JGRSGIS / rayshader

R Package for Raytracing Elevation Matrices to Produce Global Illumination Relief Maps

rayshader

Overview

rayshader is an open source package for producing hillshaded maps of elevation matrices with raytracing and spherical texture mapping.

Installation

# To install the latest version from Github:
# install.packages("devtools")
devtools::install_github("tylermorganwall/rayshader")

Functions

Rayshader has five functions related to hillshading:

• ray_shade uses user specified light directions to calculate a global shadow map for an elevation matrix. By default, this also scales the light intensity at each point by the dot product of the mean ray direction and the surface normal (also implemented in function lamb_shade, this can be turned off by setting lambert=FALSE.
• sphere_shade maps an RGB texture to a hillshade by spherical mapping. A texture can be generated with the create_texture function, or loaded from an image. sphere_shade also includes 7 built-in palettes: "imhof1","imhof2","imhof3",imhof4","desert","bw","unicorn".
• create_texture programmatically creates texture maps given five colors: a highlight, a shadow, a left fill light, a right fill light, and a center color for flat areas. The user can also optionally specify the colors at the corners, but create_texture will interpolate those if they aren't given.
• ambient_shade creates an ambient occlusion shadow layer, darkening areas that have less scattered light from the atmosphere. This results in valleys being darker than flat areas and ridges.
• lamb_shade uses a single user specified light direction to calculate a local shadow map based on the dot product between the surface normal and the light direction for an elevation matrix.
• add_shadow takes two of the shadow maps above and combines them, scaling the second one (or, if the second is an RGB array, the matrix) as specified by the user.

Rayshader also has two functions to detect and add water to maps:

• detect_water uses a flood-fill algorithm to detect bodies of water of a user-specified minimum area.
• add_water uses the output of detect_water to add a water color to the map. The user can input their own color, or pass the name of one of the pre-defined palettes from sphere_shade to get a matching hue.

And two functions to display and save your maps:

• plot_map Plots the current map. Accepts either a matrix or an array.
• write_png Writes the current map to disk with a user-specified filename.

All of these functions are designed to be used with the pipe magrittr %>%.

Usage

library(rayshader)
library(magrittr)

#Here, I load a map with the raster package:
tif_file = raster::raster("dem_01.tif")

#And convert it to a matrix:
elmat = matrix(raster::extract(tif_file,raster::extent(tif_file),buffer=1000),
               nrow=ncol(tif_file),ncol=nrow(tif_file))

#We first texture the map with sphere_shade and one of rayshader's built in textures, "desert."
#By default, the highlight is towards the NW.
elmat %>%
  sphere_shade(texture = "desert") %>%
  plot_map()

#sphere_shade can shift the sun direction to the NE:
elmat %>%
  sphere_shade(sunangle = 45, texture = "desert") %>%
  plot_map()

#detect_water and add_water adds a water layer to the map:
elmat %>%
  sphere_shade(sunangle = 45, texture = "desert") %>%
  add_water(detect_water(elmat), color="desert") %>%
  plot_map()

#And we can add a raytraced layer from that sun direction as well:
elmat %>%
  sphere_shade(sunangle = 45, texture = "desert") %>%
  add_water(detect_water(elmat), color="desert") %>%
  add_shadow(ray_shade(elmat,sunangle = 45)) %>%
  plot_map()

#And finally, we add an ambient occlusion layer:
elmat %>%
  sphere_shade(sunangle = 45, texture = "desert") %>%
  add_water(detect_water(elmat), color="desert") %>%
  add_shadow(ray_shade(elmat,sunangle = 45)) %>%
  add_shadow(ambient_shade(elmat)) %>%
  plot_map()