A watertight mesh paired with a deliberately broken twin (holes, missing faces, open ends), the input and intended result for a mesh-repair / hole-filling tool.
Watertight box mesh — the intended result for a mesh-repair / hole-filling tool applied to the broken member of this group.
Deliberately broken box mesh (missing top face) — feed to a mesh-repair tool and compare the result against the watertight ground truth.
Watertight tube mesh — the intended result for a mesh-repair / hole-filling tool applied to the broken member of this group.
Deliberately broken tube mesh (open, uncapped ends) — feed to a mesh-repair tool and compare the result against the watertight ground truth.
Watertight sphere mesh — the intended result for a mesh-repair / hole-filling tool applied to the broken member of this group.
Deliberately broken sphere mesh (open hole at the base) — feed to a mesh-repair tool and compare the result against the watertight ground truth.
A welded, manifold, consistently-wound unit cube: 8 vertices, 12 triangles, 18 edges each shared by exactly two faces, and a signed volume of exactly 1.0. This is the answer key — each defect fixture in the degenerate/ subcategory is this mesh with exactly one thing wrong.
The clean reference cube as a GLB, so the same baseline is available to glTF tooling and to the site's 3D preview. Identical topology to the OBJ twin in this group.
The reference cube plus four triangles with no area, one for each way a mesh can have one: three collinear points, two coincident vertices at different indices, a repeated index, and all three indices identical. Their face normals are undefined, which is where downstream tools produce NaN.
The same four degenerate triangles inside a structurally valid GLB. The file passes every glTF schema check — nothing in the format forbids a zero-area face — so this is the fixture for geometry validation as opposed to document validation.
An ASCII STL of the reference cube with two extra facets that have no area and declare a null (0 0 0) normal — exactly what CAD tessellators emit at a sliver. Slicers either drop them, warn, or divide by zero; this is how you find out which.
The reference cube with all eight corners stored twice at bit-identical coordinates: the first six triangles use one copy, the last six use the other. It renders as a closed cube but is topologically two disconnected surface patches with a split seam, which is why smoothing, subdivision and boolean operations all misbehave on it.
The duplicated-corner cube as ASCII PLY — the format scanners and photogrammetry tools emit, and the one where unwelded duplicates are most common because each captured point arrives independently.
The duplicated-corner cube as a GLB. Because glTF stores every attribute per vertex, the duplication doubles the position and normal buffers for a shape that needs eight corners — the cheapest optimisation an asset pipeline can make, and the one this fixture measures.
The reference cube with a two-triangle fin welded along one top edge, so that edge is shared by three faces instead of two. Non-manifold edges have no defined surface orientation, which is why slicers refuse them and why subdivision and offsetting produce garbage.
The finned cube as a GLB. It renders without complaint in any viewer — rasterisation never asks about adjacency — so this is the fixture that separates tools which actually analyse topology from tools which merely draw triangles.
The reference cube with three of its six cube faces (six of its twelve triangles) wound clockwise instead of counter-clockwise, and `vn` records that follow the reversed winding into the solid. The classic symptom is a model that looks half-invisible with backface culling on and half-black with it off.
The mixed-winding cube as a GLB with a default single-sided material, so the reversed faces are culled and you can see straight through the model. Turning on doubleSided hides the defect without fixing it, which is the trap this fixture is for.
A structurally perfect ASCII PLY in which one vertex reads `nan nan nan` — the value an exporter writes after dividing by a zero-length vector. The header, counts and face list are all correct, so the file parses; every bounding box, centroid and normal computed from it is then poisoned.
The same NaN vertex in Wavefront OBJ, where the literal is the bare token `nan`. Normals are deliberately not written, because the three faces touching that vertex have no computable normal — which is exactly the state an importer must handle rather than serialise.
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