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DGN (design) is the name used for CAD file formats supported by Bentley Systems, MicroStation and Intergraph's Interactive Graphics Design System (IGDS) CAD programs.[1] The DGN format is used in construction projects, including buildings, highways, bridges, process plants, shipbuilding. DGN is a competing format to Autodesk's DWG.[1]
Versions
[edit]There are two versions of DGN:
- Intergraph Standard File Formats (ISFF) specification, published in the late 1980s by Intergraph. This is sometimes referred to as V7 DGN, or Intergraph DGN.
- In 2000, Bentley Systems created an updated version of DGN which includes a superset of DGN's capabilities, but which has a different internal data structure to the ISFF-based DGN. This version is properly referred to as V8 DGN.[2]
History
[edit]In 2003 OpenDWG™ Alliance (now Open Design Alliance), a non-profit industry consortium committed to promoting open industry-standard formats for the exchange of CAD data, and Bentley Systems, Incorporated, announced that the Alliance will support V8 DGN. Bentley increased its membership level to become the Alliance's first supporting member.[3] The Open Design Alliance provides Teigha for .dgn files (old name is DGNdirect) - a development platform available using C++ that is used with .dgn files and other graphics files.
In 2008 Autodesk and Bentley agreed on exchange of software libraries, including Autodesk RealDWG, to improve the ability to read and write the companies' respective DWG and DGN formats in mixed environments with greater fidelity. In addition, the two companies were to facilitate work process interoperability between their AEC applications through supporting the reciprocal use of available application programming interfaces (APIs).[4]
References
[edit]- ^ a b ".DGN File Extension".
- ^ "V8 DGN". Archived from the original on 2012-07-13.
- ^ "OpenDWG Alliance and Bentley Partner On Behalf Of OpenDGN | Open Design Alliance". www.opendesign.com. Archived from the original on 2016-08-15. Retrieved 2016-07-24.
- ^ "Autodesk and Bentley to Advance AEC Software Interoperability". 2008-07-08. Archived from the original on 2009-02-27. Retrieved 2012-04-16.
External links
[edit]- OpenDGN - Bentley's OpenDGN initiative
- Teigha - a software development platform used to create engineering applications including CAD with native support of .dwg and .dgn files.
- Microstation 95/ISFF Description (pdf) - Information on the ISFF/DGN file format as distributed with Microstation 95.
- ISFF Specification - Intergraph Standard File Formats (Element Structure)
from Grokipedia
Overview
Definition and Purpose
DGN (Design) is a proprietary binary file format developed by Intergraph Corporation in the early 1980s for use in computer-aided design (CAD) applications, particularly its Interactive Graphics Design System (IGDS), and later adopted and advanced by Bentley Systems as the native format for their MicroStation software, which was developed in 1987.[1][6] As the native format for Bentley's MicroStation software, DGN serves as a container for vector-based 2D and 3D geometric data, including lines, arcs, shapes, text annotations, and associated metadata such as layers, colors, and attributes.[7] The primary purpose of the DGN format is to store and exchange design information for complex engineering and construction projects, with a strong emphasis on infrastructure such as buildings, highways, bridges, and process plants in the fields of civil engineering and architecture.[7] Created as a robust alternative to Autodesk's DWG format, DGN was designed to handle large-scale, parametric models that support collaborative workflows in professional CAD environments, enabling precise drafting of technical drawings and geospatial data.[1][8] DGN files use the .dgn extension and are inherently binary to ensure efficient storage and processing of detailed design elements.[7] In addition to vector data, the format supports embedded raster images through three compression methods: straight binary (one bit per pixel), run-length encoded binary, and byte-per-pixel encoding, allowing integration of photographic or scanned references within CAD models.[7][9] Over time, DGN has evolved across multiple versions to enhance compatibility and functionality while maintaining backward support for legacy designs.[10]Key Characteristics
The DGN format supports parametric modeling, enabling users to define elements with variable parameters that control dimensions, shapes, and behaviors, allowing dynamic updates to the model without manual redrawing. This includes parametric cells, which are reusable components whose geometry adjusts based on associated variables, facilitating efficient design iteration in complex assemblies. Levels in DGN function analogously to layers in other CAD systems, organizing elements by number and name for selective display, editing, and management, which enhances workflow control in multi-disciplinary projects. Cells, akin to blocks, store graphical elements once in the file while permitting multiple instances with independent scaling, rotation, and placement, promoting reuse and reducing file redundancy. Additionally, DGN enables external file referencing, attaching other DGN, DWG, or raster files as overlays that update automatically upon source changes, supporting collaborative environments without embedding full data. In terms of 3D capabilities, DGN accommodates solids modeling through tools that construct and manipulate parametric solids from basic primitives, enabling Boolean operations for intricate assemblies. It also supports surface modeling for curved geometries and mesh representations for complex, irregular forms, often integrated with reality meshes from point clouds for photorealistic augmentation.