SubD object matching the shape of a mesh

[pagarcia (Pablo Garcia-Amorena)]

Hello,

I’m trying to create a SubD surface contouring part of a mesh. It is a small implant over the maxilla of a patient. Here the skull:

And here an example (at right, in blue) of how this implant should look like:

Source image.

It should be an object that is attached to the geometry in the back, and on the front allows some degree of modification.

I think SubD should be the best object to do so. I have tried with Sketch tool and Patch and OffsetSrf to create a polysurface, but it is hard to modify afterwards.
The only problem I find with SubD is how to make an initial shape that matches an area over the mesh, from where I can start shaping the final object.

Do you think this is possible with SubD, or any other tool in Rhino?

Here the full mesh:

54170000_FullSkull.stl (15.1 MB)

Thank you in advance,
Pablo

[maje90 (Riccardo Majewski)]

It seems the .stl is sort of mirrored but with the wrong plane… (?)
Anyway, I did this:

• delete all meshes unneeded (small fragments, the other half, etc etc)
• do AlignVertices with 0.1
• do Weld with 180
• manually delete all the faces you dont care about, keep only the portion near what you need
• do QuadRemesh with like 500 face amount and flag SubD output
  
  

… it’s a start point.

[pagarcia (Pablo Garcia-Amorena)]

Thank you Riccardo, this is a good idea. Yes, the mirroring was not very well done

I was wondering how to cover holes like this in advance, so that the patch is clean from the beginning.

I tried filling SubD holes afterwards, but the results are not very good.

Ideally, we can tell Rhino to “cover” this in advance.

[maje90 (Riccardo Majewski)]

I worked few times with pure mesh on rhino.
I think (but i am guessing) that usually you try to clean the mesh with the software that created it, like the 3d scan software, or what was used in this case (x-ray?).
I don’t know how advanced are rhino tools to do this kind of “clean up” with meshes…
I really liked meshmixer, when i needed.

Maybe try to use the select by brush tool in rhino, then make a rough cap (even triangulated), then quadremesh will pass over everything and be better. Probably.

---

Another way is to use WIP version and try shrinkwrap command, but I have never tried it yet.
This way How to smooth a curve but preserve area? - #3 by DanielPiker

[pagarcia (Pablo Garcia-Amorena)]

I tried Shrink Wrap and works quite well:

It’s a way to close the hole and provide a closed mesh, that can be quad-remeshed afterwards. I will try to work on this line.

Definitely, there’s other software for mesh cleaning. In our case, we develop a plug-in that makes the scan-to-raw-mesh part, in Rhino. Ideally we could keep all the workflow in Rhino.

Thank you for the hints!

[theoutside (Kyle Houchens)]

another way to handle this which is not widely known in rhino circles for some unknown reason:
Use the patchsingleface command which allows you to make a polygon “bridge” over large holes, breaking them up into smaller, easier to handle holes, that you can then use the fillmeshhole or fillmeshholes command to fill them completely.

granted this is tedious and can take some time to do, but it’s very effective when you have messy meshes that need to be surgically repaired.