Jump to content
Scratch

Orient attribute on vellum guides are "flipping"

Recommended Posts

Hey all,

I have some guide hairs in vellum and my orient (point-)attribute which is generated using the guide deform sop is "flipping" (sign changes on orient vector components). This causes the guides to freak out during simulation, showing randomly changing length, jittering and weird behaviour etc.

Knowing that vellum needs a stable orient attribute to produce stable sim results, I tried to delete that orient attribute coming from the guide deform sop and instead let it be calculated on the vellum constraint node using "compute missing orientation". The values are somewhat the same and somewhat also different, but I also see some "flipping" orientation values from frame to frame on some guides.

If I disable the orient attribute on the guide deform sop (create orient attribute off) and on the vellum constraints sop (compute missing orientation off), I assumed no orient is calculated for my guides, but to my surprise, I still have an orient attribute present after the vellum constraints sop. The even bigger surprise was, that this orient attribute produced a totally stable sim.

This left me rather confused, and I hope you guys can maybe shed some light on whats going on here.
Why is my orient attribute flipping, how can this be prevented, and what (where) is the best way to calculate a stable orient attribute?

I unfortunately can't provide a hip-file showing the issue cause my current project is under NDA, but I still hope you guys can make some sense of what I say. I am using Houdini 18.5.392.

Thanks in advance and all the best,
Scratch

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×