One reversed face, three inconsistent edges

Reversing one face of a closed tetrahedron leaves the four triangles in the same positions. It changes the direction of the three shared edges around that face. With four faces, you can count the affected edges before opening the file.

How this was measured

Start with the analytic four-face tetrahedron and reverse one triangle. A consistent orientation assigns opposite directions to each shared edge. Three original face orientations agree with one solution and only one agrees with its opposite, so the existing majority uniquely determines which face to reverse. Export the result as binary STL, reread it, and compare triangle coordinates and topology within the recorded float32 bound.

Recorded output from this experiment
Measurement	Value
before / triangles	4
before / dimensions	10 × 10 × 10
before / units	Not recorded
before / open Edges	0
before / inconsistent Edges	3
before / non Manifold Edges	0
before / degenerate Triangles	0
before / components	1
after / triangles	4
after / dimensions	10 × 10 × 10
after / units	Not recorded
after / open Edges	0
after / inconsistent Edges	0
after / non Manifold Edges	0
after / degenerate Triangles	0
after / components	1
changed Faces	1
verified	true

What the result does not establish

This experiment resolves a local orientation disagreement. It does not determine inside versus outside, interpret nested shells as cavities, or test self-intersections. A tied orientation vote, an open component, or a non-manifold component is a refusal case rather than a repair result.

Try these files

These samples were created by this project and released under CC0. They contain no visitor files. Sizes and SHA-256 hashes identify the exact bytes measured in this experiment.

One reversed face disagrees on its three shared edges. (STL, 284 bytes)
SHA-256
65b38cbaf9678390ad31328967d80e3e84595fc16b8c1b48d9f95fdccd220fe4
The one-flipped-face sample after a verified winding correction. (STL, 284 bytes)
SHA-256
7d98ff53aa7c0ac15350e51fc0adf77ebd39df597cac09f07269e1ff3fff9aa4

Use this result

Correct an STL face that is wound backwards

Versions and reproduction

Evidence generated 2026-09-05T21:13:29.140Z. The checked-in generator rebuilds the sample collection and measurements with one command:

node --experimental-strip-types scripts/build-workbench-evidence.ts

CAD source generation: scripts/build-workbench-cad.py with cadquery-ocp 7.9.3.1.1; checked-in analytic cylinder outputs. The STEP and IGES outputs are checked in so ordinary evidence rebuilds do not require Python.

@astrojs/cloudflare: 14.3.0
@cloudflare/containers: 0.3.7
astro: 7.3.1
fflate: 0.8.3
jose: 6.2.12
occt-import-js: 0.0.23
rhino3dm: 8.32.2
three: 0.185.1

Geometry source and generator SHA-256 hashes:

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