Same curves but different results in tweening

I made two sets of tweens. Both sets are using polylines but giving different results. In both the sets, the polylines curves are exactly the same. However, in the second set, the curves are made by extracting the vertices from the source polylines.

Why is it so?


It seems your initial polylines have different parameter intervals along them.
If you create new polylines out of their discontinuities, they’ll have different parameter intervals…
This is an explicit GH method of tween curve and you’ll see what I mean.


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What exactly are you referring to when you say ‘parameter intervals’?

The input is the same for parameter while evaluating curve.

Three vertices are getting connected of the original polyline. Why does it get differentiated in the parameters? Or is it just the way it is?

And I believe Michael Pryor already gave you information about the curve parameter space…

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Use the tweens from Pufferfish and you won’t have this problem. Dividing the curves isn’t the way to go. Gh tween component has issues with polylines as it is using a ruled surface approach.
Tween Two (6.8 KB)

You can see the difference here with GH native one:

And the reason to not divide is because you want to have same amount of control points as the input polylines.

Okay, Grasshopper automatically giving wrong parameters in the evaluate curve even though you inserted the same range component as doodled in my screenshot.

Alright. Using a ruled surface approach. That’s the issue with the component. Thanks!

I made a ruled surface and compared it to lofted one understand exactly what is happening.

The parameters are not wrong, parameters have nothing to do with lengths.

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I mean Grasshopper is wrongly processing the input parameters and evaluating the resultant lengths incorrectly.

I just took one curve this time and made polylines out of extraction of vertices, then did the evaluation using same parameters. Unequal division of length happens in the case of polyline created in Grasshopper. On the other hand when native polyline made in Rhino is directly referenced, the length is distributed uniformly.

curve (12.3 KB)

This Grasshopper bug is solved using your Pufferfish plugin in case of tweening the curves.