getParallel_(lat, minLon, maxLon, squaredTolerance, index) {
    const flatCoordinates = parallel(
      lat,
      minLon,
      maxLon,
      this.projection_,
      squaredTolerance,
    );
    let lineString = this.parallels_[index];
    if (!lineString) {
      lineString = new LineString(flatCoordinates, 'XY');
    } else {
      lineString.setFlatCoordinates('XY', flatCoordinates);
      lineString.changed();
    }
    return lineString;
  }
@param {number} lat Latitude.
@param {number} minLon Minimal longitude.
@param {number} maxLon Maximal longitude.
@param {number} squaredTolerance Squared tolerance.
@return {LineString} The parallel line string.
@param {number} index Index.
@private