What is a DGN file?
DGN, short for "design", is the file format used by MicroStation and other Bentley applications. A DGN file contains the elements of a design model, such as lines, curves, surfaces, solids, cells and text, organized on levels, together with references to other design files.
Both generations of the format use the same .dgn extension, so the version is not visible from the file name. V8 DGN removed many of the limits of V7: it stores coordinates as 64-bit floating-point values, can hold several models in a single file and supports far more levels. Recent MicroStation versions use the Parasolid kernel for their solid and surface modeling.
V7 DGN vs. V8 DGN
| Feature | V7 DGN (Intergraph) | V8 DGN (Bentley) |
| Origin | Intergraph Standard File Formats, late 1980s | Bentley Systems, 2000 |
| Coordinates | Integer-based working units | 64-bit floating-point values |
| Models per file | One | Several |
| Levels | Limited to 63 | Virtually unlimited |
| Extension | .dgn | .dgn |
What Is DGN Used For? Applications and Industry Use Cases
DGN is widely used in civil engineering, transportation, rail, utilities, plant design and construction, where MicroStation and other Bentley products have a strong presence. Departments of transportation, engineering firms and owner-operators often keep their project and asset data in DGN files for decades.
For software developers, DGN import lets AEC, BIM, plant and infrastructure applications reuse MicroStation models directly, alongside formats such as IFC, Revit and DWG, so that the same tool can cover more of a construction project's lifecycle.
Challenges or Common Pitfalls
The two DGN generations look the same from the outside but are very different inside, so a reader must recognize and handle each one correctly. Some variants are also restricted: encrypted DGN files and i-models, for example, cannot be opened by generic translators.
DGN files often rely on cells and reference attachments to reuse content and link other design files. If referenced files are missing, the model is incomplete. Content such as meshes, raster images and text, or project-specific properties, may not translate to a B-rep modeling environment, so the expected scope of the data should be agreed early.
How Spatial Helps
Our 3D InterOp SDK imports MicroStation DGN part and assembly files without requiring a MicroStation license, a capability available since Release 2018 1.0. Because MicroStation is Parasolid-based, you can choose between an importer that uses your own Parasolid installation and our MicroStation Direct importer, which needs no setup. Imported data is delivered to CGM Modeler.
3D InterOp reads B-rep topology and geometry, including solids, sheets, wires and smart solids and sheets, as well as free curves and free points. Shared cells and reference attachments are imported as instances with their names and transformations, external references and free parts are supported, and closed ellipses and splines are brought in as sheet bodies.
Body-level name, ID, color and visibility attributes are carried over, along with document information such as units, version, author and modification date. MicroStation files are imported only; writing them is not supported, and a multi-process import interface speeds up loading of large assemblies.