DGN (MicroStation Design) format: Bentley CAD 1984 — OSM export to DGN V8

DGN is the native binary file format of Bentley's MicroStation, alive since 1984. It's a contemporary of DWG but took a different path: while Autodesk's DWG conquered architects and the mid-size CAD market, MicroStation with DGN took root in large infrastructure — federal highway corridors, hundred-kilometer railway alignments, oil refinery process diagrams, water utility city-scale networks. The format lived through two fundamentally different eras: early DGN V7 (1984-2001, formally known as ISFF — Intergraph Standard File Format) with 32-bit integer coordinates in its own UOR units, and modern DGN V8 (with MicroStation V8, 2001/2002) with IEEE-754 64-bit floating point and a structure conceptually close to DWG. On osm2cdr.ru dgn_exporter.py writes DGN V7 through the GDAL OGR driver — that's the legally open part of the format, readable in MicroStation, Bentley View, AutoCAD via the ODA Teigha bridge, and QGIS.

History: from Intergraph IGDS to Bentley's infrastructure standard

A common confusion: DGN was not invented by Bentley. The format actually came from Intergraph Corporation, one of the oldest American CAD companies (founded 1969 as M&S Computing). In the 1970s Intergraph developed the closed IGDS (Interactive Graphics Design System) for its graphics workstations on DEC PDP-11. IGDS stored drawings in the binary ISFF (Intergraph Standard File Format) — the direct ancestor of DGN.

Bentley Systems started in 1984 as a small company by the Bentley brothers in Exton, Pennsylvania. Their first product was PseudoStation — a program that emulated Intergraph IGDS on standard PCs and read ISFF files. Initially just a compatibility viewer for the Intergraph ecosystem, in 1985 PseudoStation evolved into a full CAD system, MicroStation 1.0 — hardware-independent from Intergraph, but still writing and reading the same ISFF. By the early 1990s MicroStation had become AutoCAD's main competitor in the high-end segment, and in 2000 Intergraph finally handed the format rights to Bentley.

From 1984 through 2001 only one architecture existed — DGN V7 / ISFF. The file was built from a sequence of 512-byte blocks with a 1536-byte header at the front and an 0xFFFF EOF marker at the end. Coordinates lived as 32-bit integers in custom UOR units (Units of Resolution) yielding a ±2^30 range — enough for construction, but it required attention to working units (meters, millimeters, feet) configuration.

In 2001-2002 Bentley shipped MicroStation V8 with a fundamentally new DGN V8 structure — rewritten from scratch around IEEE-754 64-bit floating point, unlimited levels (instead of the strict 63 in V7), full external file references, digital signatures, and an architecture conceptually close to DWG of the same period. The V8 format is closed — an official spec exists but is available only through Bentley's licensing program. Open Design Alliance (ODA) partially reverse-engineered V8 as part of its Teigha libraries for DGN interop, which is what most third-party programs use.

Inside DGN: V7 and V8

DGN V7 (ISFF, 1984-2001). The file structure is open thanks to Intergraph publications from the 1980s and support in GDAL/OGR's OGR_DGN driver. The file starts with a 1536-byte header, then 512-byte blocks of elements. Each element has one of roughly 20 types (type 3 — Line, type 4 — LineString, type 6 — Shape for polygons, type 17 — Text, type 11 — Curve). Coordinates are 32-bit integers in UOR, anchored to a global origin. Levels are numbered 1-63 — analogous to DWG layers but with a hard limit, which sometimes forces grouping of dissimilar geometry. Colors are 8-bit indexed against a palette, analogous to AutoCAD ACI.

DGN V8 (2001-present). Conceptually close to DWG: binary, IEEE-754 64-bit coordinates (full Earth coverage with millimeter precision without UOR anchoring), unlimited levels and tags, XAttribute support (arbitrary user metadata per element), embedded references (external references can be embedded directly in the file), digital signatures, in-file version control. The V8 header magic bytes differ from V7 — programs identify the dialect instantly and choose the V7 or V8 parser.

A key point: MicroStation V8 and newer read both V7 and V8 transparently. Bentley View (the free official viewer) also reads both. But the old MicroStation V7 cannot read DGN V8 — it's one-way backward compatibility, analogous to DWG.

Who needs DGN

Road engineers and highway designers. Bentley OpenRoads Designer (on top of MicroStation) is the de facto standard for federal highway design in the US, much of Europe, and large Russian infrastructure projects. If the general contractor works in OpenRoads, a DGN basemap removes half the integration headache. Road profiles, alignments, surfaces live as native DGN elements, not proxy graphics (which is what you'd get importing DWG).

