One major benefit of parametric modeling is the intelligent design behavior of objects. Automatic low-level editing is built in, almost like one’s own design assistant. This intelligence, however, comes at a cost. Each type of system ob- ject has its own behavior and associations. As a result, BIM design applications are inherently complex. Each type of building system is composed of objects that are created and edited differently, though with a similar user interface style. Effective use of a BIM design application usually requires months to gain proficiency.
Modeling software that some users prefer, especially for early concept design, such as SketchUp, Rhino, and FormZ’s Bonzai, are not parametric modeling–based tools. Rather, they have a fixed way of geometrically editing objects, which varies only according to the surface types used. This functionality is applied to all object types, making them much simpler to use. Thus, an editing operation applied to walls will have the same behavior when it is applied to slabs. In these systems, attributes defining the object type and its functional intention, if applied at all, can be added when the user chooses, not when it is created. All of these systems allow the grouping of surfaces, giving the group a name and maybe assigning attributes. Done carefully and with a matching interface, the object can be exported and used in other areas, say solar gain studies. This is similar to the kinds of tricks people used to do with 3D AutoCAD. But one is not going to take this kind of modeling into design development because one object is not linked to other objects and must be spatially managed individually. An argument can be made that for preliminary design use, however, BIM technology with its object-specific behavior is not always warranted. This topic is explored further in Chapter 5.