Complete IGES Format Guide: CAD Interoperability, Conversion and Best Practices

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CAD data interoperability is a major challenge for companies working in multi-CAD environments. The IGES (Initial Graphics Exchange Specification) format represents one of the first established standards to solve these exchange problems. Although surpassed by more recent formats like STEP, IGES remains widely used in industry and mastering it remains essential to ensure efficient technical data exchanges.

History and Evolution of IGES Format

From military origins to industrial adoption

The IGES format was developed in the 1970s to solve geometry exchange problems between different proprietary CAD systems. Its history truly begins in 1980, as part of a US Air Force project called ICAM (Integrated Computer-Aided Manufacturing) aimed at integrating the various software and processes involved in aerospace manufacturing.

The first version, IGES 1.0, was published in 1980 and adopted as a national standard ANS Y14.26M-1981 in the United States. The format has undergone several evolutions:

  • Versions 3 and 4: progressive improvements
  • Version 5.2: last major version, approved by ANSI
  • Standardization stopped in 1996, unlike other more recent formats

The development and maintenance of the IGES standard were ensured by the IGES/PDES organization under the direction of NIST (National Institute of Standards and Technology). Despite its age, IGES remains widely used today, although gradually replaced by the STEP format for more complex exchanges.

Technical Characteristics of IGES Format

Architecture and Data Structure

The IGES format features a specific architecture based on ASCII format, making it particularly lightweight and easily shareable. IGES files use the extensions .igs or .iges.

The structure of an IGES file consists of six distinct sections:

  1. Header Section: contains general information about the file, such as software details and creation date
  2. Start Section: defines units of measurement, coordinate system, and other global parameters
  3. Global Section: describes the global structure of the file
  4. Directory Section: serves as an index for entities, assigning unique numeric identifiers
  5. Parameter Data Section: contains geometric and topological information of entities
  6. Terminate Section: marks the end of the file

Geometric Engine and Representation

The IGES format supports 2D and 3D geometry, but presents important particularities in its geometric representation:

  • Support for basic geometric shapes (points, curves, surfaces)
  • Limited B-Rep (Boundary Representation)
  • Difficulties with edge connectivity information
  • Use of bounded and trimmed surface entities to represent B-Rep geometry, but without complete topology information

These technical limitations partly explain why models exported in IGES often present inconsistent edge orientations and frequently require geometric repair operations (healing).

Advantages and Limitations for CAD Interoperability

Strengths of the IGES Format

Despite its age, the IGES format presents several significant advantages:

  • Universal compatibility: supported by almost all CAD systems on the market
  • Versatility: support for 2D and 3D geometries in the same format
  • Lightweight: compact ASCII structure facilitating file sharing
  • Accessibility: possible to open in many applications, including simple text editors
  • Stability: format proven by decades of industrial use

Limitations and Challenges

The IGES format nevertheless presents important limitations that have led to the progressive adoption of other formats:

  • Insufficient solid representation: difficulty in accurately representing complex solid models
  • Limited assembly management: poorly supported assembly structure
  • Absence of PMI: no standardized way to represent or store PMI (Product Manufacturing Information) data
  • Conversion problems: difficulties when converting to other formats, with risk of errors requiring repairs
  • Technical obsolescence: no updates since 1996, limiting the integration of advances in CAD modeling

These limitations explain why STEP is now preferred for the exchange of complex solid structures, PMI information, and assemblies in modern industrial environments.

CAD Interop Solutions Supporting IGES Format

CAD Interop distributes several specialized solutions to efficiently manage IGES files at different stages of the technical data lifecycle.

3DViewStation: advanced visualization and analysis

3DViewStation allows detailed visualization and analysis of IGES models while offering conversion features to this format. Its main characteristics include:

  • Fast loading of large IGES files
  • Precise geometric measurement and analysis tools
  • Section and annotation functions
  • Technical data extraction capabilities
  • Multi-format conversion to and from IGES
  • Export options for technical documentation

CADfix: data repair and preparation

CADfix is particularly important for the IGES format due to frequent geometric quality issues. This solution offers:

  • Automatic detection and repair of geometric errors
  • Geometric healing to address surface and edge problems
  • Tools for correcting inconsistent edge orientations
  • Model simplification for downstream applications
  • Data translation to other formats with quality control
  • Generation of detailed validation reports

SimLab: immersive experiences from IGES models

SimLab transforms IGES data into immersive experiences for advanced visualization and collaboration:

  • Conversion of IGES models into interactive 3D environments
  • Creation of immersive scenes for design review
  • Integration of metadata and annotations into the experience
  • Compatibility with virtual and augmented reality technologies
  • Cloud-based collaboration support for simplified sharing
  • Preservation of original model accuracy

