Detecting location, timetable and travel time estimations for barrier crossing in a digital map
A method for determining barrier crossing information for convoyed objects ( 22 ) using historic trajectory data ( 28 ). Trajectories ( 28 ) having similar geographical and directional properties are bundled so that trajectory density can be measured as a function of position and time (s, t). Visual presentation of the trajectory information can be used to determine certain types of barrier crossing information useful in a digital map. Frequency analysis on a number of trajectory density time series may be performed to determine specific barrier crossing locations ( 26 ) through the detection of vehicle bursts. Such frequency analysis may also indicate barrier crossing times and schedules in the case of crossing patterns.
1. A method for determining barrier crossing information using historic trajectory data, said method comprising the steps of:
receiving trajectory data representative of the movements of a plurality of objects over a network of travel paths with respect to time, said trajectory data for an object comprising a plurality of sequential time-stamped geo-positions, and said network of travel paths comprising at least one barrier crossing which periodically impedes or restricts the free flow of objects along the network of travel paths;
associating the received trajectory data with segments of a digital map, said segments being representative of the network of travel paths;
determining the trajectory density along at least some of the segments as a function of position and time from the trajectory data, the trajectory density being indicative of the number of objects at a particular location and time;
identifying locations at which the trajectory density changes periodically from zero to substantially greater than zero;
using a frequency distribution for the trajectory density changes at said identified locations to determine the location of a barrier crossing and augmenting the digital map with the determined location of the barrier crossing, the barrier crossing being between a first segment and a second segment;
determining at least one of a crossing timetable or crossing frequency for the barrier crossing from the changes in trajectory density; and
associating the determined at least one of the crossing timetable or crossing frequency with the barrier crossing in the digital map.
2. The method according to claim 1 , further including bundling trajectory data from a plurality of objects having similar geographical and directional properties, and associating the one or more bundles with segments of the digital map.
3. The method according to claim 1 , further including determining at least one of a crossing travel time and an average crossing speed for the barrier crossing from the changes in trajectory density.
4. The method according to claim 1 , wherein said step of using the frequency distribution for the trajectory density changes at said identified locations to determine the location of a barrier crossing includes establishing a threshold criterion (C) equal to the ratio between the two highest frequency peaks of the frequency distribution of trajectory density changes as expressed by the formula:
C=A ( v 1 )/ A ( v 0 )
where: V 0 =frequency of highest peak in amplitude spectrum
V 1 =frequency of 2nd highest peak in amplitude spectrum
A(v)=|amplitude| in amplitude spectrum of frequency v.
5. The method according to claim 4 , wherein the threshold criterion (C) is 0.3.
6. The method according to claim 1 , wherein said step of determining a crossing frequency for the barrier crossing from the changes in trajectory density includes making separate frequency determinations for work days and non-work days.
7. The method according to claim 1 , further including the step of determining crossing timetables for different days.