Hello,

Im new to Houdini, and am exploring hair simulation. More specifically, I'm looking into simulating curves/guides brought in from outside sources. In this case im bringing in curves/guides and animated geo as alembic. I'm able to bring it in using the guide groom and guide deform object nodes. While I have used and explored just adding a guide sim node after, I've wanted to look into doing a sim building a vellum network. I am currently stuck where I run the vellum solver and curves/guides just fall off. I know i need to add a pin to target vellum constraint in-between the hair constraint and the vellum solver. However I'm having trouble finding and creating a group that have the base points of the curves/guides that are attached to the animated geo. I've heard of a roots group, but when i put it into the group section on the pin to target constraint nothing happens and the vellum solver just shows a static non animating pose. This let me to believe that the roots group does not exist and that i have to create the group, but i'm not sure how to do that. Any help would be greatly appreciated.

Thanks

You need to pin your points on the hair vellum constraint and for that you can use the group expression sop and it has as a snippet code for this "first point of primitive" `vertexprimindex(0, @vtxnum)==0` also make sure you have match animation and depending on your needs you can play with the pin type orient pin type

Awesome. I'll give it a go. Thanks for your help.