Hi Stefan, the t-spline result is very interesting! The interior region of each area seems to be nice but it kind of looks a bit odd at the borders between every shape, I think there may be some fairly tight little bends in the shapes where pieces meet up.

Notice here how dark the "fillet" surfaces are right where they meet up with the planar area:



I think there is some kind of little small sized lump or tiny dip in those areas, it kind of makes the juncture between all the cylinder shaped fillets and the adjacent planes to be kind of more accented then they normally are, that's kind of what catches my eye as being slightly weird looking with this example.

I also extracted some of the edges of those surfaces and examined them in Rhino using a curvature graph and yeah you can see that there is a sudden spike in curvature right at that plane/fillet juncture area, so there does seem to be some irregularity in shape in these plane/cylinder juncture areas when using this technique, you kind of basically lose the accuracy of planes and cylinders with things all glommed together into big surfaces like this. Here's the curvature graph of one of those surface edges:



A normal cylinder/plane juncture would not have that sudden spike in curvature where they connect together, there would normally be no curvature for the planar part, and then only a constant circle curvature for the cylinder part, this has a kind of little dip or bump where the 2 shapes (planar and cylindrical) come together.

So it kind of opens a bag of worms of problems in the plane/cylinder areas where the regular NURBS objects are well behaved...

- Michael