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Slope, aspect, curvature, and partial slopes

Source: R/terrain.r
terrain.Rd

terrain() calculates topographic indices, including slope, aspect, curvature, and partial slopes (slopes in the east-west or north-south directions).

Usage

# S4 method for class 'GRaster'
terrain(
  x,
  v = "slope",
  units = "degrees",
  undefinedAspect = NA,
  northIs0 = TRUE
)

Arguments

x

A GRaster (typically representing elevation).

v

Name of the topographic metric(s) to calculate. Valid values include one or more of:

  • "slope": Slope. Units are given by argument units.

  • "aspect": Aspect. When argument northIs0 is TRUE (default), then aspect is given in degrees from north going clockwise (0 = north, 90 = east, 180 = south, 270 = west). Units are given by argument units.

  • "profileCurve": Profile curvature.

  • "tanCurve": Tangential curvature.

  • "dx": Slope in east-west direction.

  • "dy": Slope in north-south direction.

  • "dxx": Second partial derivative in east-west direction.

  • "dyy": Second partial derivative in north-south direction.

  • "dxy": Second partial derivative along east-west and north-south direction.

  • "*": All of the above.

units

Character: "Units" in which to calculate slope and aspect: either "degrees" for degrees (default), "radians", or "percent". Partial matching is used.

undefinedAspect

Numeric or NA (default): Value to assign to flat areas for which aspect cannot be calculated.

northIs0

Logical: If TRUE (default), aspect will be reported in "north orientation," such that 0 is north, and degrees run clockwise (90 is east, 180 south, 270 west). If FALSE, then aspect will be reported in "east orientation," such that 0 is east, and degrees run counterclockwise (90 is north, 180 west, 270 south). The latter is the default in GRASS, but the former is the default in terra::terrain() function, so is used here as the default. Note: The sun() function requires aspect to be in east orientation.

Value

A GRaster with one or more layers.

See also

terra::terrain(), ruggedness(), wetness(), geomorphons(), tool r.slope.aspect in GRASS

Examples

if (grassStarted()) {

# Setup
library(terra)

# Example data
madElev <- fastData("madElev")

# Convert a SpatRaster to a GRaster
elev <- fast(madElev)

# Calculate all topographic metrics
topos <- terrain(elev, v = "*")
topos

plot(topos) # NB Aspect has values of NA when it cannot be defined

# Calculate a hillshade raster
hs <- hillshade(elev)
plot(hs)

}