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Detect steps from tri-axial acceleration

Source: R/steps.R
detectSteps.Rd

Counts steps by peak-detecting the dynamic acceleration magnitude (vector magnitude minus gravity). Peaks must exceed a prominence threshold and be separated by at least the shortest plausible step interval (1 / max_step_hz), which suppresses double counts.

Usage

detectSteps(
  accel,
  sampling_rate,
  min_step_hz = 0.5,
  max_step_hz = 4,
  threshold = NULL,
  min_amplitude = 0.05
)

Arguments

accel

An n x 3 matrix of acceleration in g units, or a numeric vector already representing an acceleration magnitude.

sampling_rate

Sampling rate in Hz.

min_step_hz, max_step_hz

Plausible step-frequency range in Hz (defaults 0.5 and 4).

threshold

Minimum peak height in the dynamic magnitude (g). NULL uses max(0.5 * sd(dynamic magnitude), min_amplitude); the absolute floor stops sensor noise in a still recording from being counted as steps.

min_amplitude

Absolute floor (g) for the automatic threshold (default 0.05).

Value

A wearable_steps list with n_steps, step_index (sample indices of detected steps), and cadence_spm (steps per minute).

References

Any peak-based pedometer (e.g. Zijlstra & Hof 2003).

See also

computeENMO()

Examples

fs <- 50; t <- seq(0, 10, 1 / fs)
walk <- cbind(0, 0, 1 + 0.4 * sin(2 * pi * 1.8 * t))  # 1.8 steps/s
detectSteps(walk, fs)$n_steps
#> [1] 18