[11] These features are particularly emphasized in civil engineering applications, where DGN files store alignments—horizontal and vertical paths for roadways and utilities—and profiles, which define elevation changes along those paths, facilitating terrain-adaptive design in tools like OpenRoads Designer.[12] Despite these strengths, DGN's proprietary nature, owned by Bentley Systems, historically restricted third-party access and interoperability until the release of the V8 DGN File Format Reference in 2005, which provided detailed specifications for developers.[7] Early versions lacked native georeferencing, requiring external workarounds like world files or affine transformations to align DGN data with real-world coordinates, unlike more integrated GIS formats.[13] To address challenges in large-scale projects, DGN incorporates compression mechanisms that purge deleted elements, clear undo buffers, and optimize storage of complex geometries, significantly reducing file sizes while preserving data integrity. Compared to DWG, DGN's openness has improved post-2005 but remains tied to Bentley's ecosystem.[7]Technical Specifications
File Structure
The DGN file format organizes data in a binary structure consisting of sequential elements, each representing geometric or non-graphic information, with the file beginning with specialized header elements for global settings. In the V7 DGN format, the file starts with three fixed header elements of types 9, 8, and 10, which collectively provide file identification, version information, and foundational configuration data before the main user elements begin. Type 9, known as the file control block or TCB (Table of Contents Block), stores essential file-wide parameters including the file type identifier, seed file references for template-based creation, master and sub-units for coordinate scaling, and the global origin defined as VAX D-format double-precision floating-point values at offsets 1240–1263 (with X at 1240–1247, Y at 1248–1255, Z at 1256–1263; 24 bytes for X, Y, Z coordinates). Type 8 handles legacy digitizer setup details, which are typically ignored in modern implementations like MicroStation. Type 10 defines level symbology, specifying attributes such as color, line style, and weight for up to 64 levels across 128 bytes of symbology data starting at byte offset 36 (after the 36-byte element header), enabling consistent rendering across the design. These header elements are not consolidated into a single fixed-size block like 512 bytes but form a variable-length prologue totaling around 1700 bytes or more depending on specific settings.[9][14] Following the header, V7 DGN files store elements sequentially without an index, allowing direct parsing from the start after the prologue, with no dedicated element catalog section but implicit organization via level and type tags embedded in each element. Each element begins with a fixed 36-byte header (18 16-bit words in little-endian byte order), encoding core metadata: word 0 packs the element type (7 bits, values 1–66 for primitives like lines or complex headers), graphic level (6 bits, 0–63), and a deleted flag (1 bit); word 1 specifies the total number of words in the element (16 bits, up to 65,535 total words including header); words 2–13 define the bounding range as six 32-bit signed integers for minimum and maximum X, Y, Z coordinates in units of resolution (UOR, where 1 UOR ≈ 0.001 mm); and words 14–17 cover attributes including graphic group number (16 bits), attribute linkage index (16 bits, for extended properties), properties word (16 bits, e.g., for view-independent flags), and symbology (16 bits, incorporating color index from 0–255 and other display flags). Transformation matrices, when present for complex elements like cells or 3D shapes, follow in the variable data section as sequences of 32-bit floating-point values or quaternions for rotation, scaling, and positioning relative to the global origin. Coordinates within elements use 32-bit signed integers for design-plane points (efficient for 2D/3D precision up to planetary scales in UOR) and 64-bit VAX D-format doubles for off-plane or high-precision values, while attributes like line weight or style are encoded in 16-bit integers for compactness. This structure supports both primitive elements (e.g., simple points) and complex chained elements, where sub-components reference the parent header without repeating the full prologue.[9][14] In V8 DGN files, the structure diverges to use the Microsoft Compound File Binary Format (also known as OLE Structured Storage), featuring a 512-byte fixed header for overall file identification (signature "D0 CF 11 E0 A1 B1 1A E1" at bytes 0–7), version info (byte 24 as major version, byte 26 as minor), and sector allocation details, followed by a directory of streams containing user data sections for multiple models, shared symbology, and elements organized into indexed blocks rather than pure sequence.[15]Data Elements and Features
