function getLengthInternal(coordinates, radius) {
  let length = 0;
  for (let i = 0, ii = coordinates.length; i < ii - 1; ++i) {
    length += getDistance(coordinates[i], coordinates[i + 1], radius);
  }
  return length;
}
Get the cumulative great circle length of linestring coordinates (geographic).
@param {Array} coordinates Linestring coordinates.
@param {number} radius The sphere radius to use.
@return {number} The length (in meters).