  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 in examples how quasi-objective coherence diagnostics
highlight elliptic and hyperbolic Lagrangian coherent structures even from very
sparse trajectory data.
