R：4D图，x，y，z，颜色

Question

你能举个例子说明如何使用rgl在x，y和z轴上绘制3个变量，用第四个变量绘制不同颜色的变量吗？

感谢

Answer 1

根据单独的功能使用persp和颜色的组合。这是一些示例代码：

## Create a simple surface  f(x,y) = -x^2 - y^2
## Colour the surface according to x^2 only
nx = 31; ny = 31
x = seq(-1, 1, length = nx)
y = seq(-1, 1, length = ny)
z = outer(x, y, function(x,y) -x^2  -y^2)
## Fourth dim
z_col = outer(x, y, function(x,y) x^2)

## Average the values at the corner of each facet
## and scale to a value in [0, 1].  We will use this
## to select a gray for colouring the facet. 
hgt = 0.25 * (z_col[-nx,-ny] + z_col[-1,-ny] + z_col[-nx,-1] + z_col[-1,-1])
hgt = (hgt - min(hgt))/ (max(hgt) - min(hgt))

##  Plot the surface with the specified facet colours.
persp(x, y, z, col = gray(1 - hgt))
persp(x, y, z, col=cm.colors(32)[floor(31*hgt+1)], theta=-35, phi=10)

这给出了：

<强> RGL

将上述技术用于rgl库是相当简单的：

library(rgl)
## Generate the data using the above commands
## New window
open3d()

## clear scene:
clear3d("all")

## setup env:
bg3d(color="#887777")
light3d()

surface3d(x, y, z, color=cm.colors(32)[floor(31*hgt+1)], alpha=0.5)

Answer 2

如果你在谈论在3d空间中绘制点并着色它们，那么？plot3d就有一个例子：

x <- sort(rnorm(1000))
y <- rnorm(1000)
z <- rnorm(1000) + atan2(x,y)
plot3d(x, y, z, col=rainbow(1000))

但是如果你的意思是用第4个变量（比如分组变量）给点着色，那么我们可以通过创建分组变量来修改上面的例子

grp <- gl(5, 200) ## 5 groups 200 members each
## now select the colours we want
cols <- 1:5

## Now plot
plot3d(x, y, z, col=cols[grp])

---

好的，这更像是你想要的吗？

X <- 1:10
Y <- 1:10
## Z is now a 100 row object of X,Y combinations
Z <- expand.grid(X = X, Y = Y)
## Add in Z1, which is the 3rd variable
## X,Y,Z1 define the surface, which we colour according to
## 4th variable Z2
Z <- within(Z, {
    Z1 <- 1.2 + (1.4 * X) + (-1.9 * Y)
    Z2 <- 1.2 + (1.4 * X) - (1.2 * X^2) + (1.9 * Y) + (-1.3 * Y^2)
    Z3 <- 1.2 + (1.4 * X) + (-1.9 * Y) + (-X^2) + (-Y^2)})
## show the data
head(Z)
## Set-up the rgl device
with(Z, plot3d(X, Y, Z1, type = "n"))
## Need a scale for Z2 to display as colours
## Here I choose 10 equally spaced colours from a palette
cols <- heat.colors(10)
## Break Z2 into 10 equal regions
cuts <- with(Z, cut(Z2, breaks = 10))
## Add in the surface, colouring by Z2
with(Z, surface3d(1:10,1:10, matrix(Z1, ncol = 10),
                   color = cols[cuts], back = "fill"))
with(Z, points3d(X, Y, Z1, size = 5)) ## show grid X,Y,Z1

以下是平面Z1弯曲（Z3）的修改。

## Set-up the rgl device plotting Z3, a curved surface
with(Z, plot3d(X, Y, Z3, type = "n"))
with(Z, surface3d(1:10,1:10, matrix(Z3, ncol = 10),
                   color = cols[cuts], back = "fill"))

我所做的事情Z2的详细信息可能并不重要，但我试图获得类似您链接的图表。

如果我还没有得到你想要的东西，你可以用一些示例数据编辑你的Q并让我们更好地了解你想要的东西吗？

HTH

Answer 3

看看example(points3d)。

r3d帮助页面显示了如何绘制轴。

x <- c(0, 10, 0, 0)
y <- c(0, 0, 100, 0)
z <- c(0, 0, 0, 1)
i <- c(1,2,1,3,1,4)
labels <- c("Origin", "X", "Y", "Z")
text3d(x,y,z,labels)
segments3d(x[i],y[i],z[i])

现在你添加一些点

dfr <- data.frame(x = 1:10, y = (1:10)^2, z = runif(10), col = rainbow(10))
with(dfr, points3d(x, y, z, col = col))