Railway designers. Bentley OpenRail (sibling to OpenRoads) is the standard for long railway corridors: Eurostar, Crossrail, high-speed rail projects. Huge models spanning hundreds of kilometers with millions of objects — DGN V8 handles them where DWG starts choking.

Industrial plant designers. OpenPlant (Bentley) is process plant design for oil and gas, chemistry, water utilities. Process diagrams, pipe routing, equipment placement — all in DGN.

Hydrogeology and engineering surveys. In Russia, the central transport surveying institutes (TsPS, TsNIIS) have historically worked with MicroStation for large infrastructure surveys — a historical decision from the early 2000s.

Brownfield asset management. Large industrial owners (utilities, water authorities) often have huge archives of historical V7 DGNs from the 1990s — modernization requires reading those drawings and binding them to modern GIS, which makes DGN export from OSM useful as contextual basemap.

DGN-reading software

MicroStation (Bentley). Paid, subscription from about 2400 USD/year for the full CONNECT Edition. Windows. The reference implementation — what MicroStation writes is by definition correct DGN. Reads V7, V8, and all intermediate dialects. bentley.com/microstation

Bentley View. Free official viewer from Bentley, Windows. Doesn't edit but opens any DGN (V7 and V8), reads all Bentley custom objects including OpenRoads, OpenRail, OpenPlant. Best choice if you just need to view DGN. bentley.com/software/bentley-view

AutoCAD. Paid, subscription from 1690 USD/year. Since 2004 AutoCAD has imported and exported DGN through the built-in Bentley DGN Translator. V7 reading — no issues. V8 — via the ODA bridge. Geometry converts to DWG entities, but Bentley-specific custom objects become proxy graphics.

BricsCAD. Paid, perpetual license around 360 USD/year (Pro). Linux/Windows/macOS. Uses ODA Teigha for DGN — reads both V7 and V8 with base geometry. For two-way DGN ↔ DWG interoperability, one of the best options on the market.

QGIS. Free, cross-platform. Reads DGN V7 through the GDAL OGR_DGN driver — open-source V7 reverse engineering. V8 is not supported in GDAL. Suitable for using DGN as a vector layer in GIS analysis but not for editing. qgis.org

ODA File Converter. Free official converter from Open Design Alliance. Converts DGN ↔ DWG ↔ DXF across all supported dialects. If you received a DGN from a contractor and need to open it in AutoCAD, ODA File Converter solves the problem.

TerraSolid (Solid Edge / Siemens). Paid niche tool for LiDAR processing on top of MicroStation — reads DGN, but this is a narrow specialized case.

OSM2CDR pipeline

Our dgn_exporter.py writes DGN V7 (ISFF) — a deliberate choice for two reasons. First, V7 is formally open and fully covered by the GDAL OGR_DGN driver, so the exporter doesn't depend on closed SDKs. Second, modern MicroStation and Bentley View read V7 without issues (back-compat), and any user needing V8 has trivial conversion available via MicroStation Save As → V8 or ODA File Converter.

OSM data arrives from PostGIS through layer_builder.py (WKB fast-path, 10-50x speedup vs Overpass). Geometry maps like this: - Roads (highway, railway) → Type 4 elements (LineString) on level 10 - Buildings (building) → Type 6 elements (Shape) on level 20 - Hydrography (waterway, water) → Type 4/6 elements on level 30 - Green areas (leisure, landuse) → Type 6 elements on level 40 - POIs (when enabled) → Type 17 elements (Text) on level 50

Coordinates convert from WGS84 to UOR with the global origin at the user-selected centroid. Working units are configured as meters (master units) + millimeters (sub units) — the standard for most infrastructure projects. If a user picks an MSK zone (Russia) or State Plane (US), real metric coordinates persist in the DGN UOR system.

Caveat: our exporter writes V7 with a maximum of 101 vertices per element (ISFF limit). Long curves are automatically split into multiple LineString segments — transparent for most uses, but may require a MERGE in MicroStation if topologically continuous lines are needed.

DGN vs DWG: when to pick which

If the recipient is the Bentley ecosystem (MicroStation, OpenRoads, OpenRail, OpenPlant, ProjectWise) — DGN, no question. Geometry lands in the project directly, without proxy objects, and integrates with the native Bentley tool workflow.

If the recipient is the Autodesk ecosystem (AutoCAD, Civil 3D, Revit, Map 3D) — DWG. Covered in detail in the DWG guide. Importing DGN into AutoCAD is possible but adds a step and can lose Bentley-specific objects.

For universal portability (any CAD program, scripting pipeline, diffs in git) — DXF. DGN and DWG are both closed binary; DXF is open text.

