Convert OBJ to ASAT in your application
3D InterOp is a CAD interoperability SDK that lets your software read OBJ files and write ASAT, writing the OBJ facets as faceted geometry, since OBJ stores triangles rather than solids.
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 OBJ · Writes ACIS assembly
- Triangle mesh → faceted B-Rep
- C++ / C# APIs
OBJ to ASAT at a glance
OBJ stores triangles; ACIS assembly is an exact-geometry format. The mesh is written as faceted geometry: 3D InterOp doesn’t rebuild smooth surfaces from triangles.
| OBJ (source) | ACIS assembly (target) | |
|---|---|---|
| Full name | Wavefront OBJ | ACIS assembly, text (ASAT) and binary (ASAB) |
| Standard / owner | Open format | Spatial (3D ACIS Modeler) |
| File extensions | .obj | .asat, .asab |
| Geometry | Polygon mesh | Exact B-Rep |
| Assemblies / structure | No assembly hierarchy | Yes |
| 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 OBJ to ACIS assembly.
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Changes
Faceted geometryOBJ stores triangles, so the ASAT file holds faceted bodies, not solids. 3D InterOp doesn’t rebuild exact B-Rep from a mesh.
Why software vendors add OBJ to ASAT conversion
Hand models to kernel-based applications
Many CAD, CAM and CAE applications are built on the ACIS assembly kernel. Writing ACIS assembly gives them exact geometry they can load without another translation step.
Downstream modeling and analysis
An exact ACIS assembly B-Rep can still be edited, meshed or machined by downstream tools, which a tessellated export would not allow.
Exchange within one ecosystem
Partners whose tools share the ACIS assembly kernel often prefer to exchange ACIS assembly files directly.
Things to check before you ship
- Written ASAT versions: ACIS R18 to 2026 1.0.
- Supported OBJ input: any OBJ version.
- 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 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.
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Target format
What is an ASAT (.asat) file?
ASAT and ASAB are the assembly versions of the ACIS save file, in text and binary form. They store the product structure of models built on Spatial’s 3D ACIS Modeler kernel.
Frequently asked questions
No. OBJ stores triangles, and 3D InterOp writes them to ASAT as faceted geometry. It doesn’t rebuild exact B-Rep from a mesh.
An ACIS assembly (ASAT/ASAB) doesn’t support layers or colors at instance level, suppressed or hidden instances, or units at instance level.
Yes. 3D InterOp reads the visual material properties of OBJ files on import.
3D InterOp reads any OBJ version, as visualization data.
3D InterOp writes ACIS R18 to 2026 1.0.
Yes. 3D InterOp reads and writes both formats, so ASAT to OBJ is supported too.
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Building software that needs to convert OBJ to ASAT?
3D InterOp is an SDK that lets your application read OBJ and write ACIS assembly alongside 30+ CAD and BIM formats.