Create an IMU vector — acc • move2imu

Construct an acc, mag, or gyro vector from a list of burst matrices and the sampling frequency at which they were recorded.

The three constructors share the same signature and semantics — they differ only in the sensor type recorded by the resulting vector and in the units typically attached to its samples (acceleration, magnetic field strength, angular velocity).

Usage

acc(
  bursts = list(),
  frequency = units::set_units(double(), "Hz"),
  start = NULL
)

mag(
  bursts = list(),
  frequency = units::set_units(double(), "Hz"),
  start = NULL
)

gyro(
  bursts = list(),
  frequency = units::set_units(double(), "Hz"),
  start = NULL
)

Arguments

bursts

A list of matrices, one per burst. Each matrix has one row per sample and named columns drawn from "X", "Y", and "Z" indicating which axes were recorded. Entries can be NULL to represent missing bursts.

frequency

Sampling frequency of the recordings in bursts, either length 1 (recycled to all bursts) or the same length as bursts. Frequencies with compatible units are converted to Hz internally. If no units are specified, the frequency is assumed to be in Hz.

start

Optional; burst start times. Either length 1 (recycled), the same length as bursts, or NULL if start times are unknown.

Accepts POSIXct, POSIXlt, Date, or numeric values. Date objects are treated as being recorded at midnight, UTC. Numeric values are interpreted as the number of seconds since 1970-01-01 00:00:00 UTC. Inputs are all converted to POSIXct. For inputs with a specified time zone, it is retained.

Value

An IMU vector of the corresponding sensor type (acc, mag, or gyro).

Examples

# Accelerometer: a single burst on X, Y, Z at 40 Hz
acc(
  bursts = list(cbind(
    X = sin(1:30 / 10),
    Y = cos(1:30 / 10),
    Z = 1:30 / 10
  )),
  frequency = units::as_units(40, "Hz")
)
#> <acceleration[1]>
#> [1] (0.67 0.01 1.55)
#> # frequency: 40 [Hz]

# Multiple bursts with different axes — combined into one vector
acc(
  bursts = list(
    cbind(X = sin(1:20 / 10), Y = cos(1:20 / 10)),
    cbind(X = sin(1:20 / 10 + 2), Y = cos(1:20 / 10 + 3))
  ),
  frequency = units::as_units(30, "Hz")
)
#> <acceleration[2]>
#> [1] (0.73 0.42)  (0.08 -0.52)
#> # frequency: 30 [Hz]

# The same API for magnetometer and gyroscope data:
mag(
  bursts = list(cbind(X = 1:10, Y = 11:20, Z = 21:30)),
  frequency = units::as_units(10, "Hz")
)
#> <magnetometer[1]>
#> [1] (5.5 15.5 25.5)
#> # frequency: 10 [Hz]

gyro(
  bursts = list(cbind(X = sin(1:20 / 10), Y = cos(1:20 / 10))),
  frequency = units::as_units(50, "Hz")
)
#> <gyroscope[1]>
#> [1] (0.73 0.42)
#> # frequency: 50 [Hz]