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, color = "black", linewidth = 1 )
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. |
Semi-transparent overlay with contours.
#Add contours to the montereybay dataset
#Only run these examples if the `magick` package is installed.
if ("magick" %in% rownames(utils::installed.packages())) {
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()
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