如何增加rgl中spheres3d的光滑度

Question

當我使用rgl::spheres3d() ，渲染的球體具有笨重的刻面邊緣。

spheres = data.frame(x = c(1,2,3), y = c(1,3,1),
                     color = c("#992222" , "#222299", "#229922"))
open3d()
spheres3d(spheres$x, spheres$y, radius = 1, color = spheres$color)

設置material3d(smooth = TRUE, line_antialias = TRUE)不會改善這一點。 增加半徑也無濟於事。 有沒有辦法增加它們的平滑度？

Answer 1

雖然rgl::spheres3d()不能這樣做，但另一種方法是編寫自己的函數來繪制球體。 這是一個將球體渲染為以相等緯度和經度間隔的四邊形網格的函數。

drawSphere = function(xc=0, yc=0, zc=0, r=1, lats=50L, longs=50L, ...) {
  #xc,yc,zc give centre of sphere, r is radius, lats/longs for resolution
  vertices = vector(mode = "numeric", length = 12L * lats * longs)
  vi = 1L
  for(i in 1:lats) {
    lat0 = pi * (-0.5 + (i - 1) / lats)
    z0   = sin(lat0)*r
    zr0  = cos(lat0)*r
    lat1 = pi * (-0.5 + i / lats)
    z1   = sin(lat1)*r
    zr1  = cos(lat1)*r
    for(j in 1:longs) {
      lng1 = 2 * pi *  (j - 1) / longs
      lng2 = 2 * pi *  (j) / longs
      x1 = cos(lng1)
      y1 = sin(lng1)
      x2 = cos(lng2)
      y2 = sin(lng2)
      vertices[vi] = x1 * zr0 + xc;    vi = vi + 1L
      vertices[vi] = y1 * zr0 + yc;    vi = vi + 1L 
      vertices[vi] = z0 + zc;          vi = vi + 1L
      vertices[vi] = x1 * zr1 + xc;    vi = vi + 1L
      vertices[vi] = y1 * zr1 + yc;    vi = vi + 1L
      vertices[vi] = z1 + zc;          vi = vi + 1L
      vertices[vi] = x2 * zr1 + xc;    vi = vi + 1L
      vertices[vi] = y2 * zr1 + yc;    vi = vi + 1L
      vertices[vi] = z1 + zc;          vi = vi + 1L
      vertices[vi] = x2 * zr0 + xc;    vi = vi + 1L
      vertices[vi] = y2 * zr0 + yc;    vi = vi + 1L
      vertices[vi] = z0 + zc;          vi = vi + 1L
    }
  }
  indices = 1:(length(vertices)/3)
  shade3d(qmesh3d(vertices, indices, homogeneous=F), ...)
}

應該可以對此進行改進，例如使用icospheres （ 即將球體拉伸為拉伸的二十面體）。 但是這個版本已經吸引了相當不錯的領域，如果你做足夠多的拉特和多頭。

實際功能的一個例子：

spheres = data.frame(x = c(1,2,3), y = c(1,3,1), z=c(0,0,0), color = c("#992222" , "#222299", "#229922"))
open3d() 
material3d(ambient = "black", specular = "grey60", emission = "black", shininess = 30.0)
rgl.clear(type = "lights")
rgl.light(theta = -30, phi = 60, viewpoint.rel = TRUE, ambient = "#FFFFFF", diffuse = "#FFFFFF", specular = "#FFFFFF", x = NULL, y = NULL, z = NULL)
rgl.light(theta = -0, phi = 0, viewpoint.rel = TRUE,  diffuse = "gray20", specular = "gray25", ambient = "gray80", x = NULL, y = NULL, z = NULL)
sapply(1:NROW(spheres), function(i) 
  drawSphere(spheres$x[i], spheres$y[i], spheres$z[i], r=1, lats = 400, longs = 400, color=spheres$color[i]))

Answer 2

一種更簡單的方法是使用subdivision3d() 。 在這里， depth=4並不是那么順利，但你可以增加它。

library(rgl)
sphere <- subdivision3d(cube3d(),depth=4)
sphere$vb[4,] <- apply(sphere$vb[1:3,], 2, function(x) sqrt(sum(x^2)))
open3d()
shade3d(sphere, col="red")

Answer 3

這並不容易; 我想如果你想這樣做，你將不得不這樣做

• 從CRAN下載rgl源代碼
• 解壓縮並修改src/sphereSet.cpp第24行，這是當前的

sphereMesh.setGlobe(16,16);

調用具有更大值的函數（此函數在src/SphereMesh.cpp第25行定義;參數為in_segments和in_sections ......）

• 從源代碼構建/安裝包; 這不僅需要標准的編譯工具，還需要相關的OpenGL庫（在Debian Linux操作系統上你可以使用sudo apt-get build-dep r-cran-rgl來獲取它們，我認為...）

我沒試過這個。 祝你好運......或者，您可以要求軟件包維護者通過materials3d或其他方式將其設置為可設置參數...

Answer 4

這是我使用persp3d.function()

sphere.f <- function(x0 = 0, y0 = 0, z0 = 0, r = 1, n = 101, ...){
  f <- function(s, t) cbind(r * cos(s) * cos(t) + x0,
                            r * sin(s) * cos(t) + y0, 
                            r * sin(t) + z0)
  persp3d(f, slim = c(0, pi), tlim = c(0, 2*pi), n = n, add = T, ...)
}

sphere.f(col = rainbow)

Answer 5

擴展了烏賊44的優秀答案 ，我發現一個更好的參數化 - 即它在極點沒有缺陷（圖像中的淺藍色球體上的黑色偽影）。

library(rgl)
sphere.f <- function(x0 = 0, y0 = 0, z0 = 0, r = 1, n = 101, ...){
  f <- function(s, t) cbind(r * cos(s) * cos(t) + x0,
                            r * sin(s) * cos(t) + y0, 
                            r * sin(t) + z0)
  persp3d(f, slim = c(0, pi), tlim = c(0, 2*pi), n = n, add = T, ...)
}


sphere1.f <- function(x0 = 0, y0 = 0, z0 = 0, r = 1, n = 101, ...){
  f <- function(s,t){ 
    cbind(   r * cos(t)*cos(s) + x0,
             r *        sin(s) + y0,
             r * sin(t)*cos(s) + z0)
  }
  persp3d(f, slim = c(-pi/2,pi/2), tlim = c(0, 2*pi), n = n, add = T, ...)
}


sphere.f( -1.5,0, col = "lightblue")
sphere1.f( 1.5,0, col = "pink")

圖片：

Answer 6

另一種可能性是使用Rvcg包的vcgSphere函數。

library(Rvcg)
sphr <- vcgSphere(subdivision = 4) # unit sphere centered at (0,0,0)
library(rgl)
shade3d(sphr, color="red")

# sphere with given radius and center
radius <- 0.5
center <- c(2,1,1)
sphr2 <- translate3d(
  scale3d(sphr, radius, radius, radius), 
  center[1], center[2], center[3])
shade3d(sphr2, color="green")