All About External References
The Drawing Management feature in AutoCAD® Architecture 2013 uses external references (xrefs) as a means to create a project and maintain it. This means that elements are referenced into constructs, constructs are referenced into views, and views are referenced into sheets. The mechanism of referencing is identical to the regular AutoCAD External References Management feature. However, the background methods employed have additional features.
Xrefs that have been created in drawing management can automatically make use of project data, while those that are created manually through the xref palette or command line cannot. For example, a construct that is placed on a specific level will use that level's elevation data to control the Z-axis insertion point when being xrefed into a view. If you are working in a project environment, the best practice for referencing project drawings into other project drawings is to use the Project Navigator rather than the standard AutoCAD Architecture Xref Manager. The AutoCAD Architecture Xref Manager cannot differentiate between project drawings and non-project drawings. If you reference a non-project file into a project file by mistake, you cannot use the full Drawing Management functionality on that file.
Keep these considerations in mind when working with a project:
- Do not delete any XML files generated by the Drawing Management feature. They are vital for the project.
- Use the Project Navigator to create, modify and reference project files within the project. If you want to use existing non-project files in a project, convert them to project files first.
- Drawing Management supports the use of relative paths for external references. In the project setup, you can decide whether to use full paths or relative paths. Working with relative xref paths makes moving the project and transmitting it easier and reduces the need to repath the project.
External References Palette
The External References palette in AutoCAD Architecture organizes, displays, and manages referenced files such as DWG files (xrefs), DWF, DWFx, PDF, and raster images. These files can be opened directly from the External References palette. The External References palette contains several buttons and is split into two panes (see Figure 1). The upper pane, called the File References Pane, can display file references in a list or in a tree structure. Shortcut menus and function keys provide options for working with the files. The lower pane, called the Details/Preview Pane, can display properties for the selected file references or it can display a thumbnail preview of the selected file reference.
It is important to note that when using the External References palette, it is recommended that you turn on the Auto-hide feature or anchor the palette. The palette will then hide automatically when you move the cursor away from the palette.
You can use the buttons at the top of the External References palette to choose the types of files to attach to the drawing and to refresh the status of file references that you already have attached. The following options are displayed:
- Attach (file type) Button - The Attach button displays a list of file types that you can attach (see Figure 2).
- Refresh/Reload All References Button – The Refresh button synchronizes the status data of referenced drawing files with the data in memory. Reload All References updates all file references to ensure that the most current version is used. Updating also occurs when you first open a drawing that contains file references.
Figure 1: External References palette
Figure 2: Attach file types
Attaching and Detaching Xrefs
You can attach an entire drawing file to the current drawing as a referenced drawing (xref). With xrefs, changes made in the referenced drawing are reflected in the current drawing. Attached xrefs are linked to, but not actually inserted in, another drawing. Any changes to a referenced drawing are displayed in the current drawing when it is opened or reloaded. With xrefs you can build drawings without significantly increasing the drawing file size.
By using referenced drawings in AutoCAD Architecture, you can:
- coordinate your work with the work of others by referencing other drawings in your drawing to keep up with the changes being made by other designers.
- ensure that the most recent version of the referenced drawing is displayed. When you open your drawing, each referenced drawing is automatically reloaded, so it reflects the latest state of the referenced drawing file.
- keep the names of layers, dimensioning styles and text styles in your drawing separate from those in referenced drawings.
- bind attached referenced drawings permanently with your current drawing when the project is complete and ready to be archived.
A drawing file can be attached as an xref to multiple drawings at the same time. Also, multiple drawings can be attached as referenced drawings to a single drawing. To attach an xref click the Insert tab, Reference panel, Attach. Select the file you wish to reference and select Open. This will bring up the Attach External Reference dialog box where you can choose to attach or overlay, scale, insertion point, path type, and rotation (see Figure 2). Click OK when finished. It is important to note that if an xref contains any variable block attributes, they are ignored. Once the xref is attached to the drawing, an xref icon will be displayed in the lower-right corner of the application window. When one or more xrefs are not found, an exclamation point is added to the xref icon. If you click the xref icon, the External References palette will be displayed.
To completely remove xrefs from your drawing, you need to detach them rather than erase them. Erasing xrefs does not remove layer definitions associated with those xrefs. Using the Detach option removes the xrefs and all associated information.
Sometimes it becomes necessary to find an xref in a complex drawing. To do this, select an item in the External References palette to highlight all visible instances in the drawing. Also, you can select an external reference in the drawing to highlight its name in the External References palette.
You can control the visibility, color, and linetype of an xref's layers and make these changes temporary or permanent. If the VISRETAIN system variable is set to 0, these changes apply only to the current drawing session. They are discarded when you end the drawing session or when you reload or detach the xref. You can also control the fade display of the DWG xref. The XDWGFADECTL system variable defines the fade percentage for all DWG xrefs.
