function linearRings(flatCoordinates, offset, ends, stride) {
  let area = 0;
  for (let i = 0, ii = ends.length; i < ii; ++i) {
    const end = ends[i];
    area += linearRing(flatCoordinates, offset, end, stride);
    offset = end;
  }
  return area;
}
@param {Array<number>} flatCoordinates Flat coordinates.
@param {number} offset Offset.
@param {Array<number>} ends Ends.
@param {number} stride Stride.
@return {number} Area.