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Multi-CAD environments: new software technologies are focusing on editing and sharing 3D geometry.

Article Excerpt
In the beginning, "you had a lump of model," explains Paul Brown, director of NX marketing for Siemens PLM Software (Plano, TX; www.siemens.com/plm). Solids modelers based on boundary representation (brep) were all about topology. Then came parametrics, adding intelligence to the model through dimensions that determined design intent by driving geometry. Then came feature-based, history-based modeling: "As you build the model, the 'recipe,' you built up the relationships," continues Brown. This recipe and all its ingredients-the model and its features, and relationships between those features--are all dependent upon each other.

While feature-based parametric modeling isn't about to go away anytime soon. assures Brown, it does have limitations. First, changing the model, especially complex models with highly interdependent features, can be time consuming. Every change to a model requires recalculating its feature tree. Conversely, he says, "explicit modeling provides direct interaction with geometry and provides flexible editing. But it lacks control and the ability to establish design rules to manage change."

Second, "once a model is built, it cannot be changed in any ad-hoc or freeform way," writes the Aberdeen Group (Boston, MA; www.aberdeen.com) in a market alert. "It must be changed within the constraints of the original feature definitions or rebuilt. Overall, this limits the freedom the user has to make significant changes." Adds Brown, "To get reliable edits, I have to preplan how I build my model. I'm...

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