d3.svg.line.radial = function() {

  var line = d3_svg_line(d3_svg_lineRadial);

  line.radius = line.x, delete line.x;

  line.angle = line.y, delete line.y;

  return line;

};

function d3_svg_lineRadial(points) {

  var point,

      i = -1,

      n = points.length,

      r,

      a;

  while (++i < n) {

    point = points[i];

    r = point[0];

    a = point[1] + d3_svg_arcOffset;

    point[0] = r * Math.cos(a);

    point[1] = r * Math.sin(a);

  }

  return points;

}