Obtaining smooth surface division of a 3D scan


I’ve never used Blender before but I was told that this software might help me achieve my goal. I have some 3D scans in stl format that I want to convert to volumes and export to step or iges. The geometry is quite complex so I can’t recreate it in CAD software. The thing is that normally conversion of stl to CAD format results in lots of triangular faces created directly from the surface mesh. But I need a smooth division into a few faces defined by me. Something like that:

The blue face was specially created and the rest (gray) is just a single continuous surface.

Is it possible to achieve such an effect in Blender ? It seems that it’s the only free software that might be able do something like that.

Thanks in advance for your help.

You can’t do this in Blender.
You need a tool that can interpolate meshes to CAD surfaces.

Rhino has some ability to do this with Quad remesh and then subd, then convert subd result to Nurbs.
However, its going to generate patches, not a single surface.
And you won’t have a good indication of how the result will deviate from the original.

Most reverse engineering tools will generate multiple nurbs patches from scans.

You are not going to find a free solution that will accomplish this task, and if you need to understand how the resulting CAD surface deviates from the scanned surface as you are working you will need to spend some serious cash on a dedicated reverse engineering tool.

So you are looking at Rhino plus the Mesh2Surface plugin on the low end and roughly $4000 combined cost or DesignX or similar on the high end, over $10,000

Thanks for the reply. I was told that Blender + FreeCAD might work but I’m not sure about that. Maybe at least Fusion 360 or SolidWorks could help. This problem doesn’t seem so hard but it turns out that it’s far from being trivial.

The goal here is to obtain a model for numerical simulation (stress analysis). There’s no need for huge accuracy since the model will be meshed with tetrahedral elements anyway. Maybe this will make the task a bit easier to accomplish.

Fusion360 has a T-Splines derivative and you need a good, clean, quad mesh with a relatively low quad count to get a reasonable result .
SolidWorks cannot do this, it has no interpolation of mesh to CAD surfaces.

Maybe someone can add their experience with FreeCAD.