If the project is infrastructure-focused with roads, profiles, alignments — consider LandXML as an exchange format: MicroStation, Civil 3D, and Trimble all understand it.

For Russian projects with KOMPAS-3D — KOMPAS export writes a DXF equivalent (KOMPAS reads DXF natively), and KOMPAS ↔ MicroStation interop goes through the DXF/DWG bridge.

Strengths and weaknesses

Strengths. Native for the whole Bentley ecosystem — no losses importing into MicroStation/OpenRoads/OpenRail. Efficient storage for very large models: V8 DGN spanning hundreds of kilometers of infrastructure (e.g. a high-speed rail line from Lisbon to Madrid) runs smoother than equivalent DWG. 3D-native since V8 — coordinates are 3D by default with no separate mode toggle. XAttribute support (custom metadata per element) is handy for asset management. Embedded references — external files can be embedded directly inside, like in an archive. Digital signatures — important for regulated industries (medical, defense). A free official viewer (Bentley View) — better than DWG's situation, where Autodesk's DWG TrueView is also free but less capable.

Weaknesses. Closed format — all open-source implementations (GDAL OGR_DGN, ODA Teigha) depend on reverse engineering. V8 in open-source is less supported than V7 — GDAL reads V7 fully but V8 only partially. Less widespread than DWG, especially in the architectural mid-market segment: a typical freelance architect more likely has AutoCAD than MicroStation. Complex V7 dialect history (dozens of sub-versions over 17 years) — sometimes old 1990s DGNs require conversion through MicroStation V8 as an intermediate step. On our platform — V7-only export; for V8 you need MicroStation or ODA File Converter.

How to make a DGN map from OpenStreetMap

Step 1. Open osm2cdr.ru and pick DGN from the format dropdown (CAD category).

Step 2. Draw the area on the map. For a city basemap — 1-3 km². For an infrastructure project (road, rail corridor) — extended 5-15 km bbox along the alignment.

Step 3. Pick a coordinate system. For Russian projects — the appropriate MSK zone. For the US — State Plane. For Europe — UTM or a national grid. DGN working units auto-set to "meters" (master) + "millimeters" (sub).

Step 4. Style and detail. Detail level 4 of 6 is the optimal balance for a city basemap. The standard style distributes OSM objects across levels 10/20/30/40/50 (roads/buildings/water/greenery/POI).

Step 5. Click "Export". The Celery queue processes the job in 40-120 seconds. Download the .dgn file and open in MicroStation, Bentley View, or QGIS via File → Open.

Get a DGN Map of Nevsky in 90 Seconds

FAQ

How is DGN different from DWG? Both are closed binary CAD formats from different ecosystems. DWG is native to AutoCAD/Autodesk and dominates the architectural mid-market. DGN is native to MicroStation/Bentley and dominates large infrastructure (highways, rail, plants). DGN V8 scales better to huge multi-hundred-kilometer models. DWG has better third-party software support.

V7 vs V8 — which version do you write? We write V7 (ISFF) through the GDAL OGR_DGN driver. Modern MicroStation and Bentley View read V7 without problems. If you specifically need V8, open the V7 in MicroStation and Save As → V8, or use the free ODA File Converter.

Can you open DGN without MicroStation? Yes. Bentley View — the free official viewer from Bentley (Windows). QGIS reads V7 through OGR_DGN. BricsCAD reads both formats through ODA Teigha. AutoCAD has imported DGN via the built-in Bentley DGN Translator since 2004.

What's UOR in DGN? Units of Resolution — V7's internal integer units. Coordinates store as 32-bit integers in the ±2^30 range, anchored to a global origin via working units setting (e.g. 1 UOR = 1 mm). DGN V8 dropped UOR in favor of IEEE-754 64-bit floats — that lifted the coordinate range limits.

Are OpenRoads/OpenRail objects supported? No — our exporter writes the base OSM geometry (lines, polygons, points, text) without Bentley-specific custom objects like OpenRoads alignments or OpenPlant equipment. Sufficient for using OSM as a contextual basemap inside an OpenRoads/OpenRail project.

Related

• DWG — AutoCAD format: history and OSM export
• DXF — complete guide to the 1982 format
• LandXML — infrastructure design exchange format
• KOMPAS — Russian CAD: OSM export

Sources

• MicroStation — bentley.com/software/microstation
• MicroStation DGN Family — Library of Congress — loc.gov/preservation/digital/formats/fdd/fdd000603.shtml
• GDAL OGR_DGN driver — gdal.org/drivers/vector/dgn.html
• Open Design Alliance Teigha for DGN — opendesign.com
• Wikipedia, MicroStation — en.wikipedia.org/wiki/MicroStation