OBJ — Zero-area Triangles
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.
Interactive preview rendered from the equivalent glTF (zero-area-triangles.glb); drag to orbit. Download the file above for the OBJ original.
Specifications
- Format
- Wavefront OBJ
- Vertices
- 13
- Triangles
- 16
- Zero Area Triangles
- 4
- Null Normal Records
- 4
- Defects
- collinear, coincident, repeated index, all-same
- Note
- the 12 cube triangles are intact
Testing contract
Expected to recover- Scenario
- Compute a face normal for every triangle, then run a cleanup pass that removes degenerate faces.
- Expected result
- Four faces have a zero-length cross product and must be dropped, leaving exactly the 12 cube triangles; a tool that normalises without a guard emits NaN normals instead.
What is a .obj file?
OBJ (Wavefront OBJ) is a text-based 3D geometry format defining vertices, texture coordinates, normals, and faces, and referencing materials through a companion MTL file. It is simple, widely supported, and can represent polygonal meshes with UV mapping. It is a common interchange format across 3D tools.
How to use this file
Use an example OBJ to test mesh and UV parsing, MTL material resolution, and importers in 3D engines, renderers, and modeling applications.
How to use this file for testing
“OBJ — Zero-area Triangles” is a deterministic Novus Examples fixture for Mesh repair testing, Mesh processing QA. 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.
Documented properties for this file: Wavefront OBJ. Compare results against paired or grouped companions on this page when present (clean↔damaged, searchable↔scanned, or format twins) so scores stay reproducible across runs.
Download the file once, keep the path stable in CI or local scripts, and treat the spec table as the contract: dimensions, seeds, field lists, and roles are intentional. Corrupt or invalid samples are labelled as such — expect parsers to fail loudly rather than silently accept them.
3D and CAD fixtures carry one small, documented solid or scene. Convert and inspect against the known geometry, units, and structure; format twins let you diff interchange fidelity, and the 3D viewer previews the actual mesh.
Code examples
import trimesh # pip install trimesh
mesh = trimesh.load("zero-area-triangles.obj")
print(mesh.bounds, mesh.faces.shape)Related files
- glbGLB — Clean Reference CubeThe 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.
- glbGLB — Duplicate Vertices, Split SeamThe 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.
- glbGLB — Inverted Normals / Mixed WindingThe 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.
- glbGLB — Non-manifold Edge (three faces on one edge)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.
- objOBJ — Clean Reference CubeA 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.
- objOBJ — Duplicate Vertices, Split SeamThe 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.
Generated by generation/models_p7.py. Free for any use, no attribution required — license.