Surfacing... just a nightmare

Can I propose we flip your question on its head? Why are you approaching modelling in the way you are? As far as I can tell you are using Grasshopper as a panacea to reduce rework of a model? Is this model being used for manufacture? If so, it’d be handy to know how the object is being manufactured; eg, a tool for a rotomould does not need as fine a tangency tolerance as a polished injection moulding tool. Once you provide information such as this then the answers may be more focused, as your quest is fairly nebulous at the moment.

One thing I would add to the mix - edge surface. This is the main way I create surfaces that have a fairly even UV length ratio. This is because it respects the degree and CV point count of the input curves when creating the surface. As others have mentioned, use either smaller and multiple surfaces to capture a complex form instead of expecting a high degree single span surface to do the same. Or use lower degree multispan curves and surfaces, as you can increase the CV count and also benefit from the localised curve change present in a multispan curve/surface.

The problem with almost any car tutorials on youtube or ebooks is, that they are made from people never worked in the industry. They simply teach the wrong stuff, doing more wrong than good for your understanding.
The only valuable tutorial source shown in this thread are the videos created by Raymundo Burgueno using Alias. He is more explaining about the why and what and not about the how.
You cannot fully teach yourself or others modelling cars or other complex shapes, if you never seen a design studio from within. But at least you can tell that a 16 years old car modelling expert using Blender is not a trusted source of truth :slight_smile:
In times of google its really difficult to filter the right information, but at least you get some information nowadays.
So the only solution to become better in surface modelling is doing it again and again. Listen to the right people, and ask for the why. Ask questions like: Why are twisted surfaces bad? Why do I need to curve any surface. Why should’t I match on trimmed shapes, Why using static and not dynamic highlights and why do I need a curvature graph? What is it telling me? Why did software developer developed this tool? You see, if you understand what the purpose of many things are, then it really doesn’t matter which tool to choose. You can reach many things on different ways, with different software packages.

Really learn from the space ship tutorial shown above.

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Can I propose we flip your question on its head?

Sure. Why not.

Grasshopper as a panacea to reduce rework of a model?

Yes, mostly. I am not bright enough to be able to remember the path through the maze 30 days ago, or even 2 days for that matter. But GH is a parametric tool. Once I have summited this mountain, there are more. a structure must be built to stiffen this “bathtub”, and once that is done, we have to see if what remains is big enough. If not, some sliders will be moved.

it’d be handy to know how the object is being manufactured

NOT injection moulded, welded sheet metal of some sort probably, so next is a thread on panneling challenges. Brace yourselves )

your quest is fairly nebulous at the moment.

Well yes, and deliberately so. Diving into specifics doesnt really help the big picture. Like for example this little chiken and egg surfacing problem:


The intersection of these two surfaces produces a curve. That curve is the tangent transition along the two surfaces BUT, the red surface was created without a vertical curvature that the finished surface will have, so the curve will change. The red surface is a lofted surface from two curves. It needs three curves or more, but to make a curve in between the intersection of these two surfaces is required… another iteration problem that must be approximated somehow.

If I use the curve generated above, then when the red surface is lofted using the now completed set of vertical curves, it will have an artifact resulting from the innacuracy.

I dont even know if its possible to curve the red surface using a curve, an arc in the vertical direction. My current idea is to use NETWORK SURFACE and thus include the arc to derive that curve (which will be different)

Regardless of the model, the approach you take to modeling is crucial. I began thinking that I could just trim away and join surfaces to get a perfect result. I have abandoned that approach. I now use the trimmed surfaces to generate curves from which to loft one surface that forms the entire side of the bathtub excluding the bottom which I hope to join with a fillet along the length.

Why are twisted surfaces bad?

Forgive me for being snarky:
This deliberate strategy seems to work really well for you, since you are trying to communicate your problem unsuccessfully for about 9 month to an extremely knowledgeable and helpful community of experienced users and still keep whining about how difficult it is to get meaningful information.

As I said this was meant to be snarky, I hope you are not offended.
But wouldn’t it be a good idea to at least once hear out the vast majority of people that have been trying to help you?
Present some pictures and files that show clearly what your modeling goal is.
Then let THEM show you how to approach this specific scenario.


Im not thin skinned. As long as you have a valid point to make, you are good )
I think there is a misunderstanding shall we say. This is not a small project. If post the enire problem, no one is going to pick it up, work through it, solve these kinds of problems and present me with map through the maze. Its just waaaaaaaay too much work, and im not sure the solution would be right. I am the designer. I need to create the model

So, I have broken the problem into small pieces like this:

Getting your head around the problem takes time. One person very kindly provided a solution, but it turned out not to be sufficient. I edned up re-writing this section 3 times before I realized that I could approximate a smooth curve with an arc. An arc is part of a circle. Calucating circle tangency is deterministic and this led to a solution that matched 3 curves tangentially without changing the curves.

