terrain: Slope, aspect, curvature, and partial slopes

In adamlilith/fasterRaster: Faster Raster and Spatial Vector Processing Using 'GRASS GIS'

Slope, aspect, curvature, and partial slopes

Description

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

Usage

## S4 method for signature '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(), module 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)

}

adamlilith/fasterRaster documentation built on Oct. 26, 2024, 4:06 p.m.