Create SubD Cap / Form from Edges

Hey all,

Very newly getting back into Rhino so please excuse any general lack of knowledge. I’m modeling some rockwork forms for a tunnel system, and had been advised to build out of SubD forms. The walls went great and I was easily achieving what I wanted, but now I’m really struggling with how to generate a ceiling to cap the forms. See image:

I highlighted in red the form I’m trying to achieve, with the hopes of being able to join and merge the resulting form to to the wall SubDs to then create a smooth transition tunnel ceiling look. I’ve been banging my head for hours to no luck, any help would be greatly appreciated!

Hi Creighton - it’s hard to see how that could work as you show it - there would be non-manifold edges for example here:


Ok so since they’re separate forms there isn’t a great option for it? I was just able to get something by lofting across the tunnel, worked pretty well just needed some stitching and hole filling. Not ideal but the only thing close I’ve found so far.

If it was a continuous edge, what would I use?

Hi Creighton - I take it back - if the ‘back’ does not need to be closed/capped then you don’t get a nonmanifold.
Bridge can help to start with, pick the same number of edges on either side of the gap to fill.


Any reason you couldn’t convert this object to a nurbs poly surface, then trim and cap?

Keep a copy of your original subD, and use the toNurbs command to do the conversion.

I was thinking of that, the issue just being the SubD elements are flexible and easy to grab and adjust and this project is still in early development, so if I was able to keep it all SubD that would be ideal. That might be my route but am finding like with the SubD Loft tool now and patching up holes.


He mentioned that he needs a smooth transition not a flat cap.

that and bridge will be your friends for this job…

if you get stuck feel free to post the file, or you can email it to attn Kyle and I’ll be happy to take a peek at it.