# Difference between revisions of "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', [, ],
{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(),
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();