This function creates an overlay with a scale bar of a user-specified length. It uses the coordinates of the map (specified by passing an extent) and then creates a scale bar at a specified x/y proportion across the map. If the map is not projected (i.e. is in lat/long coordinates) this function will use the `geosphere` package to create a scale bar of the proper length.

generate_scalebar_overlay(
  extent,
  length,
  x = 0.05,
  y = 0.05,
  latlong = FALSE,
  thickness = NA,
  bearing = 90,
  unit = "m",
  flip_ticks = FALSE,
  labels = NA,
  text_size = 1,
  decimals = 0,
  text_offset = 1,
  adj = 0.5,
  heightmap = NULL,
  width = NA,
  height = NA,
  color1 = "white",
  color2 = "black",
  text_color = "black",
  font = 1,
  border_color = "black",
  tick_color = "black",
  border_width = 1,
  tick_width = 1,
  halo_color = NA,
  halo_expand = 1,
  halo_alpha = 1,
  halo_offset = c(0, 0),
  halo_blur = 1
)

Arguments

extent

A `raster::Extent` object with the bounding box for the height map used to generate the original map. If this is in lat/long coordinates, be sure to set `latlong = TRUE`.

length

The length of the scale bar, in `units`. This should match the units used on the map, unless `extent` uses lat/long coordinates. In that case, the distance should be in meters.

x

Default `0.05`. The x-coordinate of the bottom-left corner of the scale bar, as a proportion of the full map width.

y

Default `0.05`. The y-coordinate of the bottom-left corner of the scale bar, as a proportion of the full map height.

latlong

Default `FALSE`. Set to `TRUE` if the map is in lat/long coordinates to get an accurate scale bar (using distance calculated with the `geosphere` package).

thickness

Default `NA`, automatically computed as 1/20th the length of the scale bar. Width of the scale bar.

bearing

Default `90`, horizontal. Direction (measured from north) of the scale bar.

unit

Default `m`. Displayed unit on the scale bar.

flip_ticks

Default `FALSE`. Whether to flip the ticks to the other side of the scale bar.

labels

Default `NA`. Manually specify the three labels with a length-3 character vector. Use this if you want display units other than meters.

text_size

Default `1`. Text size.

decimals

Default `0`. Number of decimal places for scale bar labels.

text_offset

Default `1`. Amount of offset to apply to the text from the scale bar, as a multiple of `thickness`.

adj

Default `0.5`, centered. Text justification. `0` is left-justified, and `1` is right-justified.

heightmap

Default `NULL`. The original height map. Pass this in to extract the dimensions of the resulting RGB image array automatically.

width

Default `NA`. Width of the resulting image array. Default the same dimensions as height map.

height

Default `NA`. Width of the resulting image array. Default the same dimensions as height map.

color1

Default `black`. Primary color of the scale bar.

color2

Default `white`. Secondary color of the scale bar.

text_color

Default `black`. Text color.

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.

border_color

Default `black`. Border color of the scale bar.

tick_color

Default `black`. Tick color of the scale bar.

border_width

Default `1`. Width of the scale bar border.

tick_width

Default `1`. Width of the tick.

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 `1`. 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, as a proportion of the full scene.

halo_blur

Default `1`. Amount of blur to apply to the halo. Values greater than `30` won't result in further blurring.

Value

Semi-transparent overlay with a scale bar.

Examples

#Only run these examples if the `magick` package is installed.
if (length(find.package("magick", quiet = TRUE)) > 0) {
# \donttest{
#Create the water palette
water_palette = colorRampPalette(c("darkblue", "dodgerblue", "lightblue"))(200)
bathy_hs = height_shade(montereybay, texture = water_palette)

#Generate flat water heightmap
mbay = montereybay
mbay[mbay < 0] = 0

base_map = mbay %>%
height_shade() %>%
add_overlay(generate_altitude_overlay(bathy_hs, montereybay, 0, 0))  %>%
add_shadow(lamb_shade(montereybay,zscale=50),0.3)

#For convenience, the extent of the montereybay dataset is included as an attribute
mb_extent = attr(montereybay, "extent")

#Add a scalebar
base_map %>%
add_overlay(generate_scalebar_overlay(extent = mb_extent, length = 40000,
                                      heightmap = montereybay, 
                                      latlong=TRUE)) %>%
plot_map()


#Change the text color
base_map %>%
 add_overlay(generate_scalebar_overlay(extent = mb_extent, length = 40000,
                                       text_color = "white",
                                       heightmap = montereybay, 
                                       latlong=TRUE)) %>%
 plot_map()


#Change the length
base_map %>%
 add_overlay(generate_scalebar_overlay(extent = mb_extent, length = 30000,
                                       text_color = "white",
                                       heightmap = montereybay, 
                                       latlong=TRUE)) %>%
 plot_map()

#Change the thickness (default is length/20)
base_map %>%
 add_overlay(generate_scalebar_overlay(extent = mb_extent, length = 30000,
                                       text_color = "white", thickness = 30000/10,
                                       heightmap = montereybay, 
                                       latlong=TRUE)) %>%
 plot_map()

#Change the text offset (given in multiples of thickness)
base_map %>%
 add_overlay(generate_scalebar_overlay(extent = mb_extent, length = 30000,
                                       text_color = "white", thickness = 30000/10,
                                       text_offset = 0.75,
                                       heightmap = montereybay, 
                                       latlong=TRUE)) %>%
 plot_map()

#Change the primary and secondary colors, along with the border and tick color
base_map %>%
 add_overlay(generate_scalebar_overlay(extent = mb_extent, length = 30000,
                                       text_color = "white", border_color = "white",
                                       tick_color = "white",
                                       color1 = "darkolivegreen4", color2 = "burlywood3",
                                       heightmap = montereybay, 
                                       latlong=TRUE)) %>%
 plot_map()

#Add a halo
base_map %>%
 add_overlay(generate_scalebar_overlay(extent = mb_extent, length = 40000,
                                       halo_color = "white", halo_expand = 1,
                                       heightmap = montereybay, 
                                       latlong=TRUE)) %>%
 plot_map()

#Change the orientation, position, text alignment, and flip the ticks to the other side
base_map %>%
 add_overlay(generate_scalebar_overlay(extent = mb_extent, length = 40000, x = 0.07,
                                       bearing=0, adj = 0, flip_ticks = TRUE,
                                       halo_color = "white", halo_expand = 1.5,
                                       heightmap = montereybay, 
                                       latlong=TRUE)) %>%
 plot_map()
 
 
#64373.8 meters in 40 miles
#Create custom labels, change font and text size, remove the border/ticks, and change the color
#Here, we specify a width and height to double the resolution of the image (for sharper text)
base_map %>%
 add_overlay(generate_scalebar_overlay(extent = mb_extent, length = 64373.8, x = 0.07,
                                       labels = c("0", "20", "40 miles"), thickness=2500,
                                       text_size=3, font = 2, text_offset = 0,
                                       text_color="white", color2="#bf323b", border_color=NA,
                                       tick_color="red", tick_width=0,
                                       bearing=0, adj = 0, flip_ticks = TRUE,
                                       halo_color="black", halo_blur=3, halo_alpha=0.5,
                                       width = ncol(montereybay)*2,
                                       height = nrow(montereybay)*2,
                                       latlong=TRUE), rescale_original=TRUE) %>%
 plot_map()
# }
}