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Manifoldness or Watertightness:
Manifold meshes are characterized by strong connectivity. In simple words, each triangle of a mesh should be connected to exactly 3 neighbor triangles.
Strong connectivity guarantees that none of the following problems occurs:Holes
Redundant triangles
Merged objects
Correct triangle orientation:
Meshes with correct triangle orientation uniquely define the inside and the outside of the object. If this requirement is not met, printers may not be able to correctly distinguish between printing volume and empty space. Triangles with incorrect orientation (in black) may also not be visualized incorrectly by CAD programs.
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