[R] RGL- Drawing Circle

[Duncan Murdoch]

On 09/01/2012 10:12 AM, gli wrote:
> hi, i want to draw a simple circle by using 3d  package RGL.
>
> i think i can use the command rgl.lines by studying the code  from:
>
> http://www.swiftless.com/tutorials/opengl/circle.html
>
> but is there a faster and easier way to do it??

The code on that page is much more complicated than necessary.  rgl will 
handle most of the calls to OpenGL; you just need to work out the 
geometry of the circle.

The difficulty you might have is whether you want something that appears 
to be a circle, or something that is a circle in user-coordinates.  For 
the latter, try something like:

n <- 300
theta <- seq(0, 2*pi, len=n)
x <- cos(theta)
y <- sin(theta)
z <- rep(0, n)
lines3d(x,y,z)

The former is harder; I'd probably do it by drawing a sphere and turning 
off lighting, but the overlaps don't look quite right if they aren't all 
the same colour:

spheres3d(rnorm(10), rnorm(10), rnorm(10), lit=FALSE, col=rainbow(10))

Duncan Murdoch