* the dimensional collapse of two or more edges. It has
* the same location on both sides of the edge, so it
* has collapsed to a line.
*/
if (depth.getDelta(i) == 0) {
lbl.toLine(i);
} else {
/**
* This edge may be the result of a dimensional
* collapse, but it still has different locations on
* both sides. The label of the edge must be updated