Convert SAT to STP in your application
3D InterOp is a CAD interoperability SDK that lets your software read ACIS files (SAT, SAB) and write STEP AP203, AP214 or AP242, with exact B-Rep geometry carried across.
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 · Writes STEP
- Exact geometry → exact geometry
- C++ / C# APIs
SAT 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 (source) | STEP (target) | |
|---|---|---|
| Full name | ACIS model file (text SAT, binary SAB) | Standard for the Exchange of Product model data |
| Standard / owner | Proprietary — Spatial (Dassault Systèmes) | ISO 10303 — AP203, AP214, AP242 |
| File extensions | .sat, .sab | .stp, .step |
| Geometry | Exact B-Rep | Exact B-Rep |
| Assemblies / structure | Parts in SAT/SAB, assemblies in ASAT/ASAB | Yes |
| PMI | PMI annotation classes | Graphical and semantic (AP242) |
| 3D InterOp support | Read and write · ACIS R18 to 2026 1.0 | Read and write |
What's preserved, what changes
Here is what your application can expect to carry across from ACIS to STEP.
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Preserved
Exact geometryACIS solids and surfaces are written to STEP as exact B-Rep.
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Changes
STEP versionThe STEP writer writes AP214 by default. Your application can choose AP203, AP214 or AP242 to match the systems your users exchange with.
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Not carried
2D curvesThe STEP writer cannot write 2D curves.
Why software vendors add SAT 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
- Set the STEP version explicitly if your users need AP203 or AP242: the default is AP214.
- Semantic PMI is written to STEP AP242 only, and requires a license in addition to the STEP Writer.
- ACIS assemblies are stored in ASAT/ASAB files rather than SAT: read those files to keep the assembly structure.
- 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 ACIS SAT file?
SAT is the native file format of 3D ACIS Modeler, Spatial's geometric modeling kernel used in CAD, CAM and CAE applications. It stores exact B-Rep models as text (.sat) or binary (.sab); ACIS assemblies use the .asat and .asab extensions.
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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
The STEP writer supports AP203, AP214 and AP242, with AP214 as the default. Your application sets the version at export, and semantic PMI is written to AP242 only.
Yes. This page covers both ACIS text (SAT) and binary (SAB) files, and 3D InterOp reads both.
Yes. ACIS solids and surfaces are written to STEP as exact B-Rep, with no tessellation.
3D InterOp reads ACIS R1 to 2026 1.0.
ACIS assemblies are stored in ASAT/ASAB files rather than SAT. Read those files to keep the assembly structure in STEP.
No. The STEP writer can’t write 2D curves.
Yes. 3D InterOp reads and writes both formats.
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Building software that needs to convert SAT to STP?
3D InterOp is an SDK that lets your application read ACIS and write STEP alongside 30+ CAD and BIM formats.