RMS Spectral Slope

An experimental descriptive image of the nonnegative RMS magnitude of the wavelength derivative of each pixel's piecewise-linear spectrum.

Usage

hsa_spectral_gradient(
  cube,
  palette = "inferno",
  stretch = c("percentile", "range", "none"),
  probs = c(0.02, 0.98),
  display_limits = c(0, 1),
  value_label = "input value",
  interpolate = TRUE
)

Arguments

cube

An hsi_cube (from hyperspectR) or a 3-D array with dimensions (rows, cols, bands), of integer or double values. Optional wavelengths metadata must be finite, unique and strictly increasing in nm. Without it, coordinates are band indices. An optional logical spatial mask has dimensions (rows, cols) and no missing entries; FALSE excludes a pixel. Arrays may carry these as attributes; an hsi_cube may carry them as list fields. Nonfinite observations are excluded.

palette

Palette name passed to hsa_palette().

stretch

Contrast stretch: "percentile" (default), "range" or "none".

probs

Percentiles for stretch = "percentile". Default c(0.02, 0.98).

display_limits

Two increasing finite endpoints used as the fixed colour domain for stretch = "none". Default c(0, 1).

value_label

A truthful label for the input values. Default "input value". A reflectance label requires known upstream calibration; numeric range alone cannot establish calibration.

interpolate

Logical; interpolate raster pixels. Default TRUE.

Value

A ggplot object with raw values and original-rendering provenance.

Details

For interval widths h = diff(wavelengths) and endpoint span L, G = sqrt(sum(h * (diff(x)/h)^2)/L). Values have input-value units per nm. This is neither a signed derivative, a spatial gradient, nor uncertainty. Short intervals and measurement noise can dominate the result. Gaps in sampling bridge unresolved structure; no smoothing or noise correction is applied. Physical wavelength metadata in nm and at least two bands are required, with finite positive representable intervals and span. A masked or incomplete spectrum is transparent; missing bands are never bridged. Nonrepresentable requested arithmetic raises an error.

Examples

hsa_spectral_gradient(hsa_demo_cube())