Generate Altitude Overlay — generate_altitude

Using a hillshade and the height map, generates a semi-transparent hillshade to layer onto an existing map.

generate_altitude_overlay(
  hillshade,
  heightmap,
  start_transition,
  end_transition = NULL,
  lower = TRUE
)

Arguments

hillshade: The hillshade to transition into.
heightmap: A two-dimensional matrix, where each entry in the matrix is the elevation at that point. All grid points are assumed to be evenly spaced.
start_transition: Elevation above which `hillshade` is completely transparent.
end_transition: Default `NULL`. Elevation below which `hillshade` is completely opaque. By default, this is equal to `start_transition`.
lower: Default `TRUE`. This makes `hillshade` completely opaque below `start_transition`. If `FALSE`, the direction will be reversed.

Value

4-layer RGB array representing the semi-transparent hillshade.

Examples

#Create a bathymetric hillshade
if(run_documentation()) {
water_palette = colorRampPalette(c("darkblue", "dodgerblue", "lightblue"))(200)
bathy_hs = height_shade(montereybay, texture = water_palette)
plot_map(bathy_hs)
}


if(run_documentation()) {
#Set everything below 0m to water palette
montereybay %>%
 sphere_shade(zscale=10) %>%
 add_overlay(generate_altitude_overlay(bathy_hs, montereybay, 0, 0))  %>%
 add_shadow(ray_shade(montereybay,zscale=50),0.3) %>%
 plot_map()
}


#Add snow peaks by setting `lower = FALSE`  
snow_palette = "white"
snow_hs = height_shade(montereybay, texture = snow_palette)

if(run_documentation()) {
#Set the snow transition region from 500m to 1200m
montereybay %>%
 sphere_shade(zscale=10, texture = "desert") %>%
 add_overlay(generate_altitude_overlay(bathy_hs, montereybay, 0, 0))  %>%
 add_overlay(generate_altitude_overlay(snow_hs, montereybay, 500, 1200, lower=FALSE))  %>%
 add_shadow(ambient_shade(montereybay,zscale=50,maxsearch=100),0) %>%
 plot_map()
}