The export process translates basic DWG file data into the corresponding DGN file
data. There are several translation options to determine how certain data such as
external references are handled, the dynamic range of the DGN file as controlled by
the master and subunits specified, and whether the DGN file is to accept data with
non-zero Z coordinates.

Exchanging and reusing basic drawing data is very useful in collaborative projects.
For example, service organizations such as AEC and design-build firms using an AutoCAD-based
product might need to export a site plan to DGN format for access by a landscape firm
or perhaps a city planning department.

A Standard (default) mapping translation is used to map DWG-format layers, linetypes,
lineweights, and colors to DGN-format levels, linestyles, lineweights, and colors.
You can remap these elements based on your company CAD standards, therefore, streamlining
the export process while minimizing the need for editing the resulting DGN file (see
DGNMAPPING).

Understand the Limitations

The DGN import and export capabilities are designed to provide a fundamental exchange
of information between MicroStation DGN files and AutoCAD DWG files. However, translating
data from one format to a completely different format inevitably requires compromises
and substitutions.

• Simple geometric objects such as lines, arcs, and circles, and properties such as
  layer assignments correlate directly between the DWG and DGN data formats.
• Data with built-in features or variations are visually approximated. For example,
  text and dimensions might have specialized formatting, and color definitions might
  be customized.
• Some data cannot be translated completely. For example, product-specific features
  such as dynamic blocks, can be represented visually but not behaviorally.
• Nested references are not merged into the host DGN file when exporting a DWG file
  with nested references as V7 DGN. The nested reference is not displayed in the host
  DGN file but the reference chain still exists.
• AEC objects are not supported and users must use EXPORTTOAUTOCAD command to convert
  the objects to base ACAD objects before exporting to DGN.
• AutoCAD does not support exporting linetype definitions with DGN files. If a DGN file
  contains linetype definitions, but .rsc files do not contain these linetype definitions
  in the Symbology path in MicroStation, then when the DGN file is exported from AutoCAD
  and opened in MicroStation, the linetypes do not display correctly because of missing
  linetype definitions.

See the DGNEXPORT Conversion Table specific details about the scope of exporting DWG
objects and other data to DGN files.

Recommendations

To optimize the data transfer to the MicroStation DGN file format, consider the following
recommendations:

• Minimize the use of custom objects and other data unique to AutoCAD-based products
• Use simple linetypes as much as possible
• Use simple hatches and hatch styles
• Use simple gradients and gradient styles
• Use simple dimension styles if possible
• Use TrueType text fonts rather than SHX text fonts
• Work primarily in one format, DWG or DGN, rather than switching back and forth

When exporting DWG data to DGN files, you need to specify the conversion units of
the DGN seed file (master units or sub-units) correctly based on the drawing units of the DWG file.
For example, if the DWG file you are exporting to DGN is drawn in inches, and the
DGN seed file you are exporting to has master units set to feet and sub-units set
to inches, you need to select sub-units in the Export DGN dialog box. If you select
master units instead of sub-units, the scale of the imported DWG file will be incorrect.
For example, a 36-inch door would display as a 36-foot door.