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deadsy / sdfx

A simple CAD package using signed distance functions
MIT License
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Hollow out 3D meshes by this tool? #53

Closed Megidd closed 2 years ago

Megidd commented 2 years ago

Background

There is a Go source code already available. The source code imports 3D STL surface meshes and stores the index and vertex buffers corresponding to the 3D STL surface mesh.

It's desired to hollow out the imported 3D STL surface meshes by a thickness. To do so, this algorithm might be possible:

  1. Represent the original 3D surface mesh by signed distance field - SDF.
  2. Extract an iso-surface from SDF.
    1. Marching Cube algorithm to extract the iso-surface from SDF.
    2. A negative offset/distance is the threshold passed to marching cube algorithm.
    3. Negative offset means the new iso-surface would be inside SDF.
    4. The offset/distance is actually the thickness of the hollowing process.
  3. Flip the normal vectors of the new internal iso-surface.
    1. This step is trivial.
  4. Merge new internal iso-surface with the original external surface mesh.
    1. This step is trivial.

Question

It's noticed that this package may contain the necessary code for steps 1 and 2 above. Is it right? Is it possible to hollow out 3D STL surface meshes by this package? Can anyone provide a boilerplate code to do so?

deadsy commented 2 years ago

The function you are looking for is sdf.Offset3D() You can see an example of it's use in ./examples/offset_box. Note that the "hollowing out" operation just occurs on the SDF. It has nothing to do with the source being an STL.

Pseudo code is something like:

s0 := ImportSTL("file.stl) s1 = Offset3D(s0, thickness) s2 := Difference3D(s0, s1) Render(s2)

Megidd commented 2 years ago

Thanks @deadsy I'm going to try it. Probably I'll be back with some questions :slightly_smiling_face:

Megidd commented 2 years ago

Conclusion

PR #54 introduces an example to carve out the inside of the input STL surface mesh. The corresponding comments of PR #54 should be noted.

So, steps 1 and 2 of this algorithm can be done by this package:

  1. Represent the original 3D surface mesh by signed distance field - SDF.
  2. Extract an internal iso-surface from SDF. It's inside the original surface mesh.
  3. Flip the normal vectors of the new internal iso-surface.
  4. Merge new internal iso-surface with the original external surface mesh.

Steps 3 and 4 are trivial.