R：4D plot，x，y，z，colors

Question

你能否給我舉一個例子，說明如何使用rgl在軸x，y和z上繪製3個變量，用不同的顏色繪製第四個變量？

感謝

Answer 1

可以使用根據一個單獨的函數的persp的組合和顏色。下面是一些示例代碼：

## 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) 

這給：

RGL

這是相當簡單使用上述技術與RGL庫：

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

看看example(points3d)。

r3d幫助頁面顯示如何繪製座標軸。

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]) 

現在，添加一些點

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

Answer 3

有一個例子PLOT3D格式，如果你在談論3D空間繪製點和着色他們：

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

但如果你的意思是用第四個變量（例如分組變量）對點進行着色，然後我們可以通過創建一個分組變量來修改上面的例子

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，這是你想要的嗎？

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 

這裏的一個變型，其中平面表面是Z1彎曲（Z3）。

## 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")) 

的我做了什麼讓Z2可能並不重要的細節，但我試圖讓像你鏈接到圖形。

如果我還沒有得到你想要的東西，你可以用一些示例數據編輯你的Q，並給我們一個更好的想法，你想要什麼？

HTH