Segmentation of trajectories on non-monotone criteria

Boris Aronov, Anne Driemel, Marc Van Kreveld, Maarten Löffler, Frank Staals

    Research output: Chapter in Book/Report/Conference proceedingConference contribution

    Abstract

    In the trajectory segmentation problem we are given a polygonal trajectory with n vertices that we have to subdivide into a minimum number of disjoint segments (subtrajectories) that all satisfy a given criterion. The problem is known to be solvable efficiently for monotone criteria: criteria with the property that if they hold on a certain segment, they also hold on every subsegment of that segment [4]. To the best of our knowledge, no theoretical results are known for non-monotone criteria. We present a broader study of the segmentation problem, and suggest a general framework for solving it, based on the start-stop diagram: a 2-dimensional diagram that represents all valid and invalid segments of a given trajectory. This yields two subproblems: (i) computing the start-stop diagram, and (ii) finding the optimal segmentation for a given diagram. We show that (ii) is NP-hard in general. However, we identify properties of the start-stop diagram that make the problem tractable, and give polynomial-time algorithm for this case. We study two concrete non-monotone criteria that arise in practical applications in more detail. Both are based on a given univariate attribute function f over the domain of the trajectory. We say a segment satisfies an outlier-tolerant criterion if the value of f lies within a certain range for at least a given percentage of the length of the segment. We say a segment satisfies a standard deviation criterion if the standard deviation of f over the length of the segment lies below a given threshold. We show that both criteria satisfy the properties that make the segmentation problem tractable. In particular, we compute an optimal segmentation of a trajectory based on the outlier-tolerant criterion in O(n 2 log n+kn2) time, and on the standard deviation criterion in O(kn2) time, where n is the number of vertices of the input trajectory and k is the number of segments in an optimal solution.

    Original languageEnglish (US)
    Title of host publicationProceedings of the 24th Annual ACM-SIAM Symposium on Discrete Algorithms, SODA 2013
    PublisherAssociation for Computing Machinery
    Pages1897-1911
    Number of pages15
    ISBN (Print)9781611972511
    DOIs
    StatePublished - 2013
    Event24th Annual ACM-SIAM Symposium on Discrete Algorithms, SODA 2013 - New Orleans, LA, United States
    Duration: Jan 6 2013Jan 8 2013

    Publication series

    NameProceedings of the Annual ACM-SIAM Symposium on Discrete Algorithms

    Other

    Other24th Annual ACM-SIAM Symposium on Discrete Algorithms, SODA 2013
    CountryUnited States
    CityNew Orleans, LA
    Period1/6/131/8/13

    ASJC Scopus subject areas

    • Software
    • Mathematics(all)

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