Proceedings of the third ACM international workshop on Video surveillance & sensor networks
Proceedings of the 2nd ACM international workshop on Events in multimedia
Motion trajectory clustering for video retrieval using spatio-temporal approximations
VISUAL'05 Proceedings of the 8th international conference on Visual Information and Information Systems
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This paper describes a comparative evaluation of three different similarity metrics for trajectory-based indexing and retrieval of video motion clips. The motion paths are generated using a low-level tracking algorithm incorporating first-order Kalman filter and colour appearance models. For simple motion paths, a RANSAC approach can be used to generate smooth trajectories for each tracked object described by low-order polynomials. This allows us to obtain a representative trajectory model even in the case of high numbers of outlier points caused by target mis-detection and multiple occlusions. We show that more complex trajectories including stop-start motions, can be modelled as time series using high order Chebyshev polynomials. Similarity metrics based on coefficient descriptors are shown to have comparable performance to a Hausdorff distance measure when retrieving trajectory-based motion clips but at substantially reduced computational cost. Experimental results are presented to illustrate the comparative performance of different matching metrics on real-world trajectory data collected by a retail store CCTV installation.