3D folks, I'm trying to find a good formal definition of "manifold" and "watertight" in relation to meshes.
Most definitions say something like "every edge is connected to exactly two faces", but that would imply that an inside-out mesh, a self-intersecting mesh, or a pair of triangles connected back-to-back (with zero volume) would also be manifold.
Is there a definition somewhere that covers these cases? And what is the difference between "watertight" and "manifold", or are they synonyms?
@nicklockwood watertight to me always meant "if you {3D printed it, but this was before we had 3D printers lol} put it in a bathtub, it wouldn't take on water".
Never thought about manifold 🤔 so I guess this reply is generally unhelpful
@nicklockwood Did a little lookup, the consensus seems to be that "manifold" is the 3D model's idea of no holes, and has a distinct inside and outside. Watertight is the practical implementation of this when that becomes a physical mesh.
Since we're talking about 3D printing – I find that a lot of the software I've tried handle it similarly (probably because most use Klipper anyway?).
Cura, for example, has a ton of settings to explicitly tell it what to do when it encounters ambiguity.
Nick Lockwood
Brandon