DGN files support a variety of geometric elements that form the core of 2D and 3D design representations in MicroStation. Basic primitives include lines, which can be single segments or connected as LineStrings and SmartLines for efficient polyline creation; arcs for curved segments defined by center, radius, and angles; and ellipses, which encompass circular and elliptical paths with major and minor axes. More advanced curves utilize B-splines for smooth, parametric approximations of complex contours, while complex shapes aggregate multiple elements into closed or open forms, such as shapes and multi-lines that repeat patterns along paths. In 3D contexts, primitives like cones and spheres enable volumetric modeling as foundational solids.[16][17][18] Non-geometric elements enhance designs with informational and associative content without contributing to spatial geometry. Text elements allow for single- or multi-line annotations, supporting fonts and styles for labeling. Dimensions provide measurement annotations that maintain associativity with geometry, updating automatically upon modifications. Hatches and patterns fill enclosed areas with repetitive symbols or linework for representation, such as cross-hatching in sections. Tags serve as metadata attachments, linking elements to external data like attributes or databases for querying and reporting.[16][19][17][18] Advanced features extend DGN capabilities for parametric and multimedia integration. Smart solids represent modifiable 3D volumes constructed from primitives or extrusions, allowing non-destructive editing of parameters like radii or heights. Raster attachments embed or reference image files (e.g., BMP, TIFF) into the design plane, supporting underlays for tracing or visualization without altering vector data. Dimension-driven design elements constrain geometry through relational dimensions, enabling dynamic adjustments where changes to one dimension propagate to associated features. All elements in DGN files carry attributes that control appearance and behavior. Color assignments use a palette of up to 256 indices mapped to RGB values for visual differentiation. Style defines line patterns, such as solid, dashed, or custom from resource files, influencing rendering. Weight specifies thickness in master units or screen pixels, affecting plot output. Priority determines draw order and visibility in views, ensuring overlapping elements display correctly. These attributes are inherited from levels or overridden per element for precise control.[20][17]Versions
V7 DGN
V7 DGN, also known as Intergraph DGN, represents the original iteration of the DGN file format developed by Intergraph Corporation in the late 1980s as part of the Intergraph Standard File Formats (ISFF) specification.[7] This binary format was designed primarily for 2D CAD applications within Intergraph's Interactive Graphics Design System (IGDS) and early versions of MicroStation, emphasizing efficient storage of vector-based design data through variable-length records.[14] The file structure begins with a design file header composed of three specific elements (types 8, 9, and 10), each featuring a fixed 18-word (36-byte) element header that defines attributes such as type, level, and spatial range, followed by variable data sections for symbology and primitives.[7][14] Key specifications of V7 DGN center on its 2D orientation, with basic support for 3D through elements like 3D lines, shapes, and surfaces using Point3d coordinates (x, y, z as 32-bit integers) and transformation matrices or quaternions for orientation.[14] Element types are limited to primitive geometries such as lines, arcs, ellipses, and text, alongside complex forms including cells and B-spline curves, but exclude advanced parametric or parametric solids native to later formats.[7][14] Coordinates are stored in absolute units of resolution (UORs) with little-endian short integers and middle-endian long integers for compatibility with Intergraph hardware, and floating-point values use VAX D-Float format; however, the format lacks native compression, relying on uncompressed binary storage that can lead to larger file footprints for intricate designs.[14] Despite its foundational role, V7 DGN has notable limitations, including a maximum file size of 32 MB due to internal addressing constraints, which restricts its use for large-scale projects.[21][22] Individual complex elements are capped at 65,535 words (approximately 128 KB), and the absence of built-in interoperability features often requires third-party conversion tools to exchange data with formats like DWG, potentially resulting in loss of 3D attributes or symbology.[7][14] In the 1990s, V7 DGN found primary application within MicroStation and IGDS software for engineering and architectural drafting in industries such as manufacturing and civil infrastructure, where its straightforward structure supported efficient 2D workflows on Intergraph workstations.[7] This format laid the groundwork for subsequent evolutions, such as V8 DGN introduced with the initial MicroStation V8 release in 2001, which addressed many of these constraints through enhanced addressing and compression.[14][23]V8 DGN
