Convert STP to IGES in your application
3D InterOp is a CAD interoperability SDK that lets your software read STEP files and write IGES, with exact B-Rep geometry carried across — no tessellation, no CAD license.
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 IGES
- Exact geometry → exact geometry
- C++ / C# APIs
STP to IGES 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) | IGES (target) | |
|---|---|---|
| Full name | Standard for the Exchange of Product model data | Initial Graphics Exchange Specification |
| Standard / owner | ISO 10303 — AP203, AP214, AP242 | ANSI |
| File extensions | .stp, .step | .igs, .iges |
| Geometry | Exact B-Rep | Exact B-Rep and surfaces |
| Assemblies / structure | Yes | No native assembly hierarchy |
| PMI | Graphical and semantic (AP242) | None documented in 3D InterOp |
| 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 IGES.
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Preserved
Exact geometrySolids and surfaces stay as exact B-Rep. The model is never reduced to a triangle mesh, unlike a conversion to STL.
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Improved
Topological quality3D InterOp repairs and heals STEP data during translation, so the IGES output starts from a clean, valid model.
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Changes
Assembly structureIGES 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 IGES conversion
Legacy CAD and CAM systems
Many established engineering tools still consume IGES first. Writing it lets your users hand data to them without leaving your application.
Supplier and partner exchange
Some suppliers and manufacturing partners still specify IGES in their exchange requirements. Your software can meet them directly.
Geometry-only workflows
When a downstream process needs exact part geometry and nothing more, IGES is a simple, widely readable target.
Things to check before you ship
- Semantic PMI from STEP AP242 requires a license in addition to the STEP reader and writer.
- If your users exchange PMI or full product structure, offer STEP AP242 as an output alongside IGES.
- 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 an IGES (.igs) file?
IGES is one of the earliest neutral CAD formats, an ANSI standard for exchanging 2D and 3D geometry. It stores exact curves, surfaces and solids, but not the product structure and manufacturing data STEP can carry.
Frequently asked questions
Yes. Both formats store exact B-Rep geometry, so the model is translated without being tessellated into triangles.
3D InterOp reads STEP AP242 PMI and product structure, but the IGES output carries neither. Your application can access this data before export, or offer STEP AP242 as the output when PMI and structure must be kept.
3D InterOp writes IGES 5.3.
Yes. 3D InterOp repairs and heals STEP data during translation, so the IGES output starts from a clean, valid model.
AP203, AP214 and AP242, from .stp, .step and .stpx files. Compressed .stpZ and .stpxZ files and .stpa files are read too.
Yes. 3D InterOp reads and writes both formats, and heals IGES geometry automatically on import.
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Building software that needs to convert STP to IGES?
3D InterOp is an SDK that lets your application read STEP and write IGES alongside 30+ CAD and BIM formats.