code: function (coord) {
          var radius = coord[0];
          var radian = coord[1] / 180 * Math.PI;
          var x = Math.cos(radian) * radius + this.cx;
          // Inverse the y
          var y = -Math.sin(radian) * radius + this.cy;
  
          return [x, y];
      }
docs: Convert a (radius, angle) coord to (x, y) point
  @param {Array.<number>} coord
  @return {Array.<number>}