function parallel(lat, lon1, lon2, projection, squaredTolerance) {
  const epsg4326Projection = getProjection('EPSG:4326');
  return line(
    /**
     * @param {number} frac Fraction.
     * @return {import("../../coordinate.js").Coordinate} Coordinate.
     */
    function (frac) {
      return [lon1 + (lon2 - lon1) * frac, lat];
    },
    getTransform(epsg4326Projection, projection),
    squaredTolerance,
  );
}
Generate a parallel (line at constant latitude).
@param {number} lat Latitude.
@param {number} lon1 Longitude 1.
@param {number} lon2 Longitude 2.
@param {import("../../proj/Projection.js").default} projection Projection.
@param {number} squaredTolerance Squared tolerance.
@return {Array<number>} Flat coordinates.