The Changing Face of Parametric Modeling

Push-pull editing -- commonly found in direct modeling programs like SpaceClaim, CoCreate, and Siemens products with Synchronous Technology -- has now been embraced by many leading parametric CAD brands. Despite having Parametric for its first name, PTC or Parametric Technology Corp becomes the latest to implement push-pull functions. This appears in the company's flagship Pro/ENGINEER Wildfire 5.0 software under the name Dynamic Editing.

Originally, the distinction between parametric and direct modelings seemed straightforward enough. If a CAD system let you construct and modify geometry by preserving a feature history, it was a parametric modeler. On the other hand, if it let you create and edit geometry on the fly -- in other words, directly in 3D space -- without bothering to record the process in a series of steps, it was a direct modeler. Regardless of the type of program you were using, you would most likely be executing your commands via menu bars and dialog boxes.

Now that you have the option to directly push, pull, poke, and pinch on surfaces and edges to reshape your geometry in both parametric and direct modeling programs, direct modeling may become a muddled term, up for grab, open to misinterpretation. At best, it risks confusion.

While many leading parametric CAD modelers have made it possible for you to directly interact with your geometry as described above (SolidWorks, Alibre Design, and Pro/ENGINEER, to name but a few), some direct modelers like Kubotek's KeyCreator continues to use an interface that relies on menu bars and dialog boxes instead of push-pull modeling. Yet, it creates and edits geometry without keeping a history tree, so strictly speaking, it's a direct modeler.

If merging parametric and direct modelings into a single package (something Autodesk is publicly pursuing via Autodesk Inventor and Inventor Fusion) becomes the future of CAD, the distinction between history-based (or parametric) modeling and history-free (or direct) modeling might just become history -- a moot point. Instead, you might care more about whether you can push and pull on your parts.

To illustrate my point, here's a CAD blind test.