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GGIR (version 1.4)

g.calibrate: function to estimate calibration error and make recommendation for addressing it

Description

Function starts by identifying ten second windows of non-movement. Next, the average acceleration per axis per window is used to estimate calibration error (offset and scaling) per axis. The function provides recommended correction factors to address the calibration error and a summary of the callibration procedure.

Usage

g.calibrate(datafile, use.temp = TRUE, spherecrit = 0.3, minloadcrit = 72, printsummary = TRUE,chunksize=c(),windowsizes=c(5,900,3600),selectdaysfile=c(), dayborder=0)

Arguments

datafile
name of accelerometer file
use.temp
use temperature sensor data if available (Geneactive only)
spherecrit
the minimum required acceleration value (in g) on both sides of 0 g for each axis. Used to judge whether the sphere is sufficiently populated
minloadcrit
the minimum number of hours the code needs to read for the autocalibration procedure to be effective (only sensitive to multitudes of 12 hrs, other values will be ceiled). After loading these hours only extra data is loaded if calibration error has not been reduced to under 0.01 g.
printsummary
if TRUE will print a summary when done
chunksize
number between 0.2 and 1 to specificy the size of chunks to be loaded as a fraction of a 12 hour period, e.g. 0.5 equals 6 hour chunks. The default is 1 (12 hrs). For machines with less than 4Gb of RAM memory a value below 1 is recommended.
windowsizes
see g.getmeta
selectdaysfile
see g.part1
dayborder
see g.part1

Value

References

  • van Hees VT, Fang Z, Langford J, Assah F, Mohammad A, da Silva IC, Trenell MI, White T, Wareham NJ, Brage S. Auto-calibration of accelerometer data for free-living physical activity assessment using local gravity and temperature: an evaluation on four continents. J Appl Physiol (1985). 2014 Aug 7

Examples

Run this code
## Not run: 
# datafile = "C:/myfolder/testfile.bin"
# 
# #Apply autocalibration:
# C = g.calibrate(datafile)
# print(C$scale)
# print(C$offset)
# ## End(Not run)

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