Convert DGN to STL in your application
3D InterOp is a CAD interoperability SDK that lets your software read DGN files and write STL, generating the STL mesh from the geometry it reads, with tessellation settings your application controls.
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 MicroStation DGN · Writes STL
- Exact geometry → triangle mesh
- C++ / C# APIs
DGN to STL at a glance
MicroStation DGN stores exact geometry; STL stores triangles. The translation is a tessellation, and the settings you choose decide how close the mesh stays to the original.
| MicroStation DGN (source) | STL (target) | |
|---|---|---|
| Full name | MicroStation Design file | Stereolithography |
| Standard / owner | Bentley Systems | Open format |
| File extensions | .dgn | .stl |
| Geometry | Exact B-Rep | Triangle mesh |
| Assemblies / structure | Yes: models and references | No |
| 3D InterOp support | Read only | Read and write |
What's preserved, what changes
Here is what your application can expect to carry across from MicroStation DGN to STL.
-
Changes
Geometry is tessellatedThe exact MicroStation DGN B-Rep is replaced by a triangle mesh, generated by 3D InterOp from the exact geometry it reads. Accuracy depends on the tessellation settings your application uses.
-
Changes
Assembly structureSTL has no native assembly hierarchy. Decide in your application how MicroStation DGN product structure is grouped or flattened before writing.
Why software vendors add DGN to STL conversion
Additive manufacturing
STL is still the input most slicers and print services expect. Writing it lets your users send parts to print directly.
Mesh-based processing
Inspection, scan comparison and mesh-editing tools work on triangles. A mesh output gives them a model they can open anywhere.
Lightweight sharing
A mesh is simpler than the native CAD file and needs no CAD system to open.
Things to check before you ship
- Supported DGN input: DGN V7 to V8.
- Test tessellation settings on your heaviest parts: finer meshes mean larger files.
- 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 a DGN (.dgn) file?
DGN is the native design file format of Bentley MicroStation, widely used for infrastructure, plant and civil engineering projects. It exists in two generations, V7 and V8.
-
Target 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.
Frequently asked questions
3D InterOp tessellates the geometry it reads from DGN when it writes STL. Your application sets the tolerances, so it controls the trade-off between accuracy and file size.
STL has no assembly hierarchy, so your application decides how the DGN structure is grouped or flattened before writing.
No. STL stores triangles only, with no units, colors or textures. Agree on the unit with the application that reads the file; the 3D InterOp STL reader assumes millimeters.
3D InterOp reads DGN V7 to V8.
No. 3D InterOp reads DGN but doesn’t write it. To send data back to MicroStation users, write a neutral format they can import, such as IFC or STEP.
-
Building software that needs to convert DGN to STL?
3D InterOp is an SDK that lets your application read MicroStation DGN and write STL alongside 30+ CAD and BIM formats.