The New External Reference Manager31 Dec, 1997 By: Lynn Allen
It hasn't been long since my last article on external references ("Making the Most of Xrefs," CADENCE, February 1997, pp. 79-81). But AutoCAD R14 has so much more to offer when it comes to xrefs that I've been asked by many to write about these changes. If you've realized the value of external references in the past but found them cumbersome (not to mention confusing), you'll love the modifications. Now, using external references is easier and more powerful then ever.When do you use external references? Whenever you need to reference another drawing but don't want to insert every object into your drawing. In addition to smaller drawing size and easier access for many people to the same drawing information, external references offer the following advantages:
- You can make modifications to the original referenced drawing, and the xrefs will update as well. This feature ensures that you always have the most up-to-date information in your drawing.
- You can clip them, displaying as much or as little as you please.
- You can use object snaps on them.
- You can control them easily with the new Xref Manager.
Rather than start from scratch, I'm going to assume that you are familiar with the basics of external references. If you're new to AutoCAD, I suggest you read the introductory article on external references in the February issue.
The biggest shift in working with external references will be the new Xref Manager, which is located in the Insert pull-down menu under External Reference..., . You will also get this dialog if you execute the XREF command via the command prompt.
One of the disadvantages of xrefs in the past has been trying to keep track of them within your drawing. You might have xrefs within xrefs (nested). You might have some xrefs that were overlaid rather than attached. You might have some xrefs that AutoCAD couldn't find. The new Xref Manager makes it easy to view all of the xrefs within a drawing and understand the relationship among them.
Let's review this dialog. This view provides the specifics of each xref. The Tree view, which we'll look at later, makes it easy to view the connections from one xref to another. The List view has six headings of detailed information. As with all MFC-compliant dialog boxes, you can click on the headings to sort/reverse sort the information. Each column can be moved to display the information in a way that works for you.
The external reference's name is listed under this heading. By clicking on the Reference name, you can change the name of the xref. If you modify the name, all dependent symbols will be modified as well. Though you can change the xref name to have more then eight characters, I recommend that you limit the number of characters to accommodate the restrictions of the symbol tables.
This column can get confusing, since your external references could be in so many different possible states. The following listing identifies all the possibilities:
- Loaded. The xref was found when the drawing was opened or reloaded. It is displayed.
- Unloaded. The xref is currently unloaded from the drawing. It is not displayed.
- Not Found. AutoCAD was unable to find the xref using the assigned path. It might have been moved to another location.
- Unresolved. AutoCAD found the xref but could not read the file (possibly a corrupt file).
- Unreferenced. This is a nested xref that is attached to another xref that is no longer attached to the current drawing; not found or unresolved.
- Orphaned. This is a nested xref that is attached to an xref that is unloaded.
As you can see, xrefs can be in a wide range of possible states at any given time.
The Size and Date headings are self-explanatory (and read-only). The Type heading indicates whether the xref is attached or if it is an overlay. You can double-click on the words Attach and Overlay to easily toggle from one to the other. This is a great new feature if you decide to change the type after the fact.
This heading contains the path that AutoCAD will take to find the external reference file. If you move the external reference, you can use the Browse button to relocate the file and the Save Path button to resave the proper path. AutoCAD will search the hard-coded path saved here first and then follow that up by looking in the Project directory. Project names are new to R14 and can be created in the Preferences dialog box (see "Circles and Lines," CADENCE, October, November and December, 1997).
The five buttons on the right side of the dialog contain the real power of the Xref Manager. These buttons permit you to Attach (or Overlay), Detach, Reload, Unload and Bind new xrefs. We'll review these options as follows in this column.
The Attach option sends you to the dialog shown in Figure 2 (not available on the web). This visual interface makes it easier to Attach or Overlay new drawings. Within this dialog, you will select the drawing name, determine the type of attachment and indicate the position, scale factor and rotation angle of the xref. Selecting the Browse button displays an Explorer-style dialog box, complete with preview images, to help you select the correct drawing. Should you choose a filename with more than eight characters, spaces or unsupported characters, a dialog box, will appear to indicate that you need to pare down the filename.
If the Include Path option is checked, AutoCAD will save the full path to the xref in the drawing database. If this option is not selected, you will be saving the xref name only. This selection will force AutoCAD to search for the xref not only in the current project, but in the AutoCAD Support File Search path as well.
After selecting the external reference file, you can choose to key in the parameters via the dialog or specify the parameters visually onscreen.
Let's briefly review of the difference between the Attach and Overlay options. If your intent for using xrefs is data sharing, you might only need to Overlay an xref. An overlaid xref is only part of the drawing it was brought into. An attached xref goes with the Parent drawing as it is xrefed into other drawings. If you find you're having issues with circular xrefs, you should change your attached xrefs to overlays.
When you no longer need an xref in your drawing for any reason, you can detach it. Erasing the external reference may remove the physical object, but not the instances of the drawing from the database. When you detach an xref, it's as though the xref never existed. You cannot detach a nested xref unless you detach the parent. You also cannot detach an xref that is referenced by another xref or block.
The Reload option is useful when the original xrefed drawing has changed during a drawing session. Use Reload to get the most up-to-date xrefs displayed in your drawing. Reload will also change the status of unloaded xrefs back to their original state.
Less extreme than Detach, the new Unload option removes the physical display of the xref from the drawing, but maintains a pointer to the xref. This feature will improve performance during a drawing session and speed up regenerations.
When you want to make the xref a permanent part of your drawing, you'll use the Bind option.
This dialog represents one of the other cool additions to the Xref Manager-the new Insert option. You are probably familiar with how Binding an xref produces long layer and block names. You get that nice "DWGNAME$#$" in front of all the named objects to distinguish them from those found in the original drawing. The new Insert option can be used to turn your attached xref into a block. It uses no cryptic symbol table names. If it encounters any duplicates, it gives precedence to the current drawing. Note: If you change a reference name, you will not be able to Bind until you exit the dialog and reenter again.
The above options don't take effect until after you've exited the dialog box. Don't forget the "what's this" help that's available if you need a brief reminder of the features in this dialog. Just pick the question mark from the upper left-hand corner and click the cursor on the area you need to know more about.
We haven't looked at the Tree view that lies within the new Xref Manager. By hitting the standard Tree View button in the upper left corner (or hitting [F4]), you will get a very different listing of the various external references within your drawing.
This new Tree View display is a great view of the relationship of one xref to another. Here you can clearly see the Parent/Child relationship between nested xrefs in hierarchical format. The icons indicate the state of each xref. I personally find that all the icons look the same and always resort back to the List View for the friendly text information. Essentially, if there's a little red question mark on the icon, that's a bad thing-something is unreferenced, not found, orphaned and so on. Any xref that's overlaid looks as though there are two sheets of paper instead of one.
You can select the List View or the Tree View by using [F3] and [F4], respectively. I think you'll find this new Xref Manager will make it much easier for you to use and control your external references.
About the Author: Lynn Allen
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