Cell-decomposition
In cell-decomposition, an object can be represented as the sum of cells into which it can be decomposed. Each cell-decomposition system defines a set of primitive cells that are typically parameterized and are often curved. Cell-decomposition differs from primitive instancing in that we can compose more complex objects from simple, primitive ones as a bottom-up fashion by "gluing" them together. The glue operation can be thought of as a restricted form union in which the objects must not intersect. Further restrictions on gluing cells often require that two cells share a single point, edge, or face. Although cell-decomposition representation of an object is unambiguous, it is not necessarily unique, as shown in Figure 6.39. Cell-decompositions are also difficult to validate, since each pair of cells must potentially be tested for intersection. Cell-decomposition is important for use in finite element analysis.