Hi danperk, thanks for posting the comparison file!
I took a close look at both of them and the Moi one is clearly far superior. I used Rhino to do a detailed analysis.
The first thing to notice is the isoparm distribution is different, Modo version on left, MoI on right:
The tricky part about SubD conversion is handling extraordinary vertices. You can see that they are handled pretty differently. The Modo/IW one generates degree 3 surfaces that are non-uniform, they have a refinement process of additional knots being inserted as they approach the extraordinary vertex. This is not too terrible in and of itself but it gives more opportunities for surface defects in areas with tightly bunched up control points. You can see the MoI one has a uniform isoparm distribution, it doesn't have refinement as it approaches the extraordinary vertex, it instead uses degree 6 patches in those areas. They kind of have a lot of points in them but they are very evenly spaced.
The shaping in the IW one is pretty good in most spots but there are some small areas that are not actually even G1 continuous, I think it looks like it has problems if there is something like a subtle inflection point in the surface right nearby an extraordinary vertex:
Zooming in on that spot in the Modo/IW one you can see the surface is perturbed in that area, and even has spots where the zebra lines do not match up meaning the surfaces are only G0 there and doesn't even have tangent continuity:
Zooming in on the same area in the Moi one:
With the simpler uniform knot structure in the Moi one there is just less that can go wrong. It's a better quality surface that is smooth and G2 curvature continuous throughout. I'm unable to find any bad shaping around any extraordinary vertex.
The thing that will be good about having this kind of very high surface quality result is that it should make a hybrid modeling approach more feasible where you can do something like a vehicle body as a sub-d cage and not have to worry about glitches in little spots of that shape.
- Michael
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