Convert STL to OBJ in your application
3D InterOp is a CAD interoperability SDK that lets your software read STL files and write OBJ, carrying the mesh data across without re-tessellating it.
Spatial does not offer an online converter or a desktop conversion app. 3D InterOp is a component that software vendors embed in their own products.
- Reads STL · Writes OBJ
- Triangle mesh → triangle mesh
- C++ / C# APIs
STL to OBJ at a glance
Both formats store triangles, so the facets carry over without re-tessellation. The differences are in structure, appearance and metadata.
| STL (source) | OBJ (target) | |
|---|---|---|
| Full name | Stereolithography | Wavefront OBJ |
| Standard / owner | Open format | Open format |
| File extensions | .stl | .obj |
| Geometry | Triangle mesh | Polygon mesh |
| Assemblies / structure | No | No assembly hierarchy |
| 3D InterOp support | Read and write | Read and write |
What's preserved, what changes
Here is what your application can expect to carry across from STL to OBJ.
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Preserved
Mesh dataThe STL facets are read and written to OBJ without being re-tessellated.
Why software vendors add STL to OBJ conversion
Lightweight review
OBJ carries tessellated geometry that opens much faster than the full CAD model, so design reviews and digital mockups stay responsive.
Sharing outside engineering
Marketing, training and sales teams rarely have CAD software. A OBJ file gives them the shape in a format their tools can open.
Easier handling of large assemblies
Without exact surfaces and feature data, OBJ files are easier to transfer and display, even for large assemblies.
Things to check before you ship
- The OBJ writer is available through the UConnect interface only.
- Supported STL input: any STL version.
- Test tessellation settings on your heaviest parts: finer meshes mean larger files.
- Validate a sample of translated files in the target system your users actually work with.
Working with Spatial was a real milestone for us: Thanks to the powerful 3DInterOp library, we were able to successfully bring our complex CAD-based solutions to the cloud while remaining flexible to meet individual customer requirements. For us, Spatial is not just a technology partner, but a true enabler of our product strategy.
Dr. Arno Michelis, Founder, Simus Systems
Read the Case StudyAbout the formats
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Source format
What is an STL file?
STL describes a 3D surface as a set of triangles, with no units, materials or assembly structure. Its simplicity makes it the usual input for 3D printing.
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Target format
What is an OBJ (.obj) file?
OBJ is a simple, widely supported text format for polygon meshes, created by Wavefront. It describes vertices, faces and texture coordinates, with materials in a separate .mtl file.
Frequently asked questions
No re-tessellation is needed. 3D InterOp reads the STL facets as visualization data and writes them to OBJ.
The OBJ writer is available through the 3D InterOp UConnect interface.
STL files store no units, so the 3D InterOp STL reader assumes millimeters. Agree on the unit with the application that wrote the file.
3D InterOp reads any STL version, as visualization data.
Yes. 3D InterOp reads and writes both formats, so OBJ to STL is supported too.
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Building software that needs to convert STL to OBJ?
3D InterOp is an SDK that lets your application read STL and write OBJ alongside 30+ CAD and BIM formats.