IGES files most typically contains objects as trimmed NURBS. When these are imported and displayed/rendered in Okino software, or re-exported to other 3D file formats, they have to be converted to polygonal meshes. This process is called "NURBS tessellation".
When a NURBS surface has 1 or more trim curves on it there is the slightest chance that the trim curves were created incorrectly in the source 3D modeling package. This was more common around the 1997 era than at the time of this writing. When a trim curve loops back on itself, or trim curves intersect each other or the main boundary, then tessellation errors will occur. In these cases the trim holes or trim boundaries are corrupted and cannot be used to trim out the surface. This will lead to the error messages printed to the message window. There is no solution to this problem other than to update your 3D modeling software or modify the trim loops in the source 3D program again (for example, trims that merge to a very narrow cusp often do not trim properly in other 3D packages).
Okino has top-notch experts in IGES. Given any tessellation error message we can always back track it to the exact entity in the IGES file which leads to the error message (this is like finding a needle in a haystack). In some cases we have been able to fix the trimming error with tweaks to the IGES importer or NURBS tessellator. In other cases we have been able to document bad trim loops and curves that the 3D modeling package manufacturer could use to fix their software. - Updated: October 19, 2007
Okino's IGES importer requires that the IGES file be written in the "Trimmed NURBS Surfaces with uv-space Trim Curves" variation. There are many variations of the IGES file format and Okino's importer uses the most commonly used version.
To verify that this is the problem press the F2 key on the keyboard inside PolyTrans or NuGraf and scroll the message window backwards after the IGES file has been imported. The IGES import converter will display a list of which primitives it found.
If no 3D entities are listed in the message window (128, 144, 142 entities) then your file cannot be accomodated. If the file only contains entities like 100, 104, 110, 112, 124, 126 then the IGES file only contains 2D drafting elements and no 3D data.
If the IGES importer printed a warning message "This IGES reader requires that trimmed NURB patches use 144/142 entities (with uv-space trim curves) rather than 143/141 entities. Please re-export IGES file with uv-space trimming curves and 144/142 entities" then you need to re-export your IGES file in the 144/142 trimmed Surfaces variation of the IGES file format and not the 143/141 bounded surfaces format.
Please refer to the Okino IGES importer documentation. - Updated: October 2, 2007
In general, going into a non-solids 3D package requires that the trimmed NURBS
surfaces be converted to polygon meshes. This will result in a many times increase in
file size and/or memory usage. As a general rule, take the size of the files on disk
and multiply by 10 -- this is roughly how much memory you will need to hold the imported
data. - Updated: October 2, 2007
Pro/E 2000i slightly changed in terms of how it output its hidden entities. The Okino IGES importer was updated in November 2000 to handle all such scenarios as well as make it compatible with CATIA hidden entities and how the hidden state is propagated down a hierarchy tree. - Updated: October 2, 2007
