Preparing Elevation Data for Visualisation with rayshader

library(magrittr)
library(viridis)
library(raster)
library(rayshader)

Using the DEM available here which the source states is using the LV03 (a.k.a. EPSG 21781) coordinate reference system:

dem.200m.rast <- raster('~/Downloads/data/DHM200.asc')

crs(dem.200m.rast) <- crs('+init=epsg:21781')

Visualising the elevation raster with raster::plot

plot(dem.200m.rast, col = viridis(n = 1e3))

My extraction of the data from the raster to a matrix results in a distorted image:

dem.200m.mat <- raster::as.matrix(dem.200m.rast)

apply(X = dem.200m.mat, MARGIN = 2, FUN = rev) %>%
  t() %>%
    graphics::image(x = ., col = viridis(n = 1e3))

So I guess what we're seeing here is that raster::plot is adjusting the aspect ratio of the plot in accordance with the coordinate reference system while there is no such information associated with the matrix for image or rayshader to use (though I don't think either of these have the functionality to estimate such an adjustment from the CRS).

dem.200m.mat.t <- t(dem.200m.mat)

system.time(
  rayshader::sphere_shade(dem.200m.mat.t, texture = 'bw') %>%
  rayshader::plot_map()
)

##    user  system elapsed 
##   3.192   0.108   3.300