There are some slippy map tile providers that can serve you tiles that represent Digital Elevation Model (DEM) data, rather than map imagery. This is the kind of data you want to make 3D maps with rayshader or quadmesh. Mapbox have an API for DEM tiles called Mapbox Terrain-RGB that we will use in this example.
Sign up for Mapbox and generate yourself an API access token. For my testing I have used a ‘public’ token with styles:tiles. Add that API token to your .Renviron file (in your home directory) as:
MAPBOX_API_KEY=<YOUR REALLY LONG TOKEN HERE>How many tiles?
library(slippymath)
tibrogargan<- c(xmin = 152.938485, ymin = -26.93345, xmax = 152.956467,
ymax = -26.921463)
slippymath::bbox_tile_query(tibrogargan)
#> x_min y_min x_max y_max y_dim x_dim total_tiles zoom
#> 1 3 2 3 2 1 1 1 2
#> 2 7 4 7 4 1 1 1 3
#> 3 14 9 14 9 1 1 1 4
#> 4 29 18 29 18 1 1 1 5
#> 5 59 36 59 36 1 1 1 6
#> 6 118 73 118 73 1 1 1 7
#> 7 236 147 236 147 1 1 1 8
#> 8 473 295 473 295 1 1 1 9
#> 9 947 591 947 591 1 1 1 10
#> 10 1894 1183 1894 1183 1 1 1 11
#> 11 3788 2366 3788 2366 1 1 1 12
#> 12 7576 4732 7576 4732 1 1 1 13
#> 13 15152 9464 15153 9465 2 2 4 14
#> 14 30304 18929 30306 18931 3 3 9 15
#> 15 60609 37859 60612 37862 4 4 16 16
#> 16 121219 75719 121225 75724 6 7 42 17
#> 17 242438 151439 242451 151449 11 14 154 18It’s a small area so we don’t need a lot. 9 tiles as zoom 15 looks good. Let’s get the tile grid.
Now we’ll fetch the tiles from Mapbox.
library(glue)
library(purrr)
library(curl)
mapbox_query_string <-
paste0("https://api.mapbox.com/v4/mapbox.terrain-rgb/{zoom}/{x}/{y}.jpg90",
"?access_token=",
Sys.getenv("MAPBOX_API_KEY"))
tibro_tiles <-
pmap(.l = tibrogargan_grid$tiles,
zoom = tibrogargan_grid$zoom,
.f = function(x, y, zoom){
outfile <- glue("{x}_{y}.jpg")
curl_download(url = glue(mapbox_query_string),
destfile = outfile)
outfile
}
)We composite the images to raster with compose_tile_grid and view the raster:
tibrogargan_raster <- slippymath::compose_tile_grid(tibrogargan_grid, tibro_tiles)
raster::plot(tibrogargan_raster)
We see this mix of layers including a psychedelic blue-green RGB landscape because in terrain-rgb tiles, the RGB values to provide additional precision to the elevation information. We’ll decode this in the next section.
Mapbox provide a formula to decode the RGB values to elevation. This was implemented in the function below by Michael Sumner.
decode_elevation <- function(dat) {
height <- -10000 + ((dat[[1]] * 256 * 256 + dat[[2]] * 256 + dat[[3]]) * 0.1)
raster::projection(height) <- "+proj=merc +a=6378137 +b=6378137"
height
}When we apply it to tibrogargan_raster we get:
*ceramic - A wrapper for quadmesh + slippymath for making 3D surfaces textured with satellite tiles.
