Creates a preprocessing constructor for resampling spectral data to a new
wavelength grid. The constructor is intended to be passed to
preprocess_recipe and executed via process.
Arguments
- grid
Either a numeric vector of length 3 specifying the target wavelength grid as
c(min_wav, max_wav, resolution), or the character string"proxiscout"to resample to the standard NeoSpectra wavenumber grid (see Details).When
gridis a numeric vector:grid[1](min_wav): minimum wavelength of the target grid.grid[2](max_wav): maximum wavelength; must be greater thanmin_wav.grid[3](resolution): spacing between wavelengths; must be positive.
Extrapolation beyond the range of the input wavelengths is never allowed.
Value
An object of class preprocessing to be used in
preprocess_recipe and executed by process.
Details
User-defined grid (grid = c(min_wav, max_wav, resolution)):
resamples spectra to the specified target grid using natural spline
interpolation via resample. Column names of
X must be coercible to numeric wavelength values. This mode is
compatible with the "proximate" device.
NeoSpectra grid (grid = "proxiscout"): resamples spectra to
the standard wavenumber grid of NeoSpectra NIR scanners
(approx. 3921.569 to 7407.407 \(cm^{-1}\), ~256 channels at ~13.617
\(cm^{-1}\) steps). Only wavenumbers overlapping with the input range are
retained. This mode is compatible with the "proxiscout" device.
Examples
data("NIRcannabis")
X <- NIRcannabis$spc
# User-defined grid (proximate)
rs <- prep_resample(grid = c(1001, 1700, 2))
recipe <- preprocess_recipe(rs, device = "proximate")
X_rs <- process(X, recipe)