Even though you can merge patches in T-splines during conversion which is kind of nice, that technique only works on square patches flowing in straight lines, and star point or triangulated areas still end up being messier (and lumpier) than with Rhino. In that area I would say your system is the best all around compromise as the patch counts are much less than what you get from Clayoo, and more consistent than what you get with T-Splines without manually trying to clean them up. I was was lucky enough to connect with Dale when he was writing the code for the conversion, and I think he’s he’s pretty much nailed it in that almost all patch conversions are 1:1, and he made the isocurve density gradually decrease as each patch gets further away from the triangle or star point rather than continue on toward the next star point in the loop. I spent many hours trying to manually simplify or rebuild patches in these areas, and don’t think there’s any geometric way around it without destroying the flow of the edge loops. I understand why the extra isocurves are required as they have to follow the flow of the the sub-d edge lines which must converge at some point in a triangle or arrowhead shaped quad. When I say Rhino is not perfect, it’s more of an “ideological comment”, as it would nice if every patch had 2 rows of control points for each edge regardless of shape, but I know that’s not mathematically possible in sub-d patches that are not “square”. Personally I found the Rhino system to be the best compromise of the three for overall surface accuracy with it’s 1:1 patch ratio, and can verify that the nurb polysurface is an exact clone of the sub-d surface with full G2 continuity, (even across most triangles). Although Rhino maintains a 1:1 sub-d to nurb patch ratio, it’s not perfect either, as does add more isocurves to patches located at star point junctions or triangles, but the isocurve count is reduced for each patch as they become further away from the star point junction. If I remember right, by default T-Splines splits nurb patches into tiny sections near star point junctions, it also creates a form of “edge loops” that span from one star point to another across a surface, which i remember not liking that much. The plus side to this method is you get a “lighter” nurb model, but with some loss in accuracy especially at sharper corners. In T-Splines I believe you have two options for nurb conversion, where on quads at least, you get one patch per sub-d face, or you can simplify the surface, and bridge patches across multiple faces as long as they do not contain any star points of triangles. Rhino will produce one nurb patch per sub-d face for all quads even at star points, except for “triangles”, which become three smaller nurb patches to maintain continuity. Nurb conversion is very different between the three programs, with Clayoo producing at least four patches per sub-d face similar to polygon based programs such as Lightwave or MODO, except in nurb format. As far as I know, all three are based on the Catmull Clark subdivision system, so the sub-d smoothing part should similar, except T-splines treats “star points”, and “triangles” a little different than the other two, and will not produce G2 continuity at these junctions. I’ve played more with Rhino and Clayoo sub-d conversion than T-Splines or Fusion, but here’s my take on the differences.
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