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Schulze Gunnar, Horn Christopher, Kern Roman

Map-Matching Cell Phone Trajectories of Low Spatial and Temporal Accuracy

2015 IEEE 18th International Conference on Intelligent Transportation Systems, IEEE, IEEE, 2015

This paper presents an approach for matching cell phone trajectories of low spatial and temporal accuracy to the underlying road network. In this setting, only the position of the base station involved in a signaling event and the timestamp are known, resulting in a possible error of several kilometers. No additional information, such as signal strength, is available. The proposed solution restricts the set of admissible routes to a corridor by estimating the area within which a user is allowed to travel. The size and shape of this corridor can be controlled by various parameters to suit different requirements. The computed area is then used to select road segments from an underlying road network, for instance OpenStreetMap. These segments are assembled into a search graph, which additionally takes the chronological order of observations into account. A modified Dijkstra algorithm is applied for finding admissible candidate routes, from which the best one is chosen. We performed a detailed evaluation of 2249 trajectories with an average sampling time of 260 seconds. Our results show that, in urban areas, on average more than 44% of each trajectory are matched correctly. In rural and mixed areas, this value increases to more than 55%. Moreover, an in-depth evaluation was carried out to determine the optimal values for the tunable parameters and their effects on the accuracy, matching ratio and execution time. The proposed matching algorithm facilitates the use of large volumes of cell phone data in Intelligent Transportation Systems, in which accurate trajectories are desirable.

Horn Christopher, Kern Roman

Deriving Public Transportation Timetables with Large-Scale Cell Phone Data

Procedia Computer Science, 2015

In this paper, we propose an approach to deriving public transportation timetables of a region (i.e. country) based on (i) large- scale, non-GPS cell phone data and (ii) a dataset containing geographic information of public transportation stations. The presented algorithm is designed to work with movements data, which are scarce and have a low spatial accuracy but exists in vast amounts (large-scale). Since only aggregated statistics are used, our algorithm copes well with anonymized data. Our evaluation shows that 89% of the departure times of popular train connections are correctly recalled with an allowed deviation of 5 minutes. The timetable can be used as feature for transportation mode detection to separate public from private transport when no public timetable is available.
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