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ENMO-abs (ENMOa) acceleration metric

Source: R/enmo.R
computeENMOa.Rd

ENMOa is the "always-positive" companion of computeENMO: the vector magnitude minus one gravity, with the absolute value taken instead of truncating negatives to zero, \({\rm ENMOa} = |r - 1|\) with \(r = \sqrt{x^2+y^2+z^2}\) (van Hees et al. 2013). It differs from ENMO only where the magnitude dips below 1 g (deceleration / partial free-fall), which ENMO truncates away; ENMOa retains that movement, so it is used when the sensor calibration is imperfect (a persistent sub-1 g offset would otherwise be lost by ENMO's truncation). When an epoch length is given, per-epoch mean ENMOa is returned.

Usage

computeENMOa(
  accel,
  sampling_rate = NULL,
  epoch_sec = NULL,
  unit = c("g", "mg")
)

Arguments

accel

An n x 3 matrix (or data frame) of acceleration in g units (columns x, y, z).

sampling_rate

Sampling rate in Hz (required if epoch_sec is set).

epoch_sec

Epoch length in seconds for aggregation; NULL returns the per-sample ENMOa.

unit

"g" (default) or "mg" (milli-g).

Value

A numeric vector of ENMOa values (per sample, or per epoch).

References

van Hees VT, et al. (2013). PLoS ONE 8(4):e61691.

See also

computeENMO(), computeMAD()

Examples

set.seed(1)
acc <- matrix(rnorm(300, c(0, 0, 1), 0.1), ncol = 3, byrow = TRUE)
mean(computeENMOa(acc))          # >= mean(computeENMO): retains sub-1 g dips
#> [1] 0.07291543