1
$\begingroup$

When I’m working with path curves, I sometimes like to dissolve the middle control points and then subdivide the path in order to achieve an even distribution.

However, a problem arises when I leave only the two endpoints and do just that.

How the curve SHOULD look when you move the middle point:

Original Path

What actually happens:

Subdivided Path

I end up with these unwanted sharp corners, and I can’t figure out how to achieve the smooth look of the un-subdivided curve again. I could always make a new curve or use a Bezier point instead, but I'm curious as to what's going on and how to remedy it.

$\endgroup$
2
  • $\begingroup$ Can reproduce. I suspect bug with subdivide operation on a NURBS curve, but I want to investigate further. In the meantime, the workaround is simple. You dissolved three controls, then subdivided; instead, dissolve only two of those controls, and don't subdivide. $\endgroup$
    – Nathan
    Commented Nov 27, 2021 at 5:59
  • $\begingroup$ @Nathan Well, if it's the only way, I guess that's what I'll do. Thanks for looking into it! $\endgroup$
    – Trasche
    Commented Nov 28, 2021 at 2:05

1 Answer 1

2
$\begingroup$

So, the issue with this is a little, easy to miss variable that gets updated by dissolving the controls, because it no longer makes sense with only two controls; when you then increase the number of controls again, it updates only to its minimum value, rather than your original value.

enter image description here

Those two NURBS curves (paths are NURBS curves, not sure why Blender offers two different ways to create them, probably just legacy) are identical in every way except for the "Order U", seen in the property windows (one pinned.) The active selection has an Order U of 2, while the other has an Order U of 3.

The default for this on creating a new NURBS object is 3. These values are destroyed when the curve is reduced to two control points, because two controls in a NURBS cannot support any kind of curve. When a third point is then added, whether it be via subdivision, extrusion, or any other method, the Order U is updated to the minimum for a 3-control curve, which is 2, leading to the shape you see.

If you have a curve that is not yet reduced to two controls, my recommendation is, don't reduce it to two controls. Such a structure isn't any use at all (you might as well use a line.) If you already have a curve that has been reduced to 2 controls and you need it for something, then you can fix the problem by increasing the Order U to 3 in properties/object data/active spline.

$\endgroup$
1
  • $\begingroup$ Thank you so much!! It's good to finally know the answer. $\endgroup$
    – Trasche
    Commented Nov 30, 2021 at 3:43

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .