getMeridian_(lon, minLat, maxLat, squaredTolerance, index) {
    const flatCoordinates = meridian(
      lon,
      minLat,
      maxLat,
      this.projection_,
      squaredTolerance,
    );
    let lineString = this.meridians_[index];
    if (!lineString) {
      lineString = new LineString(flatCoordinates, 'XY');
      this.meridians_[index] = lineString;
    } else {
      lineString.setFlatCoordinates('XY', flatCoordinates);
      lineString.changed();
    }
    return lineString;
  }
@param {number} lon Longitude.
@param {number} minLat Minimal latitude.
@param {number} maxLat Maximal latitude.
@param {number} squaredTolerance Squared tolerance.
@return {LineString} The meridian line string.
@param {number} index Index.
@private