Orientation issues transferring rotation from animated points to Vellum Hair

[odforce123]

Hi everyone,

I’m working on a setup involving two animated control points. My goal is to animate these points manually (both position and rotation) and generate a line between them. I want the position and rotation from these points to transfer to the line via a Vellum Hair simulation.

From there, I’m scattering points along the simulated "stem" to copy leaves onto it. However, I’m running into issues with the orientation because the leaves do not follow the rotation or twist of the line correctly. I suspect I’m not transferring the transform attributes properly before or after the simulation.

I’m still learning Houdini by solving tasks like this, so I realize this might be a basic mistake. I’ve attached a preview and my current .hip file. Any suggestions on how to correctly setup the orientation transfer would be greatly appreciated.

Thanks!

Stem_sim.zip

[fencer]

Seems need to make proper orient for curve to help vellum understand how to rotate.

Tried to do something towards this direction.

Previz_forum_v02.hipnc

[odforce123]

Thank you so much @fencer! I really appreciate your help, that VOP setup for the orient is working perfectly. Exactly what I needed.

[David Tom]

Glad that helped!

Yeah, this kind of setup usually comes down to having a stable orient (or N + up) before the Vellum sim, otherwise the solver has no consistent frame to preserve twist.

What worked for me in similar cases:

Build a proper orient quaternion along the curve (Polyframe or VOP like you did) *before* Vellum
Make