Hello. I think there should be a way to have a continuous crease transition. Or eliminate hard creases altogether (100% = hard crease).
Try inserting two edge loops near the border with InsertEdge.
This is one of the reasons why I rarely use SubD for design work. I mainly see it as a tool for more artistic modeling rather than technical product design.
transizione.3dm (68.7 KB)
I can’t bevel. My models would reach 200-300 faces to micro manage minimum, to be re-adjusted incessantly. It would become an untouchable brick. This is the value I saw in graded creases. But I wonder why did they not close the continuity gap?
Maybe @theoutside can help you here—he’s the SubD expert.
You are right.
This is most likely a known flaw , but just in case > @pierrec
In the meantime I suggest you to go ToBrep as is and fix your problem manually with a couple of isotrims and then blends.
200% disagree, but this is totally unrelated to the thread, let’s avoid useless polemic.
I’d use either a soft crease for the entire edge with appropriate values to get the edge you want, or a hard crease for the entire thing, and fillet it as desired after converting to nurbs. (best for if you need a specific numerical radius)
I tend not to mix a hard and soft crease on the same edge for exactly this reason.
fwiw, I typically use bevels for breaking edges as opposed to any type of creasing. In my opinion they are more controllable if you are closely following rule of three.
It seems to be worse, with the issue extending to the transition to orthogonal faces, not just having them on the same edge. When soft creases end in hard creased caps there are sometimes distorsions and strange cuts that are carried into Nurbs conversions. I thought it was a shading artifact but it turns out it’s not. In the case SubD is used as part of an object (e.g. the bulk of a structure) these flat hard creased terminations would be an interface to Nurbs / BRep through lofts, to connect to other more CAD-style parts. This is an actual problem.
It’s unfortunate because the potential of full graded creases is to cut geometry in half, or even /3. I surveyed a lot of softwares with a SubD environment and could only find them in Rhino, not even Blender has them. But they are not working well enough at the moment, as far as I can tell.
That’s exactly the point: a crease isn’t actual geometry, it’s just an edge attribute. That’s why the transition from a soft crease to a hard crease on the same edge is abrupt. The only way I know to make that transition more gradual is to add geometry, for example with InsertEdge or a bevel (if you’re using Blender, the MeshMachine add-on does a great job with this kind of edge workflow, although it’s paid).
That’s basically what I suggested with InsertEdge, and it’s what you’ll see in pretty much every mesh modeling software and in almost every tutorial, regardless of the software. People add edge loops near the border and then use edge slide to move them closer or farther away depending on how sharp or smooth they want the transition to be.
As you mentioned, though, the downside is that the mesh becomes heavier and you can end up affecting areas that shouldn’t change. In some tutorials you’ll also see people using the Knife tool to stop an edge loop at a certain point and limit its area of influence, something you can’t really do with InsertEdge, since it creates a full edge loop.
In the video I linked, near the end, you can see one of these “solutions,” but it’s basically the same approach I used, and it’s what you’ll find in thousands of tutorials. Personally, I don’t consider it a real solution. If you need a clean and fully controlled result, the only real solution is to convert to NURBS and work there.
It’s an edge attribute that should be converted to geometry properly. For example here is the same SubD cage brought to Blender. Hard creased cap and 0.6 soft creased edges (roughly simulates 100% Rhino soft creases), 6 SubD levels set to limit surface, I don’t see any distorsion in the distribution of polygons. The underlying math handles the transition well, so it can be done.
On the same piece converted to Nurbs in Rhino lofts are failing: “Unable to loft - select either open or closed curves, but not both.”
G1 lofts are failing in Fusion too (imported STEP). G0 lofts land but need to be stitched, and are bad transitions.
The problem with bevels is that if you have a midsize complicated manufacturing piece (as opposed to a presentation intent) and start bevel-bombing it, it soon results into an uneditable brick. This isn’t even concerning parametric, it is a brick to direct editing tools. I remember testing mesh machine the past year but I couldn’t get over the fact that Blender basically makes bricks, furthermore transitioning to CAD tools is not possible.
Sample_Part.3dm (92.3 KB)
The pain is the conversion. Hard crease G0, soft G1/G2: an edge that shifts continuity along its length has nowhere to sit on a single NURBS boundary, and that’s what kills the loft. To do it properly you’d have to drop blend geometry right there — which is exactly what graded creases let you avoid.
Then again, a lot depends on how you set it up. I can’t open the file you shared at the moment — is it the original one, with the transition that breaks continuity? I might try to have a go at it. I’m away from my PC this weekend, but I’d be happy to take a look next week if you want to stay on SubD — unless someone else has already found you the right solution by then.
If you’ve tried MeshMachine, the way it handles fillets and chamfers, and really most of what that addon does, is what makes it so useful. The whole workflow is non destructive, or “re-constructive” as the dev calls it. The core idea is the Fuse tool, which builds the transitional surface straight from a chamfer, so you can move back and forth between chamfer and fillet whenever you want instead of locking the shape down the moment you bevel. On top of that you get variable fillets and washouts, and you can Unbevel or Unchamfer back to a hard edge at any point. There are several approaches the developer shows for exactly this kind of edge work, and honestly it’d be pretty cool to see some of that here in Rhino.
