slope | R Documentation |
Calculates topographic slope 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.
slope(x, na_flag = -9999)
x |
A raster (class |
na_flag |
Value used to mark |
A stars
raster with topographic slope, i.e., the azimuth where the terrain is tilted towards, in decimal degrees (0-360) clockwise from north.
Slope calculation results in NA
when at least one of the cell neighbors is NA
, including the outermost rows and columns. Given that the focal window size in slope calculation is 3*3, this means that the outermost one row and one column are given an slope value of NA
.
The raster must be in projected CRS, and units of x/y resolution are assumed to be the same as units of elevation (typically meters).
The topographic slope algorithm is based on the How slope works article in the ArcGIS documentation:
https://desktop.arcgis.com/en/arcmap/10.3/tools/spatial-analyst-toolbox/how-slope-works.htm
# Small example
data(dem)
dem_slope = slope(dem)
plot(
dem, text_values = TRUE, breaks = "equal",
col = hcl.colors(11, "Spectral"), main = "input (elevation)"
)
plot(
dem_slope, text_values = TRUE, breaks = "equal",
col = hcl.colors(11, "Spectral"), main = "output (slope)"
)
# Larger example
data(carmel)
carmel_slope = slope(carmel)
plot(
carmel, breaks = "equal",
col = hcl.colors(11, "Spectral"), main = "input (elevation)"
)
plot(
carmel_slope, breaks = "equal",
col = hcl.colors(11, "Spectral"), main = "output (slope)"
)
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