The V8 DGN format was introduced in 2001 alongside MicroStation V8 by Bentley Systems, marking a significant revision to the previous V7 format to accommodate modern design needs.[23] Unlike the fixed 18-word header in V7 DGN files, V8 employs a more flexible structure based on one or more models as containers for elements, eliminating many file format-based constraints such as limits on levels, references, and components. This variable header design, combined with the adoption of an OLE2 document container format, enables support for 64-bit addressing and removes the 32 MB file size limitation inherent in V7, allowing for much larger datasets exceeding 2 GB without performance degradation.[7][24] Key enhancements in V8 DGN focus on advanced geometric capabilities and efficiency. It provides robust support for true 3D modeling, including solids and parametric surfaces, enabling the creation of complex volumetric elements with up to 5,000 vertices for line strings and shapes, a substantial increase over V7's constraints. Improved compression mechanisms, such as shared cell libraries where a single definition is stored once in the DGN file for multiple instances, significantly reduce file sizes while maintaining editability and placement speed. Additionally, V8 introduces support for XML-based metadata, allowing export and management of element templates, custom toolboxes, and header information in XML format for better interoperability and data exchange.[7] As of 2025, the V8 DGN format remains stable with no major overhauls since its inception, receiving only minor updates for enhanced compatibility, such as integration with Autodesk RealDWG 2026 in MicroStation 2025 to improve DWG handling without altering the core structure. Backward compatibility is maintained such that V8 files can reference V7 elements directly, but full editing of V7 content requires upgrading the file to V8 format or opening it in read-only V7 workmode to preserve legacy data integrity.[25][26]Development History
Origins
The DGN file format was developed in the late 1980s by Intergraph Corporation as an integral component of its Interactive Graphics Design System (IGDS), a pioneering CAD platform designed for advanced engineering applications.[27][7] IGDS itself originated in the 1970s but underwent significant enhancements in the early 1980s, including the adoption of 32-bit data formats in 1981 to support more complex designs on Digital Equipment Corporation's VAX minicomputers.[27] The DGN format, formalized under Intergraph's Standard File Formats (ISFF) specification, emerged to handle binary storage of vector-based graphic elements and associated data, enabling efficient management of 2D and 3D designs.[7] The initial purpose of DGN was to facilitate workstation-based computer-aided design (CAD) for engineering and architectural firms, providing a digital alternative to traditional paper-based drafting methods that improved accuracy, scalability, and collaboration in technical drawing production.[7][28] Intergraph's emphasis on high-end graphics hardware, such as its custom workstations and graphics accelerators, profoundly influenced the format's design, optimizing it for real-time visualization and manipulation of complex models on dedicated systems rather than general-purpose PCs.[27] This hardware-centric approach ensured DGN's robustness for demanding tasks like plant layout and civil infrastructure modeling, aligning with Intergraph's roots in aerospace and defense computing since its founding in 1969.[27] DGN saw its formal release alongside Bentley Systems' MicroStation software in 1987, specifically with version 2.0 in February of that year, which first supported writing to .dgn design files compatible with IGDS.[28][7] Early adoption was rapid, particularly in U.S. government projects—such as contracts with the Army Corps of Engineers—and civil engineering applications.[28][29] Major engineering firms like Bechtel and DuPont also embraced it for AEC workflows, establishing DGN as a standard for high-fidelity design data exchange in regulated industries.[27]Major Milestones
In 1994, Bentley Systems and Intergraph Corporation reached a settlement that amended their software license agreement to non-exclusive status and granted Bentley control over MicroStation distribution after December 31, 1994, while Intergraph retained limited rights for certain licensees. This agreement shifted primary maintenance and development responsibilities for MicroStation—and by extension the DGN format—to Bentley.[30] In 2000, Bentley introduced the V8 DGN format with MicroStation 8, updating the internal data structure for enhanced capabilities.[7] A key advancement occurred in 2003 when the Open Design Alliance (ODA), formerly known as the OpenDWG Alliance, announced support for the V8 DGN format, enabling third-party developers to access and implement DGN files more reliably. Bentley Systems joined the ODA as a member that year, promoting broader interoperability and ensuring DGN's viability as an open standard for CAD applications beyond proprietary ecosystems. This partnership facilitated accurate reading and writing of V8 DGN files in diverse software, enhancing collaborative workflows in engineering projects.