# doshade: Cast shadows In insol: Solar Radiation

## Description

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

## Usage

 `1` ```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.

## 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.

## 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.

## Author(s)

Javier G. Corripio

## 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

 ``` 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 67``` ```# 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) ## plot cast shadows on mountain terrain, sun at NW, 25 degrees elevation zipfile=tempfile() download.file("http://www.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)) ## Not run: ## plot cast shadows on mountain terrain using raster sv=normalvector(65,315) require(rgdal) require(raster) demfile=tempfile() download.file("http://www.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) ```

insol documentation built on May 29, 2017, 3:22 p.m.