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Updated: Oct 29, 2025

Trajectory Data Analyses for Pedestrian Space-time Activity Study
Published on: February 25, 2013
Quasi-objective coherent structure diagnostics from single trajectories
George Haller1, Nikolas Aksamit1, Alex P Encinas-Bartos1
1Institute for Mechanical Systems, ETH Zürich, 8092 Zürich, Switzerland.
Abstract:
We derive measures of local material stretching and rotation that are computable from individual trajectories without reliance on other trajectories or on an underlying velocity field. Both measures are quasi-objective: they approximate objective (i.e., observer-independent) coherence diagnostics in frames satisfying a certain condition. This condition requires the trajectory accelerations to dominate the angular acceleration induced by the spatial mean vorticity. We illustrate on examples how quasi-objective coherence diagnostics highlight elliptic and hyperbolic Lagrangian coherent structures even from very sparse trajectory data.
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