Primitive Instancing
In primitive instancing, the modeling system defines a set of primitive 3D solid shapes that are relevant to the application area. Primitive instances are similar to parameterized solid objects. A parameterized primitive may be thought of as defining a family of parts whose members vary in a few parameters, an important CAD concept known as Group Technology. Primitive instancing is often used for relatively 'complex objects', such as gears and bolts, that are tedious to define in terms of Boolean combinations of simpler objects, yet are readily characterized by a few high-level parameters. It is easier to sew and create unambiguous and unique solids. The main disadvantage is clearly the limited domain of objects that can be handled.
In primitive instancing, no provisions are made for combining objects to form a new higher-level object, using the regularized Boolean set operations. Thus, the only way to create a new kind of object is to write the code that defines it. Similarly, the routines that draw the objects or determine their mass properties must be written individually for each primitive. The main disadvantage is clearly the limited domain of objects that can be handled. The method is restricted to the primitives predefined in the system and they are quite limited.