Add Overlay

Overlays an image (with a transparency layer) on the current map.

add_overlay(hillshade, overlay, alphacolor = NULL, alphalayer = 1,
  alphamethod = "max", gamma_correction = TRUE)

Arguments

hillshade	A three-dimensional RGB array or 2D matrix of shadow intensities.
overlay	A three or four dimensional RGB array, where the 4th dimension represents the alpha (transparency) channel. If the array is 3D, `alphacolor` should also be passed to indicate transparent regions.
alphacolor	Default `NULL`. If `overlay` is a 3-layer array, this argument tells which color is interpretted as completely transparent.
alphalayer	Default `1`. Defines minimum tranparaency of layer. If transparency already exists in `overlay`, the way `add_overlay` combines the two is determined in argument `alphamethod`.
alphamethod	Default `max`. Method for dealing with pre-existing transparency with `layeralpha`. If `max`, converts all alpha levels higher than `layeralpha` to the value set in `layeralpha`. If `multiply`, multiples all pre-existing alpha values with `layeralpha`. If `none`, keeps existing tranparencies and only changes opaque entries.
gamma_correction	Default `TRUE`. Controls gamma correction when adding colors. Default exponent of 2.2.

Value

Hillshade with overlay.

Examples

#Here, we overlay a base R elevation plot with our raytraced shadow layer:

fliplr = function(x) {
 x[,ncol(x):1]
}
tempfilename = tempfile()
old.par = par(no.readonly = TRUE)
on.exit(par(old.par))
png(tempfilename,width = 401,height=401)
par(mar = c(0,0,0,0))
raster::image(fliplr(montereybay),axes = FALSE,col = rev(terrain.colors(1000)))
dev.off()
#> pdf 
#>   2 
tempmap = png::readPNG(tempfilename)

montereybay %>%
  ray_shade(zscale=50,maxsearch = 500,anglebreaks = seq(20,30,0.1)) %>%
  add_overlay(tempmap,alphalayer = 0.5) %>%
  plot_map()

#Combining base R plotting with rayshader's spherical color mapping and raytracing:
montereybay %>%
  sphere_shade() %>%
  add_overlay(tempmap,alphalayer = 0.4) %>%
  add_shadow(ray_shade(montereybay,zscale=50,maxsearch = 500)) %>%
  plot_map()