Mobile devices leave a huge number of digital traces that are collected as trajectories, describing the movement of its users or a path followed by any moving object in geographical space over some period of time. However, those mobile devices provide just raw trajectories (x, y, t), ignoring information about their related contextual data, these additional data contribute in producing significant knowledge about movements and provide applications with richer and more meaningful knowledge. Therefore, researchers focus on transforming raw trajectories into semantic trajectories by combining the raw mobility tracks with related contextual data and creating a new type of trajectories called "semantic trajectories", then applying mining techniques. This paper study closely the current researches on modeling and mining semantic trajectories so far, and try to investigate by proposing a descriptive schema including all steps that users can browse from the construction of the trajectories to the analyze of behaviors extracted.
Spatiotemporal data mining studies the field of discovering interesting patterns from large spatiotemporal databases. Although these databases generate a huge volume of data daily from satellite images and mobile sensors like GPS, among these data we find first spatiotemporal and geographical data; secondly, the trajectories browsed by moving objects in some time intervals. Combination of these types of data leads to producing semantic trajectory data. Enriching trajectories with semantic geographical information leads to ease queries, analysis, and mining, in order to give more meaning to behaviors potentially extracted from trajectories. Therefore, applying mining techniques on semantic trajectories continue to prove to be a success story in discovering useful and nontrivial behavioral patterns of moving objects. The purpose of this paper is to make an overview of spatiotemporal knowledge discovery (STKD) and techniques recently used to extract knowledge from spatiotemporal data based on analysis of recent literature. Then leading towards a deeper analysis about semantic trajectory knowledge discovery as a specified field from STKD that integrates trajectory sample points with geographical data before applying mining techniques in order to extract behavioral knowledge from semantic trajectories which can be more useful and significant for the application users.
Abstract-The increasing use of location-aware devices has led to generate a huge volume of data from satellite images and mobile sensors; these data can be classified into geographical data. And traces generated by objects moving on geographical territory, these traces are usually modeled as streams of spatiotemporal points called trajectories. Integrating trajectory sample points with geographical and contextual data before applying mining techniques can be more gainful for the application users. It contributes to produce significant knowledge about movements and provide applications with richer and more meaningful patterns. Trajectory Outliers are a sort of patterns that can be extracted from trajectories. However, the majority of algorithms proposed for discovering outliers are based on the geometric side of trajectories; our approach extends these works to produce outliers based on semantic trajectories in order to give meaning to the outliers extracted, and to understand the unusual behaviors that can be detected. To prove the efficiency of the approach proposed we show some experimental results.
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