i
Index of path1. This is not the row of path1, but the implied node,
where the first node is the first point, the second node is the first
segment, the third node is the second point, and so on.
j
Index of path2. This is not the row of path1, but the implied node,
where the first node is the first point, the second node is the first
segment, the third node is the second point, and so on.