Convert ASAT to STP in your application
3D InterOp is a CAD interoperability SDK that lets your software read ASAT files and write STP, 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 ACIS assembly · Writes STEP
- Exact geometry → exact geometry
- C++ / C# APIs
ASAT to STP at a glance
Both formats store exact geometry, so the model stays exact. The differences are in the product data each one can carry.
| ACIS assembly (source) | STEP (target) | |
|---|---|---|
| Full name | ACIS assembly, text (ASAT) and binary (ASAB) | Standard for the Exchange of Product model data |
| Standard / owner | Spatial (3D ACIS Modeler) | ISO 10303 — AP203, AP214, AP242 |
| File extensions | .asat, .asab | .stp, .step |
| Geometry | Exact B-Rep | Exact B-Rep |
| Assemblies / structure | Yes | Yes |
| PMI | Assembly-level PMI written as attributes | Graphical and semantic (AP242) |
| 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 ACIS assembly to STEP.
-
Preserved
Exact geometrySolids and surfaces stay exact B-Rep. The model is never reduced to a triangle mesh.
-
Preserved
Product structureThe ASAT product structure is written to STP.
Why software vendors add ASAT to STP conversion
Supplier and OEM exchange
STEP is the ISO standard most supply chains specify for exchanging 3D models. Writing it lets your users send data to partners on any CAD system.
Model-based definition
STEP AP242 can carry semantic PMI next to exact geometry, so your users can share models together with their manufacturing data.
Long-term archiving
As an ISO standard independent of any CAD vendor, STEP is widely used to archive product data.
Things to check before you ship
- Written STP versions: AP203, AP214 or AP242 (.stp, .step or .stpx).
- Supported ASAT input: ACIS R1 to 2026 1.0.
- 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
-
Source 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.
-
Target 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).
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 ASAT product structure and writes it to STP.
The STEP writer supports AP203, AP214 and AP242, with AP214 as the default. Your application sets the version at export; semantic PMI is written to AP242 only.
3D InterOp reads ACIS R1 to 2026 1.0.
Yes. 3D InterOp reads and writes both formats, so STP to ASAT is supported too.
-
Building software that needs to convert ASAT to STP?
3D InterOp is an SDK that lets your application read ACIS assembly and write STEP alongside 30+ CAD and BIM formats.