The DGN and DWG File Formats

The V8 DGN file format is MicroStation's native file format. MicroStation also opens and saves files in the AutoCAD DWG format.

As of MicroStation V8i SELECTseries 1, the DWG files created by MicroStation are saved using Autodesk-authored code called RealDWG. Because of this the files are accepted as "trusted" by AutoCAD. Therefore, you can open in AutoCAD a DWG file created or modified in MicroStation and you will not see an alert message saying that the DWG file is "Foreign" because it was saved in a non-Autodesk program.

When a DGN file containing DGN-specific entities not understood by AutoCAD is saved in MicroStation as a DWG file, these entities are automatically converted to DWG-compatible entities so that they can be displayed properly in AutoCAD.

MicroStation V8i SELECTseries 3 also supports materials and lights created in AutoCAD R2007 and later. The old materials and lights, also known as AVE objects, created in versions prior to AutoCAD R2007 are not supported. These AVE objects become regular shared cells and have no effect on rendering.

MicroStation supports all DWG entity types and objects from AutoCAD 2006 and earlier. The following AutoCAD entities and objects introduced in AutoCAD versions 2007 and later are supported as read-only:

annotative objects in paper space (sheet models)
layer viewport overrides
column mtext
visual styles
geometric constraints

Note: The DXF file format is an ASCII text representation of the DWG format. DXF is an interchange format historically used to exchange data between AutoCAD and other applications. You work with DXF data in MicroStation in the same manner as DWG data. DWG is preferable because its compact binary representation results in smaller files. For the remainder of this topic, the term DWG refers to both DWG and DXF files.

Transparency in DWG Files

When a DWG entity has a transparency that is the same or greater than its layer’s transparency, the effective transparency is calculated and displayed the same as it is in AutoCAD. However, when the entity’s transparency is less than its layer’s transparency, the effective transparency will be the same as ByLayer. As a result, when this type of element is edited in MicroStation and saved as a DWG file, the entity will have ByLayer transparency.

For example, assume a DWG entity has transparency set to 70% and the layer transparency set to 60%. While calculating transparency in MicroStation, the DWG entity transparency is considered as the effective transparency, and the effective transparency formula is rearranged to get the element transparency. The element transparency in this case comes to 25%. Now with element transparency equal to 25%, the effective transparency is calculated using the same formula. It comes to 70%, which is same as the DWG entity transparency. But if a DWG entity has transparency set to 40% and the layer transparency is set to 60%, the effective transparency will be zero and the element transparency will be the same as layer transparency that is 60%.