The External Reference Dialog Box

The External Reference Dialog Box
The External Reference dialog box, shown in Figure 7.10 earlier in this chapter, offers these options:
Browse Opens the Select Reference File dialog box to enable you to change the file you’re
importing as an Xref.
Attachment Tells AutoCAD to include other Xref attachments that are nested in the selected file.
Overlay Tells AutoCAD to ignore other Xref attachments that are nested in the selected file.
This avoids multiple attachments of other files and eliminates the possibility of circular references
(referencing the current file into itself through another file).
Path Type Offers options for locating Xrefs. Xref files can be located anywhere on your system,
including network servers. For this reason, links to Xrefs can be easily lost either by moving
them or rearranging file locations. To help you manage Xrefs, the Path Type option offers three
options: Full Path, Relative Path, and No Path. Full Path retains the current full path. Relative
Path maintains paths in relation to the current drawing. The current drawing must be saved
before using the Relative Path option. The No Path option is for drawings in which Xrefs are
located in the same folder as the current drawing or in the Support File Search Path specified in
the Files tab of the Options dialog box (choose Tools  Options).
Specify On-Screen Appears in three places. It gives you the option to enter insertion point,
scale factors, and rotation angles in the dialog box or in the Command window, in a way similar
to inserting blocks. If you clear this option for any of the corresponding parameters, the parameters
change to allow input. If they’re selected, you’re prompted for those parameters after you
click OK to close the dialog box. With all three Specify On-Screen check boxes cleared, the Xref
is inserted in the drawing using the settings indicated in the dialog box.

Clipping Xref Views and Improving Performance
Xrefs are frequently used to import large drawings for reference or backgrounds. Multiple Xrefs,
such as a floor plan, column grid layout, and site-plan drawing, might be combined into one file.
One drawback to multiple Xrefs in earlier versions of AutoCAD was that the entire Xref was loaded
into memory, even if only a small portion of the Xref was used for the final plotted output. For computers
with limited resources, multiple Xrefs could slow the system to a crawl.
AutoCAD 2008 offers two tools that help make display and memory use more efficient when
using Xrefs: the Xclip command and the Demand Load option in the Options dialog box.

Clipping Views
The Xclip command lets you clip the display of an Xref or a block to any shape you want, as shown
in Figure 7.11. For example, you might want to display only an L-shaped portion of a floor plan to
be part of your current drawing. Xclip lets you define such a view. To access the command, choose
Modify  Clip  Xref.
You can clip blocks and multiple Xrefs as well. And you can specify a front and back clipping
distance so that the visibility of objects in 3D space can be controlled. You can define a clip area by
using polylines or spline curves, although curve-fitted polylines revert to decurved polylines. (See
Chapter 18 for more on polylines and spline curves.)