Initial Graphics Exchange Specifications
A General Description
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.
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.
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."
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.
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.
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.
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