hillshader

The hillshader package is a wrapper around the rayshader and raster packages to create hillshade relief maps using ray-tracing, and write them to (spatial) files.

Installation

You can install the development version of hillshader with the remotes package:

remotes::install_github("pierreroudier/hillshader")

First steps

Below is a quick tutorial of the hillshader capabilities:

The hillshader function

The hillshader function is the main function of that package, and allows to create a hillshade map as a RasterLayer:

library(raster)
#> Loading required package: sp
library(rayshader)

library(hillshader)

Note that the hillshader package includes the maungawhau and maungawhau_hr datasets. These are geo-referenced, raster datasets. maungawhau corresponds to the well-known volcano dataset. It is a 87 × 61 elevation matrix for Maungawhau, one of the circa 80 volcanoes in the Auckland volcano filed, in Aotearoa/New Zealand. The maungawhau_hr dataset is a “high-resolution” version of that dataset, and is a 1 m resolution, 860 × 600 elevation matrix derived from a LiDAR dataset recorded by NZ Aerial Mapping & Aerial Surveying Limited for Auckland Council, and distributed by Land Information New Zealand.

layout(matrix(c(1,2), nrow = 1, ncol = 2))
image(maungawhau, asp = 1, main = "Maungawhau", col = terrain.colors(100))
image(maungawhau_hr, asp = 1, main = "Maungawhau (high-resolution)", col = terrain.colors(100))

The hillshader function can be simply called on a elevation raster to generate a hillshade RasterLayer. By default, the shader used is rayshader::ray_shade, with its default values.

hs <- hillshader(maungawhau_hr)
plot_map(hs)

Add more shaders!

The hillshader function accept a shader option, with is a list of the successive shader functions to apply to create the hillshade layer. The accepted values must be rayshader shader functions (ray_shade, ambient_shade, lamb_shade), and the order is important.

hs <- hillshader(
  elevation = maungawhau_hr, 
  shader = c("ray_shade", "ambient_shade")
)

plot_map(hs)

Changing sun position

The hillshader function uses the rayshader options defaults, but other values can be specify and passed as arguments:

hs <- hillshader(
  elevation = maungawhau_hr, 
  shader = c("ray_shade", "ambient_shade"),
  sunangle = 180,
  sunaltitude = 25
)

plot_map(hs)

How does it compare to your usual hillshade method?

library(raster)

slope <- terrain(maungawhau_hr, out = "slope")
aspect <- terrain(maungawhau_hr, out = "aspect")
hs_raster <- hillShade(
  slope, 
  aspect, 
  angle = 40, 
  direction = 325
)

hs_hillshader <- hillshader(
  maungawhau_hr, 
  c("ray_shade", "ambient_shade"),
  sunangle = 325,
  sunaltitude = 40
)

layout(matrix(c(1,2), nrow = 1, ncol = 2))
image(hs_raster, asp = 1, main = "Classic hillshade", col = grey.colors(100))
image(hs_hillshader, asp = 1, main = "Ray-traced hillshade", col = grey.colors(100))

Saving to file

If a filename is passed to hillshader, then the resulting hillshade layer is saved to file. This is a wrapper around raster::writeRaster, and options specific to the latter function can be used.

hillshader(
  elevation = maungawhau_hr, 
  shader = c("ray_shade", "ambient_shade"),
  sunangle = 180,
  sunaltitude = 25,
  filename = "hillshade.tif"
)

Advanced use in the rayshader pipelines

The hillshader package provides three functions that can be used within the rayshader pipelines:

• add_shadow_2d: a function that multiplies a shadow map by another shadow map, a corrected 2D version of rayshader::add_shadow,
• matrix_to_raster: a function that converts a matrix (typically used by the rayshader functions) back to a RasterLayer, for input into a GIS workflow,
• write_raster: a function that a hillshade matrix to a raster file format.

library(rayshader)
library(hillshader)

# Create elevation matrix
el_mat <- raster_to_matrix(maungawhau_hr)

el_mat %>%
  # Create hillshade layer using 
  # ray-tracing
  ray_shade %>%
  # Add ambient shading
  add_shadow_2d(
    ambient_shade(
      heightmap = el_mat
    )
  ) %>% 
  # Write to GIS file
  write_raster(
    elevation = maungawhau_hr,
    filename = "hillshade.tif"
  )