Hmm, that’s strange. Where is that area? Could you post a screenshot from a bit farther away and indicate the area you’re analyzing? That way I can see where it is and take a look.
Since you mentioned that you’re new to Rhino., if you want to do yourself a big favor, watch these videos. They’ll help you a lot and save you from making the same mistakes that the vast majority of modelers make. I’d recommend spending some time really understanding what they explain.
These videos are useful even for me, and I’ve been modeling for many years. It’s always good to revisit the fundamentals, so whether you’re a beginner, intermediate, or an experienced professional, it’s definitely not time wasted.
Here’s a playlist of 13 videos. I recommend watching all of them carefully and in depth.
This will also be incredibly useful for you to know.
sorry, I believe I answered this above. Use either all soft creases with the values called out appropriately or use all hard creases and add your radii after you conver to nurbs with the fillet or blend edge commands. the problem comes from mixing the two commands on the same edge.
for me personally, I do not use creases much if at all. I bevel edges as per rule of three and control edge radii that way.
this appears to be render mesh related since it rendered fine when converted to nurbs. I’s use smooth and slower as a mesh setting and see if this repairs itself.
@E_Leo could you post this example file here or in a private message, please? It looks like one or more things going wrong in Rhino but I don’t understand the pictures you posted enough to reproduce the issue.
Interesting. I think you might be able to get something similar to this with a combination of SoftTransform and Align ToCurve. That would move vertices towards the curve, it will probably be a “bump” rather than a “pinch”. But without a pinch tool in Rhino (even without the curve), this is going to be hard to reproduce however you try.
We don’t really have mesh sculpting tools in Rhino, but if we were to implement them I like the idea that you don’t have to freehand the toolpath with your mouse, you can also draw the toolpath using a curve. Potentially other commands could benefit from drawing a toolpath using a curve on screen. The Beta has Markups (screen space drawing) and in viewport widgets that would make these kind of command extensions easy to do, for v9 and later. I’ll keep that in mind for the next time I need new projects.
@pierrec This was a plugin I used a lot in older versions of Blender because it was really useful. Once you drew a Bézier curve, you could use it to influence the nearby mesh. Take a look around the 4:15 mark in the video.
However, it’s not the same thing as a “line cage.” The main difference is that, for example, imagine I have a shoe sole. If I already have the curve defining the outline of the sole (what’s called the welt in footwear), I can influence a mesh—or any other object—simply by moving that curve. The influence could also be controlled with a falloff, similar to how it works in Blender.
Sorry it took me a while to understand this picture and the others like it. I think I’ve figured out the issue, this is a bug in ToNURBS when hard and soft creases meet at the same vertex. It’s rather unfortunate as it really affects the quality of the NURBS conversion and makes soft creases harder to interface with NURBS objects:
RH-96738 SubD Crease: Wrong subdivision level and display mesh in ToNURBS for soft to hard crease
I’ll try to get it fixed in v8 and the Beta as soon as possible.
The easiest way to workaround this issue is to delete the flat face in the SubD – the one that has all the hard creases as edges, before ToNURBS. It won’t change the geometry of the limit surface and as far as I understand you do not need this face since your object will not be closed there, you want to continue it with other NURBS geometry. After ToNURBS, you can use Cap to get back to a closed solid if needed.
The answers are already in this thread, I just want to say again that this is a fundamental limitation of soft creases in SubD surfaces as they are implemented in Rhino and most other software. As far as I know, because the soft crease is always going to be a G1 edge (surfaces on each side of the edge are tangent to each other), and the had crease has neighbor surfaces that are not tangent to each other, a smooth transition is not possible at this vertex.
If you know another software that can get this transition without the little bump in the hard crease (and without using display mesh tricks, i.e. it has to survive a conversion to NURBS), I would love to see an example.
The soft crease behaves like this: for a couple of subdivisions, subdivide using the (hard) crease rules, then subdivide using the smooth rules ad infinitum. Rhino maps “100%” soft crease to 4 levels of crease subdivision, and it looks like Blender lets you do more than that getting you closer to a smooth transition with the hard crease. But it’s not possible to continuously map a “100%” soft crease to be the same as a hard crease, so this transition will never be completely smooth.
RH-96738 SubD Crease: Wrong subdivision level and display mesh in ToNURBS for soft to hard crease
Good to know. I used to run into this kind of issue quite often whenever someone sent me subd -toNURBS models. If you manage to solve it, you’ll be doing a huge favor, especially for people like me who design molds. I used to spend quite a bit of time fixing these kinds of problems.
@pierrec I don’t use creases for the reasons I mentioned above. However, since ZBrush also has the option to apply creases, I’ll pay attention to this and, if I notice it behaves better, I’ll let you know.
