| ellipsePoints {sfsmisc} | R Documentation |
Compute points on (the boundary of) an ellipse which is given by elementary geometric parameters.
ellipsePoints(a, b, alpha = 0, loc = c(0, 0), n = 201)
a,b |
length of half axes in (x,y) direction. |
alpha |
angle (in degrees) giving the orientation of the ellipse,
i.e., the original (x,y)-axis ellipse is rotated by angle. |
loc |
center (LOCation) of the ellipse. |
n |
number of points to generate. |
A numeric matrix of dimension n x 2, each row containing the
(x,y) coordinates of a point.
Martin Maechler, March 2002.
the ‘ellipse’ package and ellipsoidhull
and ellipsoidPoints
in the ‘cluster’ package.
## Simple Ellipse, centered at (0,0), x-/y- axis parallel:
ep <- ellipsePoints(2,5)
str(ep)
plot(ep, type="n",asp=1) ; polygon(ep, col = 2)
## rotate by 30 degrees :
plot(ellipsePoints(2,5, alpha = 30), asp=1)
abline(h=0,v=0,col="gray")
abline(a=0,b= tan( 30 *pi/180), col=2, lty = 2)
abline(a=0,b= tan(120 *pi/180), col=3, lty = 2)
if(dev.interactive()) {
## Movie : rotating ellipse :
nTurns <- 4 # #{full 360 deg turns}
for(al in 1:(nTurns*360)) {
ep <- ellipsePoints(3,6, alpha=al, loc = c(5,2))
plot(ep,type="l",xlim=c(-1,11),ylim=c(-4,8),
asp=1, axes = FALSE, xlab="", ylab="")
}
## Movie : rotating _filled_ ellipse {less nice to look at}
for(al in 1:180) {
ep <- ellipsePoints(3,6, alpha=al, loc = c(5,2))
plot(ep,type="n",xlim=c(-1,11),ylim=c(-4,8),
asp=1, axes = FALSE, xlab="", ylab="")
polygon(ep,col=2,border=3,lwd=2.5)
}
}# only if interactive