insol (version 1.2.2)

hillshading: Intensity of illumination over a surface

Description

Computes the intensity of illumination over a surface, such as a DEM, according to the position of the sun.

Usage

hillshading(cgrad, sv)

Arguments

cgrad

3D array ( nrow, ncol, 3) of unit vectors normal to surface grid cells. The output of cgrad().

sv

unit vector in the direction of the sun.

Value

A matrix of illumination intensity values. Negative values are the equivalent of self shading and are set to zero.

Details

The intensity of the sun beams falling on a surface are proportional to the cosine of the angle between the sun vector and the vector normal to the surface, which in this case is the dot product between cgrad and sv.

References

Corripio, J. G.: 2003, Vectorial algebra algorithms for calculating terrain parameters from DEMs and the position of the sun for solar radiation modelling in mountainous terrain, International Journal of Geographical Information Science 17(1), 1-23.

See Also

cgrad, insolation, sunvector

Examples

# NOT RUN {
## From the "Obligatory Mathematical surface" in persp3d {rgl}
## this shows the cast shdows clearly, but there is some interference with rgl internal
## lit parameters
require(rgl)
x = seq(-10, 10, length= 300)
y = x
f = function(x,y) { r <- sqrt(x^2+y^2); 10 * sin(r)/r }
z = outer(x, y, f)
z[is.na(z)] = 1
zgr = cgrad(z,2/30)
sv = normalvector(55,315)
hsh = zgr[,,1]*sv[1]+zgr[,,2]*sv[2]+zgr[,,3]*sv[3]
hsh = (hsh+abs(hsh))/2
sh = doshade(z,sv,2/30)
hshsh = hsh*sh
hshsh = t(hshsh[nrow(hshsh):1,])
open3d()
rgl.light(viewpoint.rel = F, ambient = "#FFFFFF", diffuse = "#FFFFFF", specular = "#000000")
persp3d(x, y, z, col=grey(hshsh))
# }
# NOT RUN {
## Hillshading on mountain terrain, sun at NW, 35 degrees elevation
zipfile = tempfile()
download.file("https://meteoexploration.com/R/insol/data/dempyrenees.asc.zip",zipfile)
header = read.table(unz(zipfile,'dempyrenees.asc'),nrows=6)
dem = read.table(unz(zipfile,'dempyrenees.asc'),skip=6)
dem = as.matrix(dem)
unlink(zipfile)
cellsize = header[5,2]
sv = normalvector(55,315)
grd = cgrad(dem,cellsize)
hsh = grd[,,1]*sv[1]+grd[,,2]*sv[2]+grd[,,3]*sv[3]
## remove negative incidence angles (self shading) 
hsh = (hsh+abs(hsh))/2
sh = doshade(dem,sv,cellsize)
hshsh = hsh*sh
image(t(hshsh[nrow(sh):1,]),col=grey(1:100/100))

# }
# NOT RUN {
## Hillshading on mountain terrain, sun at NW, 45 degrees elevation. Using raster
sv = normalvector(45,315)
require(raster)
demfile = tempfile()
download.file("https://meteoexploration.com/R/insol/data/dempyrenees.tif",demfile)
dem = raster(demfile)
grd = cgrad(dem)
hsh = grd[,,1]*sv[1]+grd[,,2]*sv[2]+grd[,,3]*sv[3]
## remove negative incidence angles (self shading) 
hsh = (hsh+abs(hsh))/2
hsh = raster(hsh,crs=projection(dem))
extent(hsh) = extent(dem)
plot(hsh,col=grey(1:100/100),legend=FALSE)
unlink(demfile)
# }
# NOT RUN {
# }