ellipsexy {plothelper}

Generating Coordinates of Multiple Ellipses or Circles

Description

If radius a is equal to radius b, then the shape will be a circle. Note: the shapes are correct only when ggplot2::coord_fixed() is used.

Usage

ellipsexy(
  x = 0,
  y = 0,
  a = 2,
  b = 1,
  start = 0,
  end = 6.283185,
  angle = 0,
  n = 40,
  xytype = "middle",
  fan = FALSE,
  group = TRUE,
  todf = TRUE,
  checks = TRUE
)

Arguments

x

the x coordinates of relative points. Its length can be larger than 1. See xytype.

y

the y coordinates of relative points. Its length can be larger than 1. See xytype.

a

the radius that is parallel to x-axis before rotation. Its length can be larger than 1.

b

the radius that is parallel to y-axis before rotation. Its length can be larger than 1.

start

default is 0. The angle of the starting point of the arc. Its length can be larger than 1. Note: "radian = degree * pi / 180".

end

default is 6.283185. The angle of the ending point of the arc. Its length can be larger than 1.

angle

default is 0. The rotation angle in radian. Its length can be larger than 1. Note: "radian = degree * pi / 180". The rotation direction is anti-clockwise.

n

default is 40. The number of points used to draw an arc. The larger, the smoother. It must at least be 4. However, when checks is FALSE, this check is ignored. NOTE: to draw a triangle, you must use ellipsexy(n=4, fan=FALSE), as the first and 4th points are so close. Similarly, to draw a rectangle, use ellipsexy(n=5, fan=FALSE).

xytype

should be one of "middle/center" (default), "bottomleft", "middleleft/left/centerleft". It indicates the type of argument of the middle point of an ellipse. If it is "middleleft", x and y are the middle-left coordinates before rotation. If it is "bottomleft", x and y are the coordinates of the bottom-left corner of the rectangle that walls the ellipse.

fan

default is FALSE. If it is TRUE, the coordinates of the middle of an ellipse is added to the output data frame. Meanwhile, if, say, you set n = 50, then n becomes 49 automatically because the last position is reserved for the middle. This helps draw a fan.

group

default is TRUE. It indicates whether to add a 3rd column named "g" to label the group number of each group of points. It is useful when using aes(...group=g) with 'ggplot2'.

todf

default is TRUE. It indicates whether to combine the output (a list) into a data frame.

checks

default is TRUE. It indicates whether to check input validity. Do not turn it off unless you are sure that the input is OK.

Value

if todf = TRUE, the output will be a data frame with coordinates of possibly several polygons, otherwise, it will be a list of data frames. Data frames have 2 columns named "x" and "y", and if group = TRUE, a third column named "g" is added indicating group numbers.

Examples

library(ggplot2)
dat1=ellipsexy(x=1, y=1, 
a=seq(1, 4, length.out=8), angle=seq(0, pi, length.out=8), 
	xytype="middleleft", n=30, todf=TRUE)		
ggplot()+coord_fixed()+
	geom_polygon(show.legend=FALSE, 
		data=dat1, aes(x=x, y=y, group=g, fill=factor(g)), alpha=0.3)