如何填充由直线和曲线创建的几何图形？

Question

我正在尝试用不同的颜色填充下图中的 3 个三角形。

data = data.frame(x=c(125), y=c(220)) #this data is just to be able to use gplot to draw figures

ggplot(data, aes(x = x, y = y)) + 
  xlim(0,250) +
  ylim(-250, 0) +
  geom_curve(x = 33, xend = 223, y = -100, yend = -100, curvature = -.65) +
  geom_segment(x=128, xend = 33, y=-208, yend = -100) +
  geom_segment(x=128, xend = 223, y=-208, yend = -100) +
  geom_segment(x=128, xend = 159.67, y=-208, yend = -45) +
  geom_segment(x=128, xend = 96.33, y=-208, yend = -45) +
  coord_fixed()

我该怎么做？

Answer 1

简短的回答：这是一个非常邪恶的 hack。

现在让我们详细说明：正如 especially in this GitHub thread 中所讨论的，无法访问 geom_curve 产生的坐标（它使用 CurveGrob 进行绘图，"These values are all calculated at draw time" [ @thomasp85]）。它的 'calculation at draw time behaviour' 的一个效果如下所示 - 如果您添加或不添加 coord_plot 会有所不同。这与 geom_spline 不同：添加 coord_fixed 不会更改坐标。

参见下面的第一和第二图：红色曲线是用 geom_curve 创建的 - 它与 geom_segment 失去联系行...

@thomasp85 在 GitHub 线程中建议可以改用他的包 ggforce。现在，要真正控制曲率，需要使用 geom_bspline 并调整曲率。

一旦找到曲率，就可以使用 ggplot_build 对象中的坐标。我们可以根据这些坐标计算多边形（这也不是很简单，因为需要创建切割并为正确的 'edges' 添加点）。见下文。

library(tidyverse)
library(ggforce)

mydata = data.frame(x = 128, xend = c(33, 223, 159.67, 96.33), y = -208, yend = c(-100,-100,-45,-45))

#for spline control points.
my_spline <- data.frame(x = c(33, 128, 223), y = c(-100, 24,-100))

接下来我演示'绘制时计算（红色曲线）和'direct calculation':

的区别

和coord_fixed_{红色和黑色曲线都接触线段}

ggplot(mydata) + 
  geom_curve(aes(x = 33, xend = 223, y = -100, yend = -100), curvature = -.65, color = 'red') +
  geom_segment(aes(x = x, xend = xend, y = y, yend = yend)) +
  geom_bspline(data = my_spline, aes(x, y )) +
  coord_fixed()

没有coord_fixed _{红色曲线不接触线段，但黑色曲线仍然接触}

ggplot(mydata) + 
  geom_curve(aes(x = 33, xend = 223, y = -100, yend = -100), curvature = -.65, color = 'red') +
  geom_segment(aes(x = x, xend = xend, y = y, yend = yend)) +
  geom_bspline(data = my_spline, aes(x, y ))

# Final hack
# Get x/y coordinates from ggplot_build
p <- ggplot(mydata) + 
  geom_bspline(data = my_spline, aes(x, y )) 

pb <- ggplot_build(p)$data[[1]]

#create groups for fill
data_polygon <- data.frame(x = pb[['x']], y = pb[['y']]) %>% 
  mutate(cut_poly = cut(x, c(-Inf, 96.33, 159.67, Inf), labels = letters[1:3])) 

#add corner points - repeat extremes from b, otherwise there will be a gap
data_add <- data_polygon %>% 
  filter(cut_poly == 'b') %>% 
  slice(which.min(x), which.max(x)) %>% 
  mutate(cut_poly = letters[c(1,3)]) %>%
  bind_rows(data.frame(x = 128, y = -208, cut_poly = letters[1:3], stringsAsFactors = FALSE)) %>% 
  arrange(x) #important to arrange, otherwise you get irregular polygons

data_plot <- rbind(data_polygon,data_add)

ggplot(data_plot) +
  geom_polygon(aes(x, y, fill = cut_poly), color = 'black')

^{由 reprex package (v0.3.0)}

于 2019-12-05 创建

Answer 2

您可以访问在 ggforce 包中生成的几何图形的曲线数据，这使得从曲线创建多边形的工作变得更加容易。

然后您可以使用 geom_polygon 绘制单个多边形并用不同的颜色填充它们

library(ggforce)
p1 <- ggplot() + geom_arc(aes(x0 = 125, y0 = -200, r = 100, start = -pi/3, end = -pi/9))
p2 <- ggplot() + geom_arc(aes(x0 = 125, y0 = -200, r = 100, start = -pi/9, end = pi/9))
p3 <- ggplot() + geom_arc(aes(x0 = 125, y0 = -200, r = 100, start = pi/9, end = pi/3))


df_poly1 <- rbind(c(125,-200),data.frame(x = ggplot_build(p1)$data[[1]]$x,y = ggplot_build(p1)$data[[1]]$y),c(125,-200))
df_poly2 <- rbind(c(125,-200),data.frame(x = ggplot_build(p2)$data[[1]]$x,y = ggplot_build(p2)$data[[1]]$y),c(125,-200))
df_poly3 <- rbind(c(125,-200),data.frame(x = ggplot_build(p3)$data[[1]]$x,y = ggplot_build(p3)$data[[1]]$y),c(125,-200))

ggplot() + 
  geom_polygon(data = df_poly1, aes(x,y), fill = 'red') + 
  geom_polygon(data = df_poly2, aes(x,y), fill = 'blue') +
  geom_polygon(data = df_poly3, aes(x,y), fill = 'green')

这将产生这样的图像。

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