the sensors is prevented.
Furthermore, a vehicle navigation system that uses dead reckoning and satellite navigation (GPS) for position determination is known from patent U.S. Pat. No. 5,394,333. A position calculated by dead reckoning is plotted on a road map. A correction value for the GPS navigation is determined from the difference between the position on the road map and a position found by means of GPS.
However, position can be determined on the digital road map in an informative way only in the event of a significant change in direction of the vehicle, for example during a turning-off maneuver.
It is an object of the invention to provide a position determination method and a navigation device which can determine a precise position on a digital road map even in the event of a slight change in direction.
This aim is achieved by a position determination method operating by means of adjustment of a position determined by dead reckoning with the aid of a digital road map, comprising the following steps:
a succession of positions determined by dead reckoning is tracked on digitized roads of the digital road map and assigned to road segments of the digital road map,
during traversal of a curve the centroid of the curve is determined from measured values of a direction sensor,
the centroid of the curve of a digitized road is determined from the alignment of road segments of the digitized road which corresponds to the determined positions, and
the position determined by dead reckoning is corrected on the basis of the difference between the determined curve centroids.
The centroid of the curve recorded in the digital road map can be calculated by weighting differences in the angles of consecutive road segments in their succession and adding them, and dividing the sum thus determined by the sum of the differences in the angles of the consecutive road segments. The differences in the angles can be determined from shape points that define the road segments of the curve, and in that the differences in the angles are weighted with the time interval that has elapsed during tracking of the road segments on the digital road map. The average speed during traversal of the curve is determined, and in that the time interval between the traversal of the curve centroids is multiplied by the average speed in order to correct the position, determined by dead reckoning, with the distance thus obtained.
Another position determination method according to the present invention comprises the steps:
tracking a plurality of positions by dead reckoning on digitized roads of a digital road map and assigning the positions to road segments of the digital road map,
determining the centroid of a curve from measured values of a direction sensor while traveling along the curve,
determining a digital centroid of the curve of a digitized road from the alignment of road segments of the digitized road which corresponds to the determined positions, and
correcting the position determined by dead reckoning on the basis of the difference between the determined curve centroid and digital curve centroid.
The centroid of the curve recorded in the digital road map can be calculated by weighting differences in the angles of consecutive road segments in their succession and adding them, and dividing the sum thus determined by the sum of the differences in the angles of the consecutive road segments. The differences in the angles can be determined from shape points that define the road segments of the curve, and the differences in the angles can be weighted with the time interval that has elapsed during tracking of the road segments on the digital road map. The average speed during traversal of the curve can be determined, and the time interval between the traversal of the curve centroids can be multiplied by the average speed in order to correct the position, determined by dead reckoning, with the distance thus obtained. A curve can be defined in the digitized road by shape points. The centroid of the curve can also be determined by obtaining the individual changes in direction from consecutive direction measurements and by weighting and adding the changes with the elapsed time and by dividing the weighted and added changes by the sum of the measured changes in direction. The digital centroid of the curve recorded in the digital road map can be determined by weighting and adding the differences in the angles of consecutive road segments in their succession with the respectively elapsed time which has elapsed during tracking of the road segments on the digital road map and by dividing the sum by the sum of the differences in the angles of the consecutive road segments.
An embodiment according to the present invention is a navigation device which comprises a distance sensor, a direction sensor, a map memory for a digital road map, and at least one processor for dead reckoning, which is connected to the distance sensor, the direction sensor and the map memory, which during traversal of a curve determines the centroid of the latter from measured values of the direction sensor, which determines the centroid of the curve of the digitized road from the alignment of road segments of a digitized road which corresponds to the determined positions and which corrects the position determined by dead reckoning on the basis of the difference between the determined curve centroids.
The direction sensor can be a gyroscope. The navigation device can further comprise a satellite receiver for operating as a distance and direction sensor and a display for displaying the determined position on the digitized map.
Centroids are determined for a curve that traverses a road and whose course is determined by means of dead reckoning, and for a corresponding curve on a road of a digital road map. The curve centroids are points which are also defined in the case of lengthy curves and are available for an adjustment of the position, measured by dead reckoning, with the aid of the digital road map. Such lengthy curves typically have a radius of 500 m to 1000 m.
A time measurement or a distance measurement can serve as a basis for determining the curve centroids on the map.
If a time measurement serves as a basis for determining the curve centroids, the average speed during traversal of the curve is advantageously used for the position correction.