AutoCAD 2005 for Dummies

Layer-palooza

When you attach or overlay an xref, AutoCAD adds new layers to your current drawing that correspond to the layers in the xrefed 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 xrefed layers will be named MYSCREW|GEOMETRY, MYSCREW|TEXT, and so on. By creating separate layers corresponding to each layer in the xrefed file, AutoCAD eliminates the potential problem I warned you about with blocks when layers have the same name but different color or linetype in the two drawings.

  AutoCAD also creates new linetypes, text styles, dimension styles, and block definitions for each of these items in the xrefed file — for example, MYSCREW|DASHED, MYSCREW|NOTES, MYSCREW|A-DIMS, and MYSCREW|LOGO.

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 (or use the WBLOCK command to create a new DWG from geometry in the current drawing). That’s it. You then can create or open another drawing and create an external reference to the previous one. The xrefed drawing appears in your parent drawing as a single object, 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 xrefed geometry, but you can’t modify or delete individual objects in the xref — you open the xref drawing in order to edit its geometry.

AutoCAD 2004’s XOPEN command (Modify>Xref and Block Editing>Open Reference) provides a quick way to open an xrefed drawing for editing. You just start the command and pick on any object in the xref. Alternatively, you can use the Open button in the Xref Manager dialog box 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 xrefed file when you need to edit it is to use the REFEDIT command (Modify>Xref and Block Editing>Edit Reference In-Place). Look up “REFEDIT” in the AutoCAD online help system.

Forging an xref path

When you attach an xref, AutoCAD by default stores the xref’s full path — that is, the drive letter and sequence of folders and subfolders in which the DWG file resides, along with the filename. This default behavior corresponds to the Full path setting in the Path Type drop-down list. (Figure 13-8 shows the three xref path options.) Full path works fine as long as you never move files on your hard disk or network and never send your DWG files to anyone else — which is to say, it almost never works fine!

Figure 13-8: Chart your path when you attach an xref.

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 parent and child drawings reside in the same folder.

If you prefer to organize the DWG files for a particular project in more then one folder, then you’ll appreciate AutoCAD’s Relative path option, shown in Figure 13-8. This option permits xrefing across more complex, hierarchical folder structures, but avoids many of the problems that Full path can cause.

For example, you may have a parent drawing H:Project-XPlansFirst floor.dwg that xrefs H:Project-X CommonColumn grid.dwg. If you choose Relative path, AutoCAD will store the xref path as .. CommonColumn grid.dwg instead of H:Project-XCommonColumn grid.dwg. Now 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 will still be able to find the xrefs.

  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 parent drawing’s folder” and the double period means “the folder above this parent drawing’s folder” (in other words, the folder of which the parent drawing’s folder is a subfolder).

You can report on and change xref paths for a set of drawings with the AutoCAD Reference Manager. See Chapter 16 for more information.

  If all these path options and periods have got you feeling punchy, you can keep your life simple by always keeping parent and child drawings in the same folder and using the No path option when you attach xrefs.

Managing xrefs

The Xref Manager dialog box includes many more options for managing xrefs after you attach them. Important dialog box options include:

? List of external references: You can change between a List and a Tree view of your drawing’s external references just by clicking the appropriate button at the top of the dialog box. You also can resize the columns by dragging the column dividers or re-sort the list by clicking the column header names, just as in other Windows dialog boxes.

? Detach: Completely removes the selected reference to the external file from your drawing.

? Reload: Causes AutoCAD to reread the selected xrefed 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 xrefed.

? Unload: Makes the selected xref disappear from the on-screen display of your drawing and from any plots you do of it, but retains the pointer and attachment information. Use the Reload button to redisplay an unloaded xref.

? Bind: Brings the selected xref into your drawing and makes it a block. You might use this function, for example, 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 parent drawing.

? Open: Opens one or more xref drawings in separate drawing windows after you close the Xref Manager dialog box. After you edit and save an xref drawing, return to the parent drawing and use the Reload option in the Xref Manager dialog box to show the changes.

None of these options (other than opening and editing the xref) affects the xrefed drawing itself; it continues to exist as a separate DWG file. If you need to delete or move the DWG file that the xref refers to, do it in Windows Explorer.

  The fact that the xrefed drawing is a separate file is a potential source of problems when you send your drawing to someone else; that someone else needs all the files that your drawing depends on, or it will be useless to the receiving party. Make sure to include xrefed files in the package with your drawing. See Chapter 16 for a procedure.

  AutoCAD (but not AutoCAD LT) includes an additional xref feature called xref clipping. You can use the XCLIP command to clip an externally referenced file so only part of it appears in the parent drawing. AutoCAD LT doesn’t include the XCLIP command, but if you open a drawing containing an xref that was clipped in AutoCAD, the clipped view will be preserved.

Blocks, Xrefs, and Drawing Organization

Blocks and xrefs are useful for organizing sets of drawings to use and update repeated elements . It’s not always clear, though, when to use blocks and when to use xrefs. Applications for xrefs include

? The parts of a title block that are the same on all sheets in a project.

? Reference elements that need to appear in multiple drawings (for example, wall outlines, site topography, column grids).