References

A reference is a model that is attached to and displayed with the active model for printing or construction purposes. A MicroStation reference is analogous to an AutoCAD external reference (XREF) or an AutoCAD overlay.

Working with references that will be saved to DWG files

When you are working with a DGN file that will be saved to a DWG file:

• Use settings on the Save As DWG/DXF Options dialog box to control how MicroStation references will be handled in the DWG file format. See also Merging references when saving to a DWG file.

• Do not attach the active model to itself as a reference (self-reference), since the DWG file format does not support this type of reference.

• Use MicroStation's Live Nesting option, since it is compatible with AutoCAD's settings. See Working with nested references.

• You can set options in MicroStation to create references that can be saved to AutoCAD overlay attachments. See Defining overlay attachments.

The default Xref Block insert layer for a DGN reference attachment saved in the DWG file is the layer named “0.” To override the default insert layer for reference attachments, set the configuration variable MS_DWGINSERTLAYER to the desired layer name. For example, assigning MS_DWGINSERTLAYER to “MSINSERT” results in the assignment of inserts to the layer "MSINSERT". If this layer does not exist, it will automatically be created. MS_DWGINSERTLAYER is used to override the default insert layer for normal (unshared) cells as well as reference attachments.

Merging references when saving to a DWG file

The DWG file format does not support all of the reference types available in MicroStation. As a result, you must use the Save As DWG/DXF Options dialog box to define how the following types of references are merged into the model:

• external attachments — External attachments are separate files that can be attached to the main (default) design file as a reference. These attachments can be retained as separate attachments (and become AutoCAD XREFs), or be merged into the default model.

• self-attachments — Self-attachments are references to the main design file from within, such as in the case of reference views used to create sheet models. The DWG file format does not support self-attached references. They must be merged to be usable in AutoCAD.

• attachments to non-default models — The DWG file format only supports one design model. DGN files can have multiple design models. One of these models is defined as the default model. Attachments to non-default design models must be merged to display in AutoCAD.

• masked attachments — The DWG file format does not support clipping masks applied to references. Attachments with clipping masks must be merged, or the clipping mask will be removed in AutoCAD.

Save As DWG/DXF Options dialog box, References tab

Working with nested references

When a MicroStation design file used as a reference has its own attachments, they become nested references. The links between these files can be maintained through many levels (depths) of nesting, so that if you open only one file, you can view the contents of many files. The individual references can be updated, and the changes will be shown in the master (or parent) file. When you attach a parent reference to your model and turn on live nesting, you can also control how many levels of nested references are attached to the model.

In AutoCAD, there are two types of references that can be made to create file associations — attachments and overlays. Both allow the display of all objects in the attached file, as well as those in the nested references. Although AutoCAD allows live nested references, it does not provide control of nesting depth, and thus all data in the nested attachments is implicitly displayed.

Using live nesting in a DGN file that will be saved to DWG format

If your DGN file will be saved to a DWG file, make sure that your reference settings are compatible with AutoCAD's reference settings. To do this, turn on live nesting for the parent reference, and set the nest depth to a high number so that all nested references are included.

To attach a reference with live nesting

1. In the Primary tool box, click the References icon.
   The References dialog box opens.


2. In the dialog box's tool bar, select the Attach Reference tool.
   The Attach Reference dialog box opens.

   Attach Reference dialog box



3. Select the DGN file that contains the model to attach as a reference, and click Open.
   The Reference Attachment Settings dialog box opens.

   Attach Reference Settings dialog box



4. From the Nested Attachments options menu, choose Live Nesting.
   The Nested Attachments options are only available when the selected model has reference attachments. When the Live Nesting option is on, the hierarchical structure of any nested references are maintained when attaching the parent reference to a model.

   In MicroStation, a nested attachment is displayed only if the child reference does not have its Ignore Attachment When Live Nesting setting turned on (in the Attachment Settings dialog box), and the parent reference has Live Nesting enabled.



5. In the Nest Depth field, enter a high value (for example, 10).
   Set the depth setting to a high number to include even the most deeply nested references when the file is saved to DWG. Although the nested attachments will display in the view window, you will see only the parent reference in the References dialog box's list box.

Defining overlay attachments

An AutoCAD overlay is a type of reference. Unlike an AutoCAD attached reference, if it becomes a nested reference, it is not displayed, nor are any of the files attached to it. Thus, an overlay might be used when designers working on a portion of the project need to see information that will not necessarily be displayed at the parent file level. To create a MicroStation reference attachment that behaves like an AutoCAD overlay, turn on the Ignore Attachment When Live Nesting setting in the Attachment Settings dialog box.

When you save a DGN file to a DWG file, you can save reference attachments to DWG files as overlays. To do this, open the Save As DWG/DXF Options dialog box, and turn on Create Overlays for Reference Attachments (No Live Nesting). When this setting is on, all references are created as overlays, whether or not the Ignore Attachment When Live Nesting setting is on. This setting effectively disables live nesting in the DWG output file. It is useful for files where live nesting is turned off for all attachments.

Save As DWG/DXF Options dialog box, General tab References options

Working in DGN files with attached DWG data

A model in a DWG file can be attached as a reference to a design or sheet model in the open file (DGN or DWG). To attach the model in a DWG file as reference, follow the procedure in Attaching references.

Working with references in DWG workmode

In DWG workmode:

• When attaching a reference, you can specify a level for the reference attachment.

  In an AutoCAD DWG or DXF file, each XREF or layout viewport is placed on a specific layer. When you open the DWG file in MicroStation, XREFs and layout viewports are treated as references, and are placed on the same levels (layers). To modify a reference's level, open the References dialog box, double-click on the reference to open the Attachment Settings dialog box, and modify the Level setting.

  If a level is frozen, references on that level are not displayed.

• A model cannot be attached to itself as a reference (self-reference).

• Clipping masks cannot be used on references.

• You can work with live nested references, but cannot turn off live nesting or control nest depth, except by using the Ignore Attachment when Live Nesting setting (Attachment Settings dialog box.)