getMeridianPoint_(lineString, extent, index) {
    const flatCoordinates = lineString.getFlatCoordinates();
    let bottom = 1;
    let top = flatCoordinates.length - 1;
    if (flatCoordinates[bottom] > flatCoordinates[top]) {
      bottom = top;
      top = 1;
    }
    const clampedBottom = Math.max(extent[1], flatCoordinates[bottom]);
    const clampedTop = Math.min(extent[3], flatCoordinates[top]);
    const lat = clamp(
      extent[1] + Math.abs(extent[1] - extent[3]) * this.lonLabelPosition_,
      clampedBottom,
      clampedTop,
    );
    const coordinate0 =
      flatCoordinates[bottom - 1] +
      ((flatCoordinates[top - 1] - flatCoordinates[bottom - 1]) *
        (lat - flatCoordinates[bottom])) /
        (flatCoordinates[top] - flatCoordinates[bottom]);
    const coordinate = [coordinate0, lat];
    const point = this.meridiansLabels_[index].geom;
    point.setCoordinates(coordinate);
    return point;
  }
@param {LineString} lineString Meridian
@param {import("../extent.js").Extent} extent Extent.
@param {number} index Index.
@return {Point} Meridian point.
@private