CADIQ: validation and documentation of modifications

CADIQ ensures the quality of IGES models in exchange processes and documents modifications:

  • Automatic validation of models according to customizable criteria
  • Comparison between different versions of the same IGES model
  • Detailed documentation of modifications for ECO (Engineering Change Orders)
  • Verification of compliance with company standards
  • Detection of subtle geometric deviations
  • Creation of validation reports for quality processes

DEXcenter: automation of exchanges

DEXcenter simplifies and automates CAD data exchanges, including IGES files:

  • Web interface accessible via a standard browser
  • Secure environment for transmitting sensitive CAD data
  • Data encryption during transfer over the Internet
  • Registry of each exchange for validation and traceability
  • Automatic generation of Technical Data Packages in 2D and 3D
  • Possible integration with existing PLM systems

Best Practices for IGES File Exchange

Strategic Format Choice

Before using IGES, evaluate whether it's the most appropriate format for your use case:

  • Prefer IGES for simple surface geometry exchanges
  • Opt for STEP when working with complex solid models or assemblies
  • Consider direct CAD-to-CAD translations to preserve more design details

Robust Translation Processes

Establish standardized procedures to minimize errors:

  • Implement clear and consistent naming conventions
  • Precisely document the export, import, and verification steps
  • Prepare data by removing unnecessary elements before export

Systematic Verification and Validation

Validation is crucial when using the IGES format:

  • Systematically check reports and error files after each conversion
  • Use appropriate options depending on your conversion tool
  • Perform visual and dimensional control of models after translation
  • Don't hesitate to use geometric comparison tools between the original and the converted version

Optimal Assembly Structuring

For IGES assemblies, judiciously choose the file structure:

  • Option "Flat": exports all assembly geometry into a single IGES file
  • Option "One Level": creates an assembly file with external references to components
  • Option "All Levels": preserves the complete hierarchy with all assembly levels
  • Option "All Parts": generates multiple files containing geometric information of components

Geometric Quality Improvement

To optimize the quality of IGES models:

  • Generate the model topology if it is not correctly transferred
  • Use "Healing" functionalities to improve geometric quality
  • Analyze topology based on free sides of surfaces
  • Adjust the merge distance to reduce gaps between surfaces

Use Cases and Practical Applications

Legacy Data Migration

In a CAD data modernization project, an aerospace company had to convert thousands of historical IGES files to more recent formats. The combined use of CADfix for geometric repair and DEXcenter for automation made it possible to efficiently process this considerable volume of legacy data while maintaining the geometric integrity of the models.

Sharing with Partners Using Different CAD Systems

For companies working in complex supply chains, sharing IGES models remains a viable option when partners have various CAD systems. The use of CADIQ to validate models before exchange and DEXcenter to secure transfers ensures effective collaboration despite the diversity of technical environments.

Sharing with Non-CAD Users

To share 3D models with users without access to CAD software, several approaches are possible:

  • Creation of HTML files using 3DViewStation or SimLab, allowing visualization via a simple web browser
  • Use of 3D PDF for users with only Adobe Reader or Foxit Reader
  • Use of online visualization platforms such as 3DViewStation WebViewer for converted IGES files

Frequently Asked Questions

How to optimize the quality of IGES conversions?
The quality of IGES conversions strongly depends on the quality of the IGES translators used for both export and import. Use professional tools like those from CAD Interop and systematically check the error reports generated. For problematic models, a healing process with CADfix can significantly improve results.

Why do my IGES files present surface orientation problems?
Orientation problems are common with IGES due to the format's limitations in B-Rep representation. Most CAD exporters use limited capabilities to represent B-Reps through bounded and trimmed surface entities, which cannot contain complete topology information. This often results in inconsistent edge orientations requiring corrections.

How to choose between IGES and STEP for my data exchanges?
Prefer IGES for simple surface geometry exchanges or when working with older systems. Opt for STEP when you need to preserve complex solid structures, PMI information, or assemblies. STEP is generally superior for modern CAD interoperability, but IGES remains relevant in specific contexts.

CAD data interoperability with the IGES format represents both an important technological heritage and an ongoing challenge for modern companies. Despite its technical limitations and age, IGES continues to play a significant role in technical data exchange, particularly in industries where varied CAD systems must coexist.

The solutions offered by CAD Interop provide a complete ecosystem to efficiently manage IGES files throughout their lifecycle - from visualization with 3DViewStation or SimLab to repair with CADfix, through exchange automation with DEXcenter. By combining these tools with the presented exchange best practices, companies can overcome the challenges inherent to the IGES format and ensure smooth and efficient technical collaboration.

3DViewStation

CADfix

CADIQ

DEXcenter

SimLab