var data = [
    {innerRadius:50, outerRadius:100, angle:0},
    {innerRadius:50, outerRadius:100, angle:per},
    {innerRadius:50, outerRadius:100, angle:2*per},
    {innerRadius:50, outerRadius:100, angle:3*per},
    {innerRadius:50, outerRadius:100, angle:4*per},
    {innerRadius:50, outerRadius:100, angle:5*per},
    {innerRadius:50, outerRadius:100, angle:6*per},
    {innerRadius:50, outerRadius:100, angle:7*per},
    {innerRadius:50, outerRadius:100, angle:8*per}
];

var radialArea = d3.radialArea()
        .angle(function (d) {return d.angle;})
        .innerRadius(function(d){return d.innerRadius;})
        .outerRadius(function(d){return d.outerRadius;});