Half edges

What are half edges?

SideFX

In Houdini, edges are normally treated as undirected and shared between faces. However, for some tasks (such as simplifying or cleaning geometry) it is useful to view faces as each having their own edges. You can think of this as splitting each shared undirected edge along its length into two half edges. (Boundary edges of course will only have one “half-edge”.)

Unshared edges

Simple snippet which demonstrates how to create group for unshared edges (open edges) with vex.

Point.wrangle

string name = chs("group_name");
int ptnum = i@ptnum;
int pts[] = neighbours(0, ptnum);

foreach( int pt; pts){
    int hedge = pointhedge(0, ptnum, pt);
    int count = hedge_equivcount(0, hedge);
    if ( count == 1)
        setedgegroup(0, name, ptnum, pt, 1);
}