Note: This document was originally put together using the tools available in V2 Rhino. While these tools remain in Rhino V3 and V4, you may have developed different techniques for “repairing” troublesome IGES files. Please share those techniques here - John Brock
One powerful use of Rhino’s file translation ability is to clean up poorly written IGES files. You may have received IGES files from your clients or suppliers that do not read properly into your solid based modeling application. Often this is the result of an improperly formatted IGES file, missing or duplicate surfaces, gaps or overlaps, or bad surface trimming information.
No amount of relaxed tolerances in the healing process can automatically fix these problems. After a long wait, you end up with incomplete solids, missing surfaces, or perhaps nothing at all. Your job depends on importing and using this data. What do you do?
Rhino has the basic tools needed to overcome all of these problems. With a little practice and good problem solving skills, you can repair these problem files and get the data imported into your solid modeling application. The effort and time required will vary a great deal depending on the number of problems and the size of the IGES file.
Fortunately, most problem IGES files can be repaired fairly quickly with a little practice. However, some can take several days of effort. With Rhino you have the tools to fix the most difficult IGES problems and get on with the job.
Since Rhino is a surface modeler that supports solids, it does not require that the IGES data consist of a closed solid. Rhino will read in as much valid information from the model as it can, skipping corrupt objects but reading all the point, curve, and surface data. Rhino’s IGES importing process will often read the file and fix the problems automatically. All you have to do then is save it back as a new IGES file and read it into your application. If the repair isn’t automatic, you can use Rhino to replace missing surfaces, fix bad trim curves, smooth surface discontinuities, and export a solid model to your application.
Generally, you can salvage most of the data in the IGES file. Sometimes, there is no choice but to re-modeling portions of the file. Even in this extreme case, Rhino contains the tools to harvest isoparms, sections, and edge curves that can be used to replace these unusable surfaces while preserving the original design intent.
The general strategy in repairing IGES files will vary depending on the individual files. Over time, you will discover patterns of problems in the IGES files produced by specific applications and individual users.