Chapter 18: Everything from Arrays to Xrefs 403

One use of Overlay mode is to avoid circular references. If drawing A references drawing B, which references drawing C and then C references A, you have an infinite loop. If C references A as an overlay, though, C doesn’t see B, and so the loop is broken.

Layer-palooza

When you attach or overlay an xref, AutoCAD adds new layers to your current drawing that correspond to the layers in the xref-ed DWG file. The new layers are assigned names that combine the drawing name and layer name. For example, if you xref the drawing MYSCREW.DWG (which has the layer names GEOMETRY, TEXT, and so on), the xref-ed layers will be named MYSCREW|GEOMETRY, MYSCREW|TEXT, and so on. By creating separate layers corresponding to each layer in the xref-ed file, AutoCAD eliminates the potential problem with blocks that we warn you about in Chapter 17, when layers have the same name but different color or linetype in the two drawings.

Creating and editing an external reference file

To create a file that you can use as an external reference, just create a drawing and save it. That’s it. You can then create or open another drawing

and create an external reference to the previous one. The xref-ed drawing appears in the host drawing as a single object, very much like a block insert. In other words, if you click any object in the xref, AutoCAD selects the entire xref. You can measure or object snap to the xref-ed geometry, but you can’t modify or delete individual objects in the xref, Instead, you open the xref drawing to edit its geometry.

The XOPEN command provides a quick way to open an xref-ed drawing for editing. You just start the command and pick any object in the xref. Alternatively, you can select the xref from the External References palette

and then right-click and choose Open to open one or more xrefs for editing. See the “Managing xrefs” section, later in this chapter, for more information.

An alternative to opening the xref-ed file when you need to edit it is to use the REFEDIT command. Use REFEDIT (short for Reference Edit) to edit the external file from within the host drawing, rather than having to open the reference in its own window. Look up REFEDIT in the AutoCAD online help system’s Command Reference.

With several xrefs attached to your drawing, or with a very complex xref, it can be difficult to tell which objects belong to the drawing you’re editing, and which are part of the xref. You can fade your xrefs as follows:

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404 Part IV: Advancing with AutoCAD

1.Open a drawing containing an external reference drawing.

Alternatively, you can attach a drawing to your current drawing by following the steps in the “Becoming attached to your xrefs” section, earlier in this chapter.

2.On the Insert tab, click the Reference panel label to open the Reference slideout.

The Reference slideout also contains the Edit Reference button, which runs the REFEDIT command.

3.Click the Xref Fading button to toggle reference fading off and on.

4.Drag the Xref Fading slider to increase or decrease the level of fading in the reference file.

The default value is 70; increasing the value toward 90 (the maximum) increases the degree of fading, and lowering it reduces the fade level.

Forging an xref path

When you attach an xref, one option is to have the host drawing store the xref’s full path — that is, the drive letter and sequence of folders and subfolders all the way down to the folder in which the DWG file resides — along with the filename. This behavior corresponds to the Full Path setting in the Path Type drop-down list. Figure 18-5 shows the three xref path options. Full Path works fine as long as you never move files on your hard drive or network and never send your DWG files to anyone else — which is to say, it almost never works fine!

Figure 18-5: Follow the path less traveled when you attach an xref.

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Chapter 18: Everything from Arrays to Xrefs 405

At the other end of the path spectrum, the No Path option causes AutoCAD not to store any path with the xref attachment — only the filename is stored. This is the easiest and best option if the host drawings and the xrefs reside in the same folder. However, if the host and the xref are in different folders, you have to browse to find the reference file every time you open the host drawing.

If you prefer to organize the DWG files for a particular project in more than one folder, you’ll appreciate AutoCAD’s Relative Path option, as shown in Figure 18-5. This option permits xref-ing across more complex folder structures but avoids many of the problems that the Full Path option can cause. For example, you may have a host drawing

H:\Project-X\Plans\First floor.dwg

that xrefs

H:\Project-X\Common\Column grid.dwg

If you choose Relative Path, AutoCAD will store the xref path as

..\ Common\Column grid.dwg

instead of

H:\Project-X\Common\Column grid.dwg

This way, if you decide to move the \Project-X folder and its subfolders to a different drive (or send them to someone else who doesn’t have an H: drive), AutoCAD can still find the xrefs.

When attaching an external reference we strongly recommend you check the

Path Type window and make sure it says Relative Path. If not, select Relative

Path from the drop-down list from this window.

When you use Relative Path, you’ll see xref paths that include the special codes — . and .. (single and double period). The single period means this host drawing’s folder, and the double period means the folder above this host

drawing’s folder.

You can report on and change xref paths for a set of drawings with the

Reference Manager (not in AutoCAD LT). See Chapter 20 for more information.

If all these path options and periods leave you feeling punchy, you can keep your life simple by always keeping host and xref drawings in the same folder and using the No Path option when you attach xrefs. On the other hand, it can get a little messy when a file such as a standard title block and border is

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406 Part IV: Advancing with AutoCAD

xref-ed into many different drawings for several different projects, and you want to keep each project’s files in separate folders. The best solution is usually a bit of each; the title block and border can have a specific path in each host, but the other project files don’t.

Managing xrefs

The External References palette includes many more options for managing xrefs after you attach them. Many of these options are hiding in right-click menus. Important options include

List of external references: You can change between the List view and Tree view of your drawing’s external references by clicking the appropriate button at the top of the palette (refer to Figure 18-4). You can resize the columns by dragging the column dividers or re-sort the list by clicking the column header names, just like in Windows Explorer.

Unload: Right-click an xref and choose Unload to make the selected xref disappear from the onscreen display of your drawing and from any plots you do of it, but yet retain the pointer and attachment information. Right-click again and choose Reload to redisplay an unloaded xref.

Reload: Right-click an xref and choose Reload to force AutoCAD to reread the selected xref-ed DWG file from the disk and update your drawing with its latest contents. This feature is handy when you share xrefs on a network and someone has just made changes to a drawing that you’ve xref-ed.

Detach: Right-click an xref in the External References palette and choose Detach to completely remove the selected reference to the external file from your drawing.

Bind: Right-click an xref and choose Bind to bring the selected xref into your drawing and turn it into a block. You might, for example, use this function to roll up a complex set of xrefs into a single archive drawing.

In many offices, binding xrefs without an acceptable reason for doing so is a crime as heinous as exploding blocks indiscriminately. In both cases, you’re eliminating an important data management link. Find out

what the policies are in your company. When in doubt, keep yourself out of a bind. And even when you do have a good reason to bind, you generally should do it on a copy of the host drawing.

Open: Right-click an xref and choose Open to open one or more xref drawings in separate drawing windows. After you edit and save an xref drawing, return to the host drawing and use the Reload option in the External References palette to show the changes.

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