AlignScan / Guides / STL vs OBJ vs PLY
Guide
STL vs OBJ vs PLY for 3D scans
Scanners and scan software export a handful of mesh formats. All three below store triangles, but they differ in what else they carry, and that matters when you move a scan between tools.
| STL | OBJ | PLY | |
|---|---|---|---|
| Geometry | Triangles only | Polygons, shared vertices | Polygons, shared vertices |
| Colour | No (non-standard extensions only) | Via materials and textures | Per-vertex colour built in |
| Units | None | None | None |
| Encoding | Binary or ASCII | Text | ASCII or binary |
| Typical use | 3D printing, CAD exchange | DCC apps, textured scans | Scanners, point-cloud tools |
Practical advice for scans
- STL is the safe choice for printing and most CAD imports, but loses colour. Prefer the binary variant; ASCII STL is several times larger.
- OBJ is the best choice when the scan carries a texture. Keep the .mtl and image files next to the .obj.
- PLY keeps per-vertex colour without separate texture files and is common straight from scanners.
- None store units. Always check scale after import, especially if a tool assumes millimetres and your scanner exported metres.
Aligning without damaging the file
Alignment should only change vertex positions and normals. AlignScan rewrites just those bytes in the original file: in an STL the attribute bytes stay, in an OBJ every non-coordinate line is copied untouched (colour columns after the coordinates included), and in a PLY the colours, faces and other properties are left alone. Triangle count and order do not change.
Skip the manual work: drop your scan into AlignScan. It runs in your browser and the file is never uploaded.
Open the aligner → Try a sample first