Base R has a function for plotting circles called "symbols". Unfortunately, the size of the circles is inconsistent across devices. This function plots circles whose radius is specified in used coordinates.
circles(x, y, radius, bg = NULL, fg = "white", ...)none, used for side effect
centers (x coordinate)
centers (y coordinate)
radius (in user coordinates)
background colour
foreground colour
passed to polygon, e.g. lwd
Simon Barthelme
hough_circle