IGES File Format Specification
IGES BackgroundIn order to transfer data from one CAD system to another we have two alternatives:
1) Write a direct translator for every combination of system
2) Use an intermediate file format that all systems can write to and read from.
The advantage of the first option is that it should mean that the data transfer is very robust if the direct translator is well written. The disadvantage is that we need a translator for every possible CAD system combination. In practice, it is not necessary to provide translators for every combination. For high end CAD systems such as Catia, I-DEAs etc it would make sense but a translator between 3ds Max and Catia would have a limited audience.
The 2nd option is to use an intermediate file format - known as a neutral file format as it is defined by a commitee independant of the software providers. IGES is the earliest successful format. In theory it is now obsolete since development of the format specification ended in 1996, but in reality it is still alive and kicking! Open any current CAD system and you'll very likely find there is an IGES export / import option.
IGES FormatThe latest IGES format is 5.3, full details of which can be downloaded for free from the USPRO site. The page numbers below refer to the page numbers within the PDF.
IGES files are text files so they can be read in any text editor. An IGES file is split into 5 sections. These are the S G D P and T sections i.e. Start, Global, Directory, Parameter and Terminate. The T or Terminate section consists of only one line which defines how many lines there are in the other sections. If you ever have a problem reading an IGES file one of the first things to check would be that the T line (which is the last line of the IGES file)exists. Without it the file is not a valid IGES file.