gregjenings

First of all, thank you for pointing out the issues in my setup. You were right — I had forgotten to add the **Convert SOP**. After adding the Convert SOP, the simulation is working correctly.

I also created the two setups you suggested: one with a **lower CV count** and another with a **higher CV count**. Both simulations are now working perfectly as you described.

However, I’m now running into another issue during rendering. I’ve attached screenshots showing the error, along with the Houdini file for reference.

The error seems to be related to the **Configure Guide Deform LOP** node. Since this node is relatively new in Houdini, I’m not very familiar with the correct workflow and configuration. I’ve tried both setups — one using the low-point-count curves and another using the original high-point-count curves — but I’m still getting the same error during rendering in both.

Could you please take a look at the attached file and let me know what I might be doing incorrectly?

I would particularly like to understand:

1. **Low-CV to High-CV workflow**
If I simulate the low-CV version of the groom for better performance, what is the recommended workflow for transferring the resulting motion/deformation back onto the original high-CV curves for rendering?

In other words, I would like to use the low-point-count curves for the Vellum simulation, but retain the original high-resolution curves for the final render. What would be the correct Houdini workflow for transferring the simulated motion from the low-CV guides to the high-CV guides?

2. **Configure Guide Deform LOP vs. Hair Procedural**
In earlier Houdini workflows, there was a **Hair Procedural** node available. In Houdini 21, is the **Configure Guide Deform LOP** intended to replace the Hair Procedural workflow, or does the Hair Procedural node still have a valid use case?

If both approaches are still supported, when would you recommend using **Configure Guide Deform LOP** versus **Hair Procedural**?

I’ve attached the HIP file so the complete setup can be inspected rather than relying only on the screenshots. Hopefully the file will make it easier to identify what is causing the rendering error.

Thanks again for your help. I’m trying to understand the intended Houdini 22 groom/Vellum workflow rather than just work around the error, so any explanation of the underlying workflow would be greatly appreciated.

Thanks for the suggestion. I’ll try enabling **“Snap to Skin”** on the Guide Utility node as well.

I’m also sharing the Houdini file so the setup can be inspected directly rather than relying only on the screenshots. Since the issue may be caused by something in the Vellum data, attributes, constraints, or an interaction between nodes that isn’t visible in the screenshots, I’d appreciate it if you could take a look at the file itself.

Could you please check the file and let me know whether the behavior I’m seeing is expected or if there is something incorrect in my setup?

If the setup looks correct and the scalp still separates from the guides under these conditions, I’d like to confirm whether this could potentially be a **Houdini/Vellum bug** before submitting a support ticket to the development team.

In particular, it would be helpful to confirm whether you can reproduce the issue from the attached file and whether the Vellum data/constraints are changing unexpectedly between frame 0 and frame 1.

Thanks again for taking the time to look into it.

Hi everyone,

I’m currently working on a Vellum-based groom simulation and I’m running into an issue where the scalp starts moving/separating independently from the groom guides as soon as the simulation begins.

The guide groom looks correct before entering the Vellum simulation, but once I start simulating, the scalp appears to move separately while the guides no longer behave as expected.

I’ve attached screenshots of my node network along with additional screenshots showing the Vellum data at frame 0 and at the first simulated frame. From my inspection, the Vellum data appears to change between these two frames, and I suspect this is related to the issue, but I’m not sure exactly what is causing it or what part of my setup is incorrect.

The groom/guides look correct before the Vellum simulation.
At frame 0, the scalp and guide setup appear to be correctly connected.
On the very next frame, the scalp begins to move independently from the guides.
This causes the groom to separate/deform incorrectly during the simulation.
I suspect there may be an issue with the Vellum constraints, pinning, point/primitive attributes, or the way the scalp is being incorporated into the simulation.

I would really appreciate it if someone could take a look at the attached node network and Vellum data and point out what I might be missing.

Is there a specific attribute or constraint setup I should verify to ensure that the scalp remains properly attached to the guides throughout the simulation?

Thanks in advance for any help or suggestions.