stl to solid mesh file

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1

Hello,
I have two questions.

  1. I have a .stl mesh file that is hollow inside. Can I change this to a solid mesh file in vtk? (e.g., Convert stl file to solid (from Magics to Solidworks or Catia)?)

Or can I save vtkpolydata as a solid mesh file?
If yes, any sample code?

  1. Does the .vtu extension provide the solid mesh format? (I want to use it in glvis.)

Thank you

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2

  1. No, VTK does not have general 3D meshing capabilities. vtkDelaunay3D can fill the volume but it will output the convex hull of your input. You may look at CGAL ( or a python wrapper of CGAL), Gmsh (or a python wrapper of Gmsh) or TetGen (or PyVista Wrapper of TetGen) for more general mesh generation capabilities. All three can output to VTK formats.

  2. Yes, you can store a vtkUnstructuredGrid (which can be used to represent a 3D mesh) into a vtu file.

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I actually wrote a small function (for vedo) where the vtkDelaunay3D alone seems to do a very good job! (not sure how it compares to tetgen)

"""Tetralize a closed surface mesh
Click on the mesh and press ↓ or x to toggle a piece"""
from vedo import *

surf = Mesh(dataurl+'bunny.obj', c='g3').cap().smooth()

tmesh = surf.tetralize(side=0.015)

# Assign an id to each tetrahedron to visualize regions
seeds = surf.clone().subsample(0.3)
cids = []
for p in tmesh.cellCenters():
	cid = seeds.closestPoint(p, returnPointId=True)
	cids.append(cid)
tmesh.celldata["fragments"] = cids

pieces = []
for i in range(seeds.NPoints()):
	tc = tmesh.clone().threshold("fragments", above=i-0.1, below=i+0.1)
	mc = tc.tomesh().color(i)
	pieces.append(mc)

show(__doc__, pieces, axes=1)
# tmesh.write('mytetmesh.vtu')  # save to disk

Screenshot from 2022-04-26 20-36-34
Screenshot from 2022-04-26 20-36-34725×668 199 KB

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4

This is really nice ! I guess vedo does some kind of preprocessing on the input before passing the result to vtkDelaunay3D ?

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5

yes - to generate the internal points, and some postprocessing to prune the tets that are inside the convex hull and outside the mesh.

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6

Thank you both for the detailed guide!!
Is it possible to use vedo in c++? :cry:

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Oh if you are in c++ you better go straight to the tetgen c++ implementation as Christos indicated.