![]() ![]() In general, the “subdivision” and its iterative nature is useful during modeling. The blender 2.8, for some reason, decided to use what essentially a form of “tesselation”. Most of the 3d software (including Blender up to 2.7) uses “subdivision” in their “subdivision surface” modifiers. The density does not have to be uniform (different quads of the control cage can have different density on the tesselated surface).Nothing prohibits from, say, tesselating each quad into 9 (each edge into 3) or 25 (each edge into 5). The number quads resulting from a quad on a limit surface does not have to be a power of 4. The density of the tesselated surface does not have to be controlled by the tesselation level.Tesselation of level 2 is not the same as applying the tesselation of level 1 twice. The surface does not shrink (well, actually, in a sence, it shrinks once, when going from the control cage to the tesselated surface) The positions of the corresponding vertices remain stable regardless of the level of tesselation. The vertices of the tessellated surface are always on the limit surface.And positions of points on these patches can be computed directly, without iterative refinement of the whole cage. The “tessellation” is acheived by representing the limit surface of the Catmull-Clark algorithm as a set of spline surface patches (in trivial case, each quad converges to a B-spline patch). For example, level 0 - 1 quad level 1 - 4 quads level 3 - 16 quads, level 4 - 64 quads, … Each iteration (except first) multiplies the dencity of the subdivided surface by 4.So the change in size is less for each further iteration. ![]() ![]() The smoother the surface, the smaler this shrinking effect. Typically, the surface shrinks with each iteration. The positions of the vertexes get closer and closer to the limit surface, but they never reach it.Applying the subdivision of level 2 is the same as applying the subdivision of level 1 twice. And then the same process is repeated while using the result of the previous step as the control surface for the new one.Įach step brings the surface closer and closer to the “limit surface”, but it is never reached. On each step, each quad of a control cage is subdivided into 4 and the resulting surface is smoothed out. The “subdivision” is the Catmull-Clark algorithm as it is. The OpenSubdiv manual uses terms “subdivision” and “tesselation” to address these differences: ![]()
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