Circle with ticks

Show ticks on the circumference of a circle.

The underlying JavaScript code

var brd = JXG.JSXGraph.initBoard('jxgbox',{axis:false,boundingbox:[-5,5,5,-5],keepaspectratio:true});

var p = brd.create('point', [0,0]);
var q = brd.create('point', [3,3]);
var circ = brd.create('circle', [p, q]);

// Create an empty curve
var ticks = brd.create('curve', [[0], [0]], 
             {strokeWidth: 1, 
              strokeColor: 'blue',
              strokeOpacity: 0.5});

// Make ticks out of the curve 
ticks.updateDataArray = function() {
    var cx = circ.center.X(),
        cy = circ.center.Y(),
        r = circ.Radius(),
        i, 
        ticklen = 0.3,           // Length of ticks in user space coordinates
        steps = 20,              // Number of ticks
        d = ticklen * 0.5,
        alpha = 2 * Math.PI / steps;

    this.dataX = [];
    this.dataY = [];
    for (i = 0; i < steps; i++) {
        // Start of a tick
        this.dataX.push( cx + (r - d)* Math.cos(i * alpha) );
        this.dataY.push( cy + (r - d) * Math.sin(i * alpha) );
        // End of tick
        this.dataX.push( cx + (r + d) * Math.cos(i * alpha) );
        this.dataY.push( cy + (r + d) * Math.sin(i * alpha) );
        // Interrupt the curve
        this.dataX.push( NaN );
        this.dataY.push( NaN );
    }
};
brd.update();