Hill shading

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

See also

terrain

References

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

Examples

f <- system.file("ex/elev.tif", package="terra")
r <- rast(f)
# disaggregating because the resolution of this raster is a bit low
# you generally should not do that with your own data
r <- disagg(r, 10, method="bilinear")

slope <- terrain(r, "slope", unit="radians")
aspect <- terrain(r, "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(r, col=rainbow(25, alpha=0.35), add=TRUE)


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

hh <- shade(slope, aspect, angle = c(45, 45, 45, 80), direction = c(225, 270, 315, 135))
h1 <- Reduce(mean, hh)
h2 <- mean(hh)