Calculates and returns an overlay of contour lines for the current height map.

generate_contour_overlay(
  heightmap,
  levels = NA,
  nlevels = NA,
  zscale = 1,
  width = NA,
  height = NA,
  color = "black",
  linewidth = 1
)

Arguments

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.

levels

Default `NA`. Automatically generated with 10 levels. This argument specifies the exact height levels of each contour.

nlevels

Default `NA`. Controls the auto-generation of levels. If levels is length-2, this will automatically generate `nlevels` breaks between `levels[1]` and `levels[2]`.

zscale

Default `1`. The ratio between the x and y spacing (which are assumed to be equal) and the z axis. For example, if the elevation levels are in units of 1 meter and the grid values are separated by 10 meters, `zscale` would be 10.

width

Default `NA`. Width of the resulting overlay. Default the same dimensions as heightmap.

height

Default `NA`. Width of the resulting overlay. Default the same dimensions as heightmap.

color

Default `black`. Color.

linewidth

Default `1`. Line width.

Value

Semi-transparent overlay with contours.

Examples

#Add contours to the montereybay dataset

#Only run these examples if the `magick` package is installed.
if (length(find.package("magick", quiet = TRUE)) > 0) {
# \donttest{
montereybay %>%
 height_shade() %>%
 add_overlay(generate_contour_overlay(montereybay))  %>%
 add_shadow(ray_shade(montereybay,zscale=50),0.3) %>%
 plot_map()
 
#Add a different contour color for above and below water, and specify levels manually
water_palette = colorRampPalette(c("darkblue", "dodgerblue", "lightblue"))(200)
bathy_hs = height_shade(montereybay, texture = water_palette)
breaks = seq(range(montereybay)[1],range(montereybay)[2],length.out=50)
water_breaks = breaks[breaks < 0]
land_breaks = breaks[breaks > 0]

montereybay %>%
 height_shade() %>%
 add_overlay(generate_altitude_overlay(bathy_hs, montereybay, 0, 0))  %>%
 add_shadow(ray_shade(montereybay,zscale=50),0.3) %>%
 add_overlay(generate_contour_overlay(montereybay, levels = water_breaks, color="white"))  %>%
 add_overlay(generate_contour_overlay(montereybay, levels = land_breaks, color="black"))  %>%
 plot_map()
 
#Increase the resolution of the contour to improve the appearance of lines
montereybay %>%
 height_shade() %>%
 add_overlay(generate_altitude_overlay(bathy_hs, montereybay, 0, 0))  %>%
 add_shadow(ray_shade(montereybay,zscale=50),0.3) %>%
 add_overlay(generate_contour_overlay(montereybay, levels = water_breaks, color="white",
                                      height = nrow(montereybay)*2, 
                                      width  = ncol(montereybay)*2))  %>%
 add_overlay(generate_contour_overlay(montereybay, levels = land_breaks, color="black",
                                      height = nrow(montereybay)*2, 
                                      width  = ncol(montereybay)*2))  %>%
 plot_map()
 
#Increase the number of breaks and the transparency (via add_overlay)
montereybay %>%
 height_shade() %>%
 add_shadow(ray_shade(montereybay,zscale=50),0.3) %>%
 add_overlay(generate_contour_overlay(montereybay, linewidth=2, nlevels=100,
                                      height = nrow(montereybay)*2, color="black",
                                      width  = ncol(montereybay)*2), alphalayer=0.5) %>%
 plot_map()
 
#Manually specify the breaks with levels
montereybay %>%
 height_shade() %>%
 add_overlay(generate_contour_overlay(montereybay, linewidth=2, levels = seq(-2000,0,100))) %>%
 add_shadow(ray_shade(montereybay,zscale=50),0.3) %>%
 plot_map()
# }
}