Tensor Methods for Group Pattern Discovery of Pedestrian Trajectories

Abdullah Sawas*, Abdullah Abuolaim*, Mahmoud Afifi, and Manos Papagelis

EECS, Lassonde School of Engineering, York University, Canada

Emails: {asawas, abuolaim, mafifi, and papaggel}@eecs.yorku.ca

IEEE MDM 2018 - 19th IEEE International Conference on Mobile Data Management

Abstract

Mining large-scale trajectory data streams (of moving objects) has been of ever increasing research interest due to an abundance of modern tracking devices and its large number of critical applications. In this paper, we are interested in mining group patterns of moving objects. Group pattern mining describes a special type of trajectory mining task that requires to efficiently discover trajectories of objects that are found in close proximity to each other for a period of time. In particular, we focus on trajectories of pedestrians coming from motion video analysis and we are interested in interactive analysis and exploration of group dynamics, including various definitions of group formation and dispersion. Towards this end, we present a suite of (three) tensor-based methods for efficient discovery of evolving groups of pedestrians. Traditional approaches to solve the problem rely on well-defined clustering algorithms to discover groups (or clusters) of pedestrians at each time point, and then post-processing the discovered groups to determine varying group patterns over time. In contrast, our proposed methods are based on efficiently discovering pairs of pedestrians that move together over time, under varying conditions. Pairs of pedestrians are subsequently used as a building block for effectively discovering groups of pedestrians. The suite of proposed methods provides the ability to adapt to many different scenarios and application requirements, ranging from streaming vs off-line analysis, varying definitions of group formation and dispersion, varying constraints of proximity measures, and so on. Furthermore, a query-based method is provided that allows for interactive exploration and analysis of group dynamics over time and space. Through experiments on real data, we demonstrate the effectiveness of our methods on discovering group patterns of pedestrian trajectories against sensible baselines, for a varying range of conditions. In addition, a visual testing is performed on real motion video to assert the group dynamics discovered by each method. While motion video poses its own challenges for the analysis of pedestrian trajectories, the methods we describe are general and can be easily adopted in various domains and applications.


*Both authors contributed equally to this work

Visualization

  • A comparison between the globTgroups and timeWgroups methods
  • Pedestrians groups found by locTgroups
  • Coherent pairs found by globTgroups
  • Pedestrian pairs found by timeWgroups using 3 different window sizes (w)
    • w=4
    • w=5
    • w=6

Query-based Group Retrieval

We have developed an on-line interactive query-based group retrieval tool. This tool was built using D3JS and jQuery JavaScript libraries. Pedestrian trajectories and groups is processed once using Matlab and the results were saved in JSON format. The video frames are saved in JPG format and sent to the client through a PHP web page interface. A demonstration of this tool can be accessed through the following link: http://tiny.cc/Trajectolizer

Last update Jan 2018