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Cast shadows

Source: R/cast_shadows.R
cast_shadows.Rd

Calculates cast shadows over a matrix or SpatRaster digital elevation model (DEM) for a given illumination direction.

Usage

cast_shadows(dem, SZA, SAA, dl = 0, sombra = dem)

Arguments

dem

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

SZA

SpatRaster or numeric. Solar zenith angle in degrees.

SAA

SpatRaster or numeric. Solar azimuth angle in degrees.

dl

numeric. Grid spacing. Not needed if dem is SpatRaster.

sombra

Returned matrix or SpatRaster.

Value

Returns an object of the same class as the input DEM (matrix or SpatRaster), with values of 0 for cast-shadowed pixels and 1 for not-shaded pixels.

Details

cast_shadows() calls a fortran routine called doshade that scans the DEM in lines parallel to the sun direction. It compares the projection of the grid cells on a plane perpendicular to the sun to determine whether they are exposed to direct solar illumination or shadowed by neighbor objects, such as mountains. See Corripio (2003) for details. The doshade subroutine was originally written by Javier Corripio and it was shipped with the insol package. This function has been optimized and updated to take advantage of the infrastructure provided by the terra package.

References

Corripio JG (2003). “Vectorial algebra algorithms for calculating terrain parameters from DEMs and solar radiation modelling in mountainous terrain.” International Journal of Geographical Information Science, 17(1), 1–23. doi:10.1080/713811744 .

Examples

library(terra)
dem <- system.file("extdata/athabasca_dem.tif", package = "SatRbedo")
dem <- terra::rast(dem)
SZA <- 49
SAA <- 165
cs <- cast_shadows(dem, SZA, SAA)
plot(cs, col = grey(0:1))