Convert STP to OBJ in your application
3D InterOp is a CAD interoperability SDK that lets your software read STP files and write OBJ, generating the OBJ mesh from the geometry it reads, with tessellation settings your application controls.
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 STEP · Writes OBJ
- Exact geometry → triangle mesh
- C++ / C# APIs
STP to OBJ at a glance
STEP stores exact geometry; OBJ stores triangles. The translation is a tessellation, and the settings you choose decide how close the mesh stays to the original.
| STEP (source) | OBJ (target) | |
|---|---|---|
| Full name | Standard for the Exchange of Product model data | Wavefront OBJ |
| Standard / owner | ISO 10303 — AP203, AP214, AP242 | Open format |
| File extensions | .stp, .step | .obj |
| Geometry | Exact B-Rep | Polygon mesh |
| Assemblies / structure | Yes | No assembly hierarchy |
| PMI | Graphical and semantic (AP242) | None |
| 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 STEP to OBJ.
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Improved
Healed geometry3D InterOp repairs and heals STEP data during translation.
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Changes
Geometry is tessellatedThe exact STEP B-Rep is replaced by a triangle mesh, generated by 3D InterOp from the exact geometry it reads. Accuracy depends on the tessellation settings your application uses.
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Changes
Assembly structureOBJ has no native assembly hierarchy. Decide in your application how STEP product structure is grouped or flattened before writing.
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Not carried
PMIOBJ has no place for PMI, so the PMI read from STP isn’t written.
Why software vendors add STP 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 STP input: AP203, AP214 and AP242.
- 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 a STEP (.stp) file?
STEP is the ISO 10303 standard for exchanging 3D product data between CAD systems. Its application protocols range from exact geometry (AP203, AP214) to full model-based definition with PMI (AP242).
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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
3D InterOp tessellates the geometry it reads from STP when it writes OBJ. Your application sets the tolerances, so it controls the trade-off between accuracy and file size.
OBJ has no place for PMI, so the PMI read from STP isn’t written. Your application can still access it after import, or offer STEP AP242 as an output.
OBJ has no assembly hierarchy, so your application decides how the STP structure is grouped or flattened before writing.
The OBJ writer is available through the 3D InterOp UConnect interface.
3D InterOp reads AP203, AP214 and AP242.
Yes. 3D InterOp reads and writes both formats, so OBJ to STP is supported too.
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Building software that needs to convert STP to OBJ?
3D InterOp is an SDK that lets your application read STEP and write OBJ alongside 30+ CAD and BIM formats.