Editing Polygon mesh (section)

=== Winged-edge meshes ===
[[File:mesh we2.jpg|center|Figure 4. Winged-edge meshes]]

Introduced by Baumgart in 1975, '''winged-edge meshes''' explicitly represent the vertices, faces, and edges of a mesh. This representation is widely used in modeling programs to provide the greatest flexibility in dynamically changing the mesh geometry, because split and merge operations can be done quickly. Their primary drawback is large storage requirements and increased complexity due to maintaining many indices. A good discussion of implementation issues of Winged-edge meshes may be found in the book ''Graphics Gems II''.

Winged-edge meshes address the issue of traversing from edge to edge, and providing an ordered set of faces around an edge. For any given edge, the number of outgoing edges may be arbitrary. To simplify this, winged-edge meshes provide only four, the nearest clockwise and counter-clockwise edges at each end. The other edges may be traversed incrementally. The information for each edge therefore resembles a butterfly, hence "winged-edge" meshes. The above figure shows the "box-cylinder" as a winged-edge mesh. The total data for an edge consists of 2 vertices (endpoints), 2 faces (on each side), and 4 edges (winged-edge).

Rendering of winged-edge meshes for graphics hardware requires generating a Face index list, which is usually done only when the geometry changes. Winged-edge meshes are ideally suited for dynamic geometry, such as subdivision surfaces and interactive modeling, since changes to the mesh can occur locally. Traversal across the mesh, as might be needed for collision detection, can be accomplished efficiently.

See Baumgart (1975) for more details.<ref>Bruce Baumgart, Winged-Edge Polyhedron Representation for Computer Vision. National Computer Conference, May 1975. {{cite web|url=http://www.baumgart.org/winged-edge/winged-edge.html|title=Use of Polyhedra in computer vision|date=May 1975|website=baumgart.org|url-status=dead|archive-url=https://web.archive.org/web/20050829135758/http://www.baumgart.org/winged-edge/winged-edge.html|archive-date=2005-08-29|access-date=2005-08-29}}</ref>