Radial Spectral Mandala

Renders the scene as concentric annuli, each drawn from a sampled spectral band: the innermost ring uses the first band and the outermost uses the last. The result is a spatial composition; unequal annular areas do not estimate the spectral distribution. A single ring selects the first band.

Usage

hsa_mandala(
  cube,
  centre = NULL,
  n_rings = 36L,
  palette = "magma",
  stretch = c("percentile", "range", "none"),
  probs = c(0.02, 0.98),
  display_limits = c(0, 1),
  value_label = "input value",
  interpolate = TRUE,
  sampling = c("index", "wavelength")
)

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.

centre

Numeric length-2 vector c(x, y) in pixels. NULL (default) uses the image centre.

n_rings

Number of annuli. Default 36. More rings sample the spectrum more finely; fewer give bolder banding.

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.

sampling

Ring targets: "index" (default) or "wavelength". Wavelength sampling requires physical metadata in nm.

Value

A ggplot2 object.

Details

This uses the spectral dimension for a spatial composition. A single band or repeated ring selections can produce a degenerate single-band result. The default radius-to-band-index mapping is linear. Wavelength sampling uses equally spaced physical targets and nearest measured bands, with ties toward shorter wavelengths. Repeated selections and empty rings retain the geometry and are disclosed in the caption and provenance.

Examples

cube <- hsa_demo_cube()
hsa_mandala(cube, n_rings = 12)