function lineStringLength(flatCoordinates, offset, end, stride) {
  let x1 = flatCoordinates[offset];
  let y1 = flatCoordinates[offset + 1];
  let length = 0;
  for (let i = offset + stride; i < end; i += stride) {
    const x2 = flatCoordinates[i];
    const y2 = flatCoordinates[i + 1];
    length += Math.sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
    x1 = x2;
    y1 = y2;
  }
  return length;
}
@param {Array<number>} flatCoordinates Flat coordinates.
@param {number} offset Offset.
@param {number} end End.
@param {number} stride Stride.
@return {number} Length.