The partIndex is used to distinguish sections in sectionview with the same Network Part. As the image below, the curve pipe will have two points in the sectionview. If we want to add label for the left point, the partindex should be 0, and the right one should be 1.
But a Structure can’t have multiple parts in the sectionview, so the partIndex should always be 0 for Structure.
Thanks to Summer Ding for this interesting information.