如何通過在spatstat中錨定中點來旋轉psp對象？

Question

我有一個線段圖案，這是在90度角到另一行：

require(spatstat)  
range <- c(0,10) 

owin <- owin(xrange = range, yrange = range) 

l1 <- psp(x0 = 8, x1 = 8, y0 = 2, y1 = 8, window = owin, marks = "l1") 
l2 <- psp(x0 = 6, x1 = 6, y0 = 2, y1 = 8, window = owin, marks = "l2") 
l3 <- psp(x0 = 4, x1 = 4, y0 = 2, y1 = 8, window = owin, marks = "l3") 
l4 <- psp(x0 = 2, x1 = 2, y0 = 2, y1 = 8, window = owin, marks = "l4") 

lines <- superimpose(l1, l2, l3, l4) 

main <- psp(x0 = 8, x1 = 0, y0 = 5, y1 = 5, window = owin, marks = "main") 

angles.psp(lines)*(180/pi) 
[1] 90 90 90 90 

這裏是一個視覺表示：

plot(x = range, y = range, type = "n", main = "", asp = 1, axes = F, xlab = "x", ylab = "y") 
plot(lines, col = "darkgrey", add = T) 
plot(main, col = "black", add = T) 
axis(1) 
axis(2, las = 2) 

現在我想旋轉lines以便它們在相同的點但以45度的角度穿過main。

lines.rotated <- rotate(lines, -0.7853982) 
angles.psp(lines.rotated)*(180/pi) 
[1] 45 45 45 45 

這工作，但angles.psp功能似乎單獨旋轉，而不是行窗口（owin）因爲我想要的。

plot(x = range, y = range, type = "n", main = "", asp = 1, axes = F, xlab = "x", ylab = "y") 
plot(lines, col = "darkgrey", add = T) 
plot(lines.rotated, col = "blue", add = T) 
plot(main, col = "black", add = T) 
axis(1) 
axis(2, las = 2) 

有一種方法，以相對於lines所有旋轉到main線，使得所述角度爲45度，但交叉點保持不變？

Answer 1

迫使它回到PSP只是爲了讓答案自給。下面的代碼應該產生你正在尋找的東西（如果這是一個有用的函數，我們可以要求Adrian（spatstat的維護者）在spatstat中包含它的改進版本）。 首先先決條件：

require(spatstat) 

linerotate.psp <- function(X, L, angle){ 
    ## Window: 
    W <- as.owin(X) 
    ## Empty psp object: 
    Y <- psp(numeric(0),numeric(0),numeric(0),numeric(0),W) 
    for(i in 1:X$n){ 
     ## Line i: 
     Xi <- X[i] 
     ## Crossing of line i and test line L in the window: 
     cross <- crossing.psp(L, Xi) 
     ## Rotate line if the crossing is non-empty: 
     if(npoints(cross)>0){ 
      m <- as.numeric(coords(cross)) 
      ## Move to crossing: 
      Xi <- affine(Xi, vec = -m) 
      ## Rotate: 
      Xi <- rotate(Xi, angle = angle) 
      ## Move back: 
      Xi <- affine(Xi, vec = m) 
      ## Restrict to non-rotated window: 
      Xi <- Xi[W] 
     } 
     ## Collect results: 
     Y <- superimpose(Y, Xi) 
    } 
    return(Y) 
} 

數據：

W <- square(10) 

x0 <- c(8,6,4,2) 
x1 <- x0 
y0 <- rep(2,4) 
y1 <- rep(8,4) 

lines <- psp(x0, y0, x1, y1, window = W) 

main <- psp(x0 = 8, x1 = 0, y0 = 5, y1 = 5, window = W) 

的旋轉數據和角度比較：

rotlines <- linerotate.psp(lines, main, angle = -pi/4) 
angles.psp(lines)*(180/pi) 
[1] 90 90 90 90 
angles.psp(rotlines)*(180/pi) 
[1] 45 45 45 45 

圖形：

plot(lines, col = "darkgrey") 
plot(main, col = "black", add = T) 
plot(rotlines, col = "blue", add = T) 

圖形與非水平測試線：

main <- psp(x0 = 0, x1 = 10, y0 = 3, y1 = 7, window = W) 
rotlines <- linerotate.psp(lines, main, angle = -pi/4) 

plot(lines, col = "darkgrey") 
plot(main, col = "black", add = T) 
plot(rotlines, col = "blue", add = T) 

Answer 2

我不確定是否有你的想法。

對於一個簡單的方法，可以從maptools elide是一個選項？

是這樣的：

library(maptools) 
# convert lines to SpatialLines 
slines <- as(lines, 'SpatialLines') 

plot(x = range, y = range, type = "n", main = "", asp = 1, axes = F, 
    xlab = "x", ylab = "y") 
plot(lines, col = "darkgrey", add = T) 
plot(main, col = "black", add = T) 
axis(1) 
axis(2, las = 2) 
# Plot slines object on top of your data 
plot(elide(slines, rotate = 45, center = c(5, 5)), add = T) 

# plot it 

但你可能想從旋轉線交叉線與主之間的交叉每一行。真的嗎？

如果是這樣，在每個PSP線上循環。對於PSP L4：

plot(elide(slines[4], rotate = 45, center = c(2, 5)), add = T) 

您可以用

as.psp.Lines(from, ..., window=NULL, marks=NULL, fatal)