ggplot绘制嵌套圆：限制坐标轴后多边形异常截断或消失

我尝试使用ggforce::geom_circle在ggplot对象中绘制两个嵌套圆，正常绘制时显示正常，但当使用scale_x/scale_y或coord_cartesian限制x、y坐标轴范围后，多边形要么被异常截断，要么完全不显示。

复现代码 #

library(ggforce)

set.seed(4242)
dd <- data.frame(x = runif(20, min=0, max=2),
                 y = runif(20, min=0, max=2))


ggplot(dd) +
  
  geom_circle(aes(x0 = 0, y0 = 0, r = 2),
              inherit.aes = FALSE, fill = 'grey90',
              lty = 'dotted', color = 'grey70', alpha = 0.5) +
  geom_circle(aes(x0 = 0, y0 = 0, r = 0.5),
              inherit.aes = FALSE, fill = 'grey70',
              lty = 'dotted', color = 'grey50', alpha = 0.5) +
  geom_point(aes(x = x, y = y), size=1)+
  geom_abline(intercept = 0, slope=0.5, col='red') +
  geom_abline(intercept = 0, slope=1.8, col='blue') +
  #scale_x_continuous(expand = c(0, 0), limits = c(0, 2)) +
  #scale_y_continuous(expand = c(0, 0), limits = c(0, 2)) +
  coord_cartesian(xlim = c(0,2.5),   # 尝试两种坐标轴限制方式
                  ylim = c(0,2.5)) +
  theme_bw() +
  theme_update(legend.position = 'bottom') +
  theme_update(aspect.ratio=1) 

会话信息 #

R version 4.1.1 (2021-08-10)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 17763)

Matrix products: default

locale:
[1] LC_COLLATE=English_United States.1252 
[2] LC_CTYPE=English_United States.1252   
[3] LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C                           
[5] LC_TIME=English_United States.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] ggforce_0.4.1 ggplot2_3.3.6

loaded via a namespace (and not attached):
 [1] Rcpp_1.0.7       magrittr_2.0.2   MASS_7.3-54      tidyselect_1.1.2
 [5] munsell_0.5.0    colorspace_2.0-2 R6_2.5.1         rlang_1.0.2     
 [9] fansi_1.0.2      dplyr_1.0.8      tools_4.1.1      grid_4.1.1      
[13] gtable_0.3.0     utf8_1.2.2       cli_3.2.0        DBI_1.1.2       
[17] withr_2.5.0      ellipsis_0.3.2   digest_0.6.28    assertthat_0.2.1
[21] tibble_3.1.6     lifecycle_1.0.1  crayon_1.5.0     farver_2.1.0    
[25] tweenr_1.0.2     purrr_0.3.4      vctrs_0.3.8      glue_1.6.2      
[29] labeling_0.4.2   polyclip_1.10-4  compiler_4.1.1   pillar_1.7.0    
[33] generics_0.1.2   scales_1.1.1     pkgconfig_2.0.3 

解决方案 #

这个问题的核心是geom_circle通过多边形路径模拟圆形，坐标轴范围限制会触发ggplot的图形裁剪逻辑，导致圆形顶点被截断。以下两种方法可解决：

方法一：用coord_fixed替代aspect.ratio=1 #

coord_fixed会先保持图形宽高比，再应用坐标范围限制，不会提前裁剪圆形顶点，能完整显示图形：

library(ggforce)

set.seed(4242)
dd <- data.frame(x = runif(20, min=0, max=2),
                 y = runif(20, min=0, max=2))

ggplot(dd) +
  geom_circle(aes(x0 = 0, y0 = 0, r = 2),
              inherit.aes = FALSE, fill = 'grey90',
              lty = 'dotted', color = 'grey70', alpha = 0.5) +
  geom_circle(aes(x0 = 0, y0 = 0, r = 0.5),
              inherit.aes = FALSE, fill = 'grey70',
              lty = 'dotted', color = 'grey50', alpha = 0.5) +
  geom_point(aes(x = x, y = y), size=1)+
  geom_abline(intercept = 0, slope=0.5, col='red') +
  geom_abline(intercept = 0, slope=1.8, col='blue') +
  coord_fixed(xlim = c(0,2.5), ylim = c(0,2.5), ratio = 1) +
  theme_bw() +
  theme(legend.position = 'bottom')

方法二：关闭坐标裁剪（可选） #

如果必须使用coord_cartesian，可通过clip="off"关闭裁剪，同时调整绘图边距避免图形超出画布：

ggplot(dd) +
  geom_circle(aes(x0 = 0, y0 = 0, r = 2),
              inherit.aes = FALSE, fill = 'grey90',
              lty = 'dotted', color = 'grey70', alpha = 0.5) +
  geom_circle(aes(x0 = 0, y0 = 0, r = 0.5),
              inherit.aes = FALSE, fill = 'grey70',
              lty = 'dotted', color = 'grey50', alpha = 0.5) +
  geom_point(aes(x = x, y = y), size=1)+
  geom_abline(intercept = 0, slope=0.5, col='red') +
  geom_abline(intercept = 0, slope=1.8, col='blue') +
  coord_cartesian(xlim = c(0,2.5), ylim = c(0,2.5), clip = "off") +
  theme_bw() +
  theme(legend.position = 'bottom',
        plot.margin = margin(10, 10, 10, 10))

内容的提问来源于stack exchange，提问作者maycca