如何在ggplot2中顯示曲線的方向？

Question

我有我繪製在R參數化的輪廓。我正在試圖做的是添加箭頭沿着曲線顯示哪個方向的曲線在會觀衆

下面是我使用生成曲線代碼：

library(ggplot2) 
library(grid) 
set.seed(9) 
T<-sort(runif(2^12,min=2^-5, max=16)) 

U<-function(t) exp(4*log(t) - 4*t)*(cos(log(t) + 3*t)) 
#Re(t^(4+1i)*t)*exp(-(4-3i)*t)) 
V<-function(t) exp(4*log(t) - 4*t)*(sin(log(t) + 3*t)) 
#Im(t^(4+1i)*t)*exp(-(4-3i)*t)) 


X<-sapply(T,U) 
Y<-sapply(T,V) 

df<-data.frame(X=X,Y=Y) 

p<-ggplot(data=df,aes(x = df$X, y = df$Y)) 

p+theme_bw()+ 
geom_path(size=1,color='blue',linetype=1) #+ 
#geom_segment(aes(xend=c(tail(X, n=-1), NA), yend=c(tail(Y, n=-1), NA)), 
#arrow=arrow(length=unit(0.2,"cm")),color='blue') 
dev.off() 

最後第一部分註釋掉：

#+ 
#geom_segment(aes(xend=c(tail(X, n=-1), NA), yend=c(tail(Y, n=-1), NA)), 
#arrow=arrow(length=unit(0.2,"cm")),color='blue') 

做類似我想要的東西，但箭頭是非常接近的，曲線最終看起來「模糊」，而不是導演。

這裏是曲線的模糊和非模糊的版本：

謝謝！

Answer 1

它看起來更好，如果箭頭爲more equally spaced along the curved path，如

library(ggplot2) 
library(grid) 
set.seed(9) 
T <- sort(runif(2^12,min=2^-5, max=16)) 
U <- function(t) exp(4*log(t) - 4*t)*(cos(log(t) + 3*t)) 
V <- function(t) exp(4*log(t) - 4*t)*(sin(log(t) + 3*t)) 
drough <- data.frame(x=sapply(T,U), y=sapply(T,V)) 


p <- ggplot(data = drough, aes(x = x, y = y)) + 
     geom_path() 

## because the parametric curve was generated with uneven spacing 
## we can try to resample more evenly along the path 
parametric_smoothie <- function(x, y, N=1e2, phase=1, offset=0) { 

    lengths <- c(0, sqrt(diff(x)^2 + diff(y)^2)) 
    l <- cumsum(lengths) 
    lmax <- max(l) 
    newpos <- seq(phase*lmax/N, lmax-phase*lmax/N, length.out = N) + offset*lmax/N 
    xx <- approx(l, x, newpos)$y 
    yy <- approx(l, y, newpos)$y 
    data.frame(x = xx, y = yy) 
} 

## this is a finer set of points 
dfine <- parametric_smoothie(X, Y, 20) 

gridExtra::grid.arrange(p + geom_point(data = drough, col="grey"), 
         p + geom_point(data = dfine, col="grey"), ncol=2) 

## now we use this function to create N start points for the arrows 
## and another N end points slightly apart to give a sense of direction 
relay_arrow <- function(x, y, N=10, phase = 0.8, offset = 1e-2, ...){ 

    start <- parametric_smoothie(x, y, N, phase) 
    end <- parametric_smoothie(x, y, N, phase, offset) 

    data.frame(xstart = start$x, xend = end$x, 
      ystart = start$y, yend = end$y) 

} 

breaks <- relay_arrow(drough$x, drough$y, N=20) 

p + geom_point(data = breaks, aes(xstart, ystart), col="grey98", size=2) + 
    geom_segment(data = breaks, aes(xstart, ystart, xend = xend, yend = yend), 
       arrow = arrow(length = unit(0.5, "line")), 
       col="red", lwd=1) 

Answer 2

一種方式來做到這一點是後畫他們。你也許可以得到方向通過使用角度的審美更好（如果它是很容易摸出）：

p<-ggplot(data=df,aes(x = X, y = Y)) 
p + 
    geom_path(size=1,color='blue',linetype=1)+ 
    geom_segment(data = df[seq(1, nrow(df), 20), ], aes(x = X, y = Y, xend=c(tail(X, n=-1), NA), yend=c(tail(Y, n=-1), NA)), 
    arrow=arrow(length=unit(0.2,"cm"), type = "closed"), color="blue", linetype = 0, inherit.aes = FALSE) 

注意封閉的箭頭類型。我不得不這樣做，所以他們不被解釋爲線條，因此當linetype = 0消失。

Answer 3

與你的代碼稍加修改試試這個（你不想通過具有點的數量較少妥協曲線的質量，並在同一時間，你想有較小的段數來繪製箭頭更好箭頭的質量）：

library(ggplot2) 
library(grid) 
set.seed(9) 
T<-sort(runif(2^12,min=2^-5, max=16)) 

U<-function(t) exp(4*log(t) - 4*t)*(cos(log(t) + 3*t)) 
#Re(t^(4+1i)*t)*exp(-(4-3i)*t)) 
V<-function(t) exp(4*log(t) - 4*t)*(sin(log(t) + 3*t)) 
#Im(t^(4+1i)*t)*exp(-(4-3i)*t)) 


X<-sapply(T,U) 
Y<-sapply(T,V) 

df<-data.frame(X=X,Y=Y) 
df1 <- df[seq(1,length(X), 8),] 

p<-ggplot(data=df,aes(x = df$X, y = df$Y)) 

p+theme_bw()+ 
    geom_path(size=1,color='blue',linetype=1) + 
    geom_segment(data=df1,aes(x=X, y=Y, xend=c(tail(X, n=-1), NA), yend=c(tail(Y, n=-1), NA)), 
      arrow=arrow(length=unit(0.3,"cm"),type='closed'),color='blue') 
#dev.off()