Recently someone asked me if I could briefly go over some computer-aided drafting terms.

First of all, I’ll briefly discuss feature-based vs. primitive-based modeling.

Primitive-based modeling involves the direct creation of basic shapes which undergo Boolean operations to create models. That means you create two cubes then subtract one cube from the other cube to create the shape you want. These “primitive” shapes such as cubes, spheres, cylinders, etc. are added and subtracted from each other to obtain the desired result. Primitive modeling has generally fallen out of favor over time. A point worth remembering is that some CAD systems that use primitive modeling are unable to conduct Boolean operations if only an edge or single point of two models intersect.




Feature-based modeling involves the creation of sketches which are padded, revolved, pocketed, or otherwise modified three-dimensionally. These three-dimensional manipulations are called “features” of the part. Solidworks uses feature based geometry exclusively.

The final two terms worth considering are parametric modeling and direct modeling.

Direct modeling is a much less precise method of modeling where the general concept of a model is created without regards to dimensions or tolerances. Parametric modeling involves an exact definition of engineering intent. That means the modeler will use tolerances to ensure adequate fit between parts of an assemble. The modeler will ensure that all parts are completely constrained dimensionally. Parametric modeling will usually make use of relational design which allows for automatic updating of a model. This means that a parametric model of a car may allow for changing the hubcap size to automatically update the wheel size, lug nut size and, wheel well size. If a quick concept model is required, direct modeling may be the ideal choice. If you have the time to sink into a project, parametric modeling is best.