Convert STP to CATPart in your application
3D InterOp is a CAD interoperability SDK that lets your software read STP files and write CATPart, 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 STEP · Writes CATPart
- Exact geometry → exact geometry
- C++ / C# APIs
STP to CATPart at a glance
Both formats store exact geometry, so the model stays exact. The differences are in the product data each one can carry.
| STEP (source) | CATPart (target) | |
|---|---|---|
| Full name | Standard for the Exchange of Product model data | CATIA V5 Part |
| Standard / owner | ISO 10303 — AP203, AP214, AP242 | Dassault Systèmes |
| File extensions | .stp, .step | .CATPart |
| Geometry | Exact B-Rep | Exact B-Rep |
| Assemblies / structure | Yes | Part file (assemblies are CATProduct files) |
| PMI | Graphical and semantic (AP242) | Semantic and graphical |
| 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 STEP to CATPart.
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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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Improved
Healed geometry3D InterOp repairs and heals STEP data during translation.
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Changes
Assembly structureCATPart has no native assembly hierarchy. Decide in your application how STEP product structure is grouped or flattened before writing.
Why software vendors add STP to CATPart conversion
Deliver in your customer’s CAD format
Aerospace and automotive OEMs often require supplier data in CATPart. Writing it lets your users meet that requirement directly from your application.
Exact geometry, ready to edit
CATPart keeps exact B-Rep geometry, so the receiving engineer can measure, modify or machine the model in CATIA.
No neutral-format round trip
Writing CATPart directly avoids an extra STEP or IGES step, and the loss each extra translation can add.
Things to check before you ship
- Written CATPart versions: CATIA V5 R15 to V5-6 R2026.
- Supported STP input: AP203, AP214 and AP242.
- 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 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).
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Target 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.
Frequently asked questions
Yes. Both formats store exact B-Rep geometry, so the model is translated without being tessellated into triangles.
CATPart has no assembly hierarchy, so your application decides how the STP structure is grouped or flattened before writing.
3D InterOp reads AP203, AP214 and AP242.
3D InterOp writes CATIA V5 R15 to V5-6 R2026.
Yes. 3D InterOp reads and writes both formats, so CATPart to STP is supported too.
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Building software that needs to convert STP to CATPart?
3D InterOp is an SDK that lets your application read STEP and write CATPart alongside 30+ CAD and BIM formats.