Convert CATPart to ASAT in your application
3D InterOp is a CAD interoperability SDK that lets your software read CATPart files and write ASAT, with exact B-Rep geometry carried across and nothing tessellated, without a CATIA license.
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 CATPart · Writes ACIS assembly
- Exact geometry → exact geometry
- C++ / C# APIs
CATPart to ASAT at a glance
Both formats store exact geometry, so the model stays exact. The differences are in the product data each one can carry.
| CATPart (source) | ACIS assembly (target) | |
|---|---|---|
| Full name | CATIA V5 Part | ACIS assembly, text (ASAT) and binary (ASAB) |
| Standard / owner | Dassault Systèmes | Spatial (3D ACIS Modeler) |
| File extensions | .CATPart | .asat, .asab |
| Geometry | Exact B-Rep | Exact B-Rep |
| Assemblies / structure | Part file (assemblies are CATProduct files) | Yes |
| PMI | Semantic and graphical | Assembly-level PMI written as attributes |
| 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 CATPart to ACIS assembly.
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Preserved
Exact geometrySolids and surfaces stay exact B-Rep. The model is never reduced to a triangle mesh.
Why software vendors add CATPart 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 CATPart input: CATIA V5 R8 to V5-6 R2026.
- 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 CATPart (.CATPart) file?
A CATPart file is a CATIA V5 part: one component with its exact 3D geometry, features and, often, PMI. Assemblies of parts are stored in CATProduct files.
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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
Yes. Both formats store exact B-Rep geometry, so the model is translated without being tessellated into triangles.
An ACIS assembly (ASAT/ASAB) doesn’t support layers or colors at instance level, suppressed or hidden instances, or units at instance level.
No. 3D InterOp reads CATPart files directly, without CATIA or a CATIA license on the machine.
3D InterOp reads CATIA V5 R8 to V5-6 R2026.
3D InterOp writes ACIS R18 to 2026 1.0.
Yes. 3D InterOp reads and writes both formats, so ASAT to CATPart is supported too.
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Building software that needs to convert CATPart to ASAT?
3D InterOp is an SDK that lets your application read CATPart and write ACIS assembly alongside 30+ CAD and BIM formats.