shade: Hill shading

In terra: Spatial Data Analysis

Hill shading

Description

Compute hill shade from slope and aspect layers (both in radians). Slope and aspect can be computed with function terrain.

A hill shade layer is often used as a backdrop on top of which another, semi-transparent, layer is drawn.

Usage

shade(slope, aspect, angle=45, direction=0, normalize=FALSE,
   filename="", overwrite=FALSE, ...)  

Arguments

slope	SpatRasterwith slope values (in radians)
aspect	SpatRaster with aspect values (in radians)
angle	The elevation angle(s) of the light source (sun), in degrees
direction	The direction (azimuth) angle(s) of the light source (sun), in degrees
normalize	Logical. If TRUE, values below zero are set to zero and the results are multiplied with 255
filename	character. Output filename
overwrite	logical. If TRUE, filename is overwritten
...	additional arguments for writing files as in writeRaster

References

Horn, B.K.P., 1981. Hill shading and the reflectance map. Proceedings of the IEEE 69(1):14-47

See Also

terrain

Examples

f <- system.file("ex/elev.tif", package="terra")
r <- rast(f)
alt <- disagg(r, 10, method="bilinear")
slope <- terrain(alt, "slope", unit="radians")
aspect <- terrain(alt, "aspect", unit="radians")
hill <- shade(slope, aspect, 40, 270)
plot(hill, col=grey(0:100/100), legend=FALSE, mar=c(2,2,1,4))
plot(alt, col=rainbow(25, alpha=0.35), add=TRUE)

# A better hill shade may be achieved by combining 
# different angles and directions. For example

h <- shade(slope, aspect, angle = c(45, 45, 45, 80), direction = c(225, 270, 315, 135))
h <- Reduce(mean, h)				

terra documentation built on Oct. 14, 2024, 5:07 p.m.