Nurbs modeling help

Hello, I need help from you Nurbs modeling professionals. How can I create this shape without getting such hard edges?

I’ve tried everything possible regarding division and creation but I always get a hard edge.

Züge_ICE-1.3dm (1004.4 KB)

Many thanks for every tips

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dear @bjornsmolarek
if you search a fast easy and rough solution - my guess is, there is no “vanilla” single rhino command.
The plug-in “xnurbs” will be a great help for this kind of surfaces.

parasolid patch / fill

Also the parasolid kernel (running in the background of solidworks, siemens Nx and others…) has a powerful patch / fill tool (cheapest access via or here via onshape:

Zuege_ICE-1_00_tp.3dm (5.1 MB)

vanilla rhino

if you want a pure rhino nurbs solution, you’ll have to break down the surface. And quite sure there will be different approaches.

_curvatureGraph to check curve quality
_zebra to check surface quality

if you really rely on the (unusual) curve layout - my first approach - just a sketch / concept - using above patch to illustrate - would look like this:
rework the curves (check with _curvatureGraph)

1st set

build a _extrudeCrv as helper for symmetry (green) (but it might be easier to build the entire surfaces and do not work with mirroring )
_sweep2 or _edgeSrf for the central stripe (brown-violett)
for the remaining 3-sided openings:
_sweep2 _loft _edgeSrf (violett)
you might need _matchSrf and some CV-Massage for fine-tuning.


now trim back the violett surface and build a final _sweep2 to close the upper part.
also here you might need _matchSrf and some CV-Massage for fine-tuning.

do the same workflow for the grey section.

It might be easier to have a different overall edge (and maybe the corresponding / neighbouring surfaces ) - your closed, egg-like shape / edge / curve is a quite challenging choice.

but others might come up with simpler / other / better approaches…

kind regards - tom


… if this really should become the nose of a ICE 1 - as your filename suggest.
I am quite sure the contour of the service opening / notch is not part of the curves that are used for the initial surfaces - but more a technical / design decision afterwards.

Dear Tom,
First of all, thank you very much for your detailed explanation and the time you took for it. The XNurbs plugin looks very good and is certainly worth considering for the future, but it is not worth purchasing yet as it is not a model for execution planning but only for infrastructure visualization.

I looked at the curvatureGraph command but I couldn’t really understand the display, especially why it sometimes swung very heavily. Unfortunately, I’m not that familiar with Nurbs modeling yet, apart from relatively simple geometries. For example, at the center line, the deflection at the bottom is incomprehensible to me.

I will try to model the model according to your instructions. Until now I had mostly used the command for SurfaceNetworks and didn’t know that I could also use the other “_sweep2 _loft / _edgeSrf” for this and I didn’t know the “_matchSrf” command at all until now.

Since I didn’t get any further at first, I thought about just creating the curves in Rhino and then using them in Blender to create the model there via SDS, but it’s not perfect to switch between the programs all the time, especially since the visualization runs via Rhino Vray.

I hope you can understand my English.
Many thanks for the help

My model is based on the ICE 3 and the nose of the train is similar to the ICE 1 but even more rounded/pointed. Sorry, the Filename ist misunderstanding, the ***-1 is the manually incremental.

… or use Rhino s SubD if it is just for Visualisation …

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Actually a good idea, but unfortunately I can’t handle SDS modeling in Rhino at all, but I’ve already started watching some tutorials.

Hello Tom,
Your tip regarding xnurbs was really worth its weight in gold. With Rhino you can create highly accurate Nurbs models, but you also need a lot of experience in modeling Nurbs geometries, as the curves also have to be perfectly prepared in advance so that the geometries/transitions are correct.

I downloaded the xnurbs demo and the result, especially considering that the curves are not yet perfect, is fantastic, especially for a model for visualizations. For the price the plugin costs, I will most likely buy it after the first tests.

Thank you

Looking at the zebra alone here, I think Xnurbs has given you a result which is going to give you a headache if you try to MatchSrf to that surface.

It’s worth using the PointsOn command here to see the underlying distribution on points. That will largely dictate what will happen if you try to match to even tangency on this shape.

I may be wrong, and hopefully it gives a workable surface, but I am just not sure that’s the case here; especially if it is a primary surface.

Yes, it’s not perfect yet, but for a model, for a visualization, it’s somewhat ok. But I’m still trying to see if I can do it more precisely/better. But I’m happy that with the xnurbs demo I can create geometries that are clean at the transition and don’t generate hard edges at the ends like vanilla Rhino.

Which of course is due to my experience and not to Rhino itself.
Nurbs modeling is not easy. :sweat_smile:

As long as you feel it is the right solution for you, great!

In the meantime, I’d recommend going watching the videos here as well, when you have time:

You will see that there are a couple of these items that are very close to what you can do for an approach using standard Rhino.


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Hello David,
Thanks for the link. I’ll take a look at it and I’m sure it will help me a lot.

you might get away with a single span surface, depending on the tolerance to the input points. For example:

Züge_ICE-1_singlespan.3dm (205.6 KB)


Sorry for my very late reply, I’ve been very busy lately. It looks very great and I will take a close look at your file. Thank you

Rhino 9 WIP has the SubDMatch command with a tangent option.

I extended the curves and used Sweep1 to create a surface for tangency.

The cone shape is not exactly like the curves provided but a little pushing and pulling and I think it would look alright.

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