Dead Objec ts, Zombies, and Proxies

CAD, by its very nature, is well suited to the use of objects. After all, why draw lines when you can draw walls? And why use dumb symbols when you can use smart objects? Think about it: A door object can be smart enough to know it goes in a wall instead of in the middle of a room.

AutoCAD's new object architecture promises smarter applications for a variety of disciplines, including architecture, facility management, civil engineering, mechanical engineering, numerical control, and more. The common bond between these applications will be AutoCAD's most powerful API language -- ObjectARX. ARX (AutoCAD Runtime e Xtension) is a fully featured C++ API. The version that ships with R14 suppor ts Microsoft Foundation Classes (MFC), making interface issues much easier to deal with. ObjectARX also allows developers to create their own object types -- a capability that could be a double-edged sword.

In order to prevent an all-out object war -- imagine if a door from one developer didn't recognize a wall from another -- Autodesk has been working with a number of developers to create industry foundation classes (IFC) for CAD objects. The aim is that if a developer's applications are IFC-compliant, there's a good chance that they'll play nicely with other IFC-compliant applications.

One of the more interesting side effects of AutoCAD objects created by a third-party program is that they might not be useful when that third-party program isn't loaded. These objects will show up on the screen, and be printable, but they might not be editable. The third-party developer has the option of allowing the user to explode the custom objects (i.e., break them up into their constituent geometry) but is not absolutely required to provide this functionality. Because these uneditable objects look alive but act dead, they're called "zombies." Autodesk, understandably enough, prefers to call them "proxies."

Here's the bottom line: If you're a serious CAD user, you'll get a lot of benefit from the new generation of ObjectARX-based applications for AutoCAD R14. Just be sure to ask ahead of time if an application is IFC-compliant, and whether objects created by it can be exploded when the application is not loaded.