shade.Rd
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.
shade(slope, aspect, angle=45, direction=0, normalize=FALSE,
filename="", overwrite=FALSE, ...)
SpatRasterwith slope values (in radians)
SpatRaster with aspect values (in radians)
The elevation angle(s) of the light source (sun), in degrees
The direction (azimuth) angle(s) of the light source (sun), in degrees
Logical. If TRUE
, values below zero are set to zero and the results are multiplied with 255
character. Output filename
logical. If TRUE
, filename
is overwritten
additional arguments for writing files as in writeRaster
Horn, B.K.P., 1981. Hill shading and the reflectance map. Proceedings of the IEEE 69(1):14-47
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)