Convert DGN to ASAT in your application
3D InterOp is a CAD interoperability SDK that lets your software read DGN files and write ASAT, with exact B-Rep geometry carried across and nothing tessellated.
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 MicroStation DGN · Writes ACIS assembly
- Exact geometry → exact geometry
- C++ / C# APIs
DGN 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.
| MicroStation DGN (source) | ACIS assembly (target) | |
|---|---|---|
| Full name | MicroStation Design file | ACIS assembly, text (ASAT) and binary (ASAB) |
| Standard / owner | Bentley Systems | Spatial (3D ACIS Modeler) |
| File extensions | .dgn | .asat, .asab |
| Geometry | Exact B-Rep | Exact B-Rep |
| Assemblies / structure | Yes: models and references | Yes |
| 3D InterOp support | Read only | Read and write |
What's preserved, what changes
Here is what your application can expect to carry across from MicroStation DGN 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.
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Preserved
Product structureThe DGN product structure is written to ASAT.
Why software vendors add DGN 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 DGN input: DGN V7 to V8.
- 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 DGN (.dgn) file?
DGN is the native design file format of Bentley MicroStation, widely used for infrastructure, plant and civil engineering projects. It exists in two generations, V7 and V8.
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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.
Yes. 3D InterOp reads the DGN product structure and writes it to ASAT.
An ACIS assembly (ASAT/ASAB) doesn’t support layers or colors at instance level, suppressed or hidden instances, or units at instance level.
3D InterOp reads DGN V7 to V8.
3D InterOp writes ACIS R18 to 2026 1.0.
No. 3D InterOp reads DGN but doesn’t write it. To send data back to MicroStation users, write a neutral format they can import, such as IFC or STEP.
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Building software that needs to convert DGN to ASAT?
3D InterOp is an SDK that lets your application read MicroStation DGN and write ACIS assembly alongside 30+ CAD and BIM formats.