code: function (point) {
          var dx = point[0] - this.cx;
          var dy = point[1] - this.cy;
          var angleAxis = this.getAngleAxis();
          var extent = angleAxis.getExtent();
          var minAngle = Math.min(extent[0], extent[1]);
          var maxAngle = Math.max(extent[0], extent[1]);
          // Fix fixed extent in polarCreator
          // FIXME
          angleAxis.inverse
              ? (minAngle = maxAngle - 360)
              : (maxAngle = minAngle + 360);
  
          var radius = Math.sqrt(dx * dx + dy * dy);
          dx /= radius;
          dy /= radius;
  
          var radian = Math.atan2(-dy, dx) / Math.PI * 180;
  
          // move to angleExtent
          var dir = radian < minAngle ? 1 : -1;
          while (radian < minAngle || radian > maxAngle) {
              radian += dir * 360;
          }
  
          return [radius, radian];
      }
docs: Convert a (x, y) point to (radius, angle) coord
  @param {Array.<number>} point
  @return {Array.<number>}