Draw a circle with ggplot2

Question

Maybe it is a silly question, but I couldn't find the answer in the handbook of ggplot2 nor with "aunt" google...

How do I plot a circle with ggplot2 as an additional layer if I have a middle point and a diameter? Thanks for your help.

Answer 1

A newer, better option leverages an extension package called ggforce that defines an explicity geom_circle.

But for posterity's sake, here's a simple circle function:

circleFun <- function(center = c(0,0),diameter = 1, npoints = 100){     r = diameter / 2     tt <- seq(0,2*pi,length.out = npoints)     xx <- center[1] + r * cos(tt)     yy <- center[2] + r * sin(tt)     return(data.frame(x = xx, y = yy)) } 

And a demonstration of it's use:

dat <- circleFun(c(1,-1),2.3,npoints = 100) #geom_path will do open circles, geom_polygon will do filled circles ggplot(dat,aes(x,y)) + geom_path() 

Answer 2

If the purpose is only to annotate a circle, you can simply use annotate with geometry "path". No need to create a data frame or function:

#g is your plot #r, xc, yc are the radius and center coordinates  g<-g+annotate("path",    x=xc+r*cos(seq(0,2*pi,length.out=100)),    y=yc+r*sin(seq(0,2*pi,length.out=100)))