AlignScan / Guides / Zero rotation
Guide
Zero the rotation of a 3D scan
A raw 3D scan lands in your software at whatever angle the scanner happened to see it. "Zeroing the rotation" means rotating the mesh itself so its natural axes line up with the world X, Y and Z axes, and the object's rotation fields read 0.
Zero rotation is two different things
People use the phrase for two situations, and mixing them up causes most of the confusion:
- Object transform: the rotation values stored on the object (in Blender, the Rotation fields in the N panel). Clearing them just snaps the object back to how the vertices are stored. If the scan was crooked in the file, it is still crooked.
- Mesh orientation: the actual vertex coordinates. This is what a scan needs fixed. Once the vertices are square to the axes, object rotation can sit at zero and stay meaningful.
AlignScan fixes the second one by rewriting the vertex coordinates (and nothing else) in the exported file.
Step by step
- Decide what "square" means. A scan of a mechanical part has obvious datums: the largest flat face, a wall, the axis of a bore. Organic shapes have no true zero, so choose a sensible reference (a plane of symmetry, a base).
- Run automatic alignment. AlignScan fits planes to flat regions of the mesh, which averages out scan noise, finds the dominant directions, and squares them to the axes with the smallest rotation from the pose the scan already has.
- Check from orthographic views. Use Top, Front and Right. Flat walls that should be square appear as straight lines parallel to the grid. Coloured patches show which faces were locked to X, Y and Z.
- Fix the up direction if needed. If it landed on its side, use the 90° and flip buttons, or switch to Manual and snap a clicked face to the floor.
- Recenter. Bounding-box centre is predictable; surface centroid is better for lopsided parts. See orienting an STL to the origin.
- Export and verify. Re-import and confirm the part is square. Because only coordinates change, triangle count and order stay identical.
Skip the manual work: drop your scan into AlignScan. It runs in your browser and the file is never uploaded.
Open the aligner →Why scans resist "just rotating by eye"
A tilt of one degree over a 200 mm part is 3.5 mm of drift. That is invisible while orbiting and expensive later when you sketch on a face that is not quite parallel to your plane. Measuring the flat faces numerically removes the guesswork.
When there are no flat faces
Human faces, sculptures and natural objects have nothing to square. AlignScan then falls back to mirror symmetry or principal axes and reports lower confidence. Treat that result as a starting pose, not a measurement.