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I am applying the following geometry nodes setup to a Bezier curve and getting this weird line. It seems to become less pronounced if I lower the curve P resolution, but I want to keep it high. How would it be possible to get rid of this line?

The Bezier curve has three points, and the seam seems to go away if I adjust the handles of the middle point quite dramatically, but that changes the shape significantly.

enter image description here

The line I am talking about is the one going across the mesh perpendicular to the curve.

UPDATE

I have found a workaround which does not quite solve the issue, but seems to improve the situation significantly - using a lower resolution curve with subdivision surface node. Still, it is a compromise.

The shape of the mesh does not exactly match, but the curve is the same and the unwanted line is much less pronounced.

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  • $\begingroup$ seems to work in 3.1. Hint: it is always helpful if you would provide blend file... $\endgroup$
    – Chris
    Jan 22, 2022 at 20:39
  • $\begingroup$ works in 3.0 too...pls provide blend file. Looks like your curve is strange... $\endgroup$
    – Chris
    Jan 22, 2022 at 20:40
  • $\begingroup$ Sorry, didn't notice that blend exchange didn't accept my file. Here is a link to the file: drive.google.com/file/d/1un2rPTns5D-uvnn1FNV_jTVU5MyGxltj/… $\endgroup$ Jan 22, 2022 at 21:02
  • $\begingroup$ @Timaroberts I want to be able to control the shape from edit mode using the curve. Would it be possible to do that with an empty mesh? $\endgroup$ Jan 23, 2022 at 19:52
  • $\begingroup$ @RolansKims see my answer, the segment node has all the controls for the handles and endpoints of the curve. Admittedly it does take a moment to get used to them as it is not very visual (no handles). $\endgroup$
    – Timaroberts
    Jan 23, 2022 at 19:54

3 Answers 3

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Problems like this are usually going from bad topology. So first of all, I turn on "wireframe" in "viewport display".

enter image description here

And i see that this is a crease. Faces are extremly scaled in the direction across curve. In other words there are too much cuts along curve. So the solution is to reduce number of cuts along curve. That is why you should add "Resample Curve" node, because it gives you ability to manage cuts count along curve.

enter image description here

And now you can add "Subdivision Surface" node.

enter image description here

And finally you can take a look at the ideal shape of the fixed curve. :)

enter image description here

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  • $\begingroup$ Great! Reading about a crease for a moment I thought that there's a gradual, consistent change of normals along the surface except there's some tight (holding) loops at the height of the control point. However, the density is somewhat consistent: i.imgur.com/ENJWYAo.gif yes, the density does change at the spot, but I would expect subdividing the top (less dance) part wouldn't fix it, it's the abrupt change of the angle that causes the problem. But then I added the Resample Curve and it immediately fixes the outside of the bend... i.imgur.com/vejw6RJ.gif $\endgroup$ Jan 26, 2022 at 11:24
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    $\begingroup$ ...Now the problem looks more like what I'd expect: the larger part of the curve "eats" the smaller part due to a too tight bend. And it seems your solution, s.s. is indeed the most reasonable way to smooth that out. Moving the s.s. to the modifier stack allows to add Split Edges in between and decrease the s.s. level to 1 or 2: i.imgur.com/UymMPjY.png i.imgur.com/30jDbPH.gif $\endgroup$ Jan 26, 2022 at 11:24
  • $\begingroup$ @MarkusvonBroady It is also possible to manage resamle dencity along curve. And probably in will be very helpfull in some cases when we need ideal topology. Please, take a look at my question here blender.stackexchange.com/questions/250612/… . I think that for single curve Hans Goudey answer will be best. $\endgroup$
    – 3Dhedgehog
    Jan 26, 2022 at 11:48
  • $\begingroup$ @MarkusvonBroady I love your soluthion for curve cap. Probably i can make ideal topology even on the caps of the curve, and remove any subdivision smoothing artifacts from there, using only geometry nodes. But I think it should be new question . Also it would be very intresting to attach halph of uv sphere instead of simple curve cap. $\endgroup$
    – 3Dhedgehog
    Jan 26, 2022 at 12:11
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You don't mention your end goal, but for this object at least, it seems it might be simpler to just create it with a GN setup in an empty mesh like below:

enter image description here

This produces a curve as pictured here with no artifacts:

enter image description here

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  • $\begingroup$ Thanks, I will try this approach. Would it be possible to have more than two control points and two handles per point instead of one using this method? $\endgroup$ Jan 23, 2022 at 19:57
  • $\begingroup$ @RolansKims no, I don't think so. $\endgroup$
    – Timaroberts
    Jan 23, 2022 at 20:08
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    $\begingroup$ @RolansKims geometry nodes gives you ability to create curve with any count of control points. And each control point will have two handles. Also geometry nodes give you ability to select and manage any point and any handle. Just take a look how i manage points and handles in my answer here: blender.stackexchange.com/questions/249028/… $\endgroup$
    – 3Dhedgehog
    Jan 27, 2022 at 12:45
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select your curve, tab -> edit mode, select one vertex and scale it up -> solved

enter image description here

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  • $\begingroup$ This works, but also changes the shape of the curve significantly. Is there any way to keep the shape of the curve close to the original while still getting rid of the line and keeping the curve P resolution? $\endgroup$ Jan 23, 2022 at 7:43
  • $\begingroup$ Thanks for your feedback. Yes it does, i now. Unfortunately i don't know another solution. $\endgroup$
    – Chris
    Jan 23, 2022 at 7:53

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