Initial Graphics Exchange Specification

Initial Graphics Exchange Specification. The Initial Graphics Exchange Specification is a vendor-neutral data format used to exchange digital information between computer-aided design systems. Developed in the late 1970s, it was formally published as an American National Standards Institute standard in 1980. It describes product data using a clear text ASCII structure, representing information via entities like NURBS curves and wire frame model geometry.

Overview

The primary purpose of the specification was to solve the problem of data translation between disparate CAD software packages from vendors like IBM, General Electric, and McDonnell Douglas. It functions as a neutral intermediary format, allowing a model created in one system to be interpreted in another without requiring proprietary file format access. The standard defines a wide range of entities to represent two-dimensional and three-dimensional engineering drawing information, including geometric, topological, and annotation data. This capability was crucial for large-scale projects in industries such as aerospace engineering and automotive industry manufacturing, enabling collaboration between different departments and contractors.

History and development

The development was initiated in 1979 by a consortium including the United States Air Force's Integrated Computer-Aided Manufacturing project and the National Bureau of Standards, later renamed the National Institute of Standards and Technology. A key driver was the United States Department of Defense's need to integrate CAD data from its numerous contractors, who used incompatible systems from companies like Computervision and Applicon. The first official version, designated ANSI Y14.26M, was ratified in 1980. Subsequent updates, often managed by organizations like the American Society of Mechanical Engineers, addressed limitations and expanded entity support. Its creation directly influenced later, more robust international standards efforts, notably the ISO-led Standard for the Exchange of Product model data initiative.

Technical details

The file structure is organized into five distinct sections: Start, Global parameters, Data Directory Entry, Parameter Data, and Terminate, all encoded in ASCII text. Geometric representation is achieved through defined entity types, such as lines, arcs, conics, and Bézier surfaces. For complex free-form shapes, it utilizes Non-uniform rational B-spline entities. The format supports both boundary representation and Constructive solid geometry techniques for defining solid models. Data is stored in an 80-column record format, a legacy of punched card systems, with specific fields for entity type numbers, pointers, and parameter lists. While human-readable, this structure can lead to large file sizes and does not inherently support product lifecycle management metadata or modern parametric modeling constraints.

Applications and usage

Throughout the 1980s and 1990s, it saw widespread adoption for exchanging drawings and models in major engineering sectors, particularly within NASA projects, Boeing aircraft development, and General Motors automotive design. It became a de facto requirement for contractors supplying the U.S. Department of Defense. The format is commonly used for exporting geometry for Finite element analysis in software like ANSYS and for driving Computer-aided manufacturing and Numerical control machining tools. While largely superseded by STEP AP203 and STEP AP214 for complex data exchange, it remains in use for simpler 2D computer graphics translation and is supported as a legacy import/export option in nearly all major CAD platforms, including Autodesk AutoCAD, Dassault Systèmes CATIA, and Siemens NX.

Related standards

The specification is a direct predecessor to the more comprehensive ISO 10303, universally known as STEP (standard). STEP addresses many of its shortcomings by supporting richer product structure, tessellation, and application protocols. Other contemporary or successor formats include ACIS SAT, a boundary representation-based format from Spatial Corporation, and Parasolid, the geometric modeling kernel from Siemens Digital Industries Software. For additive manufacturing, the STL (file format) became prevalent for 3D printing, while VRML and its successor X3D are used for 3D computer graphics visualization on the World Wide Web. The development of these standards was also influenced by earlier efforts like the French SET standard and the German VDA-FS format.

Category:Computer-aided design Category:Computer file formats Category:American National Standards Institute standards