About Importing MicroStation DGN Files

The import process translates basic DGN data into the corresponding DWG file data. There are several translation options to determine how certain data such as text elements and external references are handled. Users can not only manipulate text elements and xrefs, but also select the conversion units based on DGN unit settings, and most importantly, preview the default mapping translation or create and use their own mapping setups (see DGNMAPPING).

Exchanging and reusing basic drawing data is useful in collaborative projects. For example, service organizations such as AEC and design-build firms might need to import mapping data created with MicroStation into a site plan created with an AutoCAD-based product. The DGN data can serve as an accurate reference for creating the site plan.

Understand the Limitations

The DGN import and export capabilities are designed to provide a fundamental exchange of information between MicroStation V7/V8 DGN files and AutoCAD DWG files. However, translating data from one format to a completely different format inevitably require 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 data fields or dynamic blocks can be represented visually but not behaviorally.
• AutoCAD only supports colors for lines so all entities in the DGN file that have a color property set for a symbol in MicroStation lose the symbol color when imported as a block.
• When importing DGN files that contain multilines, any linetypes associated with the multilines do not display.
• Ensure that you create uniformly scaled blocks in MicroStation. Entities with DGN line styles in non-uniformly scaled blocks display differently in MicroStation.
• All line style modifier settings of an element in the DGN file are lost when exporting them from AutoCAD back to MicroStation.
• The closed property of a DGN polygon or closed polyline is automatically set to No when importing a DGN file into AutoCAD. This is done to ensure that linetypes display properly.

See the DGNIMPORT Conversion Table for specific details about the scope of importing MicroStation objects and other data.

See the DGNIMPORT Unit Mapping Table for specific details about unit conversions when importing MicroStation objects.

Recommendations

To optimize the data transfer from the MicroStation® DGN file format, request that the creator of the MicroStation drawings consider the following recommendations:

• Create a separate DGN file for each design model
• Do not reference sheet models from design models
• Minimize the use of custom objects and other data unique to MicroStation
• Use ByLevel for color, line style, and weight properties
• Use simple patterns and pattern styles
• Use TrueType text fonts rather than SHX text fonts
• Use defined styles for dimensions and text rather than a “none” style
• Use simple dimension styles if possible
• Use shared cells as opposed to normal (library) cells
• Work primarily in one format, DWG or DGN, rather than switching back and forth

When importing a DGN file, specify the conversion units (master units or sub-units) based on the DWG file's drawing units. For example, if you receive a DGN file with master units set to meters, and sub-units set to millimeters, and you need the drawing units of the DWG file to be in meters, then select master units in the Import DGN Settings dialog box. This matches the meters in the DGN file to the meters in the DWG file.

Import Custom Line Style Definitions

If a DGN file does not contain linetype definitions and these definitions do not exist in any .rsc files in the support path, then all linetypes in the DGN file are displayed as a continuous linetype in AutoCAD. To ensure that custom linetypes are displayed, copy the corresponding .rsc files to the support path or add the RSC file path to the search path in AutoCAD in the Options dialog box (Files tab, Support File Search Path).

The RSC files are specified by the MS_SYMBRSRC configuration variable setting in the directory specified in the MS_RSRCPATH setting in MicroStation.

Import DGN Settings

In the Import DGN Settings dialog box, if you select “Import into Current Drawing” and select the “Translate References to Blocks or Xrefs” option in the External DGN references section, all referenced DGN files are converted to block references. If you do not select “Import into Current Drawing” and select the “Translate References to Blocks or Xrefs” option, then all referenced DGN files are converted to DWG external references.

Microstation Standard Line Styles

You can attach a DGN file as an underlay or import the DGN fiel into a drawing. It is recommended that you do not use the MicroStation standard line styles 1 to 7 because the scaling for these line styles is based on output device coordinates. For best results, use custom line styles.

Manage Translation Mapping Setups

You can manage translation mapping setups for DGN file import and export operations. You can create, modify, rename, or delete mapping translations based on your company’s CAD standards such as:

• Change DGN level names to appropriate DWG layer names
• Remap unsupported DGN linestyles to DWG linetypes
• Remap lineweights and adjust color mapping

Therefore, you can streamline the import/export process while minimizing the need for more extensive editing.

The DGN Mapping Setups dialog box is displayed when you click the Mapping Setups button in the Import DGN Settings and Export DGN Settings dialog boxes. You can also enter DGNMAPPING at the Command prompt.