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Derive individual terrain metrics

Source: R/metrics.R
derive_slope.Rd

Convenience wrappers around terra terrain functions and lightweight geomorphometry formulas.

Usage

derive_slope(
  x,
  units = c("degrees", "radians"),
  neighbors = 8,
  filename = "",
  overwrite = FALSE
)

derive_aspect(
  x,
  units = c("degrees", "radians"),
  neighbors = 8,
  filename = "",
  overwrite = FALSE
)

derive_northness(x, neighbors = 8, filename = "", overwrite = FALSE)

derive_eastness(x, neighbors = 8, filename = "", overwrite = FALSE)

derive_hillshade(
  x,
  angle = 45,
  direction = 315,
  neighbors = 8,
  filename = "",
  overwrite = FALSE
)

derive_roughness(x, filename = "", overwrite = FALSE)

derive_tri(x, filename = "", overwrite = FALSE)

derive_tpi(x, filename = "", overwrite = FALSE)

derive_rugosity(x, window = 3, neighbors = 8, filename = "", overwrite = FALSE)

derive_curvature(x, filename = "", overwrite = FALSE)

derive_surface_area_ratio(x, neighbors = 8, filename = "", overwrite = FALSE)

Arguments

x

A raster-like object accepted by as_bathy().

units

Units for slope or aspect: "degrees" or "radians".

neighbors

Neighborhood size passed to terra::terrain().

filename

Optional output raster path.

overwrite

Logical. Allow overwriting filename.

angle

Illumination angle for hillshade.

direction

Illumination direction for hillshade.

window

Odd integer focal-window size for local metrics.

Value

A single-layer terra::SpatRaster, except where documented otherwise.

Details

Functions preserve the input raster sign. For example, slope depends on the magnitude of local gradients, while BPI/TPI interpretation depends on whether the raster stores elevation-like values or positive depth.

derive_rugosity() computes a vector-ruggedness-measure-style index from local slope and aspect vectors. Its focal means use available derivative cells, including partial focal support adjacent to a derivative boundary or missing data, but the outermost cells can remain missing because slope and aspect themselves require neighbouring elevation values.

derive_curvature() computes a four-neighbor Laplacian-style index. It is not plan, profile, mean, or Gaussian curvature, is not scaled by cell dimensions, and is consequently strongly resolution-dependent. derive_surface_area_ratio() is a slope-secant approximation, 1 / cos(slope), rather than a triangulated or directly measured benthic surface area. It clamps near-zero cosine values to avoid pathological ratios at extreme slopes.

See also

derive_terrain(), derive_bpi()

Examples

bathy <- read_bathy(blueterra_example("bathy"))
derive_slope(bathy)
#> class       : SpatRaster
#> size        : 90, 190, 1  (nrow, ncol, nlyr)
#> resolution  : 19.98372, 19.98372  (x, y)
#> extent      : 134960.3, 138757.2, 204151.7, 205950.2  (xmin, xmax, ymin, ymax)
#> coord. ref. : NAD83 / Puerto Rico & Virgin Is. (EPSG:32161)
#> source(s)   : memory
#> varname     : laparguera_slope_bathy
#> name        : slope_deg
#> min value   :  0.053986
#> max value   : 71.446951
derive_northness(bathy)
#> class       : SpatRaster
#> size        : 90, 190, 1  (nrow, ncol, nlyr)
#> resolution  : 19.98372, 19.98372  (x, y)
#> extent      : 134960.3, 138757.2, 204151.7, 205950.2  (xmin, xmax, ymin, ymax)
#> coord. ref. : NAD83 / Puerto Rico & Virgin Is. (EPSG:32161)
#> source(s)   : memory
#> varname     : laparguera_slope_bathy
#> name        : northness
#> min value   :        -1
#> max value   :   0.99997