There and back again: using fréchet-distance diagrams to find trajectory turning points

There is much interest in the automatic analysis of GPS trajectories, motivated amongst others by animal tracking, traffic modelling and tourism studies. Core questions involve for example detecting stopping points and flocking behaviour, and developing routing models. In this paper we consider turning points. We develop a formal definition of "turning point" based on analysing the structure of free-space diagrams for Fréchet distance. We give an efficient algorithm for computing an optimal set of turning points under this criterion. Our method is evaluated in the context of a current study on tourist preferences at Berchtesgaden National Park, Germany. We evaluate the suitability of our definition and the efficiency of our algorithm on a large set of real-world GPS trajectories collected by outdoor recreationists. A ground truth of turning points was established by hand for the complete data set. Experiments show that the runtime and quality of our method are suitable for practical applications.

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