3D graphics eBook - Course Materials Repository
3D graphics eBook - Course Materials Repository
3D graphics eBook - Course Materials Repository
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DooSabin subdivision surface 42<br />
External links<br />
[1] D. Doo: A subdivision algorithm for smoothing down irregularly shaped polyhedrons, Proceedings on Interactive Techniques in Computer<br />
Aided Design, pp. 157 - 165, 1978 ( pdf (http:/ / trac2. assembla. com/ DooSabinSurfaces/ export/ 12/ trunk/ docs/ Doo 1978 Subdivision<br />
algorithm. pdf))<br />
[2] D. Doo and M. Sabin: Behavior of recursive division surfaces near extraordinary points, Computer-Aided Design, 10 (6) 356–360 (1978), (<br />
doi (http:/ / dx. doi. org/ 10. 1016/ 0010-4485(78)90111-2), pdf (http:/ / www. cs. caltech. edu/ ~cs175/ cs175-02/ resources/ DS. pdf))<br />
[3] Jos Stam, Exact Evaluation of Catmull–Clark Subdivision Surfaces at Arbitrary Parameter Values, Proceedings of SIGGRAPH'98. In<br />
Computer Graphics Proceedings, ACM SIGGRAPH, 1998, 395–404 ( pdf (http:/ / www. dgp. toronto. edu/ people/ stam/ reality/ Research/<br />
pdf/ sig98. pdf), downloadable eigenstructures (http:/ / www. dgp. toronto. edu/ ~stam/ reality/ Research/ SubdivEval/ index. html))<br />
• Doo–Sabin surfaces (http:/ / <strong>graphics</strong>. cs. ucdavis. edu/ education/ CAGDNotes/ Doo-Sabin/ Doo-Sabin. html)<br />
Edge loop<br />
An edge loop, in computer <strong>graphics</strong>, can loosely be defined as a set of connected edges across a surface. Usually the<br />
last edge meets again with the first edge, thus forming a loop. The set or string of edges can for example be the outer<br />
edges of a flat surface or the edges surrounding a 'hole' in a surface.<br />
In a stricter sense an edge loop is defined as set of edges where the loop follows the middle edge in every 'four way<br />
junction'. [1] The loop will end when it encounters another type of junction (three or five way for example). Take an<br />
edge on a mesh surface for example, say at one end of the edge it connects with three other edges, making a four way<br />
junction. If you follow the middle 'road' each time you would either end up with a completed loop or the edge loop<br />
would end at another type of junction.<br />
Edge loops are especially practical in organic models which need to be animated. In organic modeling edge loops<br />
play a vital role in proper deformation of the mesh. [2] A properly modeled mesh will take into careful consideration<br />
the placement and termination of these edge loops. Generally edge loops follow the structure and contour of the<br />
muscles that they mimic. For example, in modeling a human face edge loops should follow the orbicularis oculi<br />
muscle around the eyes and the orbicularis oris muscle around the mouth. The hope is that by mimicking the way the<br />
muscles are formed they also aid in the way the muscles are deformed by way of contractions and expansions. An<br />
edge loop closely mimics how real muscles work, and if built correctly, will give you control over contour and<br />
silhouette in any position.<br />
An important part in developing proper edge loops is by understanding poles. [3] The E(5) Pole and the N(3) Pole are<br />
the two most important poles in developing both proper edge loops and a clean topology on your model. The E(5)<br />
Pole is derived from an extruded face. When this face is extruded, four 4-sided polygons are formed in addition to<br />
the original face. Each lower corner of these four polygons forms a five-way junction. Each one of these five-way<br />
junctions is an E-pole. An N(3) Pole is formed when 3 edges meet at one point creating a three-way junction. The<br />
N(3) Pole is important in that it redirects the direction of an edge loop.<br />
References<br />
[1] Edge Loop (http:/ / wiki. cgsociety. org/ index. php/ Edge_Loop), CG Society<br />
[2] Modeling With Edge Loops (http:/ / zoomy. net/ 2008/ 04/ 02/ modeling-with-edge-loops/ ), Zoomy.net<br />
[3] "The pole" (http:/ / www. subdivisionmodeling. com/ forums/ showthread. php?t=907), SubdivisionModeling.com<br />
External links<br />
• Edge Loop (http:/ / wiki. cgsociety. org/ index. php/ Edge_Loop), CG Society