An Aside - The Penny Red

Although our main focus in using rayshader’s 3D plotting capabilities will be to render 3D interactive maps, it’s worth bearing in mind that rayshader can be used as a general purpose 3D visualisation tool.

So before we start rendering 3D maps, and before we are tempted to think that maps are the only thing we can plot with rayshader, let’s visualise something completely different: the colour of a Penny Red stamp…

We can obtain an appropriate image file from Wikipedia and save a local copy of it:

image.url = 'https://upload.wikimedia.org/wikipedia/commons/a/a4/PennyRed.jpeg'
pennyred_file = 'PennyRed.jpeg'

# Download the file from a specified web location to a specifically named file
download.file(image.url, pennyred_file)

3D Rendering of Colour Images Using `rayshader`

To use rayshader to render the image file, we need to obtain some “elevation” levels that will project some attribute of the image into the vertical z dimension.

One obvious candidate is the RGB colour value (we might alternatively render just the red, green or blue components) mapped to a single elevation value by regarding it as a base 256 encoded value:

library(raster)

pennyred_image =  jpeg::readJPEG(pennyred_file)
# Also:  png::readPNG(png_file)

# Create a raster file from the image
pennyred = raster(pennyred_file)

# Isolate the reg, green and blue components
pennyred_red = pennyred_image[,,1]
pennyred_green = pennyred_image[,,2]
pennyred_blue = pennyred_image[,,3]

#https://www.maptiler.com/news/2019/03/rgb-encoded-elevation-data-in-maptiler-cloud/
# height = -10000 + ((R * 256 * 256 + G * 256 + B) * 0.1)

# Use the RGB values as a base 256 elevation encoding
# then reduce the height with a base value
# We should really calculate the base value rather than use a 
# value determined by observation...
# The values() function sets the value of the pennyred raster
values(pennyred) = -16700 + (((255-pennyred_red ) * 256 * 256 +
                              (255-pennyred_green ) * 256 +
                              (255-pennyred_blue)) * 0.001)

# The pennyred raster now has values that encode RGB-as-elevation
pennyred

## class      : RasterLayer 
## band       : 1  (of  3  bands)
## dimensions : 234, 200, 46800  (nrow, ncol, ncell)
## resolution : 1, 1  (x, y)
## extent     : 0, 200, 0, 234  (xmin, xmax, ymin, ymax)
## crs        : NA 
## source     : memory
## names      : PennyRed 
## values     : 11.42209, 58.69265  (min, max)

To create an elevation matrix from the data, we might consider scaling from the raw RGB values:

elev_matrix_pennyred <- matrix(
      raster::extract(pennyred, raster::extent(pennyred)), 
      nrow = ncol(pennyred), ncol = nrow(pennyred)
)

The rayshader package takes a simple elevation matrix and renders it in 2 or 3 dimensional relief.

For example, here’s a simple 2D rendering:

library(rayshader)

elev_matrix_pennyred %>%
  sphere_shade(texture = "desert") %>%
  #add_overlay(pennyred_image) %>%
  plot_map()

  #plot_3d(elev_matrix_pennyred)

We can also add the original image back as an overlay. In this case, we lose the 3D effect:

rayshaded_penny_red = elev_matrix_pennyred %>%
  sphere_shade(texture = "desert") %>%
  add_overlay(pennyred_image)

rayshaded_penny_red %>%
  plot_map()

However, if we view the elevated image in a 3D plot, we can see the elevation map far more clearly:

# Configuration settings to allow us to render the WebGL 
options(rgl.useNULL = TRUE,
        rgl.printRglwidget = TRUE)

rgl::clear3d()

rayshaded_penny_red %>%
  plot_3d(elev_matrix_pennyred)

rgl::rglwidget()

An Aside - The Penny Red

3D Rendering of Colour Images Using rayshader

3D Rendering of Colour Images Using `rayshader`