Draw an Ellipse

Draw one or several ellipses on an existing plot. 

DrawEllipse(x = 0, y = x, radius.x = 1, radius.y = 0.5, rot = 0,
            nv = 100, border = par("fg"), col = par("bg"),
            lty = par("lty"), lwd = par("lwd"), plot = TRUE)

Arguments

x, y

the x and y co-ordinates for the centre(s) of the ellipse(s).

radius.x

a scalar or a vector giving the semi-major axis of the ellipse.

radius.y

a scalar or a vector giving the semi-minor axis of the ellipse.

rot

angle of rotation in radians.

nv

number of vertices to draw the ellipses.

border

color for borders. The default is par("fg"). Use border = NA to omit borders.

col

color(s) to fill or shade the annulus sector with. The default NA (or also NULL) means do not fill (say draw transparent).

lty

line type for borders and shading; defaults to "solid".

lwd

line width for borders and shading.

plot

logical. If TRUE the structure will be plotted. If FALSE only the points are calculated and returned. Use this if you want to combine several geometric structures to a single polygon.

Details

Use DegToRad if you want to define rotation angle in degrees.

Value

The function invisibly returns a list of the calculated coordinates for all shapes.

Author

Andri Signorell <andri@signorell.net>

Examples

par(mfrow=c(1,2))

Canvas()
DrawEllipse(rot = c(1:3) * pi/3, col=SetAlpha(c("blue","red","green"), 0.5) )


plot(cars)
m <- var(cars)
eig <- eigen(m)
eig.val <- sqrt(eig$values)
eig.vec <- eig$vectors

DrawEllipse(x=mean(cars$speed), y=mean(cars$dist), radius.x=eig.val[1] , radius.y=eig.val[2]
  , rot=acos(eig.vec[1,1]), border="blue", lwd=3)