Dear Jeremy,
Thank you so much for your fast and helpful response!
Files for the reproducible case are in the attachment,
Folder contains:
1. Revit_IFC_Export_API_Test: this is the VS solution file.
2. RevitFile: Revit file and family file which has free-form surface.
3. Exported IFC File: IFC4 file exported from the add-in.
4. Validation Result: a validation result I generated. It contains error messages.
The workflow can be seen as below:
1. Open the Revit_IFC_Export_API_Test and compile it. The code is simple, just using the Document.Export function in API and some of the IFCExportOptions are specified.
2. Open Revit_IFC_Export_API_Test.rvt in RevitFile.
3. I use Add-In Manager, so I loaded the .dll file which is compiled from the solution. which is in the folder Revit_IFC_Export_API_Test\bin\Debug\Revit_IFC_Export_API_Test.dll
After the IFC file is successfully exported, we will see this message.
4. In the folder "Exported IFC File" we can see the IFC4 DTV file. By opening it with ifcPlusPlus, we can see the box is gone.
I hope this is clear enough. :) Thank you!
Cheers,
Gene