Generate Label Overlay — generate_label

This uses the car::placeLabel() function to generate labels for the given scene. Either use an sf object or manually specify the x/y coordinates and label.

generate_label_overlay(
  labels,
  extent,
  x = NULL,
  y = NULL,
  heightmap = NULL,
  width = NA,
  height = NA,
  resolution_multiply = 1,
  text_size = 1,
  color = "black",
  font = 1,
  pch = 16,
  point_size = 1,
  point_color = NA,
  offset = c(0, 0),
  data_label_column = NULL,
  halo_color = NA,
  halo_expand = 0,
  halo_alpha = 1,
  halo_offset = c(0, 0),
  halo_blur = 1,
  seed = NA
)

Arguments

labels: A character vector of labels, or an sf object with POINT geometry and a column for labels.
extent: Either an object representing the spatial extent of the scene (either from the raster, terra, sf, or sp packages), a length-4 numeric vector specifying c("xmin", "xmax","ymin","ymax"), or the spatial object (from the previously aforementioned packages) which will be automatically converted to an extent object.
x: Default NULL. The x-coordinate, if labels is not an sf object.
y: Default NULL. The y-coordinate, if labels is not an sf object.
heightmap: Default NULL. The original height map. Pass this in to extract the dimensions of the resulting overlay automatically.
width: Default NA. Width of the resulting overlay. Default the same dimensions as height map.
height: Default NA. Width of the resulting overlay. Default the same dimensions as height map.
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/text finer. Should be combined with add_overlay(rescale_original = TRUE) to ensure those added details are captured in the final map.
text_size: Default 1. Text size.
color: Default black. Color of the labels.
font: Default 1. An integer which specifies which font to use for text. If possible, device drivers arrange so that 1 corresponds to plain text (the default), 2 to bold face, 3 to italic and 4 to bold italic.
pch: Default 20, solid. Point symbol. 0 = square, 1 = circle, 2 = triangle point up, 3 = plus, 4 = cross, 5 = diamond, 6 = triangle point down, 7 = square cross, 8 = star, 9 = diamond plus, 10 = circle plus, 11 = triangles up and down, 12 = square plus, 13 = circle cross, 14 = square and triangle down, 15 = filled square, 16 = filled circle, 17 = filled triangle point-up, 18 = filled diamond, 19 = solid circle, 20 = bullet (smaller circle), 21 = filled circle blue, 22 = filled square blue, 23 = filled diamond blue, 24 = filled triangle point-up blue, 25 = filled triangle point down blue
point_size: Default 0, no points. Point size.
point_color: Default NA. Colors of the points. Unless otherwise specified, this defaults to color.
offset: Default c(0,0). Horizontal and vertical offset to apply to the label, in units of geometry.
data_label_column: Default NULL. The column in the sf object that contains the labels.
halo_color: Default NA, no halo. If a color is specified, the text label will be surrounded by a halo of this color.
halo_expand: Default 2. Number of pixels to expand the halo.
halo_alpha: Default 1. Transparency of the halo.
halo_offset: Default c(0,0). Horizontal and vertical offset to apply to the halo, in units of geometry.
halo_blur: Default 1. Amount of blur to apply to the halo. Values greater than 30 won't result in further blurring.
seed: Default NA, no seed. Random seed for ensuring the consistent placement of labels around points.

Value

Semi-transparent overlay with labels.

Examples

#Add the included `sf` object with roads to the montereybay dataset
if(run_documentation()) {
#Create the water palette
water_palette = colorRampPalette(c("darkblue", "dodgerblue", "lightblue"))(200)
bathy_hs = height_shade(montereybay, texture = water_palette)
#Set label font
par(family = "Arial")

#We're plotting the polygon data here for counties around Monterey Bay. We'll first
#plot the county names at the polygon centroids.
bathy_hs %>% 
 add_shadow(lamb_shade(montereybay,zscale=50),0.3) %>%
 add_overlay(generate_polygon_overlay(monterey_counties_sf, palette = rainbow, 
                                      extent = attr(montereybay,"extent"),
                                      heightmap = montereybay)) %>% 
 add_overlay(generate_label_overlay(labels=monterey_counties_sf,
                                    color="black", point_size = 1, text_size = 1,
                                    data_label_column = "NAME",
                                    extent= attr(montereybay,"extent"), heightmap = montereybay,
                                    seed=1))  %>%
 plot_map()
}

if(run_documentation()) {
#It's hard to read these values, so we'll add a white halo.
bathy_hs %>% 
 add_shadow(lamb_shade(montereybay,zscale=50),0.3) %>%
 add_overlay(generate_polygon_overlay(monterey_counties_sf, palette = rainbow, 
                                      extent = attr(montereybay,"extent"),
                                      heightmap = montereybay)) %>% 
 add_overlay(generate_label_overlay(labels=monterey_counties_sf,
                                    color="black", point_size = 1, text_size = 1,
                                    data_label_column = "NAME",
                                    extent= attr(montereybay,"extent"), heightmap = montereybay,
                                    halo_color = "white", halo_expand = 3,
                                    seed=1))  %>%
 plot_map()
}

if(run_documentation()) {
#Plot the actual town locations, using the manual plotting interface instead of the `sf` object
montereybay %>%
 height_shade() %>%
 add_overlay(generate_altitude_overlay(bathy_hs, montereybay, 0, 0)) %>% 
 add_shadow(lamb_shade(montereybay,zscale=50),0.3) %>%
 add_overlay(generate_label_overlay(labels=as.character(monterey_counties_sf$NAME),
                                    x=as.numeric(as.character(monterey_counties_sf$INTPTLON)),
                                    y=as.numeric(as.character(monterey_counties_sf$INTPTLAT)),
                                    color="black", point_size = 1, text_size = 1,
                                    extent= attr(montereybay,"extent"), heightmap = montereybay,
                                    halo_color = "white", halo_expand = 3,
                                    seed=1))  %>%
 plot_map()
}

if(run_documentation()) {
#Adding a softer blurred halo
montereybay %>%
 height_shade() %>%
 add_overlay(generate_altitude_overlay(bathy_hs, montereybay, 0, 0)) %>% 
 add_shadow(lamb_shade(montereybay,zscale=50),0.3) %>%
 add_overlay(generate_label_overlay(labels=as.character(monterey_counties_sf$NAME),
                                    x=as.numeric(as.character(monterey_counties_sf$INTPTLON)),
                                    y=as.numeric(as.character(monterey_counties_sf$INTPTLAT)),
                                    color="black", point_size = 1, text_size = 1,
                                    extent= attr(montereybay,"extent"), heightmap = montereybay,
                                    halo_color = "white", halo_expand = 3, halo_blur=10,
                                    seed=1))  %>%
 plot_map()
}

if(run_documentation()) {
#Changing the seed changes the locations of the labels
montereybay %>%
 height_shade() %>%
 add_overlay(generate_altitude_overlay(bathy_hs, montereybay, 0, 0)) %>% 
 add_shadow(lamb_shade(montereybay,zscale=50),0.3) %>%
 add_overlay(generate_label_overlay(labels=as.character(monterey_counties_sf$NAME),
                                    x=as.numeric(as.character(monterey_counties_sf$INTPTLON)),
                                    y=as.numeric(as.character(monterey_counties_sf$INTPTLAT)),
                                    color="black", point_size = 1, text_size = 1,
                                    extent= attr(montereybay,"extent"), heightmap = montereybay,
                                    halo_color = "white", halo_expand = 3, halo_blur=10,
                                    seed=2))  %>%
 plot_map()
}