function direction(target, origin, result) {
  Cartesian3.subtract(target, origin, result);
  Cartesian3.normalize(result, result);
  return result;
}
Retrieves an instance from a packed array.

@param {number[]} array The packed array.
@param {number} [startingIndex=0] The starting index of the element to be unpacked.
@param {PolygonGeometry} [result] The object into which to store the result.