R trans3d 透視圖的 3D 到 2D 轉換

說明

使用 4x4 觀察變換矩陣將 3 維點投影到 2 維點。主要用於添加透視圖，例如 persp 。

用法

trans3d(x, y, z, pmat, continuous = FALSE, verbose = TRUE)

參數

x , y , z	等長的數值向量，指定 3D 空間中的點。
pmat	4 \times 4 觀察變換矩陣，適合使用齊次 4D 坐標 (x,y,z,t) 將 3D 坐標 (x,y,z) 投影到 2D 平麵；此類矩陣由 persp() 返回。
continuous	邏輯標誌，指定轉換是否應檢查轉換後的點是否連續，即它們不會跳過 a/0 不連續點。由於這些假設 (x,y,z) 說明連續曲線，因此默認值必須為 false。然而，在投影這樣的曲線的情況下，建議設置continuous=TRUE。
verbose	僅適用於 continuous=TRUE ，指示當點被切斷時是否應發出警告。

值

包含兩個組件的列表

x , y

3d 輸入 (x,y,z) 的投影 2d 坐標。

例子

## See  help(persp) {after attaching the 'graphics' package}
##      -----------

## Example for 'continuous = TRUE' (vs default):
require(graphics)
x <- -10:10/10 # [-1, 1]
y <- -16:16/16 # [-1, 1] ==> z = fxy := outer(x,y) is also in [-1,1]

p <- persp(x, y, fxy <- outer(x,y), phi = 20, theta = 15, r = 3, ltheta = -75,
           shade = 0.8, col = "green3", ticktype = "detailed")
## 5 axis-parallel auxiliary lines in x-y  and y-z planes :
lines(trans3d(-.5 , y=-1:1, z=min(fxy),  pmat=p), lty=2)
lines(trans3d(  0 , y=-1:1, z=min(fxy),  pmat=p), lty=2)
lines(trans3d(-1:1, y= -.7, z=min(fxy),  pmat=p), lty=2)
lines(trans3d( -1,  y= -.7, z=c(-1,1) ,  pmat=p), lty=2)
lines(trans3d( -1,  y=-1:1, z= -.5    ,  pmat=p), lty=2)
## 2 pillars to carry the horizontals below:
lines(trans3d(-.5 , y= -.7, z=c(-1,-.5), pmat=p), lwd=1.5, col="gray10")
lines(trans3d( 0  , y= -.7, z=c(-1,-.5), pmat=p), lwd=1.5, col="gray10")
## now some "horizontal rays" (going from center to very left or very right):
doHor <- function(x1, x2, z, CNT=FALSE, ...)
    lines(trans3d(x=seq(x1, x2, by=0.5), y= -0.7, z = z, pmat = p, continuous = CNT),
          lwd = 3, type="b", xpd=NA, ...)
doHor(-10,  0, z = -0.5, col = 2)  # x in [-10, 0] -- to the very left : fine
doHor(-.5,  2, z = -0.52,col = 4) # x in [-0.5, 2] only {to the right} --> all fine
## but now, x in [-0.5, 20] -- "too far" ==> "wrap around" problem (without 'continuous=TRUE'):
doHor(-.5, 20, z = -0.58, col = "steelblue", lty=2)
## but it is fixed with continuous = CNT = TRUE:
doHor(-.5, 20, z = -0.55, CNT=TRUE, col = "skyblue")

也可以看看

persp