MbLoop Face Cycle

Class MbLoop is declared in file topology.h.

Face loop MbLoop is a derived class of the topological object MbTopItem and describes a sequence of edges that exhausts a certain face boundary.

The data structure of the loop contains a set of oriented edges RPArray<MbOrientedEdge> edgeList in the order of their traversal along the face boundary. The loop also has some additional data that is optional and serves to speed up loop methods.

The directions of the oriented edges coincide with the loop direction. The end of each oriented loop edge is joined with the start of the next oriented loop edge, see Fig. 1:

Fig. 1

The end of the last oriented loop edge is joined with the start of the first oriented loop edge.

Fig. 2 shows a loop of a spherical face consisting of four oriented edges, two of which are constructed on a seam edge and two of which are pole edges:

Fig. 2

If the loop of a spherical face is drawn in the parametric space of the sphere, it will be a rectangle. The loop, as well as the face boundary, is always closed. The loop is directed in such a way that the face is always on the left side when moving along the loop on the external side of the face.