Generate Contour Overlay

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,
  resolution_multiply = 1,
  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.

resolution_multiply

Default 1. If passing in heightmap instead of width/height, amount to increase the resolution of the overlay, which should make lines/polygons finer. Should be combined with add_overlay(rescale_original = TRUE) to ensure those added details are captured in the final map.

color

Default black. Color.

linewidth

Default 1. Line width.

Value

Semi-transparent overlay with contours.

Examples

#Add contours to the montereybay dataset
if(run_documentation()) {
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]

if(run_documentation()) {
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()
}

if(run_documentation()) {
#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()
}

if(run_documentation()) {
#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()
}

if(run_documentation()) {
#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()
}