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Cubic Spline Not Distort All Points?
Posted: 12 September 2018 09:42 PM   [ Ignore ]  
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Hello,

I am trying to use a Spline with the Type set to Cubic to deform my mesh and adjusting one point affects the entire Spline. This causes a part of my mesh to dip down.
Cinema 4D Cubic

When I do this in Maya using a Cubic NURBS Curve’s Control Vertex (instead of a Point), the curve has a falloff and the interpolation stops at the Curve’s midpoint.
Maya Cubic - Control Vertex Edited

Is there a way to get this behavior in Cinema 4D? It is MUCH preferred for my rig.

Thank you!

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Posted: 12 September 2018 10:34 PM   [ Ignore ]   [ # 1 ]  
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Hi blastframe,

Not that I can see a lot on these images, I typically don’t work from images. I would ask for a scene file, but this is clear. With Cubic and B-Spline you ahave certainly the strongest influence over many spline points. Akima stops at the next point. With a three point spline anything will move with Cubic, Akima, and B-Spline, and Bezier.

You need five points to have the point inside of two neighbors moved, while in Akima. Cubic would not work even with ten points, if the middle point moves extremely.

I would suggest to alter the spline in a different way then, if it needs to be three points. It needs intermediate points to work, not too little – not too much of them.
Scene file
https://www.amazon.com/clouddrive/share/y0fdUZPMDlY6whoAe6EDnQxzqutNRoS58UutKwwNwv3

I can’t change it in the app, nor do I have an idea how to simulate the the Maya algorithm in an easy way, after all it is all math only. They work all similar, based to my knowledge on the DeCasteljau algorithm, or similar. How Maya or Cinema 4D does it under the “hood”, is not documented.
https://en.wikipedia.org/wiki/De_Casteljau’s_algorithm

I have translated that into C4D here, at least to my little understanding of the “mechanic” of it. It is quite elegant to see it working. Again, this might be all different and app specific, as you said.

Scene file and screen capture:
https://www.amazon.com/clouddrive/share/K2bxNLgjZcQdC1qirUTYd7qFPLeivLxnoPxh4yTrJ7i
The “green” nulls are for moving to get a new curve.

All the best

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Dr. Sassi V. Sassmannshausen Ph.D.
Cinema 4D Mentor since 2004
Maxon Master Trainer, VES, DCS

Photography For C4D Artists: 200 Free Tutorials.
https://www.youtube.com/user/DrSassiLA/playlists

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Posted: 12 September 2018 11:31 PM   [ Ignore ]   [ # 2 ]  
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Thank you, Dr. Sassi, for the reply. I think using a 5-point Akima will work! Thank you very much for the files and video. It is very kind of you.

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Posted: 12 September 2018 11:36 PM   [ Ignore ]   [ # 3 ]  
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You’re very welcome, blastframe, thanks for the kine feedback.

Have a nice evening

P.S.: here i have moved the green nulls around to get close to your curve.
https://www.amazon.com/clouddrive/share/F6d72mCJNT9YB0kgZMUQIi2gwLHHqo1UFxz3jjZRB6I

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Dr. Sassi V. Sassmannshausen Ph.D.
Cinema 4D Mentor since 2004
Maxon Master Trainer, VES, DCS

Photography For C4D Artists: 200 Free Tutorials.
https://www.youtube.com/user/DrSassiLA/playlists

NEW:

NEW: Cineversity [CV4]

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