Introduction
IGES is one of the oldest neutral CAD formats, developed in the United States with the National Bureau of Standards (now NIST) and first published in 1980. It carries drawings, wireframes and, in later versions, exact surfaces and solids between CAD systems. Its last version, 5.3, dates from 1996, and STEP was designed to replace it.
IGES is still common for surface models, especially from older systems and in
aerospace and automotive work. Files use the extension .igs or
.iges.
Structure
An IGES file is text in fixed lines of 80 characters, a layout that comes from punched cards. Column 73 holds a letter naming the section the line belongs to, and columns 74 to 80 a sequence number. There are five sections, in order:
| Letter | Section | Holds |
|---|---|---|
S | Start | Free text for people to read |
G | Global | Delimiters, file and system names, units, precision, dates |
D | Directory entry | Two lines per entity: its type number, where its data starts, its layer, colour and other attributes |
P | Parameter data | The entity’s values, starting with its type number |
T | Terminate | One line with the number of lines in each section |
Entities are identified by number: for example 110 is a line, 126 a rational B-spline curve, 128 a rational B-spline surface, 144 a trimmed surface and 186 a solid made of faces.
Links
Software
- FreeCAD – free open source parametric CAD program (Windows, macOS, Linux)
- Rhino – McNeel’s NURBS modelling program, often used for IGES surfaces (Windows, macOS)
- SolidWorks – Dassault Systèmes’ mechanical CAD program (Windows)
- Autodesk Fusion – Autodesk’s CAD and CAM program (Windows, macOS)
Developers
- Open CASCADE Technology – open source geometry kernel that reads and writes IGES (C++)