dpdetect_s {densitr}

Detect measurement starting point automatically using changepoint segmentation

Description

A typical resistance drilling measurement starts with an increase in resistance values in between the measurement start and the immersion of the needle in the wood. These values are not useful when estimating density and should be removed before further analysis. This function will detect the starting point automatically using binary segmentation from the package changepoint, which separates the measurement in segments based on their mean and variance. Start is detected, when the segment mean is outside of the cutoff limit, see return.plot = TRUE to display the diagnostic plot. This function will only check the mean values of the first four (4) segments and compare them to the cutoff value. The function is called on a dp object and returns either a row number of the starting point or a plot displaying the segmentation and detection. The sensitivity can be adjusted using the cutoff.sd parameter, which is an indicator on how many standard deviations the segment mean value can be before cutting it off. Will return a warning if start not detected.

Usage

dpdetect_s(
  dp,
  cutoff.sd = 1,
  return.plot = FALSE,
  minseglen = 250,
  span = 0.1,
  nroll = 100
)

Arguments

dp

A dp object, see dpload.

cutoff.sd

How many standard deviations for the cutoff limit?

return.plot

If true, will return a plot displaying segment detection for the current dp file.

minseglen

Minimum segment length for segment detection, default setting of 250 points is for data resolution of 1/100 mm, test a few options with return.plot = TRUE to find the right value

span

Span for loess regression, use to adjust sensitivity of detection detection for the current dp file.

nroll

Number of points for rolling mean, use to adjust sensitivity of detection for the current dp file.

Value

Either a row number where the actual measurement starts or a plot, displaying changepoint segmentation and set limits.

See Also

dpdetect_e, dptrim, dptriml, dptrim_s, dptriml_s

Examples

## load a single file
dp <- dpload(system.file("extdata", "00010001.dpa", package = "densitr"))
## get starting point
start <- dpdetect_s(dp)
## plot the start detection

dpdetect_s(dp, return.plot = TRUE)