Figure 3: External Reference dialog box
Updating Referenced Drawing Attachments
When you open a drawing, all xrefs update automatically. You can also use the Reload option from the External References palette to update xrefs whenever you want to ensure that the most current versions are displayed in your drawing (see Figure 4). Whenever you modify and save an externally referenced drawing in a network environment, other people can access your changes immediately by reloading the xrefs in their open drawings.
When you attach xrefs to a drawing, the program periodically checks whether the referenced files have changed since the last time the xrefs were loaded or reloaded. The XREFNOTIFY system variable controls xref notification. By default, if a referenced file has changed, a balloon message is displayed near the xref icon in the lower-right corner of the application window. Click the link in the balloon to reload all changed xrefs. If you close the balloon message without reloading, an exclamation point is added to the xref icon. If you click the xref icon, the External References palette is displayed.
By default, the program checks for changed xrefs every five minutes. You can change the number of minutes between checks by setting the XNOTIFYTIME system registry variable using (setenv "XNOTIFYTIME" " n ") where n is a number of minutes between 1 and 10080 (seven days). It is important to note that when changing the value of XNOTIFYTIME, you must enter the system variable with the capitalization as shown.
Figure 4: Reload Referenced Drawings
Nesting and Overlaying Reference Drawings
Xrefs can be nested within other xrefs. This basically means that you can attach an xref that contains another xref. You can attach as many copies of an xref as you want and each copy can have a different position, scale, and rotation. It is important to note that when using the parametric drawing feature, you can only constrain objects in the drawing to the insertion point of an xref and not its nested objects. The saved path for an xref can be a full path, a relative (partially specified) path, or no path. For a nested xref, a relative path always references the location of its immediate host and not necessarily the currently open drawing.
You can also overlay an xref on your drawing. Unlike an attached xref, an overlaid xref is not included when the drawing itself is attached or overlaid as an xref to another drawing. Overlaid xrefs are designed for data sharing in a network environment. By overlaying an xref, you can see how your drawing relates to the drawings of other groups without changing your drawing by attaching an xref.
Isolating Objects in External References
When working in drawings with external references, you should note the following points.
- You can isolate an external reference within a host drawing as a whole by selecting it and isolating it.
- You can isolate individual objects within an external reference by opening the external reference, isolating and hiding objects as needed, saving the external reference drawing, and then reloading the external reference.
- You cannot isolate or hide objects in an external reference while editing it with REFEDIT in the host drawing. You need to use XOPEN and save the desired Hide/Isolate settings within the external reference.
- You cannot redisplay hidden objects in an external reference while editing it with REFEDIT in the host drawing. You need to use XOPEN and save the desired Hide/Isolate settings within the external reference.
You can save a drawing in which object isolation is currently active. The next time you open the drawing, it will display with the isolation settings you defined. It is important to note that if you want to distribute a drawing with isolated objects, make sure that you and the recipient of the drawing are working with the same version of AutoCAD Architecture. A recipient who is working with an earlier version of the software, plain AutoCAD, or Object Enabler is not able to display the hidden objects. In this case, end the object isolation before saving and distributing the drawing.
Clipping External References
You can clip external references such as DGN, DWF, IMAGE, PDF underlays, or block references. With a clipping boundary, you can determine the portions of an external reference or block reference that you want to display by hiding the redundant parts of the reference inside or outside the boundary. You can control the display of the clipping boundary with a clipping frame. The clipping system variable for XREF, PDF, DGN, DWG, and IMAGE underlays are XCLIPFRAME, PDFFRAME, DGNFRAME, DWGFRAME, and IMAGEFRAME, respectively.
The clipping boundary can be a polyline, rectangle, or a polygon with vertices within the boundaries of the image. You can change the boundary of a clipped image. When you clip a boundary, the objects in the external reference or block are not altered. Only their display has changed.
After an external reference or block reference has been clipped, it can be moved, copied, or rotated just like an unclipped external reference or block reference. The clipping boundary moves with the reference. If an xref contains nested clipped xrefs, they appear clipped in the drawing. If the parent xref is clipped, the nested xrefs are also clipped.
If you want to change the shape or size of a clipping boundary for external references and block references, you can use grips to edit the vertices just as you edit any object with grips. In the case of rectangular grip editing, you can maintain the closed four-sided rectangle or square shape of the rectangular clipping boundary because two vertices of the same side of the rectangular clipping boundary are edited together. With clipping boundaries, you cannot display self-intersecting polygonal boundaries. An error message is displayed and the boundary reverts to the last boundary.
To clip a boundary for an external reference, begin by clicking the Insert tab, Reference panel, and then select Clip (see Figure 5). Next, select an xref. At the prompt, specify New Boundary by pressing Enter. Select a polyline or specify a rectangular or polygonal clipping boundary. Specify the corners or vertices of the boundary. The xref is clipped based on the area that you specified.
Figure 5: Clip External Reference
External References are an excellent tool to help keep file sizes to a minimum yet have as much information in a drawing as possible. If you are not currently using external references in your AutoCAD Architecture projects, I encourage you to try them out.