When I export a 3D model with stairs and railings to DWG and open the file in MicroStation or AutoCAD, a flat 2D version of the railing is displayed at an elevation of 0 regardless of where the railing itself exists.
How can I export railings to DWG without seeing that 2D version?
The 2D projection seen in DWG format is actually the railing's embedded 2D symbol used by the drawing composition workflow.
This symbol is handled internally by OpenBuildings Designer, so will be visible if the DWG file is opened in any other application when the Save Application Data option is enabled under the Save As DWG > Advanced options. This has been filed as Defect 901968 and is scheduled to be resolved in a future release.
However, one way to achieve the desired result is to first publish the DGN file to an iModel (i.dgn), open that i.dgn in OpenBuildings Designer, and then export it to DWG. The result should look like this:
Because the 2D symbol is not saved when publishing the i.dgn file it’s also removed when exporting to DWG. At the same time, because the railing's DataGroup properties are mapped to Item Types during the imodel publish command the railing's properties are still available in DWG format: