starsExtra (version 0.2.8)

aspect: Calculate topographic aspect from a DEM

Description

Calculates topographic aspect given a Digital Elevation Model (DEM) raster. Input and output are rasters of class stars, single-band (i.e., only `"x"` and `"y"` dimensions), with one attribute.

Usage

aspect(x, na_flag = -9999)

Value

A stars raster with topographic slope, i.e., the azimuth where the terrain is tilted towards, in decimal degrees (0-360) clockwise from north. Aspect of flat terrain, i.e., where all values in the neighborhood are equal, is set to -1. Returned raster values are of class units (decimal degrees).

Arguments

x

A raster (class stars) with two dimensions: x and y, i.e., a single-band raster, representing a DEM.

na_flag

Value used to mark NA values in C code. This should be set to a value which is guaranteed to be absent from the input raster x (default is -9999).

References

The topographic aspect algorithm is based on the How aspect works article in the ArcGIS documentation:

https://desktop.arcgis.com/en/arcmap/10.3/tools/spatial-analyst-toolbox/how-aspect-works.htm

Examples

# Small example
data(dem)
dem_aspect = aspect(dem)
plot(
  dem, text_values = TRUE, breaks = "equal", 
  col = hcl.colors(11, "Spectral"), main = "input (elevation)"
)
plot(
  dem_aspect, text_values = TRUE, breaks = "equal", 
  col = hcl.colors(11, "Spectral"), main = "output (aspect)"
)
# \donttest{
# Larger example
data(carmel)
carmel_aspect = aspect(carmel)
plot(
  carmel, breaks = "equal", 
  col = hcl.colors(11, "Spectral"), main = "input (elevation)"
)
plot(
  carmel_aspect, breaks = "equal", 
  col = hcl.colors(11, "Spectral"), main = "output (aspect)"
)
# }