prospectr vs usmapdata

prospectr provides the signal-processing layer for near-infrared and visible spectroscopy in R — Savitzky-Golay and gap-segment derivatives, standard normal variate, detrending, continuum removal, splice correction, plus calibration sampling algorithms like Kennard-Stone and DUPLEX and readers for ASD and BUCHI NIRCal instrument files. The May release is the substantial one: a long list of corrections to functions that were returning wrong or missing values rather than failing.

The recent work is corrective rather than additive, and several items changed results silently before being caught. continuumRemoval() derived its convex-hull boundary offset from a fixed one-wavelength assumption that broke for fine-resolution spectra or non-nanometre units; cochranTest() passed an invalid argument name to prcomp() and produced incorrect principal component scores; readASD() silently dropped spectra in one branch of its text path. Two file readers were leaking connections. Alongside that runs a smaller thread of decoupling preprocessing steps from each other, most visibly detrend() gaining an snv argument so polynomial detrending can run without the SNV transform that Barnes et al. bundled with it.

The detrend() decoupling is the only recent addition and it fits a broader pipeline-composition direction, so similar separation of other bundled preprocessing steps is the plausible next move. The misspelled substraction argument now carries a deprecation warning, which schedules its removal for a future release.