That was a weeks work. I might not be overly bright, but its a lot to checw on for anyone. Are you going to do all that? I doubt it, and I wouldnt expect you or anyone else to.

I have read through a LOT of threads in these forums. There is a pattern. The most experienced users come here to chew on a problem for the challenge. They want a file, a well defined problem and derive satisfaction from chewing on it and spitting out a solution. They dont want a steaming pile of knotted problems all tangled up and poorly defined. Detangling that is hard work and not fun. Presenting this as “please design me a cool sportscar” or “please model this photo” is too much. This is journey of understanding. Relax.

We have this incredible array of tools. Grashopper and plugins for days. Modules written by professional people for download instantly. videos, forum answers, people that love creating and are willing to give freely of their time to expand the community. I am grateful. Really. But this topic is where the rubber meets the road in modeling. It needs more than a simple example to illuminate possible approaches to complex surfacing challenges.

Nobody wants to do all your work for you. But it is much easier to help you, when you give some guideline what your general goal is.
Now I might be wrong here but I somehow suspect that your project, or better the CAD perspective with which you look on your project is based on quite a few misconceptions, false “solutions” etc all leading you to more and more complex and more and more detailed micro-problems.
To me there seems to be an obvious mismatch between very detailed, very in-depth requests or problem descriptions on the one hand and a broad confusion about some of the most basic modeling rules On the other.
(I can’t really comment much on the grasshopper side of your problems, so this reflects your general surfacing questions)
I really hope for you that I am wrong here, but I cannot be the only one that sees this dissonance.

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Of course there is also a grain of truth in this observation and I guess everybody who helps out on this forum has some component of “wanting to show off” his expertise.
But I think you couldn’t be more wrong about this being the main motivation for people responding to users posting problems.
This forum is quite a unique place where the extremely motivated and prepared professionals from McNeel and a whole bunch of talented, experienced and knowledgable users work together to offer information and education for free.
One only has to be open for their suggestions.


Well I appreciate your analysis, but after this much work combined with the comments of many others that have difficulty with surfacing, I dont think so. I understand you disagree. I dont think there is much point in debating that much further. It takes the thread off track into a series of justifications about: why is that the question, none of which will be deemed satisfactory. I choose to pose it this way. you may not. Thats fine. Well just have to agree to disagree about how to pose questions. OK )

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As I said: I hope I am wrong (and I very well may be)
Good luck anyway.

A technical question: What is the difference between static highlights and dynamic highlights?

Hi -

Just FWIW - depending on the specific manufacturing process, “welded sheet metal” might require developable surfaces and thus an entirely different way of modelling…

Hi David -
As far as I understand…

Think fluorescent light tubes over a car and you walking past that car

What our current Zebra does.


The static light lines (like those used in VSR for Rhino 5) are just that, static. No matter how you rotate the camera around the 3d model, the light lines (or the Zebra stripes) remain in the exact same position on the model, thus allowing you to fine tune certain control points with the “Move UVN” tool to achieve nearly Class-A surface quality. This approach lets you move the camera at a very small angle relative to the surface to observe its continuity.

On contrary, the dynamic light lines (or the current implementation of the Zebra analysis in Rhino) are view dependent, so they always move when you rotate the camera around the 3d model. Sometimes this may be useful, but in general it’s difficult to observe a certain area of the 3d model if the lines move together with the camera.

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Thanks for the description. That behavior is fundamentally different than walking around an object looking at the reflections of lights or other objects. In the latter situation the reflections will move as the observer/camera.

The design is restricted to cylinders and planes, but not ruled surfaces because materials in the real world are not rigid and can be formed. But this is yet another rabbit hole we could all go down, but lets save that for the panneling thread. My task right now is to make a watertight surface.

This thread is going nowhere. Close it, start a new one and add a file. Even a partial file with a section you’re struggling with will do.


Sure. Lets start with the classics:


How many hours have I wasted trying to find a way to go around corners with LOFT to get a single surface I can run an ISOCURVE down and avoid merging/joining issues.

LoftClassic (5.6 KB)

A Nurbs surface has 4 edges

e (4.7 KB)

or got boxed into a corner

Its going nowhere becuase I have been sidetracked defending why I am asking surfacing questions… (6.1 KB)

One surface not two with mystery tangency

Then perhaps take a look at the 3 other problems i posted.

Then there are nasty real world problems like finding the intersection between two surfaces to make a curve to use to create a single smooth surface (15.0 KB)

Not every problem can be solved by running the rebuild command. Some surfaces have to be blended in ways that are not intuitive