Difficulty with Tween 2 Along Curve

Hi there – I’m having trouble with something in Pufflerfish. I’m attempting to tween two curves, but along an axis of rotation. The A and B curves are different lengths, and ultimately, the axis would act as a point of intersection to connect other elements. This is to rebuild a facade component seen here:


Where the fins are built off the centerlines – the tween curves in the script. What am I missing here? When I add the ‘Multiple Curves’ node, I get an empty point list as an output, and only the A and B curves intersect (plus the tween is a bit wonky) – how can I fix? The end goal is to rebuild using Rhino.Inside as a new family.

Thank you for your help!
tween2alongcrv.gh (10.5 KB)


Flip your guide curve ! It’s going from B to A.


Flatten the input ! This is a tree, not a list. You should use Merge component to detect those errors more easily.


And eventually, use Line | Line component. The guide does not guarantee the tweened curves intersect it.

tween2alongcrv.gh (11.0 KB)

Hi @magicteddy – thank you for this! Yes, your notes make sense. Looking at the points from the Line | Line component, it does seem like the points from both A and B outputs aren’t what I’m after. Is there something I’m missing in just having these tweened lines rotate at the same point along an axis? Like where this pipe is running along the guide curve, I would want the tweened lines to intersect at those points:

This thread looks familiar:

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Totally familiar, but different issue / approach (in this case the guide curve is the driver and should remain horizontal; my ask before was around an interpolated curve based along points on the perpendicular curves, so not the same condition) – thank you for always being so observant, @Joseph_Oster . How can I best handle these requests for help in a way that doesn’t offend?

I think this is mathematically impossible because the axis of rotation is not equally spaced on the two rail curves.

The curves passing through all three rails are arcs, not lines, because the intersecting points aren’t colinear.


Same thing if the three rails are lofted - either normal or straight loft, turns into curves or polylines.

A possibility is to rotate the starting line by a constant angle increment. Then, the resulting line has to be cut by something…

Cutting by closest point from the rails :


Cutting by a big cylinder :


Both result in a wave along top and bottom rails.

Mix solution : loft middle and bottom rails, and extend the intersection by 10. It’s aligned on the bottom, and wavy on the top.

tween2alongcrv.gh (27.7 KB)

Thank you for exploring this, @magicteddy – I guess I’m confused, because the build is essentially one vertical curve, one horizontal curve, connected by a perpendicular curve at a point that is the same distance from one end of each curve:


The length of the tweens changes along the rotational axis, but the point of intersection at the rotational axis should be the same. Should be, but it’s not. Is there something other than the Tween option that will get me the change in length over the course of the guide line / rotational axis, with the gradual rotational change? If not tweened, what’s the best course of action in this regard?

I did try dividing the guide, but then had trouble creating the perpendicular / change in length lines – just hitting a wall on this one, sadly. I feel like I’m just overthinking it 100%, but also grasping at straws. Really appreciate your help.