geom_ellipse_cm: Geom Layer for Ellipse with Absolute Size
In plothelper: New Plots Based on 'ggplot2' and Functions to Create Regular Shapes

Description Usage Arguments Details Examples

This layer uses centimeter as unit to draw ellipse so that its size and shape will not be influenced by the coordinate systems (even when a polar system is used).

geom_ellipse_cm(
  mapping = NULL,
  data = NULL,
  stat = "identity",
  position = "identity",
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE,
  ...
)

`mapping`	aes mapping.
`data`	data.
`stat`	stat.
`position`	position.
`na.rm`	logical, whether to remove NA values.
`show.legend`	whether to show legend.
`inherit.aes`	logical, whether to inherit aes from ggplot().
`...`	additional parameters.

Accepted properties are:

(1) rcm radius in centimeter.
(2) ab it means to what extent radius a of an ellipse is larger than radius b. However, its true meaning is the aspect ratio which is used by gridExtra::ellipseGrob and indicates the extent to which y dimension is flattened. So, say, when ab = 2, radius a is larger than b, but it is not exactly 2 times larger.
(3) color color of the the outline.
(4) fill color inside the shape.
(5) alpha alpha of color and fill.
(6) size line width of the outline.
(7) linetype line type.
(8) angle angle of rotation from 0 degree and in anti-clockwise direction.
(9) n the number of points to draw the shape. Note: it must be written inside the aes(...) function.
(10) x x coordinates of middle points.
(11) y y coordinates of middle points.

library(ggplot2)
dat=data.frame(x=c(1, 3, 5, 7, 9), y=rep(5, 5)) 
ggplot(dat)+xlim(0, 11)+ylim(1, 9)+
	geom_ellipse_cm(aes(x=x, y=y), fill="red", ab=seq(1, 4, length.out=5))  
ggplot(dat)+xlim(0, 11)+ylim(1, 9)+
	geom_ellipse_cm(aes(x=x, y=y, fill=factor(x)), ab=3, angle=c(0, pi/4, pi/3, pi/2, 0.75*pi))