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Sometimes people give me 3D models, for instance, a car. I need to process it by using the normal vectors. But sometimes some of the triangles have opposite normal vectors, which will cause trouble, I would like to correct the normal vectors automatically, Is there a way ?

Thanks!

blackball
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    If you are talking about "real" orientation issues of faces (vs. numerical issue while computing normal vectors), you can try using the function [`orient_polygon_soup`](https://doc.cgal.org/latest/Polygon_mesh_processing/group__PMP__orientation__grp.html#gaadc5bac3072b11d2313e40043c729d0a). – sloriot Jun 15 '20 at 11:09
  • Usually 3D software like Blender or commercial ones have simple ways to flip the normals. In which format do you get the models? Do you need to flip all normals or just a a part depending on some condition, e.g. flip if z < 0 or so? – Joe Jun 15 '20 at 11:28

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