rgl_globe.r

#' Title
#'
#' @param lonlatheight matrix or data.frame of lon,lat,height values
#' @param rad radius of sphere
#' @param exag exaggeration to apply to height values (added to radius)
#'
#' @return matrix
#' @export
llh2xyz <- function(lonlatheight, rad = 6378137.0, exag = 1) {
  cosLat = cos(lonlatheight[,2] * pi / 180.0)
  sinLat = sin(lonlatheight[,2] * pi / 180.0)
  cosLon = cos(lonlatheight[,1] * pi / 180.0)
  sinLon = sin(lonlatheight[,1] * pi / 180.0)
  
  rad <- (exag * lonlatheight[,3] + rad)
  x = rad * cosLat * cosLon
  y = rad * cosLat * sinLon
  z = rad * sinLat
  
  cbind(x, y, z)
}

## download Blue Marble
u <- "http://bl.ocks.org/rasmuse/raw/75fae4fee3354ec41a49d10fb37af551/0a91d6f75b95b90bda15a074ced45de454bb038f/world.topo.bathy.200411.3x540x270.png"
download.file(u, basename(u), mode = "wb")

library(raster)
library(rgl)
library(quadmesh)

## read RGB and set geo-spatial transform
r <- setExtent(brick(basename(u)), extent(-180, 180, -90, 90))  
## extract hex strings for each pixel (quad)
cols <- rgb(r[[1]][], r[[2]][], r[[3]][], max = 255) 

qm <- quadmesh(r[[1]])  ## the topology
qm$vb[3,] <- 0 ## drop the z
qm$vb[1:3, ] <- t(llh2xyz(t(qm$vb[1:3, ]))) ## geometry

## vis
shade3d(qm, col = rep(cols, each = 4), specular = "black")
light3d(cbind(0, 0, 0))
bg3d("black")

rgl_texture.r

## this time with textures

library(raster)
library(rgl)
library(quadmesh)
r <- setExtent(brick(basename(u)), extent(-180, 180, -90, 90))
## somewhat different is to forget about the geometry of the image
## and simply texture drape it on whatever surface
library(geosphere)
library(geometry)
pts <- randomCoordinates(2^12)
xyz <- llh2xyz(cbind(pts, 0))
tri <- geometry::convhulln(xyz)
library(rgl)
## rgl boilerplate: 
tm <- tetrahedron3d()
tm$vb <- t(cbind(xyz, 1))
tm$it <- t(tri)

tcoords <- xyFromCell(setExtent(r, extent(0, 1, 0, 1)), cellFromXY(r, pts))

## has to be "not-black", which is default . . . 
shade3d(tm, texture = basename(u), texcoords = tcoords[tm$it, ], col = "white", specular = "black")
light3d(cbind(0, 0, 0))
bg3d("black")

Interesting approach to actually represent it in 3D. Works well for orthographic and for "satellite" projections of course, but not for other projections (cylindrical, conical, etc) if I understand correctly?

Anyway, this approach could also be implemented with 3D WebGL I guess. But I haven't worked with WebGL myself.

Also, for me it's usually important to have coordinate transformations available for overlaying vector data, text, etc. This is a nice thing about the little d3 library I posted the other day -- it works seamlessly with d3's utilities for reprojecting vector data.

@rasmuse it can be done with planar projections too, I'm keen to learn WebGL approaches, I just need to lock away these data structures in R before I focus on that. Feeding spatial stuff to rgl requires most of the same work as feeding it to .js (I'm 99% certain . . .). And, sorry I missed your comment here, I just don't see any notification so I'm looking into that.