Option has been added to DWG Save options that allows for creating DGN underlay in DWG file
In AutoCAD underlays are references that are similar to attached raster images in that they provide visual content but also support object snapping and clipping. Unlike external references, underlays cannot be bound or merged into the drawing. You reference and place underlay files in drawing files the same as you do raster image files; they are not actually part of the drawing file. Like raster files, the underlay is linked to the drawing file through a path name.
An option has been added in MicroStation Connect to save DGN underlay in a DWG file. Underlays are essentially raster references. Following is the behavior of underlays in MicroStation:
DGN underlay in a DWG file - When you open a DGN underlay, it becomes a DGN reference attachment with the logical name "DGN Underlay" followed by a numerical index.
When you save a DWG file, a DGN reference attachment with logical name that has the prefix "DGN Underlay" becomes a DGN underlay.
You can also create DGN underlays when you Save As a DWG file. In the Save As DWG/DXF Options dialog References tab, select "DGN Underlay" for the External Attachment setting. All externally attached DGN files will become DGN underlays.
PDF underlay - A PDF underlay in a DWG file becomes a PDF raster attachment. It is supported to the extent of the raster manager's capability of attaching a PDF file.
DWF underlay - DWF underlays are not supported in MicroStation.
Note: In non-Bentley products, there are limitations to what you can do with DGN underlays. Hence, an xReference is recommended over a DGN underlay.
You can also overlay an xref (xreference)on your drawing. Unlike an attached xref, an overlaid xref is not included when the drawing is itself attached or overlaid as an xref to another drawing. Overlaid xrefs are designed for data sharing in a network environment. By overlaying an xref, you can see how your drawing relates to the drawings of other groups without changing your drawing by attaching an xref.
There has been an option merge viewport graphics when converting from DGN to DWG. In previous version of MicroStation you could merge all reference files but there would still be a reference attachment for each viewport in the sheet model. Now all files can be merged resulting in a DWG file with no attachments included.
If on, and if the Self Attachments option is set to Merge or Merge to Cell, all viewport attachments will be merged into sheet models
If off, self attachments of the default model into a sheet model will become a viewport entity when saved as DWG. This is the default behavior and in this case the Self Attachment option has no effect on the attachment.
Many times, when merging viewports into sheet models, you may also want to turn on Merge Displayed Levels Only to retain the same visibility of the sheet model in the saved DWG file.
If on, a 3D reference file attachment will have its visible edge representation merged into the master file. To check the effect of this setting refer to the example in "Merging References into the Active Model" section in MicroStation Help. If on, this setting overrides all attachment settings above it.
This setting affects all references except the ones that display wireframe geometry. This option is useful when using Dynamic Views because target formats such as DWG and V7 DGN do not support the dynamic view display options.
When you turn on this check box, a Visible Edges Settings icon appears next to it. Clicking this icon opens the Visible Edges Settings dialog. The changes made in Visible Edges Settings dialog, when accessed from here, are saved in DWG settings, such that the next time you do a Save As DWG and have the Merge Visible Edges of 3D Attachments check box turned on, your previous visible edges settings are restored.