[R-sig-teaching] plot an angle of 450 degrees and adding a circular arrow to it

[Albyn Jones]

Here is a quickly written and barely tested function.  You might want to
add a final position vector,
color, lwd, lty, etc.  It assumes the angle is given in degrees, and checks
the sign of the angle to draw
in the correct direction.

albyn
=====================================================================

DrawAngle  <- function(theta,r=1){
    # assumes angles given in degrees, not radians
    theta <- 2*pi*theta/360
    plot(0,0, xlim=c(-2,2),ylim=c(-2,2))
    abline(h=0)
    abline(v=0)
    sgn <- 1
    if(theta <0) {
        sgn  <- -1
        theta <- -theta
        }
    Theta <-  sgn*seq(0,theta,.01)
    if(theta > 2*pi) r <- seq(1,1.1,along.with=Theta)
    x <- r*cos(Theta)
    y <- r*sin(Theta)
    lines(x,y)
    n <- length(x)
    arrows(x[n-1],y[n-1],x[n],y[n])
}

On Mon, Oct 20, 2014 at 1:47 AM, Steven Stoline <sstoline at gmail.com> wrote:

> Dear All:
>
> I am wondering if someone can show me how to plot an angles around the
> center of a unit circle with x-y vertices added to it.
>
> Also how to add arrows showing the size and the direction of angle(s).
>
> Examples: 135 degrees and 450 degrees angles.
>
> with many thanks
> Steven
>
> --
> Steven M. Stoline
> 1123 Forest Avenue
> Portland, ME 04112
> sstoline at gmail.com
>
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