Extracting boundaries from a 3D scan

Hi. I am working with a 3D scanned file. Got it as a mesh (STL) and converted to polysurfaces.

I am trying to extract the outer edges/lines in order to export it to AI and laser cut it.
I am not sure if there is any other option that the one I am applying now. It is considerable time consuming. I am wondering if someone has a better idea.

I am applying a Make2D from top and then joining one by one the lines. After I get a close polyline I create a surface to check if the lines are placed in the exact same plane. I guess this could be it and I just need to accept It will take a looong time. Just in case…I leave attached images of one of my layers.

Thanks for your time :slight_smile:

Try this if open on one side:

And if a closed volume try this:

Unweld 0 Enter

drag windows to Select all the smaller edge triangles (mesh faces) and delete them.
Join the rest and run SplitDisjoinedMesh
And then select one of the two sided and then type DupBorder.

Thanks @Holo workedddddd , thanks thanks so much

One more question to make the process dynamic. Do you know if there is anyway to select all the surfaces that are above a plane? I am afraid the windows selection its too tedious since my triangles on the sides are super small and close to the bottom surface (the want I only need).


Get a view of the plane on-edge, then box-select by dragging from lower right of the screen to upper-left around only the objects above the plane?

Well, that’s where programming is handy. You could analyze every face and delete all the ones that are not facing straight up. But this manual process CAN work if your scans are clean:

Unweld 0
Weld 25

Select the part you want


Change the weld value to something esle if you want. If the part you want is very level then lover it to say 3 degrees.

Once your edge curve is generated you can project it to Cplane to flatten it.

Come to think of it…
Did you try to Make2D of the part? That can work to :slight_smile:
(if you have Rhino6)

Thanks @Holo
I am sorry for keep taking your time. I noticed the unweld command gives me a preview of exactly what I want. It highlights the boundary edges after the unweld 25 . The problem is after applying…I can not see any difference or extract just the borders.

  1. Unweld 0 = everything is highlighetd.
  2. Unweld 25 = just the borders of my top and bottom surface
  3. Splitdisjointedmeshes = no difference. The command notifies me it can not be applied (mesh can not split).
  4. Explode = all the meshes separated.
  5. dupborder = all meshes border :frowning:

Thanks so much

EDIT: I notided I applied the unweld twice…sorry

Now I understand the Weld will reconfigure those meshes to unify them. I can get rid of the lid as an entire mesh now which is great , but the sides and the bottom (the one I need) are one piece.

My bad, forget about the splitdisjoinedmesh part, my vaccation head mixed stuff up . Use explode after the weld. The reason to unweld first is that IF the mesh is allready welded at a higher than 25 value then welding with 25 will make no difference.

If you need to extract the bottom then you have to play with the weld value. try it at 5 instead.
Back to the beach now :wink:

Thanka thanks so much, at the end worked perfectly :slight_smile:

All the best to you and enjoy your vacations.

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