I remembered that somewhere on the forum, quite a while ago, there was a thread by someone who was developing a direct file switch from Blender to Rhino. In theory, if it works, you could work with MeshMachine and SubD in Blender and bring everything over to Rhino for any CAD edits. you’d have to search a bit, but I think the plug-in for doing this can still be found.
Blender is kind of a garbage truck that keeps being loaded and loaded. There is not a glimmer of effort that goes towards simplification, organizaion, ease of access for new users, etc. Hated it from day 1 and never stopped since then. It is also heavily geared towards art. It seems that you have a workflow and would enjoy inter-operation with Blender and its plugins, a sort of Blender bridge to Rhino. I’d rather have Rhino fix its own way of doing SubD which can’t be “bevel armageddon” as it lacks in mesh management tools (loop tools, “Edit by Curve”, point interpolation, easy mesh management in general). It has instead the most powerful creases but they are handicapped. It seemed that you implied that it can’t be done, but Nurbs patches can end in a point.
Can somebody check the file and say what’s going on with the surfaces? Why are they broken and what is breaking them?
Hold on, I didn’t mean it can’t be done at all. I was talking about your loft example, I was replying to that.
To me that error (open or closed curves, not both) isn’t the conversion breaking. The hard cap gives you a closed border, the soft sides open ones, and loft won’t let me mix them. I read it as a selection problem, not damaged surfaces.
And you’re right that NURBS patches can end in a point, that’s exactly the way I’d go. For that termination I’d skip the loft and use a BlendSrf or new patch between the trimmed faces, so I control G0/G1/G2 however I want, degenerate point included.
At the end of the day I see Rhino first as a NURBS modeler, not a mesh one. The SubD side is still missing a few tools and there I agree with you, but the job you want I’d do in NURBS, handling the transition there instead of baking it into the cage.
I don’t understand what’s going on at this point. Checking for updates.
@E_Leo So, I tried several approaches with the new Knife command (Rhino WIP) Rhino BETA Feature: Knife but I couldn’t get anything satisfactory. With Knife I could limit a loop to a specific area, but it did more harm than good. What worked instead was InsertEdge and Slide with crease turned off. Basically I did what 99% of mesh modelers do: insert an edge loop and use Slide to move the chain closer where you want a sharper angle, and farther away where you want a more pronounced bevel (Knife is meant for breaking the chain so it doesn’t affect other areas of the mesh).
I’d advise against using crease, since you’ve already run into that continuity problem yourself. You spotted it, but the vast majority of people modeling with SubD don’t even look at this stuff, and then it’s up to people like me to fix it before the mold. A real pain.
Regardless of that, inside the file you’ll also find how I handled the G0-to-G1 transition between the sharp edge and the rounded area after the NURBS conversion. I didn’t spend too much time on surface quality to bring it up to G2, because what matters is that you understand the process; then it’s up to you to put in a bit more time to make it even better, if you want.
blendsrf and Rhino BETA Feature: Patch re-implemented
Regardless of that, I’ve noticed SubD-to-NURBS conversion issues too. I think that if you spotted that continuity problem with the crease, you probably also noticed these issues in the other areas of the file. (But hey, no worries, by the time it reaches someone like me who has to make the mold, they become my problem, hahah. Relax, 9 out of 10 SubD modelers don’t even notice this stuff. I’ve been fighting with these problems for a while.)
Anyway, here’s the file, have a look. I’m almost completely sure that if InsertEdge plus Slide doesn’t work for you as a method (the one I show you in the video), you probably won’t find much else, unless someone comes out with something truly mind-blowing.
Sample_Part-brv.3dm (1.8 MB)
ah this will come in handy, but it’s still from the new Rhino WIP
@E_Leo I was browsing Instagram and this popped up. It seems like an interesting approach. You could give it a try. There’s also a link to the video on YouTube.
@pierrec This would be a really nice feature to have in Rhino. Curves that can influence the mesh would be very useful, unless Rhino already has something like that and I just don’t know about it.
As a complete beginner in Rhino, navigating the software by mapping from general CAD experience. Besides that soft creases can be transitioned to hard creases in the way you have shown, nobody has answered to this: What is going on here at the cap (tubular structure termination), and how to fix it? It may be a question showing inexperience, but please answer.
Note that this effect doesn’t only happen at 100%, there it is at the maximum extent and gradually smooths as the crease grade reduces.
On a copy of one of such bad corner surfaces, by just barely touching (not even moving) one of the CVs the surface “snapped” back to what it presumably was supposed to be. Which would prompt the question - if by “not even moving” a CV the surface heals itself, since Nurbs surfaces are driven by their CVs, why was the corner broken in the first place? Where to go from here?
This is an issue the developers should investigate. I’ve encountered it in other files as well.
I still think the culprit is Rhino’s crease. Of course, only the developers can say for sure, but since it seems to happen whenever a crease is involved, I suspect that’s at least part of the problem.
On the official Rhino YouTube channel, you’ll find several SubD tutorials by @theoutside . Take a look at them to get a better idea of what you can and can’t do with SubD.