Calculate tortuosity metrics over sliding windows

Computes multiple tortuosity metrics (straightness, sinuosity, E_max) over sliding windows, returning a value at each timepoint.

Usage

calculate_tortuosity(data, window_width = 11L)

Arguments

data

An aniframe with position coordinates and time. Velocity and heading columns will be computed if not already present.

window_width

Size of the sliding window (number of observations). Should be an odd number >= 3 for symmetric centering.

Value

The input aniframe with additional columns:

straightness

Straightness index (D/L), ranges 0-1

sinuosity

Corrected sinuosity index (Benhamou 2004)

emax

Maximum expected displacement (dimensionless)

Details

If required kinematic columns are missing, the function will compute them automatically by calling the appropriate helper functions.

Straightness is appropriate for directed/goal-oriented movement, while sinuosity and E_max are appropriate for random search paths.

For 2D data, heading is derived from the velocity vector, which provides smoother estimates than raw position differences.

For 3D data, turning angles are computed as the angle between consecutive velocity vectors using the dot product.

The window is centered on each timepoint. At path edges, metrics are computed from available data within the truncated window.

References

Batschelet, E. (1981). Circular statistics in biology. Academic Press.

Benhamou, S. (2004). How to reliably estimate the tortuosity of an animal’s path: straightness, sinuosity, or fractal dimension?. Journal of Theoretical Biology, 229(2), 209-220.

Cheung, A., Zhang, S., Stricker, C., & Srinivasan, M. V. (2007). Animal navigation: the difficulty of moving in a straight line. Biological Cybernetics, 97(1), 47-61.

See also

• calculate_kinematics() for computing velocity and heading

Examples

if (FALSE) { # \dontrun{
# Kinematics computed automatically if missing
data |>
  calculate_tortuosity(window_width = 11)

# Or with kinematics already computed
data |>
  calculate_kinematics() |>
  calculate_tortuosity(window_width = 11)
} # }