In barycentric units [0,1], edge-crossings within this threshold are snapped to the nearest vertex and any resulting repitition of vertex surface points are replaced with a single vertex surface point. Due to numerical precision issues, a path that 'should' intersect a surface mesh vertex may appear as a sequence of vertex adjacent edge-crossings very close to the vertex.. the threshold is applied in a post-process coalesce those crossings into a single vertex crossing.