Motorcycle Graphs: Canonical Quad Mesh Partitioning.(摩托车图: 标准的四边形网格剖分:-)
A mesh is structured if it has no extraordinary vertices, and unstructured otherwise. The main subjects of this paper are structured partitions in which the quadrilaterals of a mesh (semi-regular mesh) are partitioned into a small number of structured submeshes.

Extraordinary vertices都是作为分界点, 假如user先选择两个extraordinary vertices然后连在一起，是不是会加快计算呢?