ABSTRACT
Users of CAD systems need to be aware of the techniques used for representing architectural form, since the method of representation chosen will inevitably affect the subsequent behaviour of a CAD model, including the ways in which changes can be made to it. An illustration of this point is the study of a compositional representation of Terragni’s Casa Giuliani Frigerio (the subject of Peter Eisenman’s Ph.D. Thesis (Eisenman, 1971)), generated by means of shape grammar (Flemming 1981), as contrasted with Eisenman’s awareness that the facades on this building alternate between compositional (composed of an aggregation of planar elements) and volumetric (composed from additions and subtractions of volumetric elements) (Kane and Szalapaj, 1992). Typically shape is defined in terms of a geometry (a location and a dimension), and a topology (a set of connectivity relations). In modelling architectural design objects and spatial organisations, a number of options are open to the CAD system user:
which shape properties is it necessary to represent?
whether the model should occupy 2½-D (see CAD Objects section) or 3-D space?
what constraints on geometry need to be represented?
what shape approximations are possible?
how spatial information can be mapped onto non-graphical design information and vice-versa?
