Wings 3D/User Manual/The Nature of Subdivision Modeling/Winged Edge Topology
Winged Edge Topology
One of the reasons Wings works so well with edge loops and edge rings is the fact that it is based on a topological data structure called winged edge topology.
Winged edge topology is a method that mathematically defines all elements in a model by their relationships to other elements of the model. This is done by a set of tables; specifically, face, edge and node tables.
In the figure on the right, I have selected one face (Face 71) and then switched to Edge Mode to select its component edges. Similarly, if we had just selected Edge 72 and then done an edge loop selection, Wings would have selected edges 60, 68, 28, and the others on the back of the model that we can not see, to complete the loop. For a more detailed description of the winged edge data structure you can read The Winged Edge Data Structure by Dr. Ching-Kuang Shenefound here: http://www.cs.mtu.edu/~shene/COURSES/cs3621/NOTES/model/winged-e.html
The Status Line of Wings tells us that Face 71 is encircled by edges 9, 16, 70 and 72. (Note that newer versions of Wings place this information in a string at the top left of the workspace.) It only knows this because the winged edge topology exists to provide the information.
It is beyond the scope of a User's Manual to get into a thorough discussion of the winged edge data structure. It is enough to know that Wings is based on this data structure and it is used to make and manipulate selection sets very rapidly. You can also find winged edge topology illustrated from a geographic point of view here: http://www.bequia.swinternet.co.uk/edgeex.html