code: function (data, clamp) {
          return this.coordToPoint([
              this._radiusAxis.dataToRadius(data[0], clamp),
              this._angleAxis.dataToAngle(data[1], clamp)
          ]);
      }
docs: Convert a single data item to (x, y) point.
  Parameter data is an array which the first element is radius and the second is angle
  @param {Array.<number>} data
  @param {boolean} [clamp=false]
  @return {Array.<number>}