Question

当我使用rgl::spheres3d()时，渲染的球体具有笨重的刻面边缘。

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)

设置material3d(smooth = TRUE, line_antialias = TRUE)并没有改善这一点。增加半径也无济于事。有没有办法增加它们的平滑度？

Answer 1

虽然rgl::spheres3d()无法做到这一点，但另一种方法是编写自己的函数来绘制球体。这是一个将球体渲染为以相等纬度和经度间隔的四边形网格的函数。

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), ...)
}

应该可以对此进行改进，例如使用icospheres（即将球体绘制为拉伸的二十面体）。但是如果你做足够长的话，这个版本已经吸引了很好的领域。

行动中的一个例子：

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

更简单的方法是使用subdivision3d()。在这里，depth=4并非一帆风顺，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

这并不容易;我想如果你想这样做，你将不得不

下载rgl source from CRAN
解压缩并修改src/sphereSet.cpp的第24行，目前

sphereMesh.setGlobe(16,16);

用一些较大的值调用函数（此函数在src/SphereMesh.cpp的第25行定义;参数为in_segments和in_sections ...）

从源代码构建/安装包;这不仅需要标准的编译工具，还需要相关的OpenGL库（在Debian Linux操作系统上你可以使用sudo apt-get build-dep r-cran-rgl来获取它们，我认为......）

我没试过这个。祝你好运......或者，您可以要求软件包维护者通过materials3d或其他方式将其设为可设置的参数......

Answer 4

以下是使用persp3d.function()

的方法

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

扩展cuttlefish44's excellent answer，我发现参数化效果更好 - 即极点没有缺陷（图像中浅蓝色球体上的黑色伪影）。

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")

图片：

Answer 6

另一种可能性是使用vcgSphere包的Rvcg函数。

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")

如何增加rgl中spheres3d的光滑度

6 个答案: