Working with DGN Files, Then Delivering DWG Files

Sometimes you need to work with the MicroStation DGN file format, but the final project deliverable must be in DWG format. In other situations, you may have a legacy DGN file that you need to convert to a DWG file. If you do not need to exchange data with a DWG user for editing, the most effective strategy is to work in the DGN file, then save to a DWG file.

There are two ways to work with DGN files that will be saved to DWG:

1. Working in DGN Workmode - When you open a DGN file, MicroStation automatically selects the DGN workmode. Using this workmode, you can complete your design work using the full capabilities of MicroStation. Once you have finished changes to your design, you can use the Batch Converter utility or Save As dialog to save to a DWG file. Once you have finished changes to your design, choose Save As to save to a DWG file.

   Once you save to a DWG file or switch to the DWG workmode, you lose the ability to work with many advanced MicroStation capabilities such as Design History, level libraries, custom line styles, custom area patterns containing splines and cells, and clip masking of reference views. When you save a DGN file that uses these features to a DWG file, the entities will be displayed correctly in AutoCAD, although you may need to use the Save As DWG/DXF Options dialog to refine how the data will be converted to DWG. In some cases, the Batch Converter/Save As process drops the complex element definitions for these entities, and displays them simply as objects.

   To work effectively in a DGN file that will ultimately be saved to a DWG file, you need to understand the differences in the way that some types of data are defined in the DGN versus the DWG format, and adjust your design methods accordingly. For example, DWG files allow only one design model (model space), but DGN files allow multiple design models. To make conversion from DGN to DWG format easier, therefore, you should use only one design model in your DGN file.

   You also need to know how to adjust the Save As DWG/DXF Options for maximum effectiveness. For example, if your DGN file contains multiple design models, you can set options that determine how these models will be saved to DWG files.

2. Working in DWG Workmode - Another strategy for working with DGN files that will be saved to DWG format is to work on the DGN file with DWG workmode enabled. The DWG workmode restricts many functions to ensure that you create design data that is fully compatible with the DWG format.

   However, using DWG workmode does not ensure that existing DGN data is compatible. For example, if you open a new DGN file and enable the DWG workmode, you can only create one design model, since the DWG format only allows one model (model space) in a file. If you open an existing DGN file with multiple design models, then switch to the DWG workmode, the design models are still part of the file. In this case, you need to use the Save As DWG/DXF Options dialog to define how the design models will be saved to DWG files.

Working in a Mixed DGN/DWG Environment

MicroStation supports a mixed file format environment, which means that you can use DGN and DWG data in project files simultaneously. DWG files can stay in DWG format, and DGN files can stay in DGN format.

Typically, you might maintain the main design file in MicroStation, but have project subcontractors who provide their portion of the project in DWG format. In this case, DWG files can be attached as references, used in supplementary models, or inserted as cells. Additional DGN files, such as specification drawings, can also be incorporated. The main design would always contain a mix of DGN and DWG data, with no translation ever taking place.

Working Exclusively with DWG Files

In some situations, you may need to work directly with the DWG files in MicroStation, rather than converting them to DGN files. This strategy is most effective if you plan to continually exchange DWG files with an AutoCAD user throughout the life cycle of the project.

For example, assume that you are a MicroStation user who has been assigned a project on which you must collaborate closely with an AutoCAD user. You receive DWG files from this collaborator, work on them in MicroStation, return the modified versions back to the collaborator for review and revision, and receive them back for further editing. At the end of the project, you deliver a DWG file that conforms to a set of project standards.

By directly opening the DWG file in MicroStation, which automatically enables DWG workmode, you ensure that all the data that you generate is fully compatible with the DWG file format. However, while it is convenient to work directly with the DWG file, one drawback is that you cannot use some of MicroStation's advanced functionality such as Design History or some of the 3D surface modeling tools.

If you reference one DWG file in another DWG file, where both the files are created in AutoCAD, then, by default, the status of the Treat Attachment as Element for Manipulation icon will be on. The status of the Manipulate as Element check box in the References category of Preferences dialog will be the same as that of the Treat Attachment as Element for Manipulation icon. If you change the Treat Attachment as Element setting, it will be saved in the DWG file, provided you save the file with the Save Application Data check box in the Save As DWG/DXF Options dialog turned on. However, this change will take effect only in MicroStation.

Problems with Round-Tripping Data

To share design data, you may want to round-trip your data by opening a DWG file, converting it to a DGN file, then saving it back to a DWG file. However, every time that you save the file to a different format, the entire file is rewritten, not just the changes that were made to the design. If the file contains product-specific information such as AutoCAD proxy objects, this information will be lost. For this reason, round-tripping is not recommended.

In AutoCAD, proxy objects are non-native objects that are inserted into DWG files by third-party programs such as a landscaping package, mapping utility, or other industry-specific program. Although AutoCAD may not fully understand the definition of the proxy objects, it can often display them correctly even if the third party program is unavailable.

MicroStation can also display a DWG file proxy object, provided the object's definition contains sufficient display information. As long as the file stays in DWG format, MicroStation simply displays but otherwise ignores the proxy objects while the file is being modified. However, if the DWG file is saved to a DGN file, the proxy objects are lost.

To retain AutoCAD proxy objects, you can open the DWG file, modify it using DWG workmode, then save it as a DWG file.