R/icosphere.R

In sphereTessellation: Delaunay and Voronoï Tessellations on the Sphere

#' @title Icosphere
#' @description Returns the mesh of an icosphere.
#'
#' @param x,y,z coordinates of the center
#' @param r radius
#' @param iterations number of iterations (the icosphere is obtained by
#'   iteratively subdividing the faces of an icosahedron)
#'
#' @return A \strong{rgl} mesh (class \code{mesh3d}).
#' @export
#' @importFrom rgl icosahedron3d subdivision3d
#'
#' @examples
#' library(sphereTessellation)
#' library(rgl)
#' mesh <- icosphereMesh()
#' open3d(windowRect = 50 + c(0, 0, 512, 512))
#' shade3d(mesh, color = "navy")
icosphereMesh <- function(x = 0, y = 0, z = 0, r = 1, iterations = 3L) {
  stopifnot(isNumber(x), isNumber(y), isNumber(z))
  stopifnot(isPositiveNumber(r))
  stopifnot(isStrictPositiveInteger(iterations))
  sphere <- subdivision3d(icosahedron3d(), depth = iterations)
  vs <- sphere[["vb"]][1L:3L, ]
  h <- sqrt(apply(vs, 2L, function(x) sum(x * x)))
  # vs[1L, ] <- vs[1L, ] / h
  # vs[2L, ] <- vs[2L, ] / h
  # vs[3L, ] <- vs[3L, ] / h
  sphere[["vb"]] <- rbind(r*vs + h*c(x, y, z), h)
  sphere[["normals"]] <- vs
  sphere
}