[7] In 2008, Autodesk and Bentley Systems entered into a landmark agreement to exchange software libraries and APIs, including Autodesk's RealDWG toolkit, to improve bidirectional compatibility between DWG and DGN formats. This collaboration aimed to streamline data exchange in the architecture, engineering, and construction (AEC) industry by allowing seamless import and export of design files across their respective platforms, reducing conversion errors and supporting integrated project delivery. The deal marked a significant step toward industry-wide interoperability, benefiting users who relied on both vendors' tools.[31] More recently, MicroStation 2024 introduced enhanced RealDWG 2025 compatibility, optimizing DGN file handling for precise DWG integrations and custom object support. Building on this, MicroStation 2025 added native IFC export capabilities, allowing DGN models to be directly converted to Industry Foundation Classes (IFC) format for better openBIM compliance. These updates have strengthened DGN's role in digital twin development within Bentley's iTwin platform, enabling synchronized infrastructure models that incorporate real-time data for advanced visualization and analysis.[32][33]Applications
Industries and Use Cases
DGN files find primary application in civil engineering, particularly for highway and bridge design, where state departments of transportation such as the Texas Department of Transportation (TxDOT) and the Florida Department of Transportation (FDOT) provide DGN files for standard plans and project-specific modifications.[34][35] In architecture, DGN supports the drafting of technical drawings for building designs, enabling precise 2D and 3D representations of structures.[7] The format is also prevalent in process plant engineering for layout modeling and in shipbuilding for complex hull and assembly designs.[6] Key use cases include infrastructure design, such as defining alignments and cross-sections in road projects, where DGN facilitates accurate geometric data handling compliant with governmental standards.[36] For process plants, DGN enables 3D modeling of piping, equipment placements, and facility layouts to optimize operational flows.[6] Additionally, DGN integrates into Building Information Modeling (BIM) workflows, supporting collaborative data exchange among multidisciplinary teams in construction projects.[37] Notable examples demonstrate DGN's role in U.S. Department of Transportation standards, including the California Department of Transportation's (Caltrans) 2025 standard plans, which provide individual DGN files for statewide highway and bridge documentation.[38] In large-scale airport projects, such as those at Nashville International Airport, DGN is one of the accepted formats (alongside DWG) for record engineering drawings, based on 2019 guidelines, to ensure consistency across planning and construction phases.[39] A core advantage of DGN in these applications is its scalability for handling massive datasets in construction documentation, allowing efficient management of intricate, high-volume designs without performance degradation.[40] This capability is enabled by software tools like MicroStation, which streamline these industry-specific workflows.Software Support
MicroStation, developed by Bentley Systems, serves as the flagship software for DGN files, providing native support for both V7 and V8 formats to enable full 2D drafting, 3D modeling, and annotation capabilities.[41] Promis.e, another Bentley product focused on electrical system design, utilizes V8 DGN as its native file format, allowing seamless creation, editing, and saving of schematics and wiring diagrams within this ecosystem.[42] Several third-party applications offer DGN compatibility through import, export, or reference functions. AutoCAD supports importing DGN files via theDGNIMPORT command, which converts content to DWG entities, or attaching them as underlays using XATTACH for reference viewing without full conversion; this relies on the RealDWG toolkit for accurate translation of MicroStation elements.[5] ArcGIS Pro enables direct read access to DGN files from MicroStation versions 95 and later (as of 2025), supporting georeferencing by treating them as feature datasets in maps and scenes for GIS integration.[43] Open-source GDAL/OGR libraries provide reading support for pre-V8 DGN files and read/write capabilities for V8 files when compiled with Teigha libraries, facilitating data conversion and geospatial processing across various tools.[44]
Recent enhancements in software support include Tekla Structures 2024, which adds direct export of 2D drawings to V8 DGN format via a dedicated dialog, configurable with level rules and templates to minimize data loss in structural workflows.[45] HOOPS Exchange offers alpha-level import for V7 and V8 DGN files, converting exact geometry like B-splines and arcs to B-rep for visualization, while supporting level-based layering though without full PMI or material attributes.[46]
Despite these options, limitations persist in non-native tools; for example, AutoCAD 2025 and prior updated versions (2023–2024) can trigger fatal errors during DGN import due to known defects, often necessitating workarounds like reverting to unupdated installations or alternative conversion methods.[47]