One of the basics of working with others involves using many types of documentation as a reference for your own work. If you'll take a look at the Insert menu, you'll see some of the options you have for directly referencing into AutoCAD®: DWG, DWF, DGN (version 8 only), and Raster Images (any of a dozen filetypes).

DGN Underlay and DGN Import are new in most of the 2008 family of Autodesk products.

Toward the bottom of this menu, you can call up the External References palette (use XREF to open it from the command line) where you can also see your underlay options.

If you like the older style dialog, you may still use it with the CLASSICXREF command, but you will not see the additional reference types.

Using DWF as a Reference
I want to insert a DWF for a reference right now.

I can select one sheet from the DWF and I choose the Reflected Ceiling Plans and adjust my options like I normally would. It looks just like a DWG reference now and I can snap to intersections, and so on. Layers were enabled during the creation of the DWF, so I can select and right-click for access to the underlay's layers and toggle them on or off.

Using an Inverted XClip on a External Reference
I want to revise a small area on the main floor, so I'm going to reference in a DWG file and snip out the area to which I'd like to make changes. In the past, my only clipping option was clipping outside of a boundary. If I wanted to mark over a given area on a referenced plan, I'd have had to use a background mask or insert the xref as a block and explode it to snip out the unwanted pieces.

Type XCLIP, select New Boundary, then Invert clip, then select Rectangular boundary. See below for the xref and its inverted clip. This is leaving me free to explore a few different options while keeping a live reference back to the rest of the project.

Here's the definition and a tip from the AutoCAD Help files entry on XCLIP's new Invert Clip option:

Inverts the mode of the clipping boundary: either the objects outside the boundary default) or inside the boundary are hidden.

Note: Use the 2D Wireframe visual style for viewing inverted clipped xrefs and blocks. Other visual styles do not display inverted clipped areas.

Using a DGN as a reference
From the External References tool palette, select 'Attach DGN' to begin inserting your underlay reference.

You'll see some of the same options you would with a normal DWG reference (like path type, scale, insertion point, and rotation). There are a couple of additional options for the DGN now, such as choosing the design model and the conversion units.

Once you have your DGN file underlaid, you'll have some of the same right-click options as you would with a DWF. You will not have any control over the layers (Microstation levels), though.

AutoCAD 2008 can also now import and export DGN V8 format, so don't be afraid to poke around a little and check out the differences.

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Melanie Perry is Facilities–Management CADD coordinator working for BJC Healthcare. In her spare time, she is president of the Gateway AUG and a freelance writer. She can be reached at mistressofthedorkness@gmail.com.