Only top parent model vertices (vertices which are not fixed to any other vertex) are discretized. For each of those vertices a node is created, classified to that vertex and registered into the octree. Generally, each new node is registered into the octree in order to allow for its fast localization during subsequent mesh generation phases. The registration consists in locating a terminal octant that contains the node and storing the node in that octant. The other mesh entities (edges, triangles, and tetrahedrons) are not stored in the octree because they can be traced up from the nodes, using the mesh topology, and because their storage in the octree would considerably increase memory requirements.