Cadtales

Proxy Objects

by Jim Rogers, CADreps

Proxy Objects, at least in the context of AutoCAD, came to be when Autodesk invented vertical applications (Architecture, MEP) with enhanced features – initially riding on top of AutoCAD – and now in more independent forms, and the desire to have a universal DWG format that could be opened and edited by all AutoCAD-family programs. If you receive drawings from outside clients, especially from the architectural and building trades, you have probably encountered the Proxy Information message when opening or external referencing a drawing in AutoCAD.

Figure 1

This Proxy Information box raises more questions than it answers. Do we check the “Do not show proxy graphics” box or not. Or, do we simply click OK and move on. Here, then, is a brief explanation of what constitutes proxy objects, where they come from and why they are necessary.

Figure 2 is an example of a simple door and wall configuration, created in Autodesk’s MEP (Mechanical, Electrical and Plumbing) program, a vertical implementation of AutoCAD with industry-specific menus and libraries. The wall and door were created by an ObjectARX application that is part of MEP (but not part of regular AutoCAD). The door and wall, as with most objects in MEP, are designed to be more “intelligent,” flexible, adaptable and useful. Note the additional grips and the list of properties for the door when viewed in MEP.  Figures 2 & 3 below.

Figure 2

Figure 3

When opening this same drawing in AutoCAD, many of the 3D characteristics of the objects are preserved, especially those that apply to 2D and 3D views and renders. This allows you to see and plot the objects.

The 2D view is composed of simple lines, arcs and circles (proxy objects) that represent the shape of the true ObjectARX items. And, since the ObjectARX application that created them is not present in AutoCAD, your editing options are few and limited. Editing can be enhanced if you check the www.autodesk.com website for an “object enabler” for the application. (Object enablers are also made by others so Google for them on the Internet).

The Autodesk Object Enabler for AutoCAD (for Architectural and MEP drawings) will permit you to erase, copy and rotate most objects. If you copy the door, for instance, it will make a new copy in the wall and cleanup where the door cuts the wall. If you erase the door it will heal the wall. Commands like stretch and scale don’t work because they alter the geometry – and that can’t be done without the original ObjectARX application, and you won’t be able to change the physical and style parameters.

Figure 4 is a view of the door and wall drawing in AutoCAD. Note that ALL the grips are missing from the highlighted door because grip-editing the object would change its physical properties. When viewed in 3D you will see that most of the 3D visibility properties are preserved and you can view and render ObjectARX objects in AutoCAD. See Figure 4.

Figure 4

There are three areas where proxy objects are a problem, mainly because of limited error trapping and inadequate information in the Help file.

Binding XREFs – When the root drawing is open in AutoCAD and you try to bind XREFs that were created by an ObjectARX application the operation may fail and you may get an error message like that shown in Figure 5. We say “may” because this doesn’t happen on every bind and there is only trial & error to test if the bind operation will be permitted. (A listing of ObjectARX items that can’t be bound or a list of ObjectARX parameters that when used would cause a bind operation to fail would be helpful).

Figure 5

Copying to the Clipboard – For many years we used what I call the “poor man’s recovery” method for recovering drawing contents when a file was so corrupt that AutoCAD would likely suffer a fatal error when opening, editing and certainly, binding XREFs. If the file would open at all and you could start the copy command, make a crossing window and copy selected objects to the Clipboard – then, you could paste those objects into a new drawing. (To be fair, recent and current versions of AutoCAD and its vertical implementations are much better in this regard and the Drawing Recovery Manager is a wonderful and welcome addition).

The problem still exists, however, when copying ObjectARX objects into an AutoCAD drawing. You can highlight the objects in the source drawing and “paste” them into the destination drawing, but the objects never appear and there is no error message. The cursor just blinks at you (it’s OK to feel stupid) and returns to the Command prompt. (This appears to happen a lot with furniture drawings and may result from third-party applications that specialize in cubicle designs).

If you are fortunate enough to have AutoCAD Architecture or MEP you can load up the resource drawing and Export to AutoCAD (selecting a version) and avoid a lot of the pitfalls noted above.

Wblock – Another common way to copy geometry from one drawing to another is the Wblock command. If you use Wblock in a drawing that contains ObjectARX objects you may get an error message to the effect that “proxy object prohibits copying.” Again, a list of object types and/or parameters that prevent such copying would be helpful. Use this method to validate if your copy-to-the-Clipboard operation fails as described above.