Convert STL to CATPart in your application
3D InterOp is a CAD interoperability SDK that lets your software read STL files and write CATPart, writing the STL facets as faceted geometry, since STL stores triangles rather than solids.
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 STL · Writes CATPart
- Triangle mesh → faceted B-Rep
- C++ / C# APIs
STL to CATPart at a glance
STL stores triangles; CATPart is an exact-geometry format. The mesh is written as faceted geometry: 3D InterOp doesn’t rebuild smooth surfaces from triangles.
| STL (source) | CATPart (target) | |
|---|---|---|
| Full name | Stereolithography | CATIA V5 Part |
| Standard / owner | Open format | Dassault Systèmes |
| File extensions | .stl | .CATPart |
| Geometry | Triangle mesh | Exact B-Rep |
| Assemblies / structure | No | Part file (assemblies are CATProduct files) |
| PMI | None | 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 STL to CATPart.
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Changes
Faceted geometrySTL stores triangles, so the CATPart file holds faceted bodies, not solids. 3D InterOp doesn’t rebuild exact B-Rep from a mesh.
Why software vendors add STL 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 STL input: any STL version.
- 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 STL file?
STL describes a 3D surface as a set of triangles, with no units, materials or assembly structure. Its simplicity makes it the usual input for 3D printing.
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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
No. STL stores triangles, and 3D InterOp writes them to CATPart as faceted geometry. It doesn’t rebuild exact B-Rep from a mesh.
STL files store no units, so the 3D InterOp STL reader assumes millimeters. Agree on the unit with the application that wrote the file.
3D InterOp reads any STL version, as visualization data.
3D InterOp writes CATIA V5 R15 to V5-6 R2026.
Yes. 3D InterOp reads and writes both formats, so CATPart to STL is supported too.
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Building software that needs to convert STL to CATPart?
3D InterOp is an SDK that lets your application read STL and write CATPart alongside 30+ CAD and BIM formats.