Description Usage Arguments Details Value Author(s) References Examples
Calculates cast shadows over matrix or Raster Layer DEM for a given illumination direction.
1 | doshade(dem, sv, dl = 0, sombra = dem)
|
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. |
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.
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.
Javier G. Corripio
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.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 | # 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)
## End(Not run)
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