insol (version 1.2.2)

doshade: Cast shadows

Description

Calculates cast shadows over matrix or Raster Layer DEM for a given illumination direction.

Usage

doshade(dem, sv, dl = 0, sombra = dem)

Arguments

dem

Digital elevation model, a matrix or RasterLayer representing terrain elevation on a regular grid.

sv

Unit vector in the direction of the sun.

dl

Grid spacing. Not needed if dem is a Raster Layer.

sombra

Returned matrix or Raster Layer, no input needed for this argument.

Value

Return an object of the same class the the input dem (either a matrix o a Raster Layer), with values 0 for shaded or 1 for not shaded.

Details

doshade calls a fortran routine that scans the DEM in lines parallel the sun direction. It compares the projection of grid cells on a plane perpendicular to the sun to determine whether they are in the sun or in the shadow of a previous cell. See Figure 6 of reference for more details.

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.

Examples

# NOT RUN {
# define the sun vector: northwest at 15 degrees elevation
sv = normalvector(75,315)

## create a pyramid 100 units by side and 50 nunits tall
m = matrix(0,nrow=100,ncol=100)
for (i in 1:100){ for (j in 1:100){
m[i,j] = 50-max(abs(i-50),abs(j-50)) }}

## place it on a large flat expanse
mm = matrix(0,nrow=500,ncol=500)
mm[201:300,201:300] = m

## calulate and plot the cast shadows from the sun 
sh = doshade(mm,sv,1)
image(t(sh[nrow(sh):1,]),col=grey(1:100/100))
contour(mm,add=TRUE,col='sienna1',nlevels=25)
## (mm is symmetrical, no need to rotate as for shadows)

# }
# NOT RUN {
## plot cast shadows on mountain terrain, sun at NW, 25 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(65,315)
sh = doshade(dem,sv,cellsize)
image(t(sh[nrow(sh):1,]),col=grey(1:100/100))

## add intensity of illumination in this case sun at NW 45 degrees elevation
sv = normalvector(45,315)
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))


## plot cast shadows on mountain terrain using raster
sv = normalvector(65,315)
require(raster)
demfile = tempfile()
download.file("https://meteoexploration.com/R/insol/data/dempyrenees.tif",demfile)
dem = raster(demfile)
sh = doshade(dem,sv)
plot(sh,col=grey(0:1),legend=FALSE)
contour(dem,add=TRUE,col='sienna1',lwd=.5,nlevels=50)

## add intensity of illumination in this case sun at NW 45 degrees elevation
sv = normalvector(45,315)
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
## convert back to raster as dem and add shadows
hsh = raster(hsh,crs=projection(dem))
extent(hsh) = extent(dem)
sh = doshade(dem,sv)
plot(hsh*sh,col=grey(1:100/100),legend=FALSE)
unlink(demfile) 
# }
# NOT RUN {
# }