The Initial Graphics Exchange Specification (IGES) is a vendor-neutral data format that allows the digital exchange of information among CAD systems. The IGESlib GoTools module contains functionality for reading and writing IGES files and for converting between an IGES file and the internal file format of GoTools.

The module depends on the GoTools core library which again depend on SISL.

The IGES converter read an IGES file and represents its entites in the internal data structure of GoTools. It can also write a model represented in GoTools to an IGES file or convert between an IGES file and `g2', the internal file format of GoTools.

The content of an IGES file is transferred to the application as a vector of type GeomObject. By checking the type of each object, the model can be stored and handled in the GoTools environment.

The IGES converter reads the following entities:

• 100 - Circular segment
• 102 - Composite curve
• 104 - Conic arc
• 106, form factor 12 - Copious data, linear path
• 108 - Plane
• 110 - Line
• 116 - Point
• 118 - Ruled surface
• 120 - Surface of revolution
• 122 - Tabulated cylinder
• 123 - Direction
• 124 - Transformation matrix
• 126 - NURBS curve
• 128 - NURBS surface
• 141 - Boundary
• 142 - Curve on parametric surface
• 143 - Bounded surface
• 144 - Trimmed surface
• 190 - Plane surface
• 192 - Right cicular surface
• 314 - Colour description

To write an IGES file, the file entities are added one by one to the IGES convertor using the function addGeom, which takes a GeomObject as parameter. The actual file is written by the function writeIGES.

The following GoTools entities can be exported using IGES:

• SplineCurve
• Spline Surface
• BoundedSurface

An example showing how data is read from and written to an IGES file can be found in intersect_with_plane.C

GoTools represent only geometric entities. Thus, IGES entities like annotation, structure, property, associativity, view, drawing and figure will be neglected. Neither are constructive solid geometry or finite element modelling entities handled. If such entities exist in a file read by the IGES converter, warning messages will be issued.

The topological entities specified in IGES 5.3 are not handled by the current version of the IGES converter. Thus, the entities vertex, edge, edge list, loop, face and shell are not handled. However, the geometric entities corresponding to these topological entities will be read. Colour information is read.

1. IGES 5.3 --- An American national standard