Cadtales

Xrefs
External References
Concept & Application

Xrefs - or external references, are “temporary” file insertions. The content of one file is inserted into the current file for viewing, editing and printing - but saved as separate files when closed. While it may be practical keep all information on a simple floor plan in one file it becomes increasingly difficult as building information expands and unwieldy for multi-story projects. A single-story house design can encompass 35 or more sheets. Multi-story buildings can grow to 60+ sheets and file sizes in the tens-of-megabytes.

Layers are used to provide separation and control so that multiple views and prints can be derived from the same model information. Xrefs work in a similar manner except that geometry, from one or more separate files, is inserted into the current file for viewing, editing and printing. The figure above shows a “stack” of xrefs but multiple xrefs can be inserted into the same file as well. The order of xref insertion is not critical since all files will appear as one when viewed in AutoCAD Model Space or as sheets in a Layout.

In most designs there will be core or base drawings that are used primarily for reference and are rarely changed. These drawings are typically named with an ‘x’ prefix (x-site plan, x-plumbing) to note their reference status. Xrefs can be used in any project or scheme that contains one or more source drawings. Some important benefits of using xrefs are:
1. Smaller files mean faster and more efficient designing.
2. Load and use only the information germane to the current design or presentation.
3. Xref information cannot be changed with regular AutoCAD edit commands.
4. Xrefs, when loaded from a read-only directory, cannot be changed by unauthorized operators.
5. Xrefs can be Attached, Detached, Loaded, Unloaded or Bound at will.
6. Xrefs provide flexible separation by disciplines (electrical, HVAC), segments (demo, new, existing), and/or spatial (floors, wings, buildings) just to name a few.

The Xref Manager is the primary tool for inserting and managing xrefs. Open this palette with the Insert>External References pull-down menu, or the Xref Manager icon at the right side of the Drawing Status Line, or by typing Xref at the command line.



The Xref Manger palette has three icons in the upper-left: Attach, Refresh & Help.

In the upper-right side note the two additional icons, List View and Tree View.

The List View is shown in the full palette view above. There is a single listing for each xref regardless of how many times, and/or at what levels, it may appear in the Tree View. The Tree View is handy for spotting circular references (a potentially serious error condition).

Use the Attach icon to open the Select Reference File dialog box. This dialog box contains a file-lookup window so you can navigate to a local disk, network or Internet location to retrieve a file. Select a file and click the Open button. This will open the External Reference dialog box.

This dialog box contains a Look in: window and settings to control the insertion or base point, scale and rotation of the reference drawing. It is important that the current drawing and the xref share a common base point to insure that drawing geometry aligns properly. The default insertion point (X, Y, Z coordinates) for an xref are (0,0,0) and most drawings will use this default for the sake of simplicity and uniformity. Xrefs are normally inserted at a 1:1 scale and a zero rotation angle. The Block Units window provides for unit conversions from other measurement systems i.e. metric to imperial, etc.

After insertion xref layers will appear prefixed with the source drawing name and separated by a “|” symbol (vertical bar).

Editing Xrefs
Xrefs can be shared by many different drawing sets, and at different levels, so editing should be done with caution. Xrefs should be edited only by authorized operators!
AutoCAD provides two methods for editing xrefs. Double clicking an xref will open the Reference Edit dialog box listing the chosen xref and any nested xrefs and blocks. Choose an item.

All other drawing components will gray-out and the Refedit Toolbar will appear.

Now you can edit the xref “in place.” Use the “+” and “-“ toolbar buttons to add or remove items from the edit list, and the “x” button to cancel and discard any changes. Use the right-most button to save changes and close the ref-edit session. If you inadvertently close the Refedit Toolbar, right click any Toolbar and select Refedit, or type Refedit at the command line.

Invoke the second xref edit method by right clicking an xref and selecting Open Xref to open the xref in a separate AutoCAD window. Make the desired changes, save and close the file. A message balloon will appear in the current drawing session notifying you that “External Reference Has Changed” and offering a command link to Reload the xref in the current drawing.



Binding Xrefs
There will be instances where it is desirable to make some or all xrefs a permanent part of the drawing file. For example, legal documents, as-built drawings, project progress benchmarks, and contract bid packages, or any other instance where you would not want uncontrolled copies of reference documents available for edit.

To Bind an xref, open the Xref Manager, select a first level xref (nested xrefs cannot be bound to their parent at this level), right click and select Bind.

The Bind command will open the Bind Xrefs dialog box.

Two Bind Types are offered. The “Bind” type includes the origin-drawing name as part of the layer name and separated by “$0$.”

The “Insert” type discards the origin-drawing name and simply merges layer names with the existing layer list.


Q What is the command to open an xref for editing?
A Type Xopen at the command line, select any xref and press enter to open for editing.

Q Will my Color Dependent xref plot with the original color settings?
A No. Color Dependent plots use a CTB plot configuration file that is independent of the drawing. The CTB file must be imported into the current drawing to support original plot settings.

Q Will the default line weights in my xref plot with the original settings?
A No. Default line weight settings are not saved with the drawing. Xrefs will be plotted with the default line weight setting in the current drawing.

Q Can I set the Bind type to default to Insert?
A Yes. Set the system variable (Sysvar) BINDTYPE to 1. (This variable is NOT saved with the drawing, however).

Q Can I insert xrefs at different elevations?
A Yes, Set Elevation (ELEV) in the current drawing to the desired level before inserting the xref.

Q Can I change an xref’s status from Attach to Overlay without detaching and re-attaching the drawing?
A Yes. Select the xref, right click and select Xref Manager. Select the xref to change. Under “Type” double click the word Attach. (The status changes each time you click the word). Choose OK to complete the process.

Xrefs add new dimensions of flexibility and control to project and drawing organization. When used in an organized project environment xrefs will support the legal, contractual, communication and cost objectives of a well-managed business.