IGES

Initial Graphics Exchange Specifications

From http://www.nist.gov/iges/

A General Description of IGES

Products may be designed as either a two-dimensional, three-view drawing layout, or as a full three-dimensional model with associated drawing views and dimensions using a Computer Aided Design (CAD) system. The IGES format serves as a neutral data format to transfer the design to a dissimilar system. Translators, developed to the IGES Standard, are used to export a design into an IGES file for exchange and for importing the IGES file into the destination system.


The IGES Domain


"This Specification establishes information structures to be used for the digital representation and communication of product definition data.

The file format defined by this Specification treats the product definition as a file of entities. Each entity is represented in an application-independent format, to and from which the native representation of a specific CAD/CAM system can be mapped. The entity representations provided in this Specification include forms common to the CAD/CAM systems currently available and forms which support the system technologies currently emerging.

In Chapters 3 and 4, the product is described in terms of geometric and non-geometric information, with non-geometric information being divided into annotation, definition, and organization. The geometry category consists of elements such as points, curves, surfaces, and solids that model the product. The annotation category consists of those elements which are used to clarify or enhance the geometry, including dimensions, drafting notation, and text. The definition category identifies groupings of elements from geometric, annotation, or property data which are to be evaluated and manipulated as single items."

Quoted from Initial Graphics Exchange Specification (IGES) Version 4.0 , NBSIR 88-3813, June 1988, pages 1-2.


IGES File Structure Overview


"The fundamental unit of data in the file is the entity. Entities are categorized as geometry and non-geometry. Geometry entities represent the definition of the physical shape and include points, curves, surfaces, solids, and relations which are collections of similarly structured entities. Non-geometry entities typically serve to enrich the model by providing a viewing perspective in which a planar drawing may be composed and by providing annotation and dimensioning appropriate to the drawing. Non-geometry entities further serve to provide specific attributes or characteristics for individual or groups of entities and to provide definitions and instances for groupings of entities. The definitions of these groupings may reside in another file. Typical non-geometry entities for drawing definition, annotation, and dimensioning are the view, drawing, general note, witness line, and leader. Typical non-geometry entities for attributes and groupings are the property and associativity entities.

A file consists of 5 ... sections, Start, Global, Directory Entry, Parameter Data, and Terminate. A file may include any number of entities of any type as required to represent the product definition. Each entity occurrence consists of a directory entry and a parameter data entry. The directory entry provides an index and includes descriptive attributes about the data. The parameter data provides the specific entity definition. The directory data are organized in fixed fields and are consistent for all entities to provide simple access to frequently used descriptive data. The parameter data are entity-specific and are variable in length and format. The directory data and parameter data for all entities in the file are organized into separate sections, with pointers providing bi-directional links between the directory entry and parameter data for each entity. The Specification provides for groupings whose definitions will be found in a file other than the one in which they are used."
Quoted from Initial Graphics Exchange Specification (IGES) Version 4.0 , NBSIR 88-3813, June 1988, page 3.


As IGES data is in ASCII clear text, any desired means of transferring the IGES file may be used, from tape and floppy disks to Internet. For the latter, an Internet message type of "model/iges" has been registered with the Internet Engineering Task Force. In addition to CAD-to-CAD (or CAM) transfer, the destination may be a graphical viewer. A number of vendors of viewing tools and adapters may be found on the Tools page of this site. Some of these tools allow editing/repair of IGES files. A general purpose text editor may be used to edit an IGES file, however as the entities and file sections in an IGES files are "pointer linked," the use of IGES-specific editing tools is desirable.


Brief History of IGES


"In 1979 events took place that catalyzed the CAD vendor community to create the first national standard for CAD data exchange. Mechanical CAD systems were less than ten years old, and there were only a handful of products with any significant market penetration. Even at this early stage, users were overwhelmed by the inability to share data among these tools and with their own internally-developed databases. Frustration was evident at a fateful two-day Society of Manufacturing Engineers (SME) meeting in the Fall of 1979. On the first day, an attendee from General Electric (GE) challenged a panel of CAD vendors, that included ComputerVision, Applicon, and Gerber, to work together to enable a common neutral exchange mechanism.

The panel reported on the second day, and the wheels were set in motion to create an 'IGES.' Once the panel admitted that a common translation mechanism was possible, it was impossible to stop the momentum of the customer's enthusiasm and expectations. Applicon and ComputerVision agreed to open their internal databases, GE offered its neutral database, and Boeing offered the structure of its Computer Integrated Information Network (CIIN) database. Both GE and Boeing contributed their existing translators. A core team was formed that included representatives from NBS, Boeing, and GE. Team members had worked closely with each of the vendors on internal integration projects. This prior experience built the expertise and trust needed to craft a solution in a very short time, and neither vendor felt it gave an unfair advantage to the other.

Soon after, an open meeting was held at the National Academy of Sciences on October 10, 1979. Approximately 200 people attended to herald the birth of IGES."
Quoted from B. Goldstein, S. Kemmerer, C. Parks, "A Brief History of Early Product Data Exchange Standards," NISTIR 6221, September 1998.


A vignette on Initial Graphics Exchange Specifications (92K PDF file) was included in A Century of Excellence in Measurements, Standards, and Technology - A Chronicle of Selected NBS/NIST Publications, 1901 - 2000, David L. Lide, Editor; NIST Special Publication 958, January 2001, available from the National Technical Information Service (NTIS), #PB2000-107702.


A series of IGES milestones may be found elsewhere in this Web site. These milestones identify the versions of IGES, adding additional product properties, solid models, and new features. Application Protocols for Three-Dimensional Piping (ANS US PRO/IPO-110-1994) and Layered Electrical Products (ANS US PRO/IPO-111-1997) have also been approved to provide a uniform representation of these products using the IGES format and data entities.


One benefit of an open standard for product data has been the ability to entertain changes from the using community. This Web site provides the forum for communicating proposed changes and open review by all concerned. The resultant versions of IGES are then reviewed for publishing as ANSI standards. Each version has, and will, include those changes which have reached consensus by the reviewers. The approved changes are termed Engineering Change Orders, such as those found in the Current Version and Next Version page of this site.


Created May 2002; CHP