gt1mAccFile: Read a single accelerometer file
In pawacc: Physical Activity with Accelerometers

gt1mAccFile

R Documentation

Read a single accelerometer file

Description

This function reads an Actigraph GT1M accelerometer file.

Usage

gt1mAccFile(file, path, fileid, counts.pos = 1,
	tz = "Europe/London", sparse = FALSE,
	fault = 32767)

Arguments

`file`	file name including file extension.
`path`	path to `file`.
`fileid`	label for file identifier.
`counts.pos`	when storage mode allows for accelerometer counts and steps to be recorded at the same time, this argument specifies the position of first measurement of accelerometer counts (default is `counts.pos` = 1).
`tz`	a character string specifying the timezone to be used for the conversion (see `strptime`).
`sparse`	logical flag: should data be stored in sparse format?
`fault`	numerical value that indicates voltage signal saturation.

Details

Raw accelerometer data are processed according to the device data format. Several data checks are performed by errorChk and infoDate. An additional check is performed on the lenght of the sequence of measurements when both accelerometer counts and steps are recorded. If the length is odd, a warning message is produced. See file 'gt1m_sample.dat' in directory '\inst\extdata' of this package.

Value

These functions return an object of two classes: accfile and additional device-specific class (i.e., gt1m).

An object of class accfile is a list containing the following components:

`df`	A `data.frame` object with accelerometer values in columns `counts` and `steps` (if present), and coded error for each accelerometer data column. See `errorChk` for error codes. If `sparse = TRUE`, all variables of the data frame `df` are returned as vectors of a matrix in sparse format (see `as.matrix.csr` for details).
`info`	A `data.frame` object with file identifier (`fileid`), device serial number (`serial`), number of recorded measurements (`nobs`), epoch (`epoch`), accelerometer mode (`mode`), start date and time (`ts_start`), time zone (`tz`), battery voltage (`voltage`), download date and time (`ts_dl`).
`error_summary`	A `list` object with file identifier (`fileid`), summary tables of error codes for each accelerometer data column, error code for date (`date`), and logical flag for odd number of measurements (`odd_number`) (see details).

Author(s)

Marco Geraci

References

Actigraph (Pensacola, Florida).

Geraci M, Rich C, Sera F, Cortina-Borja M, Griffiths LJ, and Dezateux C (2012). Technical report on accelerometry data processing in the Millennium Cohort Study. London, UK: University College London. Available at https://discovery.ucl